the synthesis and evaluation of polyaromatic ... · vanessa lussini, john colwell, james blinco,...

The Synthesis and Evaluation of

Polyaromatic Profluorescent Nitroxide

Probes for the Detection of Photo-

oxidative Polymer Degradation

Vanessa Lussini

Bachelor of Applied Science (Chemistry)

Submitted in fulfilment of the requirement for the degree of Doctorate of Philosophy

School of Molecular Design & Synthesis

Faculty of Science and Engineering

Queensland University of Technology

2019

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I. ABSTRACT

This PhD project focused on the synthesis and evaluation of novel photo-stable

profluorescent nitroxide (PFN) probes. The stability and performance of the newly

synthesised probes were assessed under harsh photolytic environments and compared

with previously synthesised PFN probes.

The synthesis of novel profluorescent mono- and bis-isoindoline nitroxides utilising

napthalimide and perylene diimide structural cores are described. Analysis of their

physical characteristics revealed that the nitroxide-fluorophore probes displayed

strongly suppressed fluorescence in comparison to their corresponding non-radical,

diamagnetic methoxyamine derivatives. Extinction coefficients, excitation wavelength

and emission wavelengths for the new probes were also determined.

Evaluation of the photo-stability of non-radical derivatives in cyclohexane,

demonstrated their enhanced longevity over 9,10-bis(phenylethynyl)anthracene, the

fluorophore used in previously prepared profluorescent nitroxide probes. The

performance and stability of the novel PFNs in two commercially available polymers

(PTMSP and TOPAS®) was also examined. The PFN containing films were exposed

to thermo- and photo-oxidative degradation conditions. In both systems, the novel

PFNs were able to detect polymer degradation by fluorescence. The alkyne linked

perylene was the most stable probe in the film according to UV-Vis. However, all

nitroxide bearing PFNs prepared from napthalimide and perylene diimide cores were

found to be more photo-stable in comparison to their corresponding non-radical

diamagnetic methoxyamine derivatives.

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Finally, the most photostable PFN, alkyne linked perylene diimide was tested against

true weathering effects in the Brisbane summer, doped within a TOPAS® film. With

the addition of additives, free tetramethylisoindoline nitroxide and commercial

additive, Tinuvin P, it was possible to extend the longevity of the film and the effective

lifetime of the PFN probe. The selective demethylation to liberate the one nitroxide

radical showed interesting properties of increased sensitivity but decreased stability

compared with the di-nitroxide containing PFN. Overall, in a true weather setting, it

was shown that with additives, the PFN could signal local degradation sites via simple

fluorescence. However, addition of highly fluorescent PFNs (spin removed) acts like

a prodegradent to the TOPAS® film according to IR-ATR.

In summary, this thesis has developed a new range of photo-stable PFN probes for

detection of photo-oxidative degradation. They were able to detect radical production

in both synthetic aging conditions and in a true weathering environment. The

synthesised PFN proved to be more sensitive than previous techniques and was more

reproducible. This shows the potential scope of this project.

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II. KEYWORDS

Degradation, Fluorescence, Fluorophore, Free radical, Isoindoline, Naphthalimide,

Nitroxide, Perylene diimide, Photo-oxidation, Polymer, Profluorescent, PTMSP,

TOPAS®, Weathering

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III. PUBLICATIONS ARISING FROM THIS

PROJECT

Journal Articles

Prasad, K.; Lekshmi, G. S.; Ostrikov, K.; Lussini, V.; Blinco, J.; Mohandas, M.;

Vasilev, K.; Bottle, S.; Bazaka, K.; Ostrikov, K., Synergic bactericidal effects of

reduced graphene oxide and silver nanoparticles against Gram-positive and Gram-

negative bacteria. Scientific Reports 2017, 7 (1), 1591.

Lussini, V. C.; Colwell, J. M.; Fairfull-Smith, K. E.; Bottle, S. E., Profluorescent

nitroxide sensors for monitoring photo-induced degradation in polymer films. Sensors

and Actuators B: Chemical. 2017, 241, 199-209.

Lussini, V. C.; Blinco, J. P.; Fairfull-Smith, K. E.; Bottle, S. E., Polyaromatic

profluorescent nitroxide probes with enhanced photostability. Chemistry. 2015, 21,

18258-18268.

Ahn, H.-Y.; Fairfull-Smith, K. E.; Morrow, B. J.; Lussini, V.; Kim, B.; Bondar, M. V.;

Bottle, S. E.; Belfield, K. D., Two-photon fluorescence microscopy imaging of cellular

oxidative stress using profluorescent nitroxides. Journal of the American Chemical

Society. 2012, 134, 4721-4730.

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Conference Lectures

Vanessa Lussini, John Colwell, James Blinco, Kathryn Fairfull-Smith, Steven Bottle.

“Nitroxide probes for monitoring photodegradation in polymers” RACI QLD

Polymers Group Student Symposium, Brisbane, Australia, February 2016.

Vanessa Lussini, John Colwell, James Blinco, Kathryn Fairfull-Smith, Steven Bottle.

“Nitroxide probes for monitoring photodegradation in polymers” Brisbane Biological

and Organic Chemistry Symposium, Gold Coast, Australia, November 2015.

Vanessa Lussini and Steven Bottle. “Monitoring degradation in aircrafts” Australian

International Aerospace Congress, Avalon, Australia, February 2015.

Vanessa Lussini and Steven Bottle. “Early detection of polymer degradation”

Nanotechnology and Molecular Science HDR Symposium, Brisbane, Australia,

February 2015. (Best Talk Prize)

Vanessa Lussini and Steven Bottle. “Nitroxide probes for monitoring photo-

degradation in polymers” DMTC Student Conference, Melbourne, Australia, October

2014.


degradation in polymers” Nanotechnology and Molecular Science HDR Symposium,

Brisbane, Australia, February 2014.


degradation in polymers” DMTC Student Conference, ANTSO, Australia, October

2013.

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Vanessa Lussini, Liam A. Walsh, John M. Colwell, Kathryn Fairfull-Smith and Steven

Bottle. “The synthesis and evaluation of novel perylene-based profluorescent nitroxide

probes for monitoring photo-stability in polymers” RACI QLD Polymers Group

Student Symposium, Brisbane, Australia, September 2012.

Vanessa Lussini, Liam A. Walsh, John M. Colwell, Kathryn Fairfull-Smith and Steven

Bottle. “The synthesis and evaluation of novel perylene-based profluorescent nitroxide

probes for monitoring photo-stability in polymers” RACI QLD Polymers Group

Student Symposium, Brisbane, Australia, August 2011.

Conference Posters

Vanessa Lussini and Steven Bottle. “Monitoring degradation in aircraft coatings”

DMTC Annual Conference, Canberra, Australia, March 2016.

Vanessa Lussini and Steven Bottle. “Monitoring degradation in aircraft coatings”

DMTC Annual Conference, Canberra, Australia, March 2015.

Vanessa Lussini and Steven Bottle. “Profluorescent nitroxides in monitoring

degradation in aircraft coatings” Australian Aerospace Innovation Awards, Avalon,

Australia, February 2015.

Media

Lussini, V (2015) Interviewed by Kelly Higgins-Devine on ABC Brisbane Radio

Women in Science, 8 March 2016

Smith, B (2015, September 21) Metal paint that reveals the rusty patches. COSMSO.

Pp 31

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Woolett, S (July 2015) Aerospace award for RACI student, Chemistry in Australia. pp

7

Amanda Weaver (May 2015) Aircraft ‘sunscreen’ wins top prize. QUT links, pp 16

Creedy, S (2015, March 6) The big ideas fly from airshow’s innovators and award

winners. The Australian. pp 33-34

Atfield, C (2015, February 24) QUT researcher takes out aviation award. The Sydney

Morning Herald. Retrieved from http://www.smh.com.au/

Atfield, C (2015, February 24) QUT researcher takes out aviation award. The Brisbane

Times. Retrieved from http://www.brisbanetimes.com.au/

Young Innovator award to DMTC PhD candidate (24 February 2015) Retrieved from

http://dmtc.com.au/young-innovator-award-to-dmtc-phd-candidate/

Lussini, V (2015) Interviewed by Natasha Mitchell on ABC Radio National Life

Matters, 24 February 2015

Young Innovator award to DMTC PhD candidate (24 February 2015) Retrieved from


QUT PhD student becomes first woman to win Aerospace Australia award (24

February 2015) Retrieved from https://www.qut.edu.au/news/news?news-id=85436

Oliver, L. (2015, February 19) Scientist’s aviation research takes flight. The

Westerner, pp 1-2,6.

http://www.smh.com.au/

http://www.brisbanetimes.com.au/


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Queensland PhD student nominated for national aviation award (6 February 2015)

Retrieved from http://www.defenceindustries.qld.gov.au/defence-industries/media-

and-resources/queensland-phd-student-nominated-for-national-aviation-award.html

Aerospace Australia Industry Innovation Award nominees announced (6 February

2015) Retrieved from http://australianaviation.com.au/2015/02/aerospace-australia-

industry-innovation-award-nominees-announced/

Aviation Innovation Awards shortlist announced (28 January 2015) Retrieved from

http://www.australiandefence.com.au/news/aviation-innovation-awards-shortlist-

announced

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IV. TABLE OF CONTENTS

I. Abstract ............................................................................................................. i

II. Keywords ........................................................................................................ iii

III. Publications Arising From This Project .......................................................... iv

Journal Articles ........................................................................................................ iv

Conference Lectures ................................................................................................. v

Conference Posters .................................................................................................. vi

Media ...................................................................................................................... vi

IV. Table of Contents ............................................................................................ ix

V. List of Figures ................................................................................................ xii

VI. List of Schemes ............................................................................................ xxii

VII. List of Tables................................................................................................ xxv

VIII. Abbreviations .............................................................................................. xxvi

IX. Declaration ................................................................................................ xxviii

X. Note to the Reader ..................................................................................... xxviii

XI. Acknowledgments ....................................................................................... xxix

1. Introduction ...................................................................................................... 1

1.1. Synthetic Polymers ........................................................................................ 1

1.2. Nitroxide Free Radicals ............................................................................... 12

1.3. Perylene Diimide ......................................................................................... 29

1.4. Applications of this Project ......................................................................... 31

1.5. Project Outline ............................................................................................. 32

1.6. Relationship of the Research Papers ........................................................... 36

2. Synthesis and Characterisation ...................................................................... 38

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2.1. Synthesis of Nitroxide ................................................................................. 38

2.2. 1st Generation Perylene Diimide based PFNs.............................................. 54

2.3. Synthesis of Naphthalimide PFNs ............................................................... 63

2.4. Synthesis of the Bay Region of Perylene Diimide PFNs ............................ 73

2.5. Experimental ................................................................................................ 84

3. Polyaromatic Profluorescent Nitroxide Probes with Enhanced Photostability

...................................................................................................................... 118

3.1. Abstract ...................................................................................................... 120

3.2. Introduction ............................................................................................... 121

3.3. Results and Discussion .............................................................................. 123

3.4. Conclusions ............................................................................................... 138

3.5. Experimental Section ................................................................................. 139

3.6. Acknowledgements ................................................................................... 155

4. Profluorescent nitroxide sensors for monitoring photo-induced degradation in

polymer films ........................................................................................................... 157

4.1. Abstract ...................................................................................................... 160

4.2. Key words .................................................................................................. 160

4.3. Introduction ............................................................................................... 160

4.4. Experimental .............................................................................................. 164


4.6. Conclusions ............................................................................................... 184


5. Profluorescent nitroxide sensors for monitoring the natural aging of polymer

materials ................................................................................................................... 186

5.1. Abstract ...................................................................................................... 189

5.2. Key words .................................................................................................. 189

5.3. Introduction ............................................................................................... 189

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5.4. Materials .................................................................................................... 193

5.5. Sample preparation .................................................................................... 194

5.6. Analysis methods ...................................................................................... 195

5.7. Results and discussion ............................................................................... 196

5.8. Conclusion ................................................................................................. 216


6. The Synthesis and Stability of Ferrari Red- Type Compounds .................. 218

6.1. Introduction ............................................................................................... 218

6.2. Experimental ............................................................................................. 220


6.4. Conclusion ................................................................................................. 232

7. Conclusions and Future Work ...................................................................... 233

7.1. Conclusions ............................................................................................... 233

7.2. Future Work .............................................................................................. 235

8. References .................................................................................................... 242

9. Appendix ...................................................................................................... 261

9.1. Supplementary Information for Polyaromatic Profluorescent Nitroxide

Probes with Enhanced Photostability (Chapter 3) ................................................ 261

9.2. Supplementary Information for Profluorescent nitroxide sensors for

monitoring the natural aging of polymer materials (Chapter 5) ........................... 300

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V. LIST OF FIGURES

Figure 1: World and European polymer production annually 1950-2016 (graph created

from data compiled from PlasticsEurope's Market Research and Statistics Group. 7-10

...................................................................................................................................... 1

Figure 2: The pathway to synthesis of the polyolefin, polyethylene, from the ethylene

monomer. ...................................................................................................................... 3

Figure 3: General schemes of oxidation of polymeric materials ................................. 6

Figure 4: Early examples of free radicals ................................................................... 13

Figure 5: Examples of Bis(t-alkyl) nitroxides ............................................................ 15

Figure 6: 1,1,3,3-tetraalkylisoindolin-2-yloxyls ........................................................ 16

Figure 7: Jablonski diagram64 .................................................................................... 19

Figure 8: Tethering of fluorophore to a nitroxide ...................................................... 21

Figure 9: Reduction of a rhodamine probe ................................................................. 22

Figure 10: PFN used by Ristovski’s group- BPEANO (23) and the PFN used by

Micallef and Colwell- TMDBIO (24) ........................................................................ 23

Figure 11: Degradation of PFN-doped polypropylene aged under O2 at 150ºC

monitored in parallel by chemiluminescence, FTIR-ATR and spectrofluorimetry. 35

.................................................................................................................................... 24

Figure 12: Comparison of non-degraded (top) and degraded (bottom) polypropylene

doped with TMDBIO104 ............................................................................................. 25

Figure 13: Polyaromatic hydrocarbons used in the PFN chromophore constructs .... 27

Figure 14: Water soluble PFNs .................................................................................. 28

Figure 15: Photo-stable PFN bases ............................................................................ 29

Figure 16: Chemical structures of PTCDA (42) , generic PDI (41) and the bay addition

locations positions in the ring system.125 ................................................................... 30

Figure 17: Target compounds for new robust PFN sensors ....................................... 33

Figure 18: Trimethylethylisoindoline by-product (53) .............................................. 41

Figure 19: Dimer (60) formed during diazonium reaction ......................................... 46

Figure 20: 1H NMR comparison of the 3 major products in deuterated chloroform.

Top: 90 (top), 89 (middle) and 44 (bottom). .............................................................. 59

Figure 21: 1H NMR comparison of the 3 major products (after the Fenton chemistry)

in deuterated chloroform. Top: 89 (top), 92 (middle) and 91 (bottom). .................... 60

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Figure 22: New and improved target compounds and their methoxyamine derivatives

.................................................................................................................................... 62

Figure 23: 1H NMR comparison of the aromatic region of 105 (top) and 104 (bottom)

in deuterated chloroform. ........................................................................................... 68

Figure 24: 1H NMR comparison of the aromatic region of 106 (bottom) and 104 (top)




Figure 26: 1H NMR of 113/121 in deuterated chloroform. Expanded regions of protons

‘f’ and ‘e’ to show the ratio of the isomers 113 and 121. .......................................... 77



Figure 28: Expanded region of the 1H NMR of 114 showing the isomer ratio between

1,6 and 1,7 .................................................................................................................. 82

Figure 29: 1H NMR comparison of the aromatic region of 117 (bottom), 115 (middle)

and 118 (top) in deuterated chloroform. .................................................................... 84

Figure 30: Chemical structures of perylene diimide 42, perylene-based profluorescent

nitroxides 44 and 129 and 9,10-bis(phenylethynyl)anthracene-based profluorescent

nitroxide 23. ............................................................................................................. 122

Figure 31: Fluorescence spectra of 1,8-napthalimide-based probes 105 (—) and 104

(···), 9 μM in cyclohexane; 106 (—) and 107 (···), 3 μM in cyclohexane, following

excitation at 350 nm. ................................................................................................ 134

Figure 32: Fluorescence spectra of perylene-based probes 114 (—), 116 (---) and 115

(···), 1 μM in chloroform, following excitation at 525 nm. ..................................... 135

Figure 33: Fluorescence loss (calculated as a percentage from the fluorescence

intensity at λmax) for cyclohexane solutions of 9,10-bis(phenylethynyl)anthracene 29

(-♦-, λmax = 470 nm), 104 (-■-, λmax = 408 nm), 106 (-Δ-, λmax = 407 nm), 113 (-x-, λmax

= 534 nm), 117 (-●-, λmax = 522 nm) and 114 (-+-, λmax = 557 nm) following photo-

irradiation at 765 Wm-2 and 40ºC. ........................................................................... 138

Figure 34: Tethering of a fluorophore to a nitroxide to form a PFN probe ............. 162

Figure 35: The structures of the polymers used in this study, PTMSP and TOPAS®

.................................................................................................................................. 163

Figure 36: Nitroxides used in this study and their non-radical (fluorescent)

methoxyamine derivatives ....................................................................................... 164

Figure 37: UV-Vis absorbance (dotted lines) and fluorescence emission (solid lines)

spectra of perylene fluorophore 114 in TOPAS® at various concentrations ranging

from 0.025 to 0.0025 w%, showing no evidence of any bathochromic shifts in the

bands or any obvious fluorescence quenching that might arise from aggregation. . 168

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Figure 38: Change in fluorescence emission of PTMSP films doped either with 29, 1

(-■-/left axis) or the nitroxide analogue, 23 (-♦-/right axis) with respect to UV ageing

time (hours). ............................................................................................................. 169

Figure 39: Change in fluorescence emission of PTMSP films doped either with ether-

linked naphthalimide fluorophore 104 (-■-/left axis) or the nitroxides analogue 105 (-

♦-/right axis) with respect to UV ageing time (hours). ............................................ 170

Figure 40: Change in fluorescence emission of PTMSP films doped either with alkyne-

linked naphthalimide fluorophore 106 (-■-/left axis) or the nitroxides analogue 107 (-

♦-/right axis) with respect to ageing time (hours). ................................................... 171

Figure 41: Change in fluorescence emission of the PTMSP films doped with either

ether-linked perylenediimide fluorophore 117 (-■-/left axis) or the nitroxides analogue

118 (-♦-/right axis) with respect to ageing time (hours)........................................... 172

Figure 42: Change in fluorescence emission of the PTMSP films doped with either

alkyne-linked perylenediimide fluorophore 114 (-■-/left axis) or the nitroxides

analogue 116 (-♦-/right axis) with respect to ageing time (hours). .......................... 172

Figure 43: Changes in the fluorescence emission of PTMSP films doped with non-

radical analogues, 29 (-■-, λmax = 470 nm), 104 (-▲-, λmax = 410 nm), 106 (-●-, λmax =

430 nm), 117 (-▬-, λmax = 560 nm) and 114 (-♦-, λmax = 615 nm) following photo-

irradiation at 250 Wm-2 and 40ºC for up to 6 h. Note: data collection was stopped at 6

hours as discolouration gave higher intensities than I0. ........................................... 173

Figure 44: Changes the fluorescence emission of PTMSP films doped with the

nitroxides, 23 (-■-, λmax = 470 nm), 154 (-▲-, λmax = 408 nm), 107 (-●-, λmax = 428

nm), 118 (-▬-, λmax = 550 nm) and 116 (-♦-, λmax = 610 nm) following photo-

irradiation at 250 Wm-2 and 40ºC for up to 10 h. ..................................................... 174

Figure 45: Change of the fluorescence emission for the PFN 116 in PTMSP from 0-10

h ageing compared to its non-radical analogue, 114 at time zero in PTMSP, showing

that the 116 has not achieved complete switch-on after 10 h ageing. ...................... 176

Figure 46: Change in fluorescence emission from PTMSP films doped with PFN non-

radical analogues (29, 105, 106, 117 and 114) over time at 70°C in the dark. ........ 177

Figure 47: UV-Vis spectra from undoped (blank) PTMSP (-) and TOPAS® (-) films.

.................................................................................................................................. 178

Figure 48: Change in the fluorescence emission from TOPAS® films doped with

PFNs (■, Right axes), relative change in UV-Vis absorbance of PFNs (♦, Left axes)

and relative change in UV-Vis absorbance of the non-radical analogues (●, Left axes)

during photo-ageing. (a) 104/105 (b) 106/107 (c) 117/118 (d) 114/116 .................. 180

Figure 49: Change of the fluorescence emission for the PFN 116 in TOPAS® from 0-

504 h ageing compared to its non-radical analogue, 114 at time zero in TOPAS®,

showing that the PFN 116 has only achieved a small fraction of complete switch-on

after 504 h ageing. .................................................................................................... 182

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Figure 50: UV-Vis absorbance at 250 nm (subtracted from UV-Vis absorbance at 400

nm) for the blank (undoped) TOPAS® film with respect to time in the suntest (left

axis, ■) and the oxidation index calculated from ATR-IR data from the blank

(undoped) TOPAS® film with respect to time in the suntest (right axis, ♦) ........... 183

Figure 51: Tethering of a fluorophore to a nitroxide to form a profluorescent nitroxide

(PFN), and trapping of carbon-centred free-radicals (formed during polymer

degradation), causing the PFN to switch from a non-fluorescent to a fluorescent state.

.................................................................................................................................. 191

Figure 52: Fluorescent and profluorescent probes used in this study. The fully

fluorescent non-radical analogue 114 is used as an indicator for the potential response

from the profluorescent probes 115 and 116............................................................ 192

Figure 53: Structure of TOPAS® (the cyclic olefin copolymer used in this study),

TMIO (55; a HALS analogue) and Tinuvin P (1; a common UV absorber). .......... 193

Figure 54: Oxidation indices as determined by FTIR-ATR for TOPAS® films aged in

the laboratory (Suntest) and outdoors (data of weather comparisons are summarised in

). ............................................................................................................................... 198

Figure 55: Fluorescence emission and oxidation indices of a laboratory-aged PFN

(115)-containing TOPAS® film. ............................................................................. 200

Figure 56: Fluorescence emission during natural weathering on the rooftop for

TOPAS® films doped with compounds 115 and 116 (0.025 wt%). ........................ 201

Figure 57: Relative change in UV-Vis absorbance for TOPAS® films doped with

compounds 114, 115 and 116 (0.025 wt%) during natural exposure on the rooftop.

.................................................................................................................................. 202

Figure 58: Relative change in fluorescence emission during natural weathering for

TOPAS® films doped with compounds 114 (fully fluorescent non-radical PFN

analogue), 115 (mononitroxide) and 116 (dinitroxide) at 0.025 wt%...................... 204

Figure 59: Oxidation indices as determined by FTIR-ATR for rooftop-exposed

TOPAS® films doped with compounds 114, 115 and 116 (0.025 wt%) and an additive-

free control sample. .................................................................................................. 206

Figure 60: Oxidation indices as determined by FTIR-ATR (left) and relative change

in UV-Vis absorbance (right) for TOPAS® films doped with compound 114,

115 and 116 (0.025 wt%) during aging in the laboratory (Suntest) and outdoors

weathering (other data for rooftop and suntest comparisons are summarised in )... 207

Figure 61: Relative change in UV-Vis absorbance of aged TOPAS® films doped

with PFN-analogue 114 (0.025 w%); compared to TOPAS® films containing PFN-

analogue 114 + TMIO (1, 2 and 4 eqv. of 114) with respect to radiant exposure (MJ/m2)

on the rooftop. .......................................................................................................... 209

Figure 62: Relative change in UV-Vis absorbance of aged TOPAS® films doped

with PFN-analogue 114 (0.025 w%); compared to TOPAS® films containing PFN-

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analogue 114 + Tinuvin P (0.1, 0.3 and 0.5 wt%) with respect to radiant exposure

(MJ/m2) on the rooftop. ............................................................................................ 210

Figure 63: Relative change in UV-Vis absorbance of aged TOPAS® films doped with

PFN-analogue 114 (0.025 w%); compared to TOPAS® film containing PFN analogue

114 + Tinuvin P (0.3 wt%), TOPAS® film containing PFN-analogue 114 + TMIO (2

eqv. of 114) and TOPAS® film containing PFN-analogue 114 + both Tinuvin P (0.3

wt%) and TMIO (2 eqv. of 114) with respect to radiant exposure (MJ/m2) on the

rooftop. ..................................................................................................................... 211

Figure 64: Relative change in UV-Vis absorbance of aged TOPAS® films doped with

PFN 115 (0.025 w%); compared to TOPAS® film containing PFN 115 + Tinuvin P

(0.3 wt%), TOPAS® film containing PFN 115 + TMIO (2 eqv. of 115) and TOPAS®

film containing PFN 115 + both Tinuvin P (0.3 wt%) and TMIO (2 eqv. of 115) with

respect to radiant exposure (MJ/m2) on the rooftop. ................................................ 212

Figure 65: Oxidation indices as determined by FTIR-ATR for aged TOPAS® films

doped with PFN 115 (0.025 w%); compared to TOPAS® film containing PFN 115 +

Tinuvin P (0.3 wt%), TOPAS® film containing PFN 115 + TMIO (2 eqv. of 115) and

TOPAS® film containing PFN 115 + both Tinuvin P (0.3 wt%) and TMIO (2 eqv. of

115) with respect to radiant exposure (MJ/m2) on the rooftop. ............................... 213

Figure 66: Fluorescence maximum trace of aged TOPAS® films doped with PFN 115

(0.025 w%); compared to TOPAS® film containing PFN 115 + Tinuvin P (0.3 wt%),

TOPAS® film containing PFN 115 + TMIO (2 eqv. of 115) and TOPAS® film

containing PFN 115 + both Tinuvin P (0.3 wt%) and TMIO (2 eqv. of 115) with respect

to radiant exposure (MJ/m2) on the rooftop. ............................................................ 214

Figure 67: Fluorescence maximum trace of aged TOPAS® films doped with PFN 116

(0.025 w%); compared to TOPAS® film containing PFN 116 + Tinuvin P (0.3 wt%),

TOPAS® film containing PFN 116 + TMIO (2 eqv. of 116) and TOPAS® film

containing PFN 3 + both Tinuvin P (0.3 wt%) and TMIO (2 eqv. of 116) with respect

to radiant exposure (MJ/m2) on the rooftop. ............................................................ 216

Figure 68: Compounds used in this study ................................................................ 219

Figure 69: Polymer films used in photo-oxidative degradation experiment ............ 220


intensity at λmax) for PTMSP films doped either with 29 (-■-, λmax = 383 nm), 131(-▲-

, λmax = 465 nm) or 114 (-♦- λmax = 568 nm) with respect to UV ageing time (hours).

.................................................................................................................................. 227


intensity at λmax) for PTMSP films doped either with 29 (-■-, λmax = 383 nm), 131(-▲-

, λmax = 465 nm) or 114 (-♦- λmax = 568 nm) with respect to ageing time (hours) at 70°C.

.................................................................................................................................. 228

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intensity at λmax) for PTMSP films doped with 116 with respect to UV (-■-) or thermal

(-♦-) ageing time (hours). ......................................................................................... 229


intensity at λmax) for TOPAS® films doped either with 29 (-■-, λmax = 383 nm), 131(-

▲-, λmax = 465 nm) or 114 (-♦- λmax = 568 nm) with respect to UV ageing time (hours).

.................................................................................................................................. 230


intensity at λmax) of 116 doped in PTMSP (-■-) or TOPAS (-♦-) films with respect to

UV ageing time (hours) ............................................................................................ 231


intensity at λmax) for TOPAS® films doped either with 29 (-■-, λmax = 383 nm), 131(-

▲-, λmax = 465 nm) or 114 (-♦- λmax = 568 nm) with respect to ageing time (hours) at

70°C. ........................................................................................................................ 232

Figure 76: Synthetic targets for varying the perylene diimide PFN ........................ 236

Figure 77: Different potential nitroxides for perylene diimide PFNs ...................... 237

Figure 78: Potential synthetic goals for photo-stable PFNs ..................................... 238

Figure 79: Synthetic route for potential new perylene diimide PFNs ...................... 240

Figure 80: 1H NMR spectrum of 5-Hydroxy-2-methoxy-1,1,3,3-

tetramethylisoindoline (64) ...................................................................................... 262

Figure 81: 13C NMR spectrum of 5-Hydroxy-2-methoxy-1,1,3,3-

tetramethylisoindoline (64) ...................................................................................... 263

Figure 82: HPLC (70% MeOH/ Water) chromatogram of 5-Hydroxy-2-methoxy-

1,1,3,3-tetramethylisoindoline (64) .......................................................................... 263

Figure 83: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-

tetramethylisoindolin-5-yloxy)-1,8-naphthalimide (104) ........................................ 264

Figure 84: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-

tetramethylisoindolin-5-yloxy)-1,8-naphthalimide (104) ........................................ 265

Figure 85: HPLC (70% MeOH/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-

4-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-1,8-naphthalimide (104) ..... 265

Figure 86: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-yloxy)-1,8-naphthalimide (105) ......................... 266

Figure 87: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-4-

(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yloxy)-1,8-naphthalimide (105) ............ 267

Figure 88: EPR (DCM) spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-yloxy)-1,8-naphthalimide (105) ......................... 267

Figure 89: Quantum Yield of fluorescence calculations for 104 and 105 ............... 268

P a g e | xviii

Figure 90: 1H NMR spectrum of 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline

(62) ........................................................................................................................... 269

Figure 91: 13C NMR spectrum of 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline

(62) ........................................................................................................................... 269

Figure 92: HPLC (70% MeOH/ Water) chromatogram of 5-Amino-2-methoxy-

1,1,3,3-tetramethylisoindoline (62) .......................................................................... 270

Figure 93: 1H NMR spectrum of 5-Diazonium-2-methoxy-1,1,3,3-

tetramethylisoindoline tetrafluoroborate (63) .......................................................... 271

Figure 94: 13C NMR spectrum of 5-Diazonium-2-methoxy-1,1,3,3-

tetramethylisoindoline tetrafluoroborate (63) .......................................................... 271

Figure 95: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-

tetramethylisoindoline-5-ethynyl)-1,8-naphthalimide (106) .................................... 272

Figure 96: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-

tetramethylisoindoline-5-ethynyl)-1,8-naphthalimide (106) .................................... 273


(2-methoxy-1,1,3,3-tetramethylisoindoline-5-ethynyl)-1,8-naphthalimide (106) ... 273

Figure 98: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-ethynyl)-1,8-naphthalimide (107) ....................... 274


(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-1,8-naphthalimide (107) ......... 275

Figure 100: EPR (DCM) spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-ethynyl)-1,8-naphthalimide (107) ....................... 275

Figure 101: Quantum yield of fluorescence calculations for 106 and 107 .............. 276

Figure 102: 1H NMR spectrum of N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-

methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-perylene-3,4,9,10-tetracarboxy

diimide (117) ............................................................................................................ 277

Figure 103: 13C NMR spectrum of N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-

methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-perylene-3,4,9,10-tetracarboxy

diimide (117) ............................................................................................................ 277

Figure 104: HPLC (75% THF/ Water) chromatogram of N,N-Di-(2,5-di-tert-

butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-perylene-

3,4,9,10-tetracarboxy diimide (117) ......................................................................... 278

Figure 105: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-3,4,9,10-tetracarboxy diimide

(118) ......................................................................................................................... 279

Figure 106: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-

butylphenyl)-1,7-di-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-

3,4,9,10-tetracarboxy diimide (118) ......................................................................... 279

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Figure 107: EPR (DCM) spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-3,4,9,10-tetracarboxy diimide

(118) ......................................................................................................................... 280


Figure 109: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-

1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide

(114) ......................................................................................................................... 281

Figure 110: 13C NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-


(114) ......................................................................................................................... 282


butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-

3,4,9,10-tetracarboxy diimide (114) ........................................................................ 282

Figure 112: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide

(116) ......................................................................................................................... 283


butylphenyl)-1,7-di-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-

3,4,9,10-tetracarboxy diimide (116) ........................................................................ 284

Figure 114: EPR (DCM) spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide

(116) ......................................................................................................................... 284

Figure 115: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-ethynyl)-7-(2-methoxy-1,1,3,3-

tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (115) .... 285

Figure 116: EPR (DCM) spectrum of N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-ethynyl)-7-(2-methoxy-1,1,3,3-

tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (115) .... 286


butylphenyl)-1-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-7-(2-methoxy-


(115) ......................................................................................................................... 286

Figure 118: Quantum yield of fluorescence calculations for 114, 116 and 115 ...... 287

Figure 119: 1H NMR spectrum of N-(Octylphenyl)-N’(1,1,3,3-tetramethylisoindolin-

2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide (98) .......................................... 288

Figure 120: HPLC (70% THF/ Water) chromatogram of N-(Octylphenyl)-N’(1,1,3,3-

tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide (98) ...... 288

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Figure 121: EPR (DCM) spectrum of N-(Octylphenyl)-N’(1,1,3,3-


Figure 122: Quantum yield of fluorescence calculations for 98 and 99 .................. 289

Figure 123: 1H NMR spectrum of N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-

tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-diimide (99) ............. 291

Figure 124: 13C NMR spectrum of N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-


Figure 125: HPLC (70% THF/ Water) chromatogram of N-(Octylphenyl)-N’(2-

methoxy-1,1,3,3-tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-diimide

(99) ........................................................................................................................... 292

Figure 126: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-


Figure 127: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-


Figure 128: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-

N’-(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide

(90) ........................................................................................................................... 294

Figure 129: EPR (DCM) spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-


Figure 130: Quantum yield of fluorescence calculations for 90 and 92 .................. 295

Figure 131: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-1,1,3,3-


Figure 132: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-

1,1,3,3-tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-diimide (92) . 296

Figure 133: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-

N’-(2-methoxy-1,1,3,3-tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-

diimide (92) .............................................................................................................. 297

Figure 134: 1H NMR spectrum of N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-

perylene-3,4,9,10-tetracarboxy diimide (130) .......................................................... 298

Figure 135: 13C NMR spectrum of N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-

perylene-3,4,9,10-tetracarboxy diimide (130) .......................................................... 298

Figure 136: HPLC (80% THF/ Water) chromatogram of N,N’-(2,5-Di-tert-

butylphenyl)-1,7-di-(phenoxy)-perylene-3,4,9,10-tetracarboxy diimide (130) ....... 299


Figure SI 138: Fluorescence maximum trace of aged TOPAS® films doped with PFN

116 (0.025 w%) during aging in the laboratory (Suntest) and outdoors weathering.

.................................................................................................................................. 301

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Figure SI 139: Oxidation indices as determined by FTIR-ATR for aged TOPAS® films

doped with PFN-analogue 114 (0.025 wt%) with respect to radiant exposure (MJ/m2)

on the rooftop. .......................................................................................................... 302

Figure SI 140: Relative change in UV-Vis absorbance for aged TOPAS® films doped

with PFN 115 (0.025 wt%) with respect to radiant exposure (MJ/m2) on the rooftop.

.................................................................................................................................. 303

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VI. LIST OF SCHEMES

Scheme 1: An example of the coupled electron and proton-transfer mechanism using

2-(2-hydroxy-5-methylphenyl)benzotriazole (1). (a) Photoinduced formation of

charge-transfer activated complex. (b) Proton transfer from the activated complex.33

.................................................................................................................................... 10

Scheme 2: Phenolic antioxidant pathway. .................................................................. 11

Scheme 3: Amine antioxidant pathway, known as the Denisov cycle. 11, 34 .............. 12

Scheme 4: Resonance of nitroxides and reversible redox structures ......................... 14

Scheme 5: Disproportionation reaction ...................................................................... 14

Scheme 6: Disproportionation of tert-butyl phenyl nitroxides .................................. 15

Scheme 7: Unfavourable α-cleavage of TMIO .......................................................... 16

Scheme 8: Radical trapping of nitroxides .................................................................. 17

Scheme 9: The quantitative reaction to detect hydroxyl radicals with the use of a

profluorescent nitroxide via Fenton chemistry ........................................................... 23

Scheme 10: An example of photo chemical induced living radical polymerization .. 27

Scheme 11: Synthetic route to 2-benzyl-1,1,3,3-tetramethylisoindoline 49 .............. 39

Scheme 12: High yielding acid catalysed condensation of phthalic anhydride 48 .... 39

Scheme 13: Exhaustive methylation of 48 with methyl magnesium iodide .............. 40

Scheme 14: Synthetic route to 5-amino-1,1,3,3-tetramethylisoindolin-2-yloxyl 57 .. 42

Scheme 15: Synthetic route to 5-hydroxy- 1,1,3,3-tetramethylisoindolin-2-yloxyl, (59)

.................................................................................................................................... 45

Scheme 16: Formation of hydroxyl radical via Fenton reaction to liberate methyl

radicals from DMSO .................................................................................................. 47

Scheme 17: The reaction pathway of the methoxyamine derivatives ........................ 48

Scheme 18: Synthetic scheme to the 5-ethynyl-1,1,3,3-tetramethylisoindolin-2-yloxyl

69 ................................................................................................................................ 49

Scheme 19: Lithiated species ..................................................................................... 50

Scheme 20: Improved iodination of TMI ................................................................... 52

Scheme 21: The reaction pathway to afford the methoxyamine derivatives ............. 53

Scheme 22: The reaction pathway to afford the cyano nitroxide 83 and its

methoxyamine derivative 84 ...................................................................................... 54

Scheme 23: The unsuccessful first synthetic pathway to form a PDI PFN ................ 55

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Scheme 24: The unsuccessful partial hydrolysis and reforming of the anhydride .... 56

Scheme 25: Single pot reaction and its side products ................................................ 58

Scheme 26: Unsuccessful single pot synthesis of PFN 94 ......................................... 61

Scheme 27: General reaction scheme for first generation perylene PFNs ................. 63

Scheme 28: The overall synthetic scheme of naphthalene-based PFNs .................... 64

Scheme 29: Nucleophilic substitution reaction employed for the synthesis of 105 .. 65

Scheme 30: Nucleophilic substitution reaction to link the protected nitroxide to

synthesis 104 and then oxidise to afford the nitroxide moiety 105............................ 66

Scheme 31: Proposed deprotection mechanism via N-oxidation and subsequent Cope-

type elimination147 ...................................................................................................... 67

Scheme 32: Sonogashira coupling to form 106 ......................................................... 69

Scheme 33: Oxidation to form nitroxide moiety of 107 ............................................ 71

Scheme 34: Overall synthetic scheme for bay region perylene PFNs ....................... 74

Scheme 35: Products of bromination reaction (112).................................................. 75

Scheme 36: Synthetic scheme for the condensation reaction to form 113 ................ 76

Scheme 37: The nucleophilic substitution reaction to form 117 from 113 ................ 78

Scheme 38: Oxidation of 117 to form PFN 118 ........................................................ 79

Scheme 39: Sonogashira reaction to form 114 .......................................................... 81

Scheme 40: Oxidation of 114 to form the nitroxide radical of 116 ........................... 82

Scheme 41: Oxidation of 114 to form the nitroxide radical of 115 ........................... 83

Scheme 42: Synthetic route to ether linked naphthalimide-based profluorescent

nitroxide 105. ........................................................................................................... 124

Scheme 43: Synthetic route to 5-hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline

64. ............................................................................................................................. 125

Scheme 44: Synthetic route to ethynyl linked naphthalimide-based profluorescent

nitroxide 107. ........................................................................................................... 126

Scheme 45: Synthetic route to ether linked perylene-based profluorescent nitroxide

118. ........................................................................................................................... 128

Scheme 46: Synthetic route to ethynyl linked perylene-based profluorescent nitroxides

116 and 115. ............................................................................................................. 129

Scheme 47: Synthetic route to imide linked perylene-based profluorescent nitroxide

98. ............................................................................................................................. 131

Scheme 48: Synthetic route to imide linked perylene-based profluorescent nitroxide

90. ............................................................................................................................. 132

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Scheme 49: Synthesis of 2,5-bis(2-octyl-1-dodecyl)-3,6-diphenylpyrrolo[3,4-

c]pyrrole-1,4(2H,5H)-dion (131) ............................................................................. 222

Scheme 50: The synthetic route to 2,5-bis(2-octyl-1-dodecyl)-3,6-di(2-methoxy-

1,1,3,3- tetramethylisoindoline)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dion, 133 ......... 224

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VII. LIST OF TABLES

Table 1: Photophysical properties of naphthalimide- and perylene diimide-based

nitroxide probes and their methoxyamine adducts................................................... 133

Table 2: Summary of PFN fluorescence changes in PTMSP films doped with PFNs or

their non-radical analogues during ageing. .............................................................. 175

Table 3: Summary of PFN sensor performance and stability in TOPAS® films

following photo-oxidative degradation. ................................................................... 181

Table 4: Solar exposure, temperature and rainfall conditions for rooftop weathering

and laboratory aging. ................................................................................................ 197

Table SI 5: Summary of aged TOPAS® films doped with PFNs (0.025 wt%) and

varying concentrations of 55 and 1 aged in the Suntest and aged on the rooftop. ... 304

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VIII. ABBREVIATIONS

Abs Absorbance

AcOH Acetic Acid

Ar: Aryl

b: Broad signal

d: Doublet

DCM: Dichloromethane

dd Doublet of doublets

dec.: Decomposed

DMF: N,N-Dimethylformamide

DMSO: Dimethyl sulfoxide

EI: Electron impact

EPR: Electron paramagnetic resonance

Eqv: Equivalent

ESI: Electrospray ionization

Et: Ethyl

Et2O: Diethyl ether

EtOAc: Ethyl acetate

EtOH: Ethanol

FTIR-ATR: Fourier transform infrared spectroscopy- attenuated total reflectance

h: Hour

HPLC: High performance liquid chromatography

HRMS: High resolution mass spectrometry

IR: Infrared

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ISC: Intersystem crossing

m: Multiplet

m-CPBA: 3-Chloroperoxybenzoic acid

me: Methyl

MeMgI: Methyl magnesium iodine

MeOH: Methanol

mol/L: Moles per litre

mol: Moles

M.p: Melting point

MS: Mass spectrometry

nm: Nanometres

NMR: Nuclear magnetic resonance

Pd/C: Palladium on charcoal

PFN: Profluorescent nitroxide

Ph: Phenyl

ppm: Parts per million

PTMSP: Poly(1-trimethylsilyl)-1-propyne

RT: Room temperature

s: Singlet

t: Triplet

THF: Tetrahydrofuran

TLC: Thin layer chromatography

TMIO: 1,1,3,3-Tetramethylisoindoline-2-yloxyl

UV: Ultraviolet

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IX. DECLARATION

This work has not previously been submitted for a degree or diploma in any university.

To the best of my knowledge and belief, this dissertation contains no material

previously published or written by another person except where due reference is made

in the dissertation itself.

Vanessa Lussini

X. NOTE TO THE READER

Chapters 3, 4 and 5, are as stated, previously published via peer review to allow thesis

by published papers. However, these paper chapters have minor changes from the

published papers to fit the flow of the thesis, and to reduce confusion. There are

changes to the numbering of the sections, compounds, figures, tables and schemes to

remove double ups within the thesis.

QUT Verified Signature

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XI. ACKNOWLEDGMENTS

Firstly, I must thank my supervisory team, Prof. Steven Bottle, Assoc. Prof. Kathryn

Fairfull-Smith, Dr. James Blinco and Dr. John Colwell (my pseudo supervisor). I know

I probably was not the easiest student to supervise and I know there were many times

where you probably wanted to kill me but thank you for sticking with me. Your

guidance and support during the long draughts of positive results did not go unnoticed.

Thank you for your pointers during design of experiments and your endless feedback

on drafts. Your doors were always open and all your advice got me to this point.

To my M6 family, thank you for all the banter. This PhD wouldn’t have been so

enjoyable without the lunch time breaks, pub crawls and random debates. You helped

me come in on the weekends because I knew there would always be someone around

to keep me from going crazy. Particular mention to the organic group, thanks for the

support in group meetings and having my back if I had a bad week.

Defence Materials Technology Centre, you did not just give me financial support; you

gave me a professional family. I have looked forward to every meeting, every

workshop and every conference, not just for the material but for the friendships I had

made. Without your connections, I would not have won the aerospace Australia award,

which has changed my life. I truly hope that I continue to work with you.

My mates, wow you guys have dealt with a lot. Sorry for disappearing for weeks at a

time and for random rants at weird hours. I know you guys didn’t always care about

my project but thanks for listening. A PhD can be very lonely but knowing you guys

were only a text away meant a lot. You keep me grounded when my ego enlarged but

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you lifted me up at my lowest. Only you guys truly know the emotional drain of a PhD

and I’m sure I have successfully turned you off doing one.

Grace, you truly witnessed how hard the last 5% is. Thank you for your moral support

and not allowing me to give up. I knew I couldn’t let you go when you selflessly

offered to proof my paper drafts. It has been a long journey, thank you for

understanding. I love you and bring on our next journey.

Last but obviously not least, my family. You guys were my support all the way

through, from big hugs to home cooked meals. No matter how bad my research was

going, you were always proud. I knew I could never disappoint you and every small

achievement was a celebration. This PhD is dedicated to you.

C H A P T E R O N E

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1. INTRODUCTION

1.1. Synthetic Polymers

The production of the current widespread, convenient and affordable synthetic

polymers and plastics has been an area of significant and ongoing research interest.1-2

Henri Braconnot was the first to discover a polymer, chitin, in 1811,3 although Jöns

Berzelius coined the term ‘polymer’ in 1827.4 The first exclusively synthetic polymer,

Bakelite, was synthesised by Leo Baekeland in 1907.5 Industrial research by Wallace

Carothers in the 1930s and a critical shortage of rubber during WWII saw a significant

increase in synthetic polymer production.6 Since 1950, there has been an exponential

growth of polymer production worldwide.7 In 1950, global polymer production was

1.3 million tonnes annually and in 2016 it reached approximately 335 million tonnes.8

Figure 1: World and European polymer production annually 1950-2016 (graph created from data

compiled from PlasticsEurope's Market Research and Statistics Group. 7-10

C H A P T E R O N E

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As the use of polymeric materials became more popular, the number of polymer

classes increased. There are now a wide assortment of polymer structural types, with

differing strengths, flexibilities, appearances and densities for different applications.7,

9 However, only five of these classes constitute almost 75% of the total global polymer

demand. 9 In order of demand these are:

1. Polyethylene (Low Density (LDPE); Linear Low Density (LLDPE) and High

Density(HDPE))

2. Polypropylene (PP)

3. Polyvinylchloride (PVC)

4. Polystyrene (Solid (PS) and Expanded (EPS))

5. Polyethylene Terephthalate (PET)

Polyolefins account for over 50% of the total global production of polymers. This

group includes polymers such as polyethylene which are synthesised with a simple

alkene monomer (Figure 2). The popularity of polyolefins is due to their inexpensive

synthesis and inert characteristics. However, as 40% of the total global polymer

production of polyolefins is for short-life products such as packaging, the degradation

and recycling of these products has become a primary focus in recent decades and will

be discussed later within this thesis.7

C H A P T E R O N E

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Figure 2: The pathway to synthesis of the polyolefin, polyethylene, from the ethylene monomer.

1.1.1. Polymer Degradation

The degradation of a polymer involves several physical and chemical reactions. As the

degradation process is accompanied by small structural changes, this can lead to the

quality of the polymeric material being significantly compromised. This results in the

properties changing and ultimately leads to a loss in functionality.11 In order to extend

the serviceable lifetime of polymeric materials, the chemical processes involved in

polymer degradation have been studied extensively.

The degradation pathway of polyolefins is typically a chain of complicated radical

reactions resulting in several products. It is said to be an auto-oxidative process and it

is proposed to follow these simplified general reactions1:

• Initiation: when radicals are generated in the presence of a source of energy.

• Propagation: when the radical is transferred from one chain to another.

Crosslinking occurs when the overall molecular weight increases and chain

scission occurs when the overall molecular weight decreases. This happens

C H A P T E R O N E

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when the concentration of radicals increases in the polymer matrix. Often once

this process has begun, it will continue at an increasing rate until termination.

• Termination: when radicals react with each other to form inert products. This

stabilises the polymer by reducing the number of radicals.

Different polymeric materials have characteristic modes of degradation.6 Each

polymer can degrade through a variety of mechanisms; yet it is often difficult to

determine the process through which degradation has occurred. For example, varying

temperatures and radiation levels provide different sources of energy and therefore

different potential pathways to aid the degradation processes.11

The sources of degradation vary, depending upon the environmental conditions in

which the polymer is used, its manufacturing history and the structure of the polymer

itself. These all play an integral role in controlling the overall rate determining step of

initiation. Degradation processes which polymers may undergo in everyday use are:12

1. Thermal: occurs when the polymer is heated to a temperature where it

undergoes chemical changes without simultaneous involvement of another

compound. This may occur during processing, and it often involves

oxidation.13

2. Mechanical: occurs with the application of forces or physical breakage,

resulting in potential chain scission.12

3. Ultrasonic: occurs with the use of sound at certain frequencies that can

induce the polymer chains to vibrate and split.12

4. Chemical: occurs when corrosive chemicals or gases (i.e. ozone), attack

the structure of the polymer, causing chain scission and oxidation.12

C H A P T E R O N E

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5. Biological: this is specific to polymers that contain functional groups that

can be attacked by microorganisms, such as esters.12, 14

6. Radiation: on exposure to sunlight or high energy radiation, either the

polymer itself or impurities which are left in the polymer from processing,

can absorb the radiation and initiate reactions. In the case of high energy

radiation, the polymer chains will split directly.12

Despite the popularity of polyolefins, they display extremely low resistance to

oxidative degradation. They need a combination of processing, heat and stabilisers to

guarantee their long-term performance.15 This is common for many polymeric

materials when exposed to an oxygen rich environment. Excess oxygen accelerates

oxidation reactions and the formation of oxygen derived radicals which further

accelerates the degradation process.16-17

1.1.2. Weathering

When polymeric materials are used in an outdoor environment, they are subjected to a

wide variety of environmental factors. This process is known as weathering and is

influenced by a number of factors which can have both individual and combined

effects on the resulting behaviour of a material.18 The outdoor environment can vary

in a number ways; sunlight, temperature, rainfall and wind. These factors also vary

widely in duration, intensity and sequence.19 However, the main influence on the

weathering of polymeric materials is the involvement of oxygen, shown below in

Figure 3.

C H A P T E R O N E

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Figure 3: General schemes of oxidation of polymeric materials

1.1.2.1. Photo-Oxidative Degradation

For most polymeric materials, the main cause of weathering is photo-oxidative attack,

which is the combined action of oxygen and sunlight on the chemical structure.19

Photo-oxidation is classified into two main types depending on the mode of light

absorption. Energy can be absorbed through units or groups which form part of the

polymer, such as aromatic pendant groups, or it can be absorbed through an impurity

within the polymer matrix which contains a chromophore.20-21 Polyolefins normally

do not contain UV absorbing chromophores, but trace amounts of chromophore-

containing impurities often remain after processing such as polymerisation catalyst

residues which can lead to photo-oxidation of the polymer.22-23

C H A P T E R O N E

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The initiation step of polymer degradation is caused by radical formation following

photon absorption. The degradation is normally concentrated on the surface of the

material. This is due to high rates of initiation which leads to oxygen depletion in the

solid state. This depletion is normally due to the low oxygen diffusion in the polymer.

1.1.3. Accelerated Weathering

The degradation of many polymer materials occurs at a slow rate outdoors, with no

apparent change in properties for extended periods. This has resulted in the need for

accelerated artificial exposure tests to reduce the significant amount of time required

to observe measurable degradation outdoors.

Accelerated ageing of polymers is often used to give insight into the serviceable

lifetime of polymers in particular environments. Relating laboratory ageing

experiments to real lifetimes is a difficult task, due to the many variables experienced

during actual in-use conditions.14 For example, one accelerated ageing protocol is

photo-oxidative testing, using xenon arc solar simulators. A range of solar simulators

are available, but these often do not emulate environmental elements such as morning

dew, pollution or changing temperatures throughout the day, all of which will affect

the degradation behaviour of polymer materials.24 Therefore, accelerated testing and

outdoor exposure should be used in combination to understand how the accelerated

ageing protocol used relates to the lifetime of a material outdoors.25

1.1.4. Degradable Materials

As mentioned, polymers are often used for short life products, therefore polymer

degradation is not always an undesirable process; with control, it can have beneficial

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outcomes to the environment. The disposal of plastics causes problems because of the

same properties which make them useful: durable, inert, and resistant. The National

Geographic Society26 believes there are 5.25 trillion pieces of plastic debris in the

ocean27, 269,000 tones float on the surface, while some four billion plastic microfibers

per square kilometre litter the deep sea.28 It is not surprising that there is currently

extensive research into environmentally degradable plastics, to alleviate plastic waste

disposal problems.

An optimal degradable material is one that is reduced to carbon dioxide, water and

minerals, leaving no environmentally harmful residues. There are three major methods

to degrade polymers:29

1. Biodegradation: The polymer is broken down by microbes metabolizing the

polymers into harmless products.

2. Chemodegradation: The polymer is degraded through chemical treatment.

3. Photo-degradation: The actions of ultraviolet light (usually sunlight) break

downs the polymer chains.

Degradable polymers benefit the environment by reducing waste, they can also present

great advantages for farmers by enabling control over moisture and weed growth.30

Biodegradable polymers have also found uses in medicine in areas such as drug

delivery, wound management and tissue engineering. 31-32 However, to gain control

over rates of degradation these polymers typically contain stabilisers and UV

absorbers.

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1.1.5. Stabilisers

Most polymers require some form of protection against the effects of solar radiation

to create control over their serviceable lifetime. Completely effective stabilisation is

never achieved in a commercial practice. In many cases, antioxidants and light

stabiliser degradation products can actually reduce the final stability of the polymer.12

As previously mentioned, polyolefins are unstable under weathering conditions but

with the addition of stabilisers, their useable life span can be increased dramatically.

To protect polyolefins from oxidative damage, antioxidant-based stabilisers are added

to trap the radical intermediates formed during degradation. This can lengthen the

initiation stage which is called the induction period. There are two main types of

antioxidants usually employed: phenolics and hindered amines.11, 21 Alternatively to

reduce the overall amount of radicals produced during degradation, a UV absorber can

be added to a polymer to absorb the UV irradiation associated with weathering.

1.1.5.1. UV Absorbers

In the case of UV absorbers, it is essential that they cause rapid dissipation of the

absorbed UV radiation via a suitable intramolecular rearrangement. Ortho-

hydroxyaromatics are designed to absorb the UV portion of the sunlight spectrum in

the range of 290-400 nm. The deactivation is thought to be due to an excited state

intramolecular proton transfer (ESIPT) mechanism.33 This results in a decrease of

energy being absorbed by the material thereby increasing its useful lifetime, Scheme

1.

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Scheme 1: An example of the coupled electron and proton-transfer mechanism using 2-(2-hydroxy-5-

methylphenyl)benzotriazole (1). (a) Photoinduced formation of charge-transfer activated complex. (b)

Proton transfer from the activated complex.33

1.1.5.2. Phenolic Antioxidants

Phenolic antioxidants are a diverse group of stabilizers. They can also absorb UV light

and chelate metals. As previously mentioned, free radicals mediate the degradation of

polymers. The two main types of radicals involved in polymer degradation are carbon-

and oxygen-centred radicals, R• and ROO•, that can be scavenged by the chain-

breaking antioxidants through an electron acceptor process, Scheme 2.

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Scheme 2: Phenolic antioxidant pathway.

1.1.5.3. Hindered Amine Stabilizers (HAS)

Hindered amine stabilizers were initially designed to act as light stabilizers (HALS)

although they have been shown to also increase thermal stability. At present, hindered

amine stabilizers are used as additives in most polymers, due to their ability to lengthen

their useable lifetime. Aromatic and heterocyclic amines are also popular stabilizers

for PO rubbers and coatings.

Aminoxyl radicals are formed during light exposure, or from chemical oxidisation.

They have antioxidant, antifatigue, antiozomant and photostabilizing properties due to

their able to scavenge R• and ROO•, which is a key stabilization pathway. The

regenerative property of the nitroxyl specie adds to the popularity as an additive. This

process known as the Denisov cycle, shown in Scheme 3.11, 34

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Scheme 3: Amine antioxidant pathway, known as the Denisov cycle. 11, 34

The stability of polypropylene during processing and its long term performance

depends on the heavy use of stabilisers which are designed to scavenge the free radicals

or their reactive precursors formed during degradation.35 The effectiveness of HAS

rely on the oxidation of the secondary or tertiary amine by the polymer-bound

hydroperoxide to form a nitroxide moiety. This then acts as a potent scavenger of

polymer alkyl radicals.11

1.2. Nitroxide Free Radicals

Free radicals are defined as an atom, compound or ion with an odd number of electrons

which are typically highly reactive and are generally short-lived transition species,

such as the radicals formed during polymer degradation. Nitroxides, however, are a

group of compounds that contain a stable, kinetically persistent free radical.

Nitroxides, also known as aminoxyl or nitroxyl radicals, contain a tertiary nitrogen

bonded to an oxygen radical which provides unique stability, allowing them to be

isolated and measured by EPR spectroscopy. The first nitroxide radical was an

inorganic nitroxide called Fremy’s salt (10) and was reported in 1845.36 Research in

this area was further progressed with the preparation of 4-oxo-2,2,6,6-

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tetramethylpiperidine-N-oxyl radical (4-oxo-TEMPO, 11) which displayed a

persistent nitroxide radical by Lebedev and Kazarnovsky in 1959.37

Figure 4: Early examples of free radicals

The popularity of nitroxides grew due to their distinctly unique physical and chemical

properties. Research into nitroxides has led to long list of applications in polymeric

materials,38 spin probes in biophysics,39 mechanistic probes in organic chemistry,40

and nitroxide-mediated polymerization control agents.41 One of the most important

features of nitroxides is their paramagnetic properties. The positive magnetic

susceptibility arising from the spin of the unpaired electron (S = ½) has in recent times

been used in the applications of spin labels which was pioneered by McConnell and

his collaborators in 1965.42-43

1.2.1. Nitroxide Stability

The stability of nitroxides is due to the stabilization energy (ca. ~120 kJmol-1 /32

kcal/mol)44 of the unpaired electron shared between the oxygen and nitrogen atoms,

shown in Scheme 4.45 In addition to this, the orbital overlap interaction between the

nitrogen non-bonding lone pair and the unpaired electron generates a three electron, 2

centre π bond, giving rise to the unique radical stability observed over other radical

species. Nitroxides can readily undergo reversible redox reactions; they can either be

oxidized to the oxoammonium ion or reduced to the hydroxylamine respectively,

Scheme 4.

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Scheme 4: Resonance of nitroxides and reversible redox structures

A radical commonly reacts with another radical species to form a stable product.

Although in the case of nitroxides, the formation of a O-O dimer is energetically

unfavourable due to the formation of a weak heteroatom nitrogen-oxygen-oxygen-

nitrogen bond being generated.46-47 The addition of steric bulk around the radical also

decreases the likelihood of bi-molecular reactions with itself.

It has been shown that nitroxides containing one or more hydrogens on the α-carbon

to the nitroxide group are typically unstable. These species preferentially undergo

disproportionation reactions to form nitrones and hydroxylamine species.48-49 The rate

of disproportionation depends on the surrounding substituents and solvent, Scheme 5.

Scheme 5: Disproportionation reaction

In addition to this, increased conjugation around the α-position may increase

thermodynamic stability to the system but it results in a less stable radical. This is due

to the formation of a stable carbon centred radical which results in a new pathway for

disproportionation.50 This is shown by tert-butyl phenyl nitroxide (12),51 in Scheme 6.

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Scheme 6: Disproportionation of tert-butyl phenyl nitroxides

Volodarsky45 summarised the factors which contribute to the stability of nitroxide free

radicals. The thermodynamic stability to the radical is due to the delocalization of the

unpaired electron over the N-O bond. The potential for dimerization is lowered due to

formation of the weak NO-ON bond. A reduction in bimolecular reactions can be

achieved by bulky substituents attached to the nitrogen atom. From these observations,

it has been widely concluded that bis(t-alkyl) nitroxides are now widely recognised as

the most stable of the nitroxide classes.52

Figure 5: Examples of Bis(t-alkyl) nitroxides

1.2.2. Isoindoline Nitroxides

Isoindoline nitroxides (17) are known for their superior chemical and thermal

stability.53 The earliest example of an isoindoline nitroxide was reported by Rozantsev

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in the 1960s with the synthesis of 1,1,3,3-tetraethylisoindolin-2-yloxyl (TEIO).54-55

Isoindoline nitroxides include all 1,1,3,3-tetraalkylisoindolin-2-yloxyls and their

aromatic-substituted derivatives, as shown in Figure 6.

Figure 6: 1,1,3,3-tetraalkylisoindolin-2-yloxyls

Isoindoline nitroxides are based on a rigid carbon framework which accounts for their

superior chemical and thermal stability.56 As previously mentioned, the absence of α-

hydrogens decreases disproportionation and α-cleavage reactions, Scheme 7. The

steric bulk around the radical group also increases the stability within the molecule as

it does not allow the radical to participate as easily in bi-molecular reactions with itself.

The aromatic ring adds rigidity to these compounds, making them less susceptible to

ring opening reactions.

Scheme 7: Unfavourable α-cleavage of TMIO

The aromatic ring also allows the incorporation of additional functionality and

therefore enables the synthesis of more complex structures with little impact to

nitroxide moiety.53 Due to the paramagnetic properties of nitroxides, they can be

difficult to characterise by NMR spectroscopy. The UV chromophore therefore is an

advantage for other analytical techniques such as HPLC and fluorescence

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spectroscopy. Nitroxides are also unreactive towards alkene radical addition and inert

to free radical attack with the exception of radical recombination at the nitroxide.57

1.2.3. Radical Trapping by Nitroxides

Nitroxide radicals are known for their stability against bimolecular reactions, however,

when in the presence of carbon, sulphur or phosphourus centred radicals, they react

readily at close to diffusion-controlled speeds (~107-109 M-1s-1).58 These rates can be

influenced by temperature59 solvent58 and the structure of the nitroxide (resonance

stabilization and steric protection).60 Nitroxides tend not to react with oxygen centred

radicals, due to the formation of a unstable product.57 The radical trapping reactions of

nitroxides with alkyl radicals results in a strong alkoxyamine product which is

diamagnetic so the process can easily be followed by loss of spin observed using EPR

spectroscopy or by the sharpening of the signals in the 1H NMR spectrum.

Scheme 8: Radical trapping of nitroxides

1.2.4. Excited State Quenching by Nitroxides

Nitroxides are known to be efficient quenchers of the excited singlet, doublet, triplet

and excimeric states. The mechanism is thought to be due to electron-exchange-

induced intersystem crossing and vibrational quenching/internal conversion from the

triplet state to the ground state.61-62

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As shown by the Jablonski diagram in Figure 7, in the normal fluorescence process, a

fluorophore can be excited from the singlet ground state (S0) to excited vibrational

energy levels through the absorption of a photon. This process is extremely rapid

taking about 10-15 s, although the return to ground state is considerably slower taking

from 10-14 s to several seconds.63 Immediately after arriving in the electronically

excited state, the molecule can dissipate some energy through vibrational relaxation

and internal conversion until it descends to the lowest vibrational level of the

electorally excited singlet state (S1). The excited molecule can then return to the

ground state via a number of pathways. This may happen through internal conversion

through excess energy being lost through molecular vibrations. This happens if the

energy difference between the ground and lowest excited state is small. Although when

there is significant difference, the excess energy can be released as the emission of a

photon (fluorescence) or by the classically spin forbidden process of intersystem

crossing (ISC).63 The molecule can also relax far from the first excited triple state (T1)

through emission of a photon, known as phosphorescence.

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Figure 7: Jablonski diagram64

Due to the lack of electronic repulsion in the triplet state compared to the singlet, the

triplet state lies below the excited singlet state in energy. Because the population of

the triplet state from the singlet state involves a change in spin angular momentum, the

process is classically forbidden. However, transitions from the lowest exited singlet

state to the triplet state are called singlet-triplet intersystem crossing. Most aromatic

molecules undergo some degree of intersystem crossing from the lowest excited

singlet state.

In paramagnetic species, such as nitroxides, fluorescence is reduced through the

enhanced prevalence of ISC. This process utilizes the unpaired nitroxide electron,

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which changes the multiplicity of the electronic states, such that doublet states (D0 and

Dn) are formed from the singlet ground state (S0) and the lowest singlet excited state

(S1) respectively, whilst the excited triplet state (T1) becomes the lowest excited

doublet state. Consequently, the previously spin forbidden transitions (S1 → T1 and T1

→ S0) become spin allowed processes.65

1.2.5. Profluorescent Nitroxides (PFNs)

The ability for a nitroxide to quench the excited singlet states of an aromatic

hydrocarbon occurs through intermolecular electron exchange interactions between

the nitroxide and the excited state compound within a collision complex.66 Stryer and

Griffith67 first proposed this could be used in applications in 1965. Fluorescence

quenching by nitroxides was utilised first by Bystryak68 but Blough66 demonstrated

the use of this property in profluorescent nitroxides with a number of seminal

publications. It has been shown that if a paramagnetic species, such as a nitroxide, is

tethered to a fluorophore, its fluorescence is quenched. However, if the nitroxide

radical is lost through a radical trapping or redox process, a diamagnetic product is

formed and this eliminates the intermolecular quenching pathway which results in the

return of the fluorophore’s fluorescence, Figure 8.66 A nitroxide tethered to a

fluorophore is therefore called a profluorescent nitroxide64 because the fluorescence is

suppressed until the radical moiety is trapped or undergoes redox chemistry to form a

diamagnetic species.

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Figure 8: Tethering of fluorophore to a nitroxide

1.2.6. Applications of Profluorescent Nitroxide Probes

Profluorescent nitroxides typically display suppressed fluorescence but the normal

fluorescence emission can be revealed by removal of the radical moiety through either

radical trapping or redox processes to yield the N-oxoammonium cation or

hydroxylamine. Profluorescent nitroxides therefore have the potential to be employed

as very sensitive probes for detecting alkyl radicals or redox changes.

Currently, PFNs have been employed to monitor overall cellular redox status and

detect oxidative stress.69-75 This is best shown by rhodamine (19) and sulforhodamine

B based PFNs which accumulated in the mitochondria due to their positive charge.

They have a unique reversible property of shuttling between the reduced and oxidized

form, allowing switch on and switch-off, functioning as cellular redox sensors, Figure

9. They also have a reasonably red-shifted wavelength for excitation and emission to

avoid simple absorbance in biological systems.74, 76-78

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Figure 9: Reduction of a rhodamine probe

Oxygen containing free radicals are involved in many pathological reactions.

Hydroxyl radical (•OH) is often reported as the most reactive and toxic oxygen radical,

and it is notoriously difficult to detect. The two most common techniques used for

hydroxyl radical detection are electron spin resonance (ESR) and aromatic

hydroxylation, however, these methods suffer from lack of selectivity, insensitivity,

limited stability and difficulties in quantification. This has resulted in the use of PFNs

to be used as a probe to detect •OH via Fenton chemistry. Fenton chemistry is the

reaction of •OH with DMSO to quantitatively to produce a methyl radical (•CH3). The

methyl radical then reacts with the PFN to produce a stable methoxyamine, Scheme 9.

This produces fluorescence increments which is proportional to the amount of •CH3

generated from the reaction of •OH with DMSO. Therefore being able to confirm the

concentration of •OH in a simple, sensitive and cost-effective manner.79-82

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Scheme 9: The quantitative reaction to detect hydroxyl radicals with the use of a profluorescent nitroxide

via Fenton chemistry

PFNs have been used extensively by the Ristovski group and others in the field of

environmental sciences.83-93 They have been shown to detect the formation of reactive

oxidative species (ROS), such as in cigarette smoke,85 burning logwood,86 diesel

exhaust89 and biodiesel exhaust.88 The ROS source is bubbled through impingers

containing a dilute PFN 23 (Figure 10) solution, which allows fluorescence detection

at the PFN’s emission wavelength.

Figure 10: PFN used by Ristovski’s group- BPEANO (23) and the PFN used by Micallef and Colwell-

TMDBIO (24)

In polymer chemistry, PFNs have been employed to monitor post polymerisation

transformations, 94-97 and to detect the aging of materials.35, 98-103 Micallef et al. used a

phenanthrene-based nitroxide, 24 (Figure 10) to detect free radical formation during

the degradation of unstabilised polypropylene.35

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The degradation was followed by infrared spectroscopy, chemiluminescence and

fluorescence, in parallel. This study showed that the profluorescent probe technique

was more sensitive than the established techniques, Figure 11. which showed little to

no information about the induction period.

Figure 11: Degradation of PFN-doped polypropylene aged under O2 at 150ºC monitored in parallel by

chemiluminescence, FTIR-ATR and spectrofluorimetry. 35

The fluorescence produced by the probe was strong enough to be imaged by

photography, Figure 12. This allowed simple and visible comparison of different

stages of degradation on the same film. This shows its true real world application in

detecting the useful lifetime of the polymer.

0

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Figure 12: Comparison of non-degraded (top) and degraded (bottom) polypropylene doped with

TMDBIO104

This study was extended further with structural changes to the PFNs used and

degradation of the polymer systems under a photo-oxidative environment. The PFNs

did show some success, however there was evidence of photo-bleaching

fluorophore.101 Colwell et al. 99 also showed that the addition of stabilizers to these

systems had no adverse interactions.

1.2.7. PFN Design

PFNs have been used to provide mechanistic insight into the initiation period of

polymer degradation which is not possible using current techniques.101 However, these

results can be complicated due to PFN degradation.35 The linkage between the

nitroxide and the fluorophore can often be cleaved, resulting in the fluorescence being

returned without the nitroxide moiety undergoing any chemical transformation. For

example, a nitroxide linked to a fluorophore through an ester or amide linkage is

potentially susceptible to hydrolysis and consequential separation of the nitroxide

moiety from the fluorophore.53 One approach to overcome this potential limitation in

the use of PFNs is to build the fluorophore into the nitroxide formwork by carbon-

carbon linkages.35, 53, 105-106 This strategy may also increase fluorescence quenching by

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decreasing the distance of the nitroxide radical to the fluorophore and holding the

nitroxide moiety in a locked geometry within the fused π system.64

Another important strategy to improve a PFN for a particular task is altering the

fluorophore used. Fluorescence switch-on can be improved by choosing a fluorophore

with a high fluorescence quantum yield. Particular fluorophores can be used to change

the excitation and emission wavelength regimes to allow the PFN to be tuneable for

the desired application.

Shorter wavelengths can be required to minimize spectral overlap in orthogonal, multi-

dye systems. However, longer wavelengths are often desired to avoid absorbance

overlap in biological chromophores. Simple polyaromatics hydrocarbons are the

simplest system use, where longer wavelength can be simply achieved with increased

aromaticity. There is a large selection of polyaromatic hydrocarbons PFNs, based on

naphthalene 25,61, 66, 79-80, 87, 95-96, 105, 107 anthracene 26,81, 87, 108 pyrene 27,70, 109

diphenylanthracene 28,53, 69, 98, 105, 110 bis(phenylethynyl)anthracene 29,53, 69, 83, 85-86, 89-

90, 92, 98 phenanthrene 30,35, 98-101, 105, 110 and stilbene 31 98-99, 111-112 chromophores which

all have tailored excitation and emission wavelengths.

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Figure 13: Polyaromatic hydrocarbons used in the PFN chromophore constructs

There are many other unique fluorophores used in PFN design, such as, azaphenalene

97, 101, 106, cyanine,113 dansyl,67, 69, 71-72, 99 coumarin,94, 109, 114-115 nitrobenzofurazan,109

benzothioxanthene,116 dibenzocyclooctyne,75 and quinoline.73, 102-103, 115, 117

Goto et al. used quinoline based PFN 31 in photo-induced living radical

polymerization (LRP).117 Alkoxyamines adducts are well known to be useful

mediators for LRP, resulting in well-defined low-polydispersity polymers.

Alkoxyamine dissociates to form the carbon-centred radical and the nitroxide radical.

This dissociation can be controlled photo-chemical reaction with the use of certain

fluorophores, Scheme 10.

Scheme 10: An example of photo chemical induced living radical polymerization

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As previously illustrated, PFNs are often used in biological systems to monitor overall

cellular redox status and detect oxidative stress. This relies on the PFN being water-

soluble and its emission wavelength not overlapping with common biological systems.

Chromophores that have been utilized include fluorescein 34,69, 118 fluorescamine 35,82,

93 9-diethylamino-5-benzo[α]phenoxazinone (Nile red) 36,78 4,4-difluoro-4-bora-

3a,4a-diaza-s-indacene (BODIPY) 37, 78, 119-120 and rhodamine 38.74, 76-77 Even metal

complexes such as ruthenium complexed with a phenanthroline ligand, 39 which can

be applied not only as a redox sensor but also as an EPR and photophysical probe for

monitoring the interaction with B-DNA has been reported.78

Figure 14: Water soluble PFNs

However, when focusing on stability, the only PFNs that can be found in literature

with suitable photo-stability, employ naphthalene imide 40 121 and perylene diimide

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bases 41,122-123 Figure 15. This is now the focus of future PFN design in detection of

photo-oxidative polymer degradation.

Figure 15: Photo-stable PFN bases

1.3. Perylene Diimide

Perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA) is the first known example of

this polyaromatic class, described as early as 1912.124 Although PTCDA was never

used as a pigment, it led to a number of perylene diimide pigments (PDI). The first of

the pigments to emerge was dimethylimide in 1913 but it was not until the 1950s that

Harmon Colours developed a number of varying pigments and made them on an

industrial scale.

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Figure 16: Chemical structures of PTCDA (42) , generic PDI (41) and the bay addition locations positions

in the ring system.125

The popularity of PTCDA is due to its two synthetic handles that can undergo a

condensation reaction with an amine to give an imide derivative (PDI). Although

PTCDA shows reasonable potential for reactions, its insolubility limits number of

possible chemical transformations.126

Perylene diimides have been extensively studied in dye and pigment research due to

their excellent chemical, thermal, photo and weather stability.124, 127 Furthermore,

many perylene diimides display other interesting properties such as near-unity

fluorescence quantum yields and high photo-chemical stability which have enabled

their use in other applications involving light harvesting and charge transport.128-130

They also have a longer wavelength of fluorescence and UV absorption which avoid

the normal absorptions and emissions of common additives. Many PDIs have been

employed as photosensitizers in energy and electron-transfer reactions131 and have

very high resonance stabilization energy and π-π interactions due to their planar

molecular structure.132

Modification of PTCDA to increase solubility by the addition of substituents at the

N,N0 positions (PDIs) was first employed by the Langhals, Figure 16.133 It was noted

that addition of groups to form imide bonds increased the solubility of the resulting

PDI in organic solvents (parent compound is PTCDA). An alternative approach to

overcome solubility limitations is to incorporate substituents in the “bay”-region of the

perylene unit as substitution at these positions increases solubility through slightly

twisting the perylene unit to disrupt planar π-π stacking interactions, Figure 16.134-136

It has been stated that incorporated bulky groups into the bay positions can increase

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solubility by several orders of magnitude,136 which can be linked to easier purification,

high yields and assumed better polymer distribution.

As a class, perylene diimide pigments offer high tinctorial strength; as well as excellent

light and weather fastness. They have excellent solvent stability; good migration

stability in plastics; fastness to overcoating paints; high chemical inertness and

superior thermal stability.124 Due to these properties they are used in high grade paints

where their relative high cost is outweighed by their quality and durability.

1.3.1. Perylene-based PFNs

For the chromophore properties alluded to above, perylene diimides represent an

attractive base structure from which to build new generation PFNs with superior photo-

stability to enable potential monitoring of the photo-oxidative degradation of organic

materials. The structurally rigid, isoindoline-based nitroxides are attractive target

moieties for enhanced stability PFNs, as the aryl ring extends the conjugation without

delocalizing the spin. Isoindoline nitroxides are more photo-stable than the piperidine-

based nitroxides, being less prone to degradation by hydrogen atom abstraction and by

α-cleavage with UV irradiation.137

1.4. Applications of this Project

Weathering effects that result in corrosion of the structure can be prevented using

protective coatings, such as polymers. Although, as the polymer degrades, small

surface cracks can appear in the polymer’s physical structure that result in the failure

of the coating to adequately protect the surface. Therefore, careful monitoring of the

coating is essential to maintain the integrity of the structure, yet current techniques

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lack sensitivity in detecting materials failure. This has resulted in the necessity for

periodic maintenance of coatings to avoid the potential catastrophic failure of

materials.

In this work, it was hypothesised that by linking a robust isoindoline nitroxide to a

known photo-stable fluorophore, it will be possible to generate a more photo-stable

PFN, able to withstand the harsh photo-oxidative environment of a degrading polymer

coating during weathering. This will avoid unnecessary maintenance of coatings,

which will save time, money and weight to the structure.

1.5. Project Outline

The main objective of this project was to synthesise new robust profluorescent

nitroxides (PFNs) which can detect the photo-oxidative degradation of polymers. The

primary focus during the design of the PFNs was the use of photo-stable fluorophores,

such as naphthalene imides and perylene diimides. The nitroxide moiety could be

linked through an imide bond by a condensation reaction with the anhydride of the

fluorophore and a primary amine containing nitroxide. Another synthetic methodology

involving halogenation of the fluorophore ring would allow a nucleophilic substitution

reaction with a hydroxyl containing nitroxide to form an ether linkage, or Sonogashira

coupling with an alkyne bearing nitroxide to form an alkyne linkage, Figure 17.

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Figure 17: Target compounds for new robust PFN sensors

The second component of this project involves the examination of the physical

properties of the prepared profluorescent nitroxides. With the synthesis of their non-

radical analogue via Fenton chemistry, determination of the extinction coefficients and

quantum yields of the new PFNs will be undertaken. This will assess the nitroxide’s

ability to quench the excited state of fluorescence, and therefore its sensitivity as a

potential probe for monitoring the photo-degradation of materials. Perylene diimides

have a longer wavelength of absorbance and fluorescence emission, which is outside

the typical absorbance window for common polymers, stabilizers and absorbers.

Further extension of this fused aromatic ring system is possible through increased

conjugation through the linker to the aromatic ring of the isoindoline moiety.

The third component of this thesis examined the photo-oxidative stability of the

synthesised PFNs. This analysis was first undertaken in a liquid model to avoid

complications with solubility within the polymer matrix. The irradiation source, a

Heraeus Suntest CPS+, is a laboratory based artificial irradiation source. The analysis

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of the irradiated PFNs was followed by UV absorbance and fluorescence, in parallel.

The diamagnetic methoxyamine analogues were also examined to avoid complications

arising from the presence of the nitroxide unit. All photo-oxidative stability tests were

done in comparison with the known, thermal stable, 9,10-

bis(phenylethynyl)anthracene (BPEA) fluorophore. The nitroxide containing PFNs

were then tested to observe the potential antioxidant effect of the nitroxide moiety on

the degradation rate of the fluorophore.

In the forth component of this thesis, the novel PFNs were assessed as probes for

monitoring the photo-oxidative degradation of two different polymer matrixes,

PTMSP and TOPAS® using artificial weathering. This involved evaluation of their

solubility, photo-stability, thermal stability and finally their ability to detect

degradation by fluorescence compared with classical techniques.

Numerous additives can typically be found in traditional commercial polymer

coatings. The PFN therefore also needs to be examined in the presence of antioxidant

species (the parent isoindoline nitroxide is employed as a model antioxidant) and UV

absorbers (commercially available UV absorber, Tinuvin P). This demonstrates the

amenability of the PFN to be an effective probe in the presence of other additives. This

is important as different polymer applications will in turn lead to different weathering

conditions and additive levels.

Finally, laboratory accelerated artificial exposure results were compared against

photo-degradation achieved using true weathering conditions. This was done to ensure

that the PFNs were only affected by UV irradiation and no other weathering effects

such as moisture, wind, pollution, etc.

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1.6. Relationship of the Research Papers

The flow diagram below shows the relationship between the aims of the PhD project

and the outcomes reported in published manuscripts. Note published paper chapters

have minor changes to fit the flow of the thesis, changes to the numbering of the

sections, compounds, figures, tables and schemes to remove double ups within the

thesis.

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Chapter 1- Introduction

An overview of the literature in polymers, polymer

degradation/stability, nitroxides, PFNs and the

perylene diimide fluorophore.

Chapter 2- Synthesis and Characterisation

A more detailed discussion around the synthesis and the characterisation of nitroxides, PFNs and

their non-radical derivatives. Including an experimental section of compounds that are not

included in the following chapters

Chapter 4: Profluorescent nitroxide sensors for monitoring photo-induced degradation in polymer films

Analysis of laboratory based photo-oxidative and thermal-oxidative stability studies of all PFNs and their non-radical analogues doped in PTMSP and

TOPAS® films. 10.1016/j.snb.2016.09.104

Chapter 5: Profluorescent nitroxide sensors for monitoring the natural aging of polymer materials

A detailed study into the differences between accelerated weathering conditions compared to a true Brisbane summer. With focus on photo-degradation rates of

films doped with PFNs compared to blank TOPAS films, with the addition of radical traps in different concentration and addition of UV absorbers in different

concentrations and their effect of photo-degradation rates.

Chapter 3: Polyaromatic Profluorescent Nitroxide Probes with Enhanced

Photostability

A brief discussion about the synthesis of PFNs with analysis of their physical

characteristics such as excitation and emission wavelengths, extinction

coefficients and quantum yields. Photo-oxidative stability of the non-radical

analogues was analysed in cyclohexane which gave promising results.

10.1002/chem.201503393

Chapter 6: The synthesis and stability of novel Ferrari-Red PFN

Analysis of laboratory based photo-oxidative and thermal-oxidative

stability studies of the novel Ferrari red based compounds doped in

PTMSP and TOPAS® films.

http://dx.doi.org/10.1016/j.snb.2016.09.104

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2. SYNTHESIS AND CHARACTERISATION

A note to the reader: This chapter does discuss reactions which have been previously

published and/or are discussed in the later chapters. However, this chapter investigates

mechanisms, purification, characterisation and additional reactions that remain

unpublished in detail.

2.1. Synthesis of Nitroxide

To prepare the target photo-stable PFNs, amine, hydroxyl and alkyne bearing

isoindoline nitroxide were required. As discussed in the previous chapter (1.2),

Rozantsev synthesised the earliest example of an isoindoline nitroxide.54-55 Giroud and

Rossat pioneered the first development of the 1,1,3,3-tetramethylisoindolin-2-yloxyl

based nitroxides in 1979.138 However, Griffins139 and co-workers developed the

synthetic pathway to TMIO (55) in moderate yield which is followed below.

Developments by Bolton140 showed their synthetic potential for nitration at the 5

position of the aromatic ring which was followed by synthetic advancements 141 142

Research within the QUT Free Radical research group101, 105-106, 143-145 has optimised

the synthetic pathway to yield amino, phenolic and alkyne bearing isoindoline

nitroxides.

2.1.1. Synthesis of 2-benzyl-1,1,3,3-tetramethylisoindoline (49)

Scheme 11 was first published by Griffiths in 1973.139 A number of improvements143

have since been developed with remarkable scale-ups.

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Scheme 11: Synthetic route to 2-benzyl-1,1,3,3-tetramethylisoindoline 49

The first step of the synthetic pathway involved the synthesis of N-benzylphthalimide

48 through the acid catalysed condensation of commercially available phthalic

anhydride 47 and benzylamine (50), Scheme 12.

After reflux for one hour, the reaction is complete, and the product precipitates out

once poured into ice water. The desired N-benzylphthalimide 48 can then be

recrystallised from hot ethanol giving quantitative yields.

Scheme 12: High yielding acid catalysed condensation of phthalic anhydride 48

The first step of the reaction is a ring opening reaction by nucleophilic attack by the

amine of the benzylamine on the carboxyl group of the starting material. If the

temperature is not high enough, the intermediate (51) often precipitates out of solution.

During reflux, the acid promotes the ring closing reaction to generate the hemiaminal

(52) that then undergoes dehydration to produce the desired N-benylphthalimide 48.

Melting point was found to be 116-120 °C which agrees with the literature146 melting

point of 115- 117 °C. Proton NMR of the product agreed with published values, with

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particular notice of the benzyl CH2 hydrogens having a singlet signal, integrating for

2 at 4.871 ppm.

The second step in Scheme 11 is conversely more difficult. This step uses the Grignard

reaction to form the desired tetramethylisoindoline product from the N-

benzylphthalimide 48 starting material. The reaction was performed on a large 100 g

scale and gives the modest yield of 20% after recrystallisation.

The Grignard reagent is synthesised by drop-wise addition of methyl iodide to a

solution of magnesium in diethyl ether under an argon atmosphere. Once the Grignard

reagent is formed, it was concentrated by distillation. N-benzylphthalimide 48

dissolved in anhydrous toluene was then added drop-wise at a rate that allowed the

temperature to remain constant. This step can be extremely exothermic due to the

reactivity of the methyl magnesium iodine to the carbonyl groups of N-

benzylphthalimide, Scheme 13. However, elimination of the magnesium salt for

tetramethylation via the iminium ion is difficult due to the poor leaving group qualities

of the salt. High temperatures are needed for the modest 20% yield of the

tetramethylated product. Any ether needs to be removed by distillation before heating

to reduce the yield of the by-product, trimethylethyl product 53 (Figure 18) which was

first isolated by Griffiths139. The mixture was refluxed for 3 hours.

Scheme 13: Exhaustive methylation of 48 with methyl magnesium iodide

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Any remaining Grignard reagent was then quenched, the product is extracted, passed

through a basic alumina column, and recrystallised from hot methanol.

Recrystallisation is also necessary to remove the trimethylethylisoindoline by-product

(53) which is an oil at room temperature.

Figure 18: Trimethylethylisoindoline by-product (53)

Melting point was found to be 58-62 °C which agreed with the literature139 value of

63-64 °C. The addition of methyl protons was observed in 1H NMR by a singlet signal

integrating for 12 hydrogens at 1.3 ppm. Furthermore, the [MH+] parent peak was

observed at 266.1934 m/z (calc. 266.1903) in the ESI high resolution mass spectrum.

Quenching and purification of 49 has become personalised due to its difficulty, size

and solubility issues of the reaction work-up. Hexane should be poured into the

mixture when the reaction mixture is still warm. This aids the breakdown of

magnesium complexes that form during the quenching of the reaction, if complexes

persist, refluxing for an hour to help disturb the solids. This removes complications of

product being stuck in the insoluble purple salt complexes. It also eliminates the

tedious scraping and washing with hexane. Previously, the quenched hexane solution

is bubbled with air overnight. However, the hexane solution can be reduced under

vacuum with a small amount of alumina gel present. This technique removes the

excess toluene with more confidence and the dried alumina can be dry loaded for a

shorter and therefore quicker filtration. If toluene persists, the purple impurity passes

through the basic alumina filtration and elutes with the product. If the yield is

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considerably lower, the filtrate can be back extracted with chloroform, which dissolves

all solids. The complex mixture is then purified via column chromatography. This

process is longer and more expensive, but all solids are processed to increase the yield

of 49.

The synthesis is now split into many synthetic pathways to yield a number of nitroxides

which can be coupled to the fluorophore in different reactions to form novel PFNs.

2.1.2. Synthesis of 5-amino-1,1,3,3-tetramethylisoindolin-2-yloxyl

(57)

Scheme 14: Synthetic route to 5-amino-1,1,3,3-tetramethylisoindolin-2-yloxyl 57

Debenzylation of the Grignard product to form 54 was achieved in quantitative yield.

This reaction involves a hydrogenation at 50 psi for 3 hours when no starting material

can be observed, and the more polar product, 1,1,3,3 tetramethyllisoindoline 54 is

formed. 1,1,3,3-tetramethylisoindolin-2-yloxyl (TMIO) 55 can then be synthesised

through oxygenation using meta-chloroperoxybenzoic acid (m-CPBA). It was found

that the hydrogenation reaction could be skipped, going straight from 49 to the

nitroxide product 55. However, avoiding this reaction resulted in a number of side

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products. This step was thus included, to avoid complicated purification with an

increased yield.

Characterization of the debenzylation was achieved through 1H NMR spectroscopy

and ESI+ HRMS. The 1H NMR spectrum was particularly valuable for confirming

successful debenzylation of the 2-benzyl-1,1,3,3-tetramethylisoindoline 49 precursor,

the loss of the characteristic CH2 (4.0 ppm), simplification of the aromatic region and

the broad singlet which corresponds to the secondary amine. Parent [MH+] peaks were

observed using ESI HRMS analysis with a peak at 176.1418 m/z, calculated at

175.1361.

The formation of the nitroxide moiety of the desired 1,1,3,3-tetramethylisoindine-2-

yloxyl 55 was formed by mild oxidation of 1,1,3,3-tetramethylisoindoline 54 using m-

CPBA. m-CPBA contains a weak peroxide bond which is displaced by the isoindoline

secondary amine. It then forms a hydroxylamine species, which is further oxidised by

oxygen in the atmosphere to form the desired nitroxide moiety. Previously Bottle et

al. have used the H2O2 -tungstate oxidation approach to generate the nitroxide moiety.

The disadvantage of this reaction is the 3 day reaction time in comparison to the near

instant reaction using m-CPBA. The reaction was left to stir overnight but peers have

quoted reactions at 30 minutes on smaller scales.147

Once the nitroxide radical has been formed, normal characterisation using NMR can

no longer be used due to their paramagnetic characteristic. The liberated methyl radical

via Fenton chemistry as able to trap the nitroxide in the presence of DMSO, this

reaction will be spoken about in more detail in the Section 2.1.4.

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This compound was characterised by melting point, HRMS (ESI) and EPR. The

melting point of 125-127 °C agreed with literature139 (128-129 °C). HRMS (ESI)

showed a peak which corresponded to [M+Na]+ at 213.1124 m/z (calcd. for

C12H16NNaO• [M+Na]+ 213.1130). The broadened NMR nicely complements the

sharp 3 peak EPR signal, confirming the nitroxide radical spin.140, 148

Nitration of the 1,1,3,3-tetramethylisoindolin-2-yloxyl 55 was first performed by

Bolton in 1993.140 However, it had previously been performed on the 1,1,3,3-

tetraethylisoindine-2-yloxyl.138 It resulted in a high yield of the desired product

1,1,3,3-tetramethyl-5-nitroisoindoline-2-yloxyl 56. This reaction demonstrates the

stability of the isoindoline nitroxide even when treated with concentrated acids. The

nitroxide product was obtained in high yield, with no evidence of decomposition after

work-up.

During addition of concentrated sulfuric acid, there is an immediate, strong colour

change to the reaction mixture. This is due to oxidation of the nitroxide to form the

oxoammonium salt. The nitroxide is easily recovered with oxidisation during work-up

to recover the desired product.

The desired compound 56 has a melting point of 155-158 °C was seen which agreed

with literature139 (160-162 °C). IR (ATR) showed the NO2 absorbance at 1526 cm-1.

HRMS (ESI) showed the parent [M+] 235.1207 m/z and the 258.1119 (1) [M+Na]

(calcd. for C12H15N2O3• [M] 235.11).

The simple reduction of the nitro group of the 1,1,3,3-tetramethyl-5-nitroisoindoline-

2-yloxyl 56 to the amine is the final reaction for one of the target nitroxides, 5-amino-

1,1,3,3-tetamethylisoindolin-2-yloxyl 57. Reduction at 50 psi in a hydrogen

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environment with use of Pd/C as the catalyst resulted in a quantitative yield of the

desired amine hydroxylamine product. The reaction resulted in the hydroxylamine

analogue due to the reducing environment being strong enough to convert the nitroxide

at the same time. This was easily overcome by re-oxidation to the nitroxide by addition

of the PdO2 in open atmosphere.

TLC showed that the compound had a reduced Rf value and no visible starting material

was present, indicating reaction completion. The product was further characterised by

HRMS (ESI) and IR (ATR). HRMS (ESI) gave the parent [M+H]+ 205.1698 m/z and

the 228.1237 m/z [M+Na] peak. IR (ATR) showed R-NH2 absorbances at 3356 and

3435 cm-1.

This product was then used in imide formation with the anhydride group of the PTCDA

(42) to form PDI PFNs. This reaction will be discussed further in Section 2.2.

2.1.3. Synthesis of 5-hydroxy-1,1,3,3-tetramethylisoindolin-2-

yloxyl (59)

Scheme 15: Synthetic route to 5-hydroxy- 1,1,3,3-tetramethylisoindolin-2-yloxyl, (59)

Previous synthesis of the phenol nitroxide by our research group was achieved through

a dilute acid catalysed reaction under reflux from the amino nitroxide which resulted

in a low overall yield of 41%.149 The diazonium salt of the nitroxide could be isolated

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in a high yield of 98%, and was moderately stable in a moisture free environment and

could be subsequently converted to the phenol in high yield.150

Nitrosyl tetrafluoroborate is extremely sensitive to moisture so the glove box was used

while weighing the reagent out. The reaction and addition were in a constant saturated

argon environment. The addition was drop-wise while stirred on an acetonitrile dry ice

bath. The acetonitrile solvent was freshly distilled, and the ether used to precipitate the

product was dried over sodium wire. It was found that if the ether was not dry it

catalysed the formation of the dimer 60, Figure 19 (isolated from the methoxyamine

starting material).151

Figure 19: Dimer (60) formed during diazonium reaction

Confirmation of the diazonium was achieved by FT-IR via the N≡N absorbance at

2200 cm-1. The melting point resulted in decomposition at 86-88°C with the assumed

evolution of nitrogen. HRMS (ESI) only showed the product without the boron counter

ion, plus lithium, 223.1062 m/z.

To prepare the phenol (59), the diazonium nitroxide 58 was simply refluxed at 100°C

for 24 hours in deionised water. The reaction was extracted periodically with ether to

remove the product and push the reaction completion. The isolation of the diazonium

salt resulted in a much higher yield of the hydoxyl nitroxide 59 than previous synthetic

routes.149

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2.1.4. Synthesis of 5-hydroxy-2-methoxy-1,1,3,3-

tetramethylisoindoline (64)

As previously mentioned, formation of the nitroxide moiety creates difficulty when

using the simple technique of NMR to characterise the compounds. The radical of the

nitroxide can also reduce stability of the compound in some reactions. To simplify the

compounds reactivity, the methyl protection group can be generated via Fenton

chemistry.

Hydroxyl radicals (OH·) can be produced from hydrogen peroxide in the presence of

a transition metal such as Fe2+. The hydroxyl radicals produced react with the solvent

(DMSO) to liberate methyl radicals that are consequently trapped by the nitroxide

moiety, to give the desired methoxyamine derivative, Scheme 16.

Scheme 16: Formation of hydroxyl radical via Fenton reaction to liberate methyl radicals from DMSO

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Scheme 17: The reaction pathway of the methoxyamine derivatives

Due to the limited stability of the 5-amino-1,1,3,3-tetramethylisoindolin-2-yloxyl (57)

and 5-hydroxy-1,1,3,3-tetramethylisoindolin-2-yloxyl (59) radicals the formation of

the methoxyamine derivative was performed on 1,1,3,3-tetramethyl-5-

nitroisoindoline-2-yloxyl (56). The normal palladium catalysed hydrogenation route

was then taken to form the amine (62), which was obtained as a low melting crystalline

solid in quantitative yield.

The diazionum salt (63) was formed using the same procedure as for the nitroxide.

Although the procedure resulted in a higher yield of 97% and cleaner product

according to its sharp melting point and white crystalline solid formed upon

precipitation from dry ether. This product was not purified any further and was

subsequently refluxed in water to offend the phenol in an 80% yield with loss of yield

probably due lower solubility of 63 in water compared to the more polar nitroxide

product.

All products showed the desired methoxyamine hydrogens, integrating for 3 protons

at ~3.8 ppm. The products also lost the characteristic yellow colour of the nitroxide

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analogues. However, this was not evident until the prducts were purified and any trace

races of iron, which is present in the Fenton chemistry reaction, were removed.

This product was used in the nucleophilic substitution reaction with the brominated

naphthalene diimide and brominated perylene diimide material which is discussed

further in Sections 2.3.1 and 2.4.3

2.1.5. Synthesis of 5-ethynyl-1,1,3,3-tetramethylisoindolin-2-

yloxyl (69)

Scheme 18: Synthetic scheme to the 5-ethynyl-1,1,3,3-tetramethylisoindolin-2-yloxyl 69

The first reaction in the, synthesis of 69, Scheme 18, was a one pot oxidative

debenzylation and bromination of the isoindoline aromatic ring to afford 5-bromo-

1,1,3,3-tetramethylisoindoline 65 which was first performed by Reid141 in a 40% yield.

Improvements were published by Micallef with an improved yield of 95%.142

However, a yield of 62% was achieved in this project, with the low yield possibly

being caused by over bromination or wet solvent during quenching.

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The Sonogashira coupling has been extensively studied within the research group. Due

to the low reactivity of the brominated isoindoline nitroxide towards palladium-

catalysed reactions, the iodo nitroxide was used to improve the viability of the reaction.

Aryl-iodides are known to undergo oxidative addition more readily in Pd-catalysed

couplings.53 This was overcome by iodination of the brominated analogue through

standard lithiation techniques. The reaction was performed at low temperature due to

the instability of the lithiated species. An excess (3 equiv.) of iodine was then added

to quench the lithiated species affording the N-iodoamine species in 2 steps, Scheme

19. Hydrogen peroxide was then used to reduce the resulting N-iodoamine species to

the desired secondary amine 5-iodo-1,1,3,3-tetramethylisoindoline 66.

Scheme 19: Lithiated species

There is no Rf change between the brominated species (65) and the newly formed iodo

product but there is a modest downfield shift of the aromatic proton peaks in the 1H

NMR spectrum. This can be rationalised by the reduced electron withdrawing

character of the iodo substituted analogue. This reaction is sensitive to water and can

result in the formation of 72 if hydrogen from the water is formed during the quenching

step.

The nitroxide moiety was achieved through oxidation with m-CPBA in quantitative

yield. At this point, the di-halogenated by-products can be separated through solubility

differences in hexane.

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Although literature procedures had shown105 that coupling of alkynes, such as

(trimethylsily)acetylene resulted in a high yield of 92%, it was found that the coupled

product had a similar Rf to the starting material and were therefore hard to separate by

column chromatography. To avoid these separation issues, 2-methyl-3-butyn-2-ol was

used despite the lower literature yield of 78%. This resulted in a much simpler

separation of trace un-reacted starting material, by- products (TMIO (55) and bromo-

TMIO (77)) and other non-polar impurities due to increased polarity of the hydoxyl

group. It was also found that addition of the protected alkyne to already refluxing KOH

resulted in a more soluble reaction mixture and a higher yield of 69.

The alkyne (69) was confirmed by HRMS (ESI), EPR and IR (ATR). The m/z, plus 2

hydrogens [M+2] was seen in HRMS (ESI) 216.1504 m/z, also 237.1254 [M+Na]+

(calcd. for C14H18NO• [M+2H]1+ 216.1388). EPR showed the desired 3 peak signal for

a nitroxide radical. Melting point agreed with literature105 value of 126-128°C. The

characteristic C≡C was seen by IR (ATR) at 2097 cm-1 and C≡C-H at 3276 cm-1.

2.1.6. Improved lodination

As described above, 5-iodo-1,1,3,3-tetramethylisoindoline (66) has characteristically

been synthesised via lithiation of the 5-bromo-1,1,3,3-tetramethylisoindoline (65).

However, a novel synthetic scheme has been developed using strongly electrophilic

iododium ions (I+).152 This method uses potassium iodide and periodic acid in

concentrated sulphuric acid to produce IOSO3H which allows direct iodination,

Scheme 20: Improved iodination of TMI.

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Scheme 20: Improved iodination of TMI

The published literature152 reported a ratio of 5-iodo-1,1,3,3-tetramethylisoindoline

(66) to 5,6-iodo-1,1,3,3-tetramethylisoindoline (73) of 7:3 respectively. However, the

literature stated addition of the starting material (54) as a solid to the previously formed

iodonium ion solution with thorough stirring. The di-iodo (73) by-product could be

reduced through slow addition of the iodonium solution to a chilled sulphuric acid

solution of 54. 1H NMR indicated an improved yield of 89 % for the mono (66), 6.8

% for the di (73) and 4.27 % unreacted 54. This had an improved yield of 89%

compared to the literature 34%. However, purification of the N-amino derivatives is

particularly difficult due to broadening of the elution bands of amines in column

chromatography coupled with the close Rf values of the di-iodo (73) and mono (66)

analogues. The product was therefore oxidised as a mixture and the nitroxide purified

by recrystallisation.

The oxidation of the secondary amine to form distinctive orange crystals of the

nitroxide moiety was achieved using m-CPBA. It was found that removal of all the m-

CPBA is difficult with only washing with base, so a short silica column was employed

using DCM as the elute.

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2.1.7. The synthesis of 5-ethynyl-2-methoxy-1,1,3,3-


Scheme 21: The reaction pathway to afford the methoxyamine derivatives

Since the Fenton reaction is performed in DMSO, solubility limitations can arise.

These limitations will be discussed in detail later in the chapter. Synthesis was

designed to remove the nitroxide moiety before tethering to the fluorophore to form

the target PFN. This methylamine can later be removed on the PFN via oxidation using

DCM as the solvent.

The synthesis of the alkyne was thus repeated for the methyloxyamine derivative, with

the only optimisation being the use of less polar solvent mixtures while performing

column chromatography. All products were white low melting point solids.

The product, 81, was used in the Sonogashira reactions with the brominated

naphthalene diimide and brominated perylene diimide material was discussed further

in Sections 2.3.2 and 2.4.5

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2.1.8. The synthesis of 5-cyano-2-methoxy-1,1,3,3-


Scheme 22: The reaction pathway to afford the cyano nitroxide 83 and its methoxyamine derivative 84

The procedure for palladium-catalyzed cyanation was adapted from Schareina,153

however it was applied to the 1,1,3,3,-tetramethylisoindoline by Thomas144 for the first

time. The reaction employs potassium hexacyanidoferrate(II) as the nitrile source. The

catalyst was removed from th reaction mixture via a plug filtrated using silica and

DCM/ethyl acetate mixture as the elute. The total elute was taken through to the next

step due to it polar properties. The secondary anime was then oxidised to afford the

nitroxide moiety. The nitroxide free radical was removed through Fenton reaction to

give the methoxyamine derivative 84.

2.2. 1st Generation Perylene Diimide based PFNs

2.2.1. Attempt 1

As mentioned in the previous chapter (1.3), PTCDA (42) can be easily solubilised

through the condensation reaction with a primary amine, ‘R-NH2’ to form an imide

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bond. It was first proposed that by the simple step-wise addition of one equivalent of

‘R-NH2’ a selective mono-addition to one anhydride of PTCDA could be achieved,

leaving the second anhydride free for secondary addition of the nitroxide (85). One

equivalent of the primary amine and one equivalent of PTCDA (42) were solubilised

by heating imidazole above its melting point of 130°C for 6 hours. However, TLC at

6 hours indicated a large amount of starting material and product with the same Rf as

the N,N′-‘R’ 3,4,9,10-perylenetetracarboxylic diimide (41) product. After purification

by column chromatography, the reaction was found to be unsuccessful with 41 as the

major product. This was due to the dramatic increase of solubility of 85 from 42, which

resulted in an increase of reactivity.125 This lead to rapid secondary addition and

consumption of the amine. This hypothesis was confirmed by the ~50% yield of the

N,N′-‘R’ 3,4,9,10-perylenetetracarboxylic diimide (41) and 50% unreacted PTCDA

(42), Scheme 23.

Scheme 23: The unsuccessful first synthetic pathway to form a PDI PFN

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2.2.2. Attempt 2

According to literature, 41 can undergo partial hydrolysis of the imide bond to form

the anhydride 85.126, 154-156 This would result in the consumption of the previous

reaction (a) by-products in Scheme 24.

Scheme 24: The unsuccessful partial hydrolysis and reforming of the anhydride

N,N′-‘R’ 3,4,9,10-perylenetetracarboxylic diimide (41) was heated at 85°C in a basic

solution of KOH for 1.5 hours. The product was then precipitated out of solution with

HCl and acetic acid. TLC showed the formation of a new product with increased

polarity. NMR indicated a reduced symmetry and a decreased number of signals in the

aromatic region. Using initial characterisation, reaction (b) appeared to have worked.

However, the subsequent condensation reaction (d) failed to result in the target

compound 85. It was assumed that the anhydride reformation was unsuccessful and

the diacid 87 was present. The successful removal of the second ‘R’ group would

show reduced symmetry and in decrease of signals in the aromatic region using NMR.

ATR-IR showed a broad OH stretching but initially that was mistaken for water. After

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the acid was assumed to be present a further experiment was performed to recyclize

the diacid 87 to give the anhydride 85 (c). This was done by refluxing in acetic

anhydride. However, TLC showed the generation of many unidentifiable products

which were unable to be purified.

2.2.3. Attempt 3

The third proposed synthesis was a one pot mixed addition. One equivalent of 2,5-di-

tert-butylaniline (88) was first reacted as the ‘R-group’. The amine was heated in

imidazole with one equivalent of 57 and one equivalent of 42 with a Lewis acid catalyst

(zinc acetate) for 6 hours at 130°C. The reaction gave 3 major products by TLC. It was

determined that the least polar product was 89 and the most polar was 44 by Rf

comparison with authentic compounds, shown in Scheme 25. The unknown middle

fraction was isolated by column chromatography in 22% yield. The product was

characterised first by 1H NMR spectroscopy which showed broadened signals which

is characteristic for the presence of a nitroxide radical. The nitroxide was also

confirmed by EPR, which showed a typical 3-line signal.

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Scheme 25: Single pot reaction and its side products

As a result of the large molecular size of the compound 90, only part of the NMR

spectra of the compound was affected by the radical, Figure 20. This resulted in the

‘aniline’ signals being visible in the NMR spectrum, Figure 20. It was noticed that the

integration was halved in the corresponding signals for 2,5- di-tert- butylphenyl

compared to aromatic hydrogens on the perylene diimide structure. Analysis by HPLC

confirmed the purity of the compound, which proved that it wasn’t a mixture of the

two symmetrical PDI compounds 89 and 44.

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Figure 20: 1H NMR comparison of the 3 major products in deuterated chloroform. Top: 90 (top), 89

(middle) and 44 (bottom).

To gain further information, a methylamine derivative of the target compound was

synthesised to sharpen the NMR signals by removal of the nitroxide moiety. The

nitroxide radical was trapped with methyl radicals generated by using Fenton

chemistry. The 1H from this product 90 revealed signals at 7.09, 7.21 and 7.30 ppm

for the aromatic isoindoline portion of the molecule, which indicates the success of the

nitroxide incorporation in the previous reaction, Figure 20.

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Figure 21: 1H NMR comparison of the 3 major products (after the Fenton chemistry) in deuterated

chloroform. Top: 89 (top), 92 (middle) and 91 (bottom).

Synthesis of the second target compounds, 94 was attempted using the first one pot

mixed addition method, using ethylene glycol solubilising chain as the ‘R-group’. It

was found to be unsuccessful due to the differing reactivities of the aromatic and

aliphatic amines, Scheme 26. The reaction gave N,N′-

Bis(methoxytetreethyleneglycol)perylene-3,4,9,10-tetracarboxyl-bisimide (95) as the

major product as identified by TLC comparison with authentic compound. It was

hypothesised that the reactivity of the primary amine on the glycol was greater than

the aniline of the TMIO.

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Scheme 26: Unsuccessful single pot synthesis of PFN 94

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2.2.4. Improved Target Compound Synthesis

Figure 22: New and improved target compounds and their methoxyamine derivatives

A series of new target compounds were proposed, all solubilising ‘R-groups’ were

aniline based amines, Figure 22. All three target compounds and methyl derivatives

were synthesised. The reaction gives a yield of ~25% for the target compound and

~50% in the Bis-R. This reaction could be improved by differing the equivalent of the

R-groups to increase yield of the target compound. The reaction is a one pot reaction

but it results in an extensive purification process by column chromatography. Due to

the low solubility of the perylene diimide derived products, this process is very time

consuming and expensive.

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Scheme 27: General reaction scheme for first generation perylene PFNs

Due to poor solubility of the perylene diimide PFNs in DMSO, the yield of the

methoxyamine via Fenton chemistry was poor in comparison to other small molecule

derivatives. It was noted that sonication in DMSO resulted in side reactions which was

further comfirmed by other group members.88 Development of a method for facile

removal of the methyl group to liberate the nitroxide radical has now been developed

and will be detailed further in the future work section, 7.2.

2.3. Synthesis of Naphthalimide PFNs

Due to the synthetic complications with the perylene diimides PFNs, the naphthalene

fluorophore (naphthalimide) was used as a model reaction. Naphthalimide’s structure

and reactivity is similar to perylene diimide’s, however due to its high solubility, it

results in higher yields. These properties will later be compared to see if these

advantages outweigh perylene’s physical stability and high quantum yields.

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Scheme 28: The overall synthetic scheme of naphthalene-based PFNs

Rotstein et al.157 electrophilic halogenation literature procedure for the bromination of

the naphthalene ring was followed due to its simplicity and near quantitative yield. A

simple condensation reaction to form the imide using the literature conditions

described by Hamel.158 It gave a cream solid with a melting form of 205-207°C in high

yield. HPLC and proton NMR was used to demonstrate its purity. Through ESI+

HRMS analysis the [M+ Na] peaks were observed for 103 at 486.0910 m/z and

488.0894 m/z in the ESI mass spectrum which corresponded to 79Br and 81Br isotopes

of 103 respectively (calc. 486.1045 and 488.1024). It was observed that there was a

notable fluorescence decrease due to heavy atom quenching.159-162

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2.3.1. Synthesis of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-yloxy)-1,8-naphthalimide

(105)

Scheme 29: Nucleophilic substitution reaction employed for the synthesis of 105

The first approach for further functionalisation of the brominated naphthalene (103)

was to react phenol nitroxide (59) in a base assisted nucleophilic phenoxide

substitution reaction. This was achieved by heating with KOH in DMF to give

substituted naphthalimide 105 in quantitative yield (99%) following the procedure

published by Hamel.158 Due to the nitroxide moiety being present, EPR was performed

to show the radical species. The product showed the desired [M+Na]+ peak at

612.28855 m/z. (cal. 589.3066) using HRMS ESI and ATR-IR showed the

characteristic absorption band due to the nitroxide moiety.

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Scheme 30: Nucleophilic substitution reaction to link the protected nitroxide to synthesis 104 and then

oxidise to afford the nitroxide moiety 105

As discussed, perylene diimides have limited solubility in DMSO, this resulted in the

nitroxide moiety being removed at an early stage in the synthesis. Therefore 5-

hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline (64) was used and undergoing the

same nucleophilic substitution with bromo naphthalimide (103) in a basic DMF

solution with mild heat to give substituted naphthalimide 104 in high yield (84%)

following the procedure published by Hamel.158 Characterisation was confirmed by

NMR and MS. Through ESI+ HRMS analysis the [M+ Na] peak were observed for

104 at 627.3095 m/z (calc. 627.3199 [M+Na]). Proton NMR showed all 11 aromatic

signals and the methoxyamine group at 3.81ppm. Removal of the methoxyamine of

104 was readily achieved to yield nitroxide 105 in good yield (78%) by oxidation with

m-CPBA in a Cope-type elimination, as illustrated in Scheme 31.147

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Scheme 31: Proposed deprotection mechanism via N-oxidation and subsequent Cope-type elimination147

Both methods proved to be successful, however Fenton chemistry is known to have

limitations. It proves to have varying yields, the large compounds have low solubility

in DMSO and is hard to scale up. Oxidation in this case seemed successful and easier

to follow because all the products could be characterised by proton NMR apart from

the final nitroxide product.

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Figure 23: 1H NMR comparison of the aromatic region of 105 (top) and 104 (bottom) in deuterated

chloroform.

Proton NMR analysis shows that with the nitroxide radical present, the signals on the

aromatic ring of TMIO (a, b and c) disappear due to the paramagnetic effect of the

radical. However, this effect is distance dependent, with only the signals within the

circle surrounding above being affected. However, the 2,5-di-tert-butylaniline signals

(d, e and f) are still strong and sharp. Due to the bent structure of the ether linkage,

signal k is not visible, however proton G which is furthest away out of the naphthalene

signals still shows its doublet characteristic properties.

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2.3.2. Synthesis of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-

1,1,3,3-tetramethylisoindolin-5-yloxy)-1,8-naphthalimide

(106)

Scheme 32: Sonogashira coupling to form 106

The alkyne link naphthalimide nitroxide, 106 was prepared via palladium-catalysed

Sonogashira coupling using similar conditions to a previously successful nitroxide

moiety coupling to a fluorophore.53 The coupling of the bromo naphthalimide 103 with

the alkyne bearing methoxyamine 81 in the presence of CuI and freshly prepared

tetrakis(triphenylphosphine)palladium(0)163 gave the desired substituted

naphthalimide 106 in high yield (90%).

As mentioned, the nitroxide moiety can be present during Sonogashira reaction,

however removal of the nitroxide radical via Fenton chemistry will cause

complications. This is due to the vulnerability of alkyne linkages to radical attack

experienced during a Fenton reaction, therefore methylamine was used due to the

previous success of oxidative removal of the methyl group. When comparing the

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methoxyamine of the ether and the alkyne linked naphthalimide, there are many

similarities, as shown in Figure 24.

Figure 24: 1H NMR comparison of the aromatic region of 106 (bottom) and 104 (top) in deuterated

chloroform.

When comparing the methoxyamine of the ether and the alkyne linked naphthalimide

there is the same multiplicity for each signal as expected and the ppm for the 2,5-di-

tert-butylaniline signals are identical. The isoindoline aromatic signals move up-field

on the ether linker PFN however, the large change is on the naphthalene ring. Where

signal ‘k’ moves almost 1 ppm downfield on the ether linked PFN. Showing the effect

of shielding due to the bent structure of the ether linkage compared to the straight

alkyne linkage.

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2.3.3. N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-ethynyl)-1,8-

naphthalimide (107)

Scheme 33: Oxidation to form nitroxide moiety of 107

Deprotection of the methoxyamine on the nitroxide of 106 was accomplished under

similar oxidative conditions as the ether linked naphthalimide to afford nitroxide 107

in excellent yield (97%). This reaction was done carefully to ensure the alkyne was

not also oxidised. Reaction was complete within 5 minutes and was quenched using

2M NaOH. EPR showed the characteristic nitroxide 3 peak signal. The product had a

slightly higher melting range of 165-170°C compared with other literature examples

but purity was confirmed by HPLC.

Due to the size of the molecules, both the ether linked and alkyne linked naphthalimide

PFN had regions within the NMR which were unaffected by the paramagnetic nature

of the nitroxide. They are affected by broadening as highlighted in Figure 25.

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chloroform.

The protons assigned to the isoindoline ring (a, b and c) do not appear when the

nitroxide moiety is present (circled above). However, as the distance increases, the

paramagnetic broadening effects decrease, and the fluorophore’s hydrogen signals

appear unaffected. This allowed comparison to the methoxyamine derivative due to

the little change in the ppm between the methoxyamine and the nitroxide.

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2.4. Synthesis of the Bay Region of Perylene Diimide PFNs

Perylene diimides have shown their photo-stability as fluorophores which has been

reviewed in the previous section (1.3). Due to the success of the naphthalene imide

reactions, the same reactions were planned for the perylene diimide fluorophore due

to their similar physical properties. However, perylene has a larger aromatic ring

system which results in multiple addition points.

Conditions for the bromination of the perylene bay region was first reported by Boehm

et al. in 1997.134 It resulted in a mixture of 1,7 and 1,6 regioisomers and a small

amount of tribromo, illustrated in Scheme 35. However, it is well known that the

separation of the regioisomers are difficult due to their limited solubility.164

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Scheme 34: Overall synthetic scheme for bay region perylene PFNs

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2.4.1. Synthesis of dibromoperylene-3,4,9,10-tetracarboxylic

dianhydride (112)

Scheme 35: Products of bromination reaction (112)

The bromination of PTCDA (42) is well reported in the literature. It requires harsh

reaction conditions with the use of Br2 in refluxing concentrated sulphuric acid and a

catalytic amount of iodine.165 Based on previous reported observations, it was

presumed that the crude mixture contains both the 1,7- dibromo-perylene dianhydride

(112) and 1,6-dibromo-perylene dianhydride (119) regioisomers and potentially a

small amount of the 1,6,7-tribromo-perylene dianhydride (120). However, limited

solubility meant that these regioisomers could not be detected by 1H NMR

spectroscopy at 400 MHz.127 The reaction mixture was neutralised which resulted in

precipitation of the products. The products were thoroughly washed with water and

dried in an oven. The products are not soluble in organic solvents and as result of this,

they are reacted as a crude mixture and purified after the following reaction step.165

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2.4.2. Synthesis of N,N′-Bis(2,5-di-tert-butylphenyl)-1,7-dibromo-

3,4,9,10-perylene dicarboximide (113)

Scheme 36: Synthetic scheme for the condensation reaction to form 113

Imidization of the crude brominated perylene dianhydride product was performed by

refluxing in propionic acid with 2,5-di-tert-butylaniline. It resulted in a dramatic

increase in solubility compared to other perylene diimide compounds by twisting the

planar structure to disfavour the formation of π-π aggregates. 1H NMR spectroscopy

of the mixture showed predominantly the 1,7-dibromo-perylene diimide 113, however

the 1,6-dibromo perylene diimide regioisomer was found in 34% of the mixture and

1% of the 1,6,7-tribromo compound, Figure 26. Separation of the desired compound

113 from the other isomers by column chromatography could not be achieved. In the

literature, purification of similar isomers could be achieved by recrystallisation,

although this was also found to be unsuccessful.166 The mixture therefore was carried

forward without further purification.

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Figure 26: 1H NMR of 113/121 in deuterated chloroform. Expanded regions of protons ‘f’ and ‘e’ to show

the ratio of the isomers 113 and 121.

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2.4.3. Synthesis of N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-

methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-perylene-

3,4,9,10-tetracarboxy diimide (117)

Scheme 37: The nucleophilic substitution reaction to form 117 from 113

The dibromo-perylene diimide 113 isomer mixture underwent nucleophilic

substitution with phenol containing methoxyamine 64. The reaction was successful in

a high yield of 87% of the perylene dimethoxyamine 117 under basic conditions. Some

literature references use strong bases such as NaH to deprotonate the phenol but K2CO3

proved to be strong enough.

The isolated product showed both the 1,7-dimethoxyamine-perylene diimide 117 and

its 1,6-dimethoxyamine-perylene diimide regioisomer in a ratio of 3:2 respectively by

1H NMR spectroscopy. This could be seen by the slight chemical shift between the 1,6

isomer to the 1,7 isomer, Figure 26. For the application of these compounds separation

of these two isomers was not required. Unfortunately, mass spectroscopy was not

possible due to poor solubility.

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2.4.4. The synthesis of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-

(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-


Scheme 38: Oxidation of 117 to form PFN 118

Oxidation of dimethoxyamine 117 with m-CPBA under mild conditions gave the

desired nitroxide 118 in excellent yield (99%). Although, 118 was not isomerically

pure (because of the previous bromination step), it was not purified further as

pronounced solubility differences between the isomers were not observed. The

presence of the 1,6-regioisomer showed no evidence of absorbance or fluorescence

shifting in the spectra.

Due to the size of the molecules, the paramagnetic broadening effect exhibited by the

nitroxide moiety only affected part of the molecule (circled). This allowed detection

of the fluorophore’s hydrogens and the 2,5-di-tert-butylaniline signals for comparison

to the methoxyamine derivative. It is noted that there is little change in the chemical

shift between the methoxyamine and the nitroxides, Figure 27.

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chloroform.

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2.4.5. Synthesis of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-

methoxy-1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-


Scheme 39: Sonogashira reaction to form 114

Sonogashira coupling of 1,7-dibromo perylene diimide 113 with the alkyne bearing

methoxyamine 81 in the presence of CuI and Pd(PPh3)4 resulted in a moderate (52%)

yield of the perylene dimethoxyamine 114. Analysis of the isolated product by 1H

NMR spectroscopy revealed the presence of 1,7-dimethoxyamine-perylene diimide

114 (54%) and the 1,6-dimethoxyamine-perylene diimide regioisomer (46%), Figure

28. The mixture was not further purified. It was found that if too much catalyst was

added a highly fluorescent spot was isolated. The structure was not able to be

ascertained, but it appeared to still have the perylene fluorophore with covalently

bonded triphenylphosphines by the presence of a signal in the phosphorous NMR.

However, the location of the covalent bond was unknown because crystals were unable

to be obtained.

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Figure 28: Expanded region of the 1H NMR of 114 showing the isomer ratio between 1,6 and 1,7

2.4.6. The synthesis of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-

(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-


Scheme 40: Oxidation of 114 to form the nitroxide radical of 116

Oxidation to yield the nitroxides moiety was facile using slow addition of 2.5

equivalents of m-CPBA to a chilled stirring solution of 114. The reaction only took 15

minutes but resulted in a quantitative yield when quenched with water and washed

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with dilute NaOH. As the alkyne linkage is also sensitive to oxidation, the reaction

was carefully monitored to ensure overoxidation did not occur. While only moderate

yields of the desired product could be isolated, it was also found to be selective to

oxidation of the nitroxide.

Scheme 41: Oxidation of 114 to form the nitroxide radical of 115

With addition of 1 equivalent of m-CPBA to a chilled solution was stirred 114 resulted

in both the production of 116 and the desired 115 with unreacted starting material. 114

could be easily isolated and further reacted to form more of the desired PFNs, both the

di and mono nitroxide. 115 would be characterised by the broadened NMR but the

methoxy group could be seen but with the EPR signal confirming the nitroxide radical.

The HPLC confirmed the pure product.

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Figure 29: 1H NMR comparison of the aromatic region of 117 (bottom), 115 (middle) and 118 (top) in

deuterated chloroform.

Proton NMR showed the distance dependent effect of paramagnetic broadening. This

is shown by the visible 2,5-di-tert-butylaniline signals but the disappearance of the

aromatic signals on the TMIO aromatic ring. The perylene diimide signals were still

seen but with a broadened effect. The stacked NMR spectrums, Figure 29 shows the

lack of shielding change between the 3 alkyne perylene diimide products and the

paramagnetic effect dependence on distance.

2.5. Experimental

Note to the reader: This section only includes the experiments which are not included

in following Sections: 3.5 and 6.2.

2.5.1. General Procedure

All other materials and reagents were of analytical reagent grade purity, or higher and

were purchased from Sigma Aldrich, Australia. All reactions were monitored using

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Merck Silica Gel 60 F254 TLC plates and visualized with UV light. Column

chromatography was performed using silica gel 60 Å (230 - 400 mesh). 1H NMR

spectra were run at 400 MHz and 13C NMR spectra at 100 MHz. Chemical shifts (δ)

for 1H and 13C NMR spectra run in CDCl3 are reported in ppm relative to the solvent

residual peak: proton (δ = 7.26 ppm) and carbon (δ= 77.2 ppm). Multiplicity is

indicated as follows: s (singlet); d (doublet); t (triplet); m (multiplet); dd (doublet of

doublet); br s (broad singlet). Coupling constants are reported in Hertz (Hz). Mass

spectra were recorded using either electrospray or electron impact (where specified)

as the ionization technique in positive ion mode. All MS analysis samples were

prepared as solutions in methanol. Infrared spectra were recorded as neat samples

using a Nicolet 5700 Nexus Fourier Transform infrared spectrometer equipped with a

DTGS TEC detector and an Attenuated Total Reflectance (ATR) accessory. Analytical

HPLC was performed on a Hewlett Packard 1100 series HPLC, using an Agilent prep-

C18 scalar column (10 μm, 4.6 × 150 mm) at a flow rate of 1 mL/min. All UV/Vis

spectra were recorded on a single beam Varian Cary 50 UV-Vis spectrophotometer.

Fluorescence measurements were performed on a Varian Cary 54 Eclipse fluorescence

spectrophotometer equipped with a standard multicell Peltier thermostatted sample

holder. Melting points were measured on a Gallenkamp Variable Temperature

Apparatus by the capillary method and are uncorrected. EPR spectroscopy was carried

out on a Magnettech MiniScope EPR spectrometer using a suitable nonpolar solvent

at room temperature. All air-sensitive reactions were carried out under ultra-high

purity argon. Diethyl ether and toluene were dried by storing over sodium wire. THF

was freshly distilled from sodium benzophenone ketal, acetonitrile from calcium

hydride and DMF from 4Å molecular sieves. TOPAS® 8007x10 was a gift from Ciba

Speciality Chemicals. PTMSP was purchased from ABCR GmbH. Cyclohexane was

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purified by washing with concentrated sulphuric acid until the wash was colourless,

followed by water, aq Na2CO3 and again water until neutral, and freshly distilled over

calcium hydride. All other materials and reagents were of analytical reagent grade

purity, or higher and were purchased from Sigma Aldrich, Australia.

2.5.2. N-Benzylphthalimide (48)

N-benzylphthalimide (48) was synthesised according to a procedure adapted from

those published by Manley-King.146

Phthalic anhydride (47) (106.64 g, 0.72 mol) was added to glacial acetic acid (500

cm3) in a round bottom flask (1 L). As the mixture stirred, benzylamine (~120cm3)

was added drop-wise. The mixture was refluxed for 1 hr, on completion the hot mixture

was poured onto a beaker of ice water (1.5 L). The mixture was then stirred until the

ice had melted. The white precipitate, N-benzylphthalimide was recovered by vacuum

filtration into a 2 L flask and washed with cold water. N-benzylphthalimide was

recrystallised with a minimum amount of boiling ethanol. The crystals were dried by

vacuum filtration to yield 48 as long white crystals. (138.9 g, 80.7 %). M.p. 116-120

°C (lit146 M.p. 115- 117 °C). 1H NMR (CDCl3): δ = 4.871 (s, 2H, N-CH2-Ar), 7.332

(m, 2H, Ar), 4.56 (d, 2H, J = 7.43 Hz, Ar), 7.725 (qu, 3H, J = 2.74 Hz, Ar) and 7.866

(qu, 2H J =2.74 Hz, Ar).

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2.5.3. 2-Benzyl-1,1,3,3-tetramethylisoindoline (49)

2-Benzyl-1,1,3,3-tetramethylisoindoline (49) was synthesised according to a

procedure adapted from those published by Griffiths et al.139

Pre-dried magnesium (120 g, 4.93 mol, 11.7 equiv.) and three small crystals of I2 were

placed in a round bottom flask (3 L) fitted with a still head, two dropping funnels,

thermometer, mechanical stirrer and two twin helix condensers connected in series

above the still head to which ice cold water was delivered with a peristaltic pump. A

positive pressure of argon was applied, with subsequent evacuation of the system

under vacuum and a positive pressure of argon reapplied.

Addition of anhydrous diethyl ether (400 mL) to the vessel was followed by the drop-

wise addition of methyl iodide (155 mL, 2.49 mol, 5.9 equiv.) via one of the dropping

funnels. The other dropping funnel was maintained with a constant supply of

anhydrous diethyl ether which was added periodically in order to keep a constant rate

of reaction. Once addition of the methyl iodide was complete, the mixture was stirred

until all activity had subsided, with subsequent concentration of the Grignard solution

by distillation until the interior temperature reached 80 °C.

Upon cooling the reaction mixture to 64 °C, a solution of N-benzylphthalimide (48)

(100 g, 0.421 mol, 1.0 equiv.) in dry toluene (800 mL) was added via both dropping

funnels at such a rate as to maintain a constant temperature. Following this addition,

diethyl ether was further reduced through distillation until a reaction temperature of

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110 °C was reached. The reaction mixture was then refluxed for 3 hours and then

further concentrated by distillation.

Once cooled, the mixture was diluted with n-hexanes (1.5 L), mixed thoroughly and

exposed to the atmosphere. The resulting purple slurry was filtered through celite

under vacuum, and the filtrate bubbled with air over night. This filtrate was

subsequently passed through a column of basic alumina, and the solvent was removed

under reduced pressure to give a golden oil which crystallized under vacuum and was

re-crystalised using methanol. (20 g, 19%) M.p. 56-58 °C (lit.139 M.p. 63-64 °C). 1H

NMR (CHCl3, 400MHz): δ= 1.3 (s, 12H, CH3-C), 3.99 (s, 2H, N-CH2-Ar), 7.13 (dd, J

= 3.08 Hz, 2H, Ar), 7.21-7.30 (m, 5H, Ar), 7.46 (d, J = 7.09 Hz, 2H, Ar). HRMS (ESI):

m/z (%) = 266.1934 (100) [MH+], calcd. for C19H24N [M+H]+ 266.1909.

2.5.4. 1,1,3,3-Tetramethylisoindoline (54)

1,1,3,3-Tetramethyllisoindoline (54) was synthesised according to a procedure

adapted from those published by Griffiths et al.139

2-Benzyl-1,1,3,3-tetramethyllisodoline (49) (1.8607 g, 7.011 mmol) was dissolved in

acetic acid and added to the reaction vessel with 10% Pd/C (0.2 g) catalyst. The vessel

was flushed with nitrogen 3 times, followed by hydrogen 3 times. The vessel was then

shaken at 40 PSI for ~6 hrs. The solution was then filtered through celite to remove

the catalyst and the bulk of the solvent was removed by reduced pressure. The mixture

was then neutialised using 5M NaOH and extracted with ether (3 x 50 mL). The

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combined organic layers were washed with water (3x 15 mL), followed by brine (30

mL) and dried over anhydrous sodium sulphate. The ether was removed by reduced

pressure to give 1,1,3,3-tetramethylisoindoline 54. The product was a low melting light

yellow solid. (1.305 g, 99 %). 1H NMR (CHCl3, 400MHz): δ= 1.46 (s, 12H, CH3-C),

7.12 (dd, J = 3.23 Hz, 2H, Ar), 7.25 (dd, J = 3.23 Hz, 2H, Ar). HRMS (ESI): m/z (%)

= 176.1418 (100) [M+H]+ calcd. for C12H18N [M+H]+ 176.1439.

2.5.5. 1,1,3,3-Tetramethylisoindolin-2-yloxyl (55)

1,1,3,3-Tetramethylisoindolin-2-yloxyl (55) was synthesised according to a procedure

adapted from those published by Chan et al.167

1,1,3,3-Tetramethylisoindoline (54) (1.029 g, 5.87 mmol) was dissolved in DCM in a

round bottom flask. 3-Chloroperoxybenzoic acid (1.4892 g, 8.63 mmol, 1.5 equiv.)

was added while stirring in an ice bath. The solution was left to stir for an hour, as it

returned to room temperature. Once completion, aqueous 2.5M sodium hydroxide was

added to deprotonate m-CPBA and the product was extracted with DCM (3 x 50 mL).

The combined organic layers were washed with water (3 x 20 mL), followed by brine

(50 mL) and dried over anhydrous sodium sulphate. The yellow liquid was

concentrated by vacuum to result in a dry yellow powder. (1.0824 g, 97 %). M.p. 115-

117 °C (lit.139 M.p. 128-129 °C). HRMS (ESI): m/z (%) = 213.1124 (15) [M+Na], calcd.

for C12H16NNaO• [M+Na] 213.1130.

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2.5.6. 1,1,3,3- Tetramethyl-5-nitroisoindolin-2-yloxyl (56)

1,1,3,3-Tetramethyl-5-nitroisoindolin-2-yloxyl (56) was synthesised according to a

procedure 138 adapted from those published by Bolton et al. 140

1,1,3,3-Tetramethylisoindolin-2-yloxyl (55) (0.5047 g, 4.625 mmol) was dissolved in

glacial acetic acid and placed in an ice bath without freezing. Sulfuric acid (2 mL, 7.2

mmol, 13.7 equiv.) was added slowly followed by conc. nitric acid (1 mL, 3.1 equiv.)

drop-wise with avoidance of overheating. The solution turned a red colour and it was

left to stir at R.T. until the solution lightened to yellow (~3 hrs). The mixture was then

quenched with 2.5M sodium hydroxide to a pH of 7. The product was extracted with

diethyl ether (3 x 25 mL). The combined organic layers were washed with water (3 x

10 mL), followed by brine (30 mL). The solvent was removed under reduced pressure

to give 1,1,3,3-tetramethyl-5-nitroisoindolin-2-yloxyl (56), as a strongly coloured

brown/orange solid. It was then recrystallised from hot ethanol to give well-formed

large orange crystals. (0.784 g, 72.13 %). M.p. 155 °C (lit.139 M.p. 160-162 °C). IR

(ATR) νmax 782 (=C-H), 839 (N-O), 1347 (R3N), 1526 (NO2), 2978 cm-1 (alkyl CH3).

HRMS (ESI): m/z (%) = 235.1207 (60) [M]+, 258.1119 (1) [M+Na], calcd. for

C12H15N2O3• [M] 235.1083

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2.5.7. 2-Methoxy-5-nitro-1,1,3,3-tetramethylisoindoline (61)

To characterise the target compound 56 the methoxyamine analogue (61) was

synthesised according to Fairfull-Smith.53, 147

1,1,3,3-Tetramethyl-5-nitroisoindolin-2-yloxyl (56) (74 mg, 0.315 mmol) was

dissolved in DMSO to which iron (II) sulphate heptahydrate (2.17 g, 7.8 mmol) was

added, where the solution changed from yellow to a dark brown. The flask was cooled

without freezing and 30 % hydrogen peroxide (1.33 mL) was added dropwise. The

reaction was then left to stir to 30 minutes at RT. The solution was poured into a beaker

of stirring ice water. The product was extracted with diethyl ether (3 x 10 mL) and

washed repeatedly with water (10 x 5 mL) to ensure DMSO had been removed. The

organic layer was concentrated by vacuum to give the desired product 61 (99 %, 78

mg). 1H NMR (CHCl3, 400MHz): δ= 1.57 (s, 12H, CH3-C), 3.78 (s, 3H, CH3-O), 7.23

(d, J = 8.36 Hz, 1H, Ar), 7.96 (d, J = 2.20 Hz, 1H, Ar), 8.12 (dd, J = 8.36, 2.20 Hz, 1H,

Ar). M.p. 60-63 °C.

2.5.8. 5-Amino-1,1,3,3-tetramethylisoindolin-2-yloxyl (57)

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5-Amino-1,1,3,3-tetramethylisoindolin-2-yloxyl (57) was synthesised according to a

procedure138 adapted from those published by Bolton et al.140

1,1,3,3-Tetramethyl-5-nitroisoindolin-2-yloxyl (56) (0.402 g, 1.71 mmol) was

dissolved in methanol (10 mL) and palladium on carbon (10% wt. loading, 41 mg)

added. The solution was placed in a Parr hydrogenator under an atmosphere of

hydrogen (40 psi) with shaking for 3 hours. The resulting suspension was filtered

through celite and the celite washed thoroughly with methanol. The combined filtrates

were concentrated at reduced pressure to give tetramethylisoindolin-2-yloxyl (57). The

product was a light yellow solid. (0.305 g, 99 %). HRMS (ESI): m/z (%) = 205.1698

(10) [MH+], 228.1237 (100) [M+Na], calcd. for C12H17N2NaO• [M+Na] 228.1239.

M.p. 172-175 °C. IR (ATR) νmax 762 (=C-H), 820 (N-O), 1336 (R3N), 2971 (alkyl

CH3), 3356 and 3435 cm-1 (RNH2).

2.5.9. 5-Diazonium-1,1,3,3- tetramethylisoindolin-2-yloxyl

tetrafluoroborate (58)

5-Diazonium-1,1,3,3-tetramethylisoindolin-2-yloxyl tetrafluoroborate (58) was

synthesised according to a procedure adapted from those published by Doyle and

Bryker.168

A solution of 5-amino-1,1,3,3-tetramethylisoindoline (57) (50 mg, 2.436x10-4 mol) in

dry acetonitrile (0.3 mL) was added dropwise to a stirring solution of nitrosyl

tetrafluoroborate (56.9 mg, 4.487 x10-4 mol) in dry acetonitrile (1.2 mL) at -30 °C (dry

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ice/acetonitrile bath). Once the addition was complete, the reaction was left to warm

to room temperature for 30 min. Dry diethyl ether (3 mL) with added dropwise to the

reaction and the mixture was left to stir to ensure precipitation. The white precipitate

of 11 was collected by filtration, washed with dry diethyl ether and stored under argon

in the freezer (47.8 mg, 97.6 %). IR (ATR) νmax 2200 cm-1 (N≡N). M.p. 86-88°C

(Dec.). HRMS (ESI): m/z (%) = 223.1062 (20) [M-(BF4-)+Li]+, calcd. for

C12H15LiN3O•+ [M-(BF4

-)+Li]+ 224.1370.

2.5.10. 5-Hydroxy-1,1,3,3-tetramethylioindolin-2-yloxyl (59)

58 (25 mg, 8.22x10-5 mol) was dissolved in deionised water (50 mL). The mixture was

refluxed at 100 °C for 48 hours, once cooled the solution was extracted with DCM (3

x 15 mL), washed with water (15 mL) and dried over sodium sulphate. The combined

organic layers were concentrated by vacuum to yield a pale yellow solid. The aqueous

layer was refluxed again at 110 °C over night worked up again to yield more product.

(15.9 mg, 93.7 %). M.p. 155 °C (lit.139 M.p. 160-162 °C). IR (ATR) νmax 782 (=C-H),

839 (N-O), 1347 (R3N), 2978 cm-1 (alkyl CH3).

2.5.11. 5-Bromo-1,1,3,3-tetramethylisoindoline (65)

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5-Bromo-1,1,3,3- tetramethylisoindoline (65) was synthesised according to a

procedure adapted from those published by Keddie.105, 145

A solution of 2-benzyl-1,1,3,3-tetramethylisoindoline 49 (2.5 g, 9.5 mmol, 1.0 equiv.)

in DCM (30 mL) was cooled in an ice bath to 0 °C and placed under an atmosphere of

argon. A solution of liquid Br2 (1.1 mL, 21.5 mmol, 2.3 equiv.) in DCM (40 mL) was

then added, followed by anhydrous AlCl3 (4.5 g, 34 mmol, 3.6 equiv.). The reaction

was maintained with stirring for one hour then poured onto ice (~ 75 mL) and stirred

for 15 mins. The resulting solution was basified (pH 14) with 10M NaOH and

extracted with DCM (3 × 100 mL). The combined organic phases were washed with

H2O (50 mL) and dried over anhydrous sodium sulphate. The solvent was removed by

vacuum to yield a yellow residue. The residue was then dissolved in methanol (~ 15

mL) and NaHCO3 (~ 100 mg) added. To this solution was added aqueous H2O2 (30%)

until no further effervescence could be detected. 2M H2SO4 (40 mL) was then added

(caution: effervescent) and the solution then washed with DCM (3 × 100 mL). The

combined organic phases were then back extracted with 2 M H2SO4 (3 × 100 mL). The

combined acidic aqueous phases were then cooled in an ice bath, basified (pH 14) with

10 M NaOH and extracted with DCM (5 × 100 mL). The combined organic phases

were then washed with H2O (100 mL) and dried over anhydrous sodium sulphate. The

solvent was removed in vacuo to afford 65 as a low melting white solid. (1.48 g, 62

%). 1H NMR (400 MHz, CDCl3): δ (ppm) = 1.45 (d, J = 3.6 Hz, 12H, 4×CH3), 1.87 (s,

1H, NH), 7.00 (d, J = 8.0 Hz, 1H, Ar), 7.25 (d, J = 1.6 Hz, 1H, Ar), 7.37 (dd, J = 8.0,

1.6 Hz, 1H, Ar).

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2.5.12. 5-Iodo-1,1,3,3-tetramethylisoindolin (66)

5-Iodo-1,1,3,3- tetramethylisoindoline (66) was synthesised according to a procedure

adapted from those published by Keddie.105

A solution of 5-bromo-1,1,3,3-tetramethylisoindoline 65 (1.6 g, 6.3 mmol, 1.0 equiv.)

in anhydrous THF (17.8 mL) was cooled to - 78 °C (dry ice / acetone). n-BuLi (1.6 M

in n-hexanes, 10.7 mL, 17.12 mmol, 2.7 equiv.) was then added (drop-wise) and the

resulting mixture stirred for 15 minutes. A solution of I2 (4.8 g, 18.9 mmol, 3.0 equiv.)

in anhydrous THF (40 mL) was then added (drop-wise) and the reaction allowed to

return to room temperature. The reaction mixture was then poured into ice / H2O (~

100 mL) and basified (pH 14) with 5M NaOH. The resulting solution was then

extracted with DCM (5 × 100 mL) and the combined organic phases washed with water

and dried over anhydrous sodium sulphate. The solvent was removed by vacuum to

yield a clear residue which was then dissolved in methanol (~ 30 mL) and NaHCO3 (~

90 mg) added. To this solution was added aqueous H2O2 (30 %) (~ 18 mL) followed

by 2M H2SO4 (500 mL) (caution: effervescent). The resulting solution was washed

with DCM (3 × 500 mL) and the combined organic phases back extracted with 2M

H2SO4 (3 × 500 mL). The combined acidic aqueous phases were then basified (pH 14)

with 10M NaOH and extracted with DCM (5 × 500 mL). The combined organic phases

were then washed with H2O (200 mL) and dried over anhydrous sodium sulphate. The

solvent was removed by vacuum to afford 66 as a low melting white solid. (0.951 g,

50.3 %). 1H NMR (400 MHz, CDCl3): δ (ppm) = 1.45 (s, 12H, 4×CH3), 1.76 (s, 1H,

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NH), 7.46 (d, J = 1.2 Hz, 1H, Ar), 7.58 (dd, J = 8.0, 1.6 Hz, 1H, Ar). HRMS (ESI):

m/z (%) = 302.0575 (30) [M+H], calcd. for C12H17IN [M+H]+ 302.0406.

2.5.13. Improved synthesis of 5-Iodo-1,1,3,3-tetramethylisoindolin

(66)

5-Iodo-1,1,3,3- tetramethylisoindoline (66) was synthesised according to a procedure

adapted from those published by Fairfull-Smith.152

Periodic acid (0.27 eqv., 3.16 g, 1.8 x10-2 mol) was dissolved in ~50 mL of conc.

sulphuric acid and stirred at 0°C, while potassium iodide (0.85 eqv., 2.55 g, 1.53x10-2

mol) was added in small portions. It was then stirred at RT for 15min, it was then

transferred into a dropping funnel. 49 was then dissolved in ~50 mL of conc. sulphuric

acid and stirred at 0°C, the potassium iodide solution was added dropwise over 30

mins, after which the reaction was further stirred at RT for 3 hours. The reaction was

then poured slowly onto ice and basified using NaOH pellets slowly until the mixture

was basic and extracted with DCM (3 x 100 mL), washed with water (5 x 50 mL) and

dried over NaSO4. The reaction was purified by filtration of a hot reaction mixture in

hexane. Yield: 4.77 g of mono iodo (89 %), 512 mg of di iodo (6.8 %) and 133 mg of

unreacted (4.27 %) by 1H NMR. No characterisation was performed due to difficult

purification.

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2.5.14. 5-Iodo-1,1,3,3-tetramethylisoindolin-2-yloxyl (67)

5-Iodo-1,1,3,3- tetramethylisoindolin2-yloxyl (67) was synthesised according to a

procedure adapted from those published by Keddie.105

5-Iodo-1,1,3,3-tetramethylisoindoline (66) (0.951 g, 3.58 x10-3 mmol, 1.0 equiv.) was

dissolved in DCM (25 mL) and cooled to 0 °C in an ice bath. m-CPBA (77%, 0.859 g,

4.98 x10-3 mmol, 1.3 equiv.) was added slowly to the stirring solution and stirred for

30 minutes at 0 °C. The reaction mixture was then allowed to return to room

temperature and H2O (200 mL) added. The organic phase was then washed with 2M

NaOH (3 × 100 mL) then brine (100 mL) and dried over anhydrous sodium sulphate.

The solvent was then removed in vacuo followed by recrystallization from ethanol to

afford 67 as an orange crystalline solid (1.0656 g, 99 %). HRMS (ESI): m/z (%) =

302.0575 (25) [M(-O•)+2] calcd for C12H17IN• [M(-O•)+2] 302.0406, EPR: g =

2.0062, aN = 1.429 mT.

2.5.15. 5-(3-Hydroxy-3-methyl)butynyl-1,1,3,3-

tetramethylisoindolin-2-yloxyl (68)

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5-(3-Hydroxy-3-methyl)butynyl-1,1,3,3-tetramethylisoindolin-2-yloxyl (68) was

synthesised according to a procedure adapted from those published by Keddie.105

A solution of 5-iodo-1,1,3,3-tetramethylisoindoline (67) (1 g, 3.163 mmol, 1.0 equiv.),

4-diazabicyclo[2.2.2]octane (DABCO) (1.1 g, 9.49 mmol, 3.0 equiv.) and palladium

(II) acetate (1.8 mg, 0.095 mmol, 0.03 equiv.) in acetonitrile (25 mL) was heated to 75

°C . 2-Methyl-3-butyn-2-ol (1.5 mL, 15.815 mmol, 5.0 equiv.) was then added and the

reaction maintained with stirring for 16 hours. The solvent was removed in vacuo and

the crude reaction mixture purified via silica gel chromatography to afford 68 as a low

melting brown solid (679 mg, 79 %). No characterisation was performed due to

difficulty in purification.

2.5.16. 5-Ethynyl-1,1,3,3-tetramethylisoindolin-2-yloxyl (69)

5-Ethynyl-1,1,3,3-tetramethylisoindolin-2-yloxyl (69) was synthesised according to a

procedure adapted from those published by Keddie et al.105

To a solution of 5-(3-hydroxy-3-methyl)butynyl-1,1,3,3-tetramethylisoindolin-2-

yloxyl 68 (679 mg, 2.49 mmol, 1.0 equiv.) in anhydrous toluene (100 mL) was added

solid KOH (1.1 g, 19.6 mmol, 7.8 equiv.). The reaction was brought to reflux and

maintained with stirring for 1 hour. The reaction was then allowed to return to room

temperature, washed with H2O (3 × 200 mL), brine (200 mL) and dried over anhydrous

sodium sulphate. The solvent was removed in vacuo and the crude reaction mixture

purified by silica gel column chromatography (30% ethyl acetate in hexane) then

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recrystallized from ethanol to afford 69 as an orange crystalline solid. (223.8 mg, 41.9

%). HRMS (ESI): m/z (%) = 216.1504 (7.5 %) [M+2] 237.1254 (2%) [M+Na]+, calcd.

for C14H18NO• [M+2H]1+ 216.1388. EPR: g = 2.0058, aN = 1.429 mT. M.p. (Lit. 126-

128°C105). IR (ATR) νmax 661 (=C-H), 835 (N-O), 1362 (R3N), 2097 (C≡C), 2978

(ArC-H), 3196 (alkyl CH3), 3276 cm-1 (C≡C-H).

2.5.17. 5-Bromo-1,1,3,3-tetramethylisoindolin-2-yloxyl (77)

5-Bromo-1,1,3,3-tetramethylisoindolin-2-yloxyl (77) was synthesised according to a

procedure adapted from those published by Chan et al.167

1,1,3,3-Tetramethylisoindoline (65) (25.92 mg, 0.102 mmol) was dissolved in DCM

(20 mL) in a round bottom flask. m-CPBA (34.32 mg, 0.153 mmol, 1.5 equiv.) was

added while stirring at room temperature. At completion of the reaction, 2.5M sodium

hydroxide was added to deprotonate m-CPBA and the product was extracted with

DCM. The organic layer was washed with water (30 mL), fellow by brine (30 mL) and

dried over anhydrous sodium sulphate. The yellow liquid was concentrated by vacuum

to result in a dry yellow powder. (24.7 mg, 90 %). EPR: g = 2.0059, aN = 1.429 mT.

2.5.18. 5-Bromo-2-methoxy-1,1,3,3-tetramethylisoindoline (78)

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5-Bromo-2-methoxy-1,1,3,3-tetramethylisoindoline (78) was synthesised according to

a procedure adapted from those published by Fairfull-Smith.53

5-Bromo-1,1,3,3-tetramethylisoindolin-2-yloxyl (77) (278.3 mg, 1.034 mmol) was

dissolved in DMSO to which iron sulphate (718.6 mg, 2.585 mmol) was added, where

the solution changed from yellow to a dark brown. The flask was cooled without

freezing and peroxide (175 uL) was added dropwise. The reaction was then left to stir

for 30 minutes at RT. The solution was poured into water and extracted with diethyl

ether and washed with water several times to ensure DMSO has been removed. The

organic layer was concentrated by vacuum to give the desired product 78, a pale yellow

low melting solid. (89.9%, 264.4 mg). 1H NMR (400 MHz, CDCl3) δ 1.423 (s, 12H,

CH3); 3.764 (s, 3H, O-CH3); 7.03 (d, 1H, Ar-H), 7.173 (s, 1H, Ar-H); 7.29 (dd, 1H,

Ar-H).

2.5.19. 5-Iodo- 2-methoxy-1,1,3,3-tetramethylisoindoline (79)

5-Iodo-2-methoxy-1,1,3,3-tetramethylisoindoline (79) was synthesised according to a

procedure adapted from those published by Keddie.105

A solution of 5-bromo-2-methoxy-1,1,3,3-tetramethylisoindoline (78) (264.4 mg, 0.93

mmol, 1.0 equiv.) in anhydrous THF (3 mL) was cooled to - 78 °C (dry ice / acetone). n-

BuLi (1.6 M in n-hexanes, 1.767 mL, 2.82 mmol, 2.7 equiv.) was then added (dropwise)

and the resulting mixture stirred for 15 minutes. A solution of I2 (793 mg, 3.1 mmol, 3.3

equiv.) in anhydrous THF (6.5 mL) was then added (dropwise) and the reaction allowed

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to return to room temperature. The solution was poured onto ice and extracted with DCM

(3x 50 mL) and washed with a satuated solution of sodium thiosulphate (3 x 50 mL) until

the solution turned colourless and washed with water. The organic layer was dried on

sodium sulphate and concentrated by vacuum. The mixture was purified by column

chromatography (n-hexanes: DCM, 1: 5) to yield a colourless oil 79. (0.109 mg, 0.329

mmol, 35.4%). 1H NMR (400 MHz, CDCl3) δ 1.41 (s, 12H, CH3); 3.76 (s, 3H, O-CH3);

6.85 (d, J = 8.01 Hz, 1H, Ar-H), 7.41 (s, 1H, Ar-H); 7.54 (dd, J = 7.41, 1.85 Hz, 1H,

Ar-H).

2.5.20. 5-(3-Hydroxy-3-methyl)butynyl-2-methoxy-1,1,3,3-


5-(3-Hydroxy-3-methyl)butynyl-1,1,3,3-tetramethylisoindolin-2-yloxyl (80) was

synthesised according to a procedure adapted from those published by Keddie.105

A solution of 5-bromo-2-methoxy-1,1,3,3-tetramethylisoindoline (79) (781 mg, 2.358

mmol, 1.0 equiv.), 4-diazabicyclo[2.2.2]octane (DABCO) (0.8 g, 9.49 mmol, 4.0

equiv.) and palladium (II) acetate (12 mg, 0.095 mmol, 0.03 equiv.) in acetonitrile (2.6

mL) was heated to 75 °C . 2-Methyl-3-butyn-2-ol (1.15 mL, 1.18 mmol, 5.0 equiv.)

was then added and the reaction maintained with stirring for 16 hours. The solvent was

removed in vacuo and the crude reaction mixture purified via silica gel

chromatography (Ether: Hexane 1:3) to afford 80 as a brown oil (408.3 mg, 60.3 %).

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1H NMR (400 MHz, CDCl3) δ 1.06 (s, 12H, CH3); 3.11 (s, 1H, OH); 3.764 (s, 3H, O-

CH3); 7.01 (d, 1H, Ar-H), 7.154 (s, 1H, Ar-H); 7.27 (dd, 1H, Ar-H).

2.5.21. 5-Ethynyl-2-methoxy-1,1,3,3-tetramethylisoindoline (81)

5-Ethynyl-2-methoxy-1,1,3,3-tetramethylisoindoline (81) was synthesised according

to a procedure adapted from those published by Keddie.105

To a solution of 5-(3-hydroxy-3-methyl)butynyl-1,1,3,3-tetramethylisoindolin-2-

yloxyl (80) (0.5 g, 1.74 mmol, 1.0 equiv.) in anhydrous toluene (50 mL) was added

solid KOH (0.8 g, 14.32 mmol, 7.8 equiv.). The reaction was brought to reflux and

maintained with stirring for 1 hour. The reaction was then allowed to return to room

temperature, washed with H2O (3 × 200 mL), brine (200 mL) and dried over anhydrous

sodium sulphate. The solvent was removed in vacuo and the crude reaction mixture

purified by silica gel column chromatography (Ether : n-hexanes, 1 : 3) to afford 81 as

an pale cream solid (0.362 g, 1.58 mmol, 90.7 % yield). 1H NMR (400 MHz, CDCl3)

δ 1.43 (s, 12H, CH3); 3.05 (s, 1H, H-C≡C), 3.78 (s, 3H, O-CH3); 7.06 (d, 1H, J = 7.63

Hz, Ar-H), 7.25 (d, J = 0.7 Hz, 1H, Ar-H); 7.38 (dd, 1H, J = 7.83 & 1.13 Hz, Ar-H).

13C NMR (62.9 MHz) δ: 28.12, 65.47, 66.98, 76.48, 83.95, 120.81, 121.57, 125.37,

131.29, 145.46, 146.17. IR (ATR) νmax 710 (=C-H), 828 (N-O), 1048 (C-O), 1373

(R3N), 2109 (C≡C), 2974 (ArC-H), 2974 (alkyl CH3), 3292 cm-1 (C≡C-H).

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2.5.22. N,N’-Bis (2,5- di-tert- butylbenyl) Perylene 3,4,9,10-

tetracarboxyl-bisimide (89)

N,N’-Bis (2,5- di-tert- butylphenyl) Perylene 3,4,9,10-tetracarboxyl-bisimide (89) was

synthesised according to the procedure published by Langnals.133

Perylen-3,4,9,10-tetracarboxylic dianhydride (42) (0.5 g, 1.275 mmol), 2,5-di-tert-

butylaniline (88) (1.025 g, 4.99 mmol, 4 equiv.) and zinc acetate (0.175 g, 0.954 mmol,

0.75 equiv.) were added to a round bottom flask, using imidazole (~2.5 g) as the

solvent. The mixture was heated at 130 °C for 6 hr under argon. The mixture was

allowed to cool, 2M HCl (100 mL) was added to dissolve imidazole, and the product

was extracted with chloroform (50 mL). The organic layer was washed with water (20

mL), brine (20 mL) and dried with anhydrous magnesium sulphate. Solvent was

removed by reduced pressure to give a red solid. Purification was performed through

column chromography in (methanol: chloroform, 1: 50). The product was then

recrystallized from hot toluene to give the clean product 89 (0.077g, 0.99%). 1H NMR

(CHCl3, 400MHz): δ = 1.33 (s, 18H, CH3-C-Ar), 1.36 (s, 18H, CH3-C-Ar), 7.05 (d,

2H, J = 2.11 Hz, Ar), 7.50 (dd, 2H, J = 8.92, 2.11 Hz, Ar), 7.63 (d, 2H, J = 8.92 Hz,

Ar), 8.83 (dd, 8H, J = 24.17, 7.75 Hz, Ar)

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2.5.23. 2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-

methylbenzenesulfonate (123)

2-[2-[2-(2-Methoxyethoxy)ethoxy]ethoxy]ethyl 4-methylbenzenesulfonate (123) was

synthesised following the procedure published by Snow.169

Tetraethyl-eneglycol monomethyl ether (9.57 g, 45.95 mmol) was added to a round

bottom flask containing THF (20 mL). Sodium hydroxide (5 g) was dissolved in water

(20 mL) and added slowly to the stirring mixture which was at 0 oC. Tosyl chloride

(15 g, 78.68 mmol, 1.7equiv.) in of THF (20 mL) was added dropwise over 15 mins.

The reaction was left to warm to room temperature then stirred O/N. The product was

basified with 1M NaOH and extracted with diethyl ether (3x 50 mL). The product was

washed with water (3x 50 mL) and dried over anhydrous sodium sulphate. The solvent

was removed by vacuum to yield a pale pink oil. (15.724 g, 98.77 %). 1H NMR

(CHCl3, 400MHz): δ= 2.44 (s, 3H, CH3-Ar) 3.36 (s, 3H, CH3-O), 3.6 (m, 14H, CH2-

CH2-O), 4.15 (t, 2H, J = 4.68 Hz, CH2-S), 7.31 (d, 2H, J = 7.79 Hz, Ar), 7.79 (d, 2H,

J = 8.26 Hz, Ar).

2.5.24. 2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-

nitrobenzene (124)

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2-[2-[2-(2-Methoxyethoxy)ethoxy]ethoxy] ethyl-4-nitrobenzene (124) was

synthesised following the procedure published by Ikeda.170

2-[2-[2-(2-Methoxyethoxy)ethoxy]ethoxy]ethyl 4-methylbenzenesulfonate (123)

(6.24 g, 17.21 mmol) was added to a flask containing 4-nitrophenol (3 g, 21.57 mmol,

1.25 equiv.) and potassium carbonate (2.98 g, 21.56 mol, 1.5 equiv.). The solids were

dissolved in acetonitrile (100 mL) and refluxed at 90 °C for 5 hours. The solid was

collected and the filtrate was concentrated by reduced pressure to yield an oil. This oil

was dissolved in DCM and washed with 1M NaOH to remove the 4-nitrophenol, and

then by water. (0.343 g, 4.5 %). 1H NMR (CHCl3, 400MHz): δ= 3.36 (s, 3H, CH3-O),

3.52- 3.73 (m, 12H, CH2CH2-O), 3.88 (t, 2H, J = 5.62 Hz, CH2CH2-O), 4.21 (t, 2H, J

= 4.71 Hz, CH2CH2-O), 6.97 (d, 2H, J = 9.19 Hz, Ar), 8.18 (d, 2H, J = 9.18 Hz, Ar).

2.5.25. 2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-aniline

(125)

2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-nitrobenzene (124) (0.343 g, 1.04

mmol) was dissolved in ethyl acetate and added to the reaction vessel with palladium

on carbon (10% wt. loading, 40 mg) catalyst. The solution was placed in a Parr

hydrogenator under an atmosphere of hydrogen (40 psi) with shaking for 5 hours. The

reaction was checked by TLC (ethyl acetate) to ensure the reaction was complete. The

resulting suspension was filtered through celite and the celite washed thoroughly with

methanol. The combined filtrates were concentrated at reduced pressure to give 125.

The product was a light brown oil. (0.3359 g, 100 %). 1H NMR (CHCl3, 400MHz): δ=

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3.37 (s, 3H, CH3-O), 3.53-3.72 (m, 12H, CH2-CH2-O), 3.81 (t, 2H, J = 4.7 Hz, CH2-

CH2-O), 4.04 (t, 2H, J = 5.09 Hz, CH2-CH2-O), 6.62 (d, 2H, J = 8.41 Hz, Ar), 6.75 (d,

2H, J = 8.81 Hz, Ar).

2.5.26. N,N’- bis (2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-

4-aniline)- perylene 3,4,9,10-tetracarboxyl-bisimide (126)

N,N’- bis (2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-aniline)- perylene

3,4,9,10-tetracarboxyl-bisimide (126) was synthesised adapting the procedure

according to Langnals.133

Perylen- 3,4,9,10- tetracarboxylic dianhydride (42) (28.2 mg, 0.07189 mmol), 125

(37.7 mg, 0.126 mmol, 1.75 equiv) and zinc acetate (30 mg, 0.164 mmol, 2.25 equiv)

were added to a round bottom flask, using imidazole (~2 g) as the solvent. The mixture

was heated at 130°C for 6 hours under an argon atmosphere. The mixture was allowed

to cool after which aqueous 2M hydrogen chloride was added to dissolve imidazole,

and the product was extracted with chloroform (5 x 50 mL). The combined organic

layers were washed with water (2 x 20 mL), brine (20 mL) and dried with anhydrous

magnesium sulphate. Solvent was removed by reduced pressure to give a red solid.

Column chromography was performed (methanol: chloroform 1: 25) and 126 was

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isolated as a red solid. (87 mg, 99%). 1H NMR (CHCl3, 400MHz): δ = 3.39 (s, 6H,

CH3-O), 3.55-3.76 (m, 24H, CH2-CH2-O), 3.91 (t, 2H, J = 4.9 Hz, CH2-CH2), 4.22 (t,

2H, J = 4.9 Hz, CH2-Ar), 7.09 (d, 4H, J = 8.83 Hz, Ar), 7.29 (d, 4H, J = 8.59 Hz, Ar),

8.45 (d,4H, J = 7.86 Hz, Ar), 8.63 (d, H, J = 7.85 Hz, Ar).

2.5.27. N- (2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-

aniline)- N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-

perylene 3,4,9,10-tetracarboxyl-bisimide (96)

N- (2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-aniline)- N’(1,1,3,3-

tetramethylisoindolin-2-yloxyl)-perylene 3,4,9,10-tetracarboxyl-bisimide (96) was

synthesised adapting the procedure according to Langnals.133

Perylen- 3,4,9,10- tetracarboxylic dianhydride (42) (102.419mg, 0.218 mmol, 1

equiv.), aniline TEG 125 (78.1 mg, 0.261 mmol, 1.2 equiv), amino-1,1,3,3-

tetramethylisoimdolin-2-yloxyl 57 (53.57 mg, 0.261 mmol, 1.2 equiv) and zinc acetate

(100 mg, 0.55 mmol, 2.2 equiv) were added to a round bottom flask, using imidazole

(~2 g) as the solvent. The mixture was heated at 130°C for 6 hr under argon. The

mixture was allowed to cool, aqueous 2M HCl was added to dissolve imidazole, and

the product was extracted with chloroform (5 x 50 mL). The combined organic layer

was washed with water (2 x 20 mL), brine (20 mL) and dried with anhydrous

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magnesium sulphate. Solvent was removed by reduced pressure to give a red solid.

Column chromography was performed (methanol: chloroform, 1: 100) showing 3

major fractions. The second fraction was found to be the target compound 96. (49.9

mg, 22.2 %). 1H NMR (CHCl3, 400MHz): δ= 1.63 (s, 6H, CH3), 3.40 (s, 3H, O-CH3),

3.56-3.93(m, 16H, CH2-O-CH2), 4.22 (b, 2H, CH2-Ar), 7.11 (b, 2H, Ar), 7.29 (b, 2H,

Ar), 8.42 (b, 2H, Ar), 8.49 (b, 2H, Ar), 8.65 (b, 4H, Ar).

2.5.28. N- (methoxy-1,1,3,3-tetramethylisoindoline N’- (2-[2-[2-(2-

methoxyethoxy)ethoxy]ethoxy] ethyl-4-aniline)- perylene

3,4,9,10-tetracarboxyl-bisimide (97)

To characterise the target compound 96 the methoxyamine analogue was synthesised

according to Fairfull-Smith.53

Hydrogen peroxide solution (30%, 5 equiv.) was added dropwise to a solution of N-

(2-[2-[2-(2-methoxyethoxy)ethoxy]ethoxy] ethyl-4-aniline)- N’(1,1,3,3-

tetramethylisoindolin-2-yloxyl)-perylene 3,4,9,10-tetracarboxyl-bisimide (96) and

iron(II) sulphate heptahydrate (2.5 equiv.) in a solution of minimal DMSO. The

resulting solution was stirred at room temperature for 30 minutes and then poured into

icy sodium hydroxide (1M). The mixture was extracted with chloroform (20 mL) and

washed (5 x 50 mL) with water several times to remove DMSO. It was dried over

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anhydrous sodium sulphate and concentrated for reduced pressure. The product was

purified by column chromography (methanol: chloroform, 3: 100) to yield a red solid.

1H NMR (CHCl3, 400MHz): δ= 1.48 (s, 6H, CH3), 1.51 (s, 6H, CH3), 3.39 (s, 3H, O-

CH3), 3.56-3.93 (m, 16H, CH2-O-CH2), 4.22 (t, 2H, J = 4.91 Hz, CH2-Ar), 7.09 (d, 1H,

J = 8.41 Hz, Ar), 7.10 (d, 2H, J = 8.41 Hz, Ar), 7.20 (dd, 1H, J = 8.08, 1.77 Hz, Ar),

7.28 (d, 3H, J = 8.52 Hz, 2xAr), 8.54- 8.77 (m, 8H, Ar). 13C NMR (62.9 MHz) δ: 13.11,

13.16, 21.68, 25.69, 28.35, 29.15, 30.19, 31.79, 32.69, 36.08, 36.37, 58.04, 64.51,

66.14, 66.7, 68.65, 69.53, 69.63, 69.66, 69.88, 70.95, 114.41, 120.92, 121.53, 122.2,

122,45, 122.51, 125.42, 126.31, 126.57, 128.54, 130.63, 133.64, 133.69, 144.72,

145.54, 157.94, 162.48, 162.58.

2.5.29. N,N’-Bis (octylphenyl)-perylene 3,4,9,10-tetracarboxyl-

bisimide (127)

N,N’-Bis (octylphenyl) Perylene 3,4,9,10-tetracarboxyl-bisimide (127) was

synthesised adapting the procedure according to Langnals.133

Perylen- 3,4,9,10- tetracarboxylic dianhdride (42) (50mg, 0.136 mmol), 4-octylaniline

(61.2 mg, 0.30 mmol, 2.2 equiv.) and zinc acetate (50mg, 0.30 mmol, 2.2 equiv.) were

added to a round bottom flask, using imidazole (~2 g) as the solvent. The mixture was

heated at 130°C for 6 hours under argon. The mixture was allowed to cool 2M aqueous

HCl was added to dissolve imidazole, and the product was extracted with chloroform

(5 x 50 mL). The combined organic layers were washed with water (2 x 20 mL), brine

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(20 mL) and dried with anhydrous magnesium sulphate. Solvent was removed by

reduced pressure to give a red solid. Column chromatography was performed

(methanol: chloroform 1: 25). 127 was isolated as a red solid. (97 mg, 98 %).1H NMR

(CHCl3, 400MHz): δ= 2.71 (t, 4H, J = 4.95 Hz, CH2-Ar), 7.25 (d, 2H, J = 7.95 Hz,

Ar), 7.39 (d, 2H, J = 7.95 Hz, Ar), 8.70 (d, 4H, J = 7.92 Hz, Ar), 8.76 (d, 4H, J = 8.42

Hz, Ar).

2.5.30. N- N’ -Bis (1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene

3,4,9,10-tetracarboxyl-bisimide (44)

N- N’ Bis (1,1,3,3-tetramethylisoindolin-2-yloxyl)- perylene 3,4,9,10-tetracarboxyl-

bisimide (44) was synthesised adapting the procedure according to Langnals.133

A mixture of 3,4,9,10-perylenetetracarboxylic dianhydride (42) (50 mg, 0.127 mmol,

1 equiv.), 5-amino-1,1,3,3-tetramethylisoindolin-2-yloxyl (57) (0.12 g, 0.51 mmol, 4

equiv.), zinc acetate (46 mg, 0.245 mmol 2 equiv.) and imidazole (0.864 g, 12.7 mmol

10 equiv.) was heated at 130oC under an atmosphere of argon for 6 hours. Aqueous

hydrochloric acid (2 M, 10 mL) was added and the mixture was diluted with

chloroform (50 mL). The organic phase was separated, washed with aqueous

hydrochloric acid (2 M, 2 × 50 mL) and water (2 × 50 mL), dried (anhydrous Na2SO4)

and concentrated in vacuo. Purification by column chromatography (eluent 2%

methanol/chloroform, sample dry loaded using chloroform) gave the desired

compound as a red powder (94 mg, 97%). Recrystallisation from DCM/MeOH/toluene

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(50: 50: 1) gave red needles. M. p. >300 °C (dec.). MS (ESI): m/z (%) = 789 (6)

[M+Na]+. HRMS: calcd. for C48H38N4O6Na [M+Na]+. Elemental analysis found

789.2689; found 789.2655. (Found: C 68.74, H 5.04 N 6.57 Calc. C48H38N4O6.4H2O:

C 68.72, H 5.53, N 6.68%), EPR: g = 2.006, aN = 1.429 mT.

2.5.31. N- N’ Bis (methoxy-1,1,3,3-tetramethylisoindoline)-

Perylene 3,4,9,10-tetracarboxyl-bisimide (91)

To characterise the target compound the methoxyamine analogue (91) was synthesised

according to Fairfull-Smith.53

To a solution of nitroxide (44) (25 mg, 0.033 mmol) in DMSO (5 mL) was added

FeSO4.7H2O (18 mg, 0.066 mmol) and H2O2 (30% aqueous solution, 100 μL). The

reaction was maintained with stirring for 30 min. at room temperature under an

atmosphere of argon. Water (10 mL) was added and the resulting mixture was

extracted with chloroform (3 × 10 mL). The combined organic layers were dried

(anhydrous Na2SO4) and concentrated in vacuo. The obtained residue was purified

using silica gel chromatography (eluent 2% methanol/chloroform, sample dry loaded

using chloroform) to give the desired compound as a red powder (21 mg, 80 %). M. p.

>300 °C (dec.) 1H NMR (400 MHz, CDCl3) δ 1.50 (br s, 24H, 4 × CH3), 3.82 (s, 6H,

OCH3), 7.09 (d, J = 1.8 Hz, 2H, Ar-H), 7.21 (dd, J = 7.9, 1.9 Hz, 2H, Ar-H), 7.30 (d,

J = 7.8 Hz, 2H, Ar-H), 8.71 (d, J = 8.1 Hz, 4H, Ar-H), 8.77 (d, J = 8.1 Hz, 4H, Ar-H).

The compound was insufficiently soluble in CDCl3 to obtain a satisfactory 13C NMR

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spectrum. MS (ESI): m/z (%) = 797 (100) [M+H]+. HRMS: calcd. for C50H45N4O6

[M+H]+ 797.3339; found 797.3298.

2.5.32. 4-Bromo-1,8-naphthalic anhydride (102)

4-Bromo-1,8-naphthalic anhydride (102) was synthesised according to a procedure

adapted from those published by Rotstein et al.157

To a two necked round-bottomed flask equipped with a magnetic stirring bar was 1,8-

naphthalic anhydride 101 2 g, (10.09 mmol) and 12 mL of 4 M aqueous potassium

hydroxide (2.7 g) and was heated slightly to dissolve. The flask was cooled to 0 °C

and the contents treated with bromine (0.77 mL) over the course of 2 hr. The flask was

fitted with a reflux condenser and heated to 60 °C for 16 h. After cooling to room

temperature, the contents of the flask were acidified with 10 mL H2SO4, and refluxed

for 1 h. When cooled to room temperature, the product was collected by suction

filtration and washed with cold water, methanol and diethyl ether to give the desired

product (3.0431 g, 99 %) as a grey solid. 1H NMR (400 MHz, CDCl3) δ 7.93 (t, J =

7.88 Hz, 1H, Ar-H), 7.13 (d, J = 7.88 Hz, 1H, Ar-H), 7.46 (d, J = 7.88 Hz, 1H, Ar-H),

8.70 (m, 2H, Ar-H), 8.77. M.p. 210-220 °C. (Lit.171 M.p. 218-220). MS (ESI): m/z (%)

= 298.9142 and 300.0122 (18) [M+Na]+, calcd for C12H5BrNaO3 [M+Na]+ 298.9320.

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2.5.33. 1,7-Dibromoperylene-3,4:9,10-tetracarboxydianhydride

(112)

1,7-Dibromoperylene-3,4,9,10-tetracarboxydianhydride (112) was synthesised

according to a procedure adapted from those published by Ahrens et al.165

3,4,9,10-Perylenetetracarboxylic dianhydride (2 g, 6.819 mmol) was added to 30 mL

concentrated sulfuric acid and stirred at 55 °C for 24 hr in a 2 necked flask. Iodine

(0.048 g,) was added to the reaction mixture and stirred for an additional 5 hr. at 55

°C. Bromine (0.582 mL) was added dropwise to the reaction flask over 1 hr. and stirred

for 24 hr. at 85 °C. Excess bromine was then displaced with N2. Water (66 ml) was

added dropwise to the cooled mixture and the precipitate filtered off through 4 filter

papers. The crude product was washed with 220 ml 86 % H2SO4 followed by water

(two times) and dried in the oven to afford crude red powder (32.32 g, 81%). This

product was used without further purification and characterisation due to

insolubility.165

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2.5.34. N-(2,5-Di-tert-butylphenyl)-4-bromo-1,8-naphthalimide

(103)

N-(2,5-di-tert-butylphenyl)-4-bromo-1,8-naphthalimide (103) was synthesised

according to a procedure adapted from those published by Hamel et al.158

In a round-bottom flask equipped with a condenser, 4- bromo-1,8-naphthalic

anhydride (1 g, 3.61 mmol) and 2,5-di-tert-butylaniline (1.48 g, 7.22 mmol) were

dissolved in quinoline. Zinc acetate dihydrate (350 mg, 1.59 mmol) was added and the

mixture was heated at 200 °C for 5 hr. After cooling to room temperature, the mixture

was poured in to acidic water (2 M, 50 mL). The aqueous layer was fully extracted

with DCM (3x 30 mL). After drying with sodium sulphate, the extract was

concentrated and the crude product was purified on silica gel chromatography to yield

a beige solid (4.58g, 93%). M.p. 205- 210 °C. (Lit.158 M.p. 214 °C). 1H NMR (400

MHz, CDCl3) δ 1.29 (s, 9H, CH3); 1.34 (s, 9H, CH3); 7.03 (d, 1H, J = 1.86 Hz, Ar-H);

7.48 (dd, 1H, J = 8.08 Hz, J = 3.11 Hz, Ar-H); 7.61 (d, 1H, J =8.70 Hz, Ar-H); 7.89 (t,

1H, J = 6.84 Hz, Ar-H); 8.08 (d, 1H, J = 8.7 Hz, Ar-H); 8.49 (d, 1H, J = 9.23 Hz, Ar-

H); 8.63 (d, 1H, J = 8.70 Hz, Ar-H); 8.73 (d, 1H, J = 7.46 Hz, Ar-H). 13C NMR (62.9

MHz) d 31.36, 31.84, 34.37, 35.62, 122.72, 123.58, 126.47, 127.82, 128.33, 128.92,

129.53, 130.70, 130.95, 131.31, 131.77, 132.61, 132.73, 133.66, 143.86, 150.23,

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164.70, 164.75 Hz. HRMS (ESI): m/z (%) = 486.0910 and 488.0894 (95) [M+Na]+,

calcd for C26H26BrNNaO2 [M+Na]+ 486.1045.

2.5.35. N,N’-(2,5-di-tert-butylphenyl)-dibromoperylene-3,4,9,10-

tetracarboxy diimide (113)

N,N-(2,5-Di-tert-butylphenyl)-dibromoperylene-3,4,9,10-tetracarboxy diimide (113)

was synthesised according to a procedure adapted from those published by Dubey et

al. 166

Crude dibromoperylene-3,4,9,10-tetracarboxylic dianhydride (112) (1.12 g, 2.0178

mmol), was suspended in propionic acid (100 mL) and subsequently di- tert-

butylaniline ( 1.12 g, 5.454 mmol) was added. The reaction mixture was refluxed at

140 °C under stirring for 48 h, cooled to room temperature and poured into water

(200mL). The precipitate was filtered off, thoroughly washed with several portions of

water, and dried in the oven to give the crude product. The crude product was

chromatographed on silica with (n-hexanes: DCM, 1:3) to yield regioisomeric mixture

of 1,7- and 1,6-dibromoperylene diimides (2.7 g, 77%) as major product and 1,6,7-

tribromoperylene diimide as the minor. 166 Trans: 1H NMR (400 MHz, CDCl3) δ 1.29

(s, 9H, CH3); 1.30 (s, 9H, CH3); 1.31 (s, 9H, CH3), 1.32 (s, 9H, CH3); 6.99 (dd, 2H, J

= 2.2 & 1.1 Hz, Ar); 7.475 (dd, 2H, J = 8.55 & 2.33 Hz, Ar); 7.60 (d, 2H, J = 8.5 Hz,

Ar); 8.78 (d, 2H, J = 8.21 Hz, Ar); 8.99 (s, 2H, Ar); 9.54 (dd, 2H, J = 8 & 1.78 Hz,

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Ar). Cis: 1H NMR (400 MHz, CDCl3) δ 1.29 (s, 9H, CH3); 1.30 (s, 9H, CH3); 1.31 (s,

9H, CH3), 1.32 (s, 9H, CH3); 6.99 (dd, 2H, J = 13.1 & 1.89 Hz, Ar); 7.475 (dd, 2H, J

= 8.55 & 2.33 Hz, Ar); 7.60 (d, 2H, J = 8.5 Hz, Ar); 8.79 (d, 2H, J = 8.21 Hz, Ar); 8.99

(s, 2H, Ar); 9.55 (dd, 2H, J = 8 & 1.78 Hz, Ar).

2.5.36. N-(2,5-di-tert-butylphenyl)-4-(phenoxy)-1,8-naphthalimide

(128)

N-(2,5-di-tert-butylphenyl)-4-(phenoxy)-1,8-naphthalimide (128) was synthesised

according to a procedure adapted from those published by Hamel et al. 158

Regent 103 (40 mg, 8.61 x10-5 mol) and phenol (9.73 mg, 1.03 x10-4 mol) were

dissolved in a small amount of freshly distilled DMF. While stirring potassium

hydroxide (4.8 mg, 1.03 x10-4 mol) was added and the mixture was refluxed at 100°C

for 24 hrs. The mixture was allowed to cool to room temperature and then diluted

slowly with 2M NaOH solution (20 mL) while stirring. The precipitate was collected

and washed with water. It was then dissolved in DCM (50 mL) and washed further

with water, dried over sodium sulphate and concentrated by vacuum. Column

chromography was performed in chloroform to yield a yellow oil. 1H NMR (400 MHz,

CDCl3) δ 1.28 (s, 9H, CH3); 1.32 (s, 9H, CH3); 6.95 (d, J = 8.22 Hz, 1H, Ar-H); 7.00

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(d, 1H, J = 2.35 Hz, Ar-H); 7.23 (d, 1H, J =7.83 Hz, Ar-H); 7.33 (t, 1H, J =7.43 Hz,

Ar-H); 7.44 (dd, 1H, J = 8.61 Hz, J = 2.35 Hz, Ar-H); 7.51 (t, 1H, J = 8.22 Hz, Ar-H);

8.57 (d, 1H, J = 8.61 Hz, Ar-H); 8.83 (t, 1H, J = 7.43 Hz, Ar-H); 8.51 (d, 1H, J = 8.61

Hz, Ar-H); 8.72 (d, 1H, J = 7.43 Hz, Ar-H); 8.78 (d, 1H, J = 8.61 Hz, Ar-H). IR (ATR)

νmax 784 (=C-H), 1105 (C-O), 1352 (R3N), 1485 (aryl C-C), 1666 (C=O), 2871 cm-1

(alkyl CH3).

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3. POLYAROMATIC PROFLUORESCENT

NITROXIDE PROBES WITH ENHANCED

PHOTOSTABILITY

The Authors listed below have certified* that:

1. They meet the criteria for authorship in that they have participated in the

conception, execution, or interpretation, of at least that part of the publication

in their field or expertise;

2. They take public responsibility for their part of the publication, except for the

responsible author who accepts overall responsibility for the publication;

3. There are no other authors of the publication according to these criteria;

4. Potential conflicts of interest have been disclosed to (a) granting bodies, (b) the

editor or publisher of journals or other publications, and (c) the head of the

responsible academic unit and

5. They agree to the use of the publication in the student’s thesis and its

publication on the Australasian Research Online database consistent with any

limitations set by the publisher requirements

In the case of this chapter:


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Polyaromatic Profluorescent Nitroxide Probes with Enhanced Photostability

Chemistry: A European Journal

Published 3 November 2015

Contributor Statement of contribution*

Vanessa Lussini Wrote the first manuscript and edited all co-author’s draft

changes. Synthesised, characterised and analysed all the

compounds used. Designed/conducted experiments and

performed the data analysis.

James P. Blinco Overall supervision of the project, guided during

experimental design and edited final manuscript

Kathryn E. Fairfull-

Smith

Overall supervision of the project, guided during synthesis

and experimental design and assisted during manuscript

design and editing.

Steve E. Bottle Original design of the project, overall supervision of the

project and edited final manuscript

Principal Supervisor Confirmation

I have sighted email or other correspondence from all Co-authors confirming their

certifying authorship.

Name Signature Date



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Polyaromatic Profluorescent Nitroxide Probes with Enhanced Photostability

V. C. Lussini,[a,b] J. P. Blinco,[a] K. E. Fairfull-Smith*[a] and S. E. Bottle*[a,b]

Received: 27 August 2015

Published Online: 3 November 2015

DOI: 10.1002/chem.201503393

[a] ARC Cenre of Excellence for Free Radical Chemistry and Biotechnology

School of Chemistry, Physics and Mechanical Engineering

Faculty of Science and Engineering

Queensland University of Technology (QUT)

GPS Box 2434, Brisbane, QLD 4001, Australia

E-Email: [email protected]; [email protected]

[b] Defence Materials Technology Centre

Level 2 Wakefield Street, Hawthorne, VIC 3122, Australia

3.1. Abstract

Novel profluorescent mono- and bis-isoindoline nitroxides linked to napthalimide and

perylene diimide structural cores are described. These nitroxide-fluorophore probes

display strongly suppressed fluorescence in comparison to their corresponding non-

radical diamagnetic methoxyamine derivatives. The perylene based probe possessing

two isoindoline systems tethered through ethynyl linkages was shown to be the most

photostable in solution, demonstrating significantly enhanced longevity over the 9,10-

mailto:[email protected]



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bis(phenylethynyl)anthracene fluorophore used in previous profluorescent nitroxide

probes.

3.2. Introduction

Profluorescent nitroxides (PFNs)64, 172 are compounds bearing a stable nitroxide free

radical covalently linked to a fluorophore moiety. These species typically display low

levels of fluorescence as a result of excited state quenching by the nitroxide radical.

However, when PFNs scavenge alkyl radicals to form diamagnetic alkoxyamines, or

undergo reduction to yield a hydroxylamine118, their fluorescence is once again

restored. PFNs have been employed as extremely responsive fluorescent probes for the

detection of free-radicals formed during the degradation and aging of polymeric

materials.101 The doping of polymers with PFNs facilitates a convenient, non-

destructive and rapid method for the real-time monitoring, imaging and mapping of

radicals formed during the degradation process.56 To this effect, we have previously

demonstrated that profluorescent nitroxide probes offer a highly sensitive method to

assess the earliest stages of radical-mediated thermo-oxidative degradation of polymer

films, where conventional methods can lack sensitivity.35 However, a limitation of this

technique is evident under photo-oxidative conditions where photobleaching of the

fluorophore can occur once non-radical adducts are generated. A potential solution to

overcome complications arising from insufficient fluorophore photostability is to

incorporate more photostable fluorophores into the structural framework of the PFN.

Perylene diimides (of general structure 42, Figure 30) have been extensively studied

in dye and pigment research due to their excellent chemical, thermal, photo and

weather stability.124 Furthermore, many perylene diimides display other interesting

properties such as near-unity fluorescence quantum yields and high photochemical


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stability which have enabled their use in other applications.128-130 For these reasons,

perylene diimides represent attractive base structures from which to build new

generation PFNs with superior photostability to potentially enable the monitoring of

the photodegradation of organic materials. In addition, structurally rigid, isoindoline-

based nitroxides are attractive moieties for novel enhanced stability PFNs, as the aryl

ring extends the conjugation without delocalizing the spin. Isoindoline nitroxides are

more photo-stable than the piperidine-based nitroxides, being less prone to degradation

by hydrogen atom abstraction and by α-cleavage with UV irradiation.137 The first

example of an isoindoline-based probe was the perylene-linked nitroxide 44 that was

developed as a non-photobleaching probe for imaging cellular oxidative stress using

two-photon fluorescence microscopy.69

Figure 30: Chemical structures of perylene diimide 42, perylene-based profluorescent nitroxides 44 and

129 and 9,10-bis(phenylethynyl)anthracene-based profluorescent nitroxide 23.

Perylene-based nitroxide containing compounds have previously been synthesised for

spintronic applications and time-resolved EPR.173-175 Recently an isoindoline and

perylene-based profluorescent nitroxide was used to monitor the degradation of


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melamine-formaldehyde crosslinked polyesters under accelerated weathering

conditions.123 This PFN probe (129), which was employed to assess the impact of both

temperature and UV-irradiance on polymer degradation for a range of polyesters,

possessed a branched alkyl substituent to enhance solubility. Perylene-based

compounds have well-known solubility limitations and this is a complication with both

PFNs 44 and 129. An alternative approach to overcome solubility limitations is to

incorporate nitroxides in the “bay”-region of the perylene unit (positions 1 and 7,

structure 42, Figure 30), as substitution at these positions increases solubility through

slightly twisting the perylene unit to disrupt planar π-π stacking interactions.134-135

Herein we describe several novel profluorescent nitroxides including perylene based

systems substituted in the bay region with mono- and bis-nitroxides. Ether and alkynyl

linkers were used to connect the nitroxide to the fluorophore and this approach was

extended to also include naphthalene PFNs. A range of perylene diimides bearing

imide linked isoindoline nitroxides and solubility enhancing ditertbuylarylamines was

also generated to compare properties with the bay region substitution approach. In

addition to the synthetic details and description of the physical properties of the new

perylene- and naphthalene-based profluorescent nitroxides, we also report a

comparison of the photostability of the new probes with 9,10-

bis(phenylethynyl)anthracene (Figure 30 Compound 23), the fluorescent core which

features in the current state-of-art applications of profluorescent probes.53, 85, 91

3.3. Results and Discussion

Before the synthesis of the perylene-based bay-region substituted profluorescent

nitroxides was attempted, the required chemistry was explored using a model system

based on the structure of N-substituted naphthalimides. It was envisioned that the


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nitroxide could be more easily tethered to the fluorophore unit through ether or ethynyl

linkages by reaction with a halogenated naphthalimide. Exploiting the recently

reported methodology for the facile transformation of a methoxyamine into a nitroxide

using m-CPBA,147 a protected nitroxide was employed in the synthesis (to allow NMR

characterization) with the protecting group removed in the final synthetic step to reveal

the paramagnetic nitroxide. Thus, bromo naphthalimide 103 was reacted with 5-

hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline 59 in a base assisted nucleophilic

phenoxide substitution reaction by heating with KOH in DMF to give substituted

naphthalimide 105 in high yield (84%) (Scheme 42). Removal of the methoxyamine

of 105 was readily achieved to yield nitroxide 104 in good yield (78%) by oxidation

with m-CPBA in a Cope-type elimination process.

Scheme 42: Synthetic route to ether linked naphthalimide-based profluorescent nitroxide 105.

The protected nitroxide 64 was accessed from the corresponding nitro methoxyamine

61 by reduction to the amino methoxyamine 62, followed by generation of the

diazonium tetrafluoroborate salt 58 and its subsequent hydrolysis to give phenol 59

(Scheme 43).


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Scheme 43: Synthetic route to 5-hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline 64.

It was envisioned that the desired ethynyl tethered naphthalimide nitroxide 107 could

be prepared via a palladium-catalysed Sonogashira coupling using similar conditions

to those that have been successfully employed previously in the presence of the

nitroxide moiety.53 The coupling of the bromo naphthalimide 103 with the alkyne

bearing methoxyamine 81 in the presence of CuI and freshly prepared

tetrakis(triphenylphosphine)palladium(0)163 gave the desired substituted

naphthalimide 106 in high yield (90%) (Scheme 44). Deprotection of 106 was

accomplished under similar facile conditions to afford nitroxide 107 in excellent yield

(97%).


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Scheme 44: Synthetic route to ethynyl linked naphthalimide-based profluorescent nitroxide 107.

Following the success of the naphthalimide nitroxide substitution reactions, we turned

our attention towards the use of this chemistry to prepare perylene-based

profluorescent nitroxides which incorporated nitroxides at the bay-region of the

perylene unit. Substitution at these positions is well known via bromine atoms which

can easily be exchanged by phenol166 or alkyne176 groups as a method to functionalise

the perylene core and thereby improve its solubility by twisting the planar structure to

disfavour the formation of π-π aggregates.

The required 1,7-dibromo-perylene dianhydride was prepared by the I2-catalysed

bromination of the corresponding perylene dianhydride in sulfuric acid following

literature procedures.165 Based on previous reported observations, it was presumed that

the crude mixture contains both the 1,7- and 1,6-dibromo-perylene dianhydride

regioisomers and potentially a small amount of the 1,6,7-tribromo compound.

However, limited solubility meant that these regioisomers could not be detected by 1H

NMR spectroscopy at 400 MHz.164 Imidization of the crude brominated perylene

dianhydride product mixture with 2,5-di-tert-butylaniline in refluxing propionic acid

afforded a more soluble product mixture which was shown by 1H NMR spectroscopy


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to predominantly contain the 1,7-dibromo-perylene diimide 121, along with the 1,6-

dibromo perylene diimide regioisomer and a small amount of the 1,6,7-tribromo

compound in a ratio of 65:34:1 respectively. Separation of the desired compound 113

by column chromatography could not be achieved and the mixture was therefore

carried forward without further purification. Nucleophilic substitution of 1,7-dibromo-

perylene diimide 113 with methoxyamine 64 under basic conditions yielded perylene

dimethoxyamine 117 in high yield (87%) (Scheme 45). The isolated product was

shown by 1H NMR spectroscopy to contain both the 1,7-dimethoxyamine-perylene

diimide 117 and its 1,6-dimethoxyamine-perylene diimide regioisomer in a ratio of 3:2

respectively. Subsequent oxidation of dimethoxyamine 117 with m-CPBA under mild

conditions gave the desired nitroxide 118 in excellent yield (99%). Although 118 was

not isomerically pure (as a result of the previous bromination step), it was not purified

further as pronounced solubility differences between the isomers were not observed

(solubility differences have previously enabled the separation of other bay-

functionalised perylene diimide regioisomers166) and it was assumed that the presence

of the 1,6-regioisomer would have little impact on the resulting absorbance and

fluorescence spectra.


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Scheme 45: Synthetic route to ether linked perylene-based profluorescent nitroxide 118.

Sonogashira coupling of 1,7-dibromo perylene diimide 113 with the alkyne bearing

methoxyamine 81 in the prescence of CuI and Pd(PPh3)4 resulted in a moderate (52%)

yield of the perylene dimethoxyamine 114 (Scheme 46). Analysis of the isolated

product by 1H NMR spectroscopy revealed the presence of 1,7-dimethoxyamine-

perylene diimide 114 (54%) and the 1,6-dimethoxyamine-perylene diimide

regioisomer (46%). The mixture was not further purified. Oxidation to yield the

nitroxide moiety was facile using 2.5 equivalents of m-CPBA and resulted in an

excellent yield (99%) of nitroxide 116 after 15 minutes. It was also established that

when only 1.0 equivalent of m-CPBA was employed, a mono-nitroxide 115 could be

formed in moderate yield (55%) by the selective removal of a single methoxyamine

protecting group.


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Scheme 46: Synthetic route to ethynyl linked perylene-based profluorescent nitroxides 116 and 115.

As a comparison to the bay-expanded perylene-based profluorescent nitroxides, we

also sought to synthesise perylene diimides bearing imide linked isoindoline

nitroxides. We have previously reported the synthesis of perylene-based dinitroxide

44 by the condensation of 5-amino-1,1,3,3-tetramethylisoindolin-2-yloxyl 57 with

3,4,9,10-perylenetetracarboxylic dianhydride 42 in the presence of zinc acetate in

molten imidazole in high (97%) yield.127 As the solubility of nitroxide 44 was

extremely poor in the majority of organic solvents, it was decided to focus on the

preparation of unsymmetrical perylene diimides which would incorporate both a

nitroxide unit and a solubilising group tethered through the covalent imide bonds onto

the perylene unit similar to the approach employed by Nagao.177

Initial attempts to generate a mono-nitroxide containing perylene diimide involved the

stepwise addition of 2,5-di-tert-butylaniline to 3,4,9,10-perylenetetracarboxylic

dianhydride 42 in the presence of zinc acetate in molten imidazole at 130ºC as a means


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to generate the monoanhydride which could subsequently be reacted with nitroxide 57.

Under these conditions, the reaction afforded a 1:1 mixture of the symmetrical N,N′-

bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenedicarboximide 89 and unreacted

3,4,9,10-perylenetetracarboxylic dianhydride 42 according to 1H NMR spectroscopy.

Attempts to selectively hydrolyse one imide bond of N,N′-bis(2,5-di-tert-butylphenyl)-

3,4,9,10-perylenedicarboximide using potassium hydroxide154 and subsequently react

the resulting monoimide monoanhydride with 5-amino-1,1,3,3-tetramethylisoindolin-

2-yloxyl 57 also did not give the desired perylene-based nitroxide (this route has been

noted to often proceed with difficulty155).

We expected that the increased solubility of the initially formed monoimide over the

dianhydride staring material (42) would lead to the rapid formation of the symmetrical

diimide, as described previously. Therefore it was reasoned that the desired nitroxide

/ N-octylaryl containing perylene diimides (98) could be accessed (after separation) in

one pot starting with a mixture of both aryl amines (Scheme 47). This simpler approach

proved to be effective, with the treatment of 3,4,9,10-perylenetetracarboxylic

dianhydride 42 with N-octylaniline and amino nitroxide 57 in the presence zinc acetate

in molten imidazole yielding the perylene nitroxide 98 in 26% yield following isolation

by chromatography (the corresponding symmetrical diimides were also isolated).


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Scheme 47: Synthetic route to imide linked perylene-based profluorescent nitroxide 98.

Similarly, perylene nitroxide 90 was synthesised from a stoichiometric mixture of 2,5-

di-tert-butylaniline and nitroxide 57 in a 22% yield following purification (Scheme

48). The corresponding methoxyamine derivatives 99 and 92 were prepared using

Fenton chemistry. The obtained isolated yields for these reactions were low, however

this can be rationalised by the poor solubility of nitroxides 99 and 92 in DMSO.


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Scheme 48: Synthetic route to imide linked perylene-based profluorescent nitroxide 90.

The naphthalimide- and perylene diimide-based profluorescent nitroxide probes (105,

107, 118, 116, 98, 90) and their corresponding methoxyamines adducts (104, 106, 117,

114, 99, 92) were then examined for their photophysical properties (Table 1). The

napthalimide-based compounds (105 and 104) displayed absorbance spectra

characteristic of their parent fluorophore, N-(2,5-di-tert-butylphenyl)-1,8-

naphthalimide (λmax = 350 nm, ε = 10 647 M-1cm-1).178 The ethynyl-linked compounds

107 and 106 both displayed a 13 nm red-shift which is consistent with extension of the

π-conjugation system. A comparison of the fluorescence quantum yields of nitroxides

105 and 107 (ΦF = 5.6 × 10-4 and 4.5 × 10-4 respectively) with their corresponding

methoxyamines 104 and 106 (ΦF = 9.04 × 10-2 and 0.169 respectively) revealed a

substantial suppression of fluorescence (Table 1, Figure 31). The values obtained for

the quantum yields of fluorescence for napthalimide methoxyamine adducts 104 and

106 were consistent with previously reported values for 1,8-naphthalimide derivatives

possessing electron rich substituents which give lowered fluorescence quantum yields


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as a result of their suggested ability to undergo photo-induced electron transfer

processes.179-180

Table 1: Photophysical properties of naphthalimide- and perylene diimide-based nitroxide probes and

their methoxyamine adducts.

Compound λabs

(nm)

Extinction

coefficient

λem (nm) Quantum

yield (ΦF)

ΦF

(NOMe/NO•)

104[a] 357 13089[c] 408 0.0904[e] -

105[a] 355 9277.7[c] 412 0.0006[e] 150.7

106[a] 370 21924[c] 428 0.169[e] -

107[a] 368 24704[c] 434 0.0005[e] 338

117[b] 542 35106[d] 576 0.295[f] -

118[b] 536 26699[d] 566 0.0174[f] 17.0

114[b] 565 28811[d] 587 0.0996[f] -

116[b] 560 13224[d] 582 0.0044[f] 22.6

115[b] 562 22052[d] 576 0.0094[f] 10.6

98[b] 525 20733 [d] 535 0.0535[f] 9.5

99[b] 525 7667[d] 535 0.508[f] -

90[b] 525 21000[d] 535 0.0267[f] 15.7

92[b] 525 19350[d] 535 0.4198[f] -

113 526 54740[d] 546 0.811[f] -

103 336 16410[c] 436 0.0069[e] -

130 536 29520[d] 572 0.7619[f] -

[a] Absorbance and fluorescence spectra recorded in cyclohexane. [b] Absorbance and

fluorescence spectra recorded in chloroform. [c] Measured at 350 nm in M-1cm-1. [d]

Measured at 525 nm in M-1cm-1. [e] Measured in cyclohexane using anthracene as


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standard (350 nm excitation, ΦF =0.36).181 [f] Measured in chloroform using N,N′-

bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenedicarboximide as standard (525 nm

excitation, ΦF =0.99).131

Figure 31: Fluorescence spectra of 1,8-napthalimide-based probes 105 (—) and 104 (···), 9 μM in

cyclohexane; 106 (—) and 107 (···), 3 μM in cyclohexane, following excitation at 350 nm.

The perylene-based compounds (98, 99, 90, 92) all displayed absorbance maxima at

525 nm (Table 1), which is consistent with their parent compound N,N′-bis(2,5-di-tert-

butylphenyl)-3,4,9,10-perylenedicarboximide 89 (DBPI, λmax = 525 nm). Substitution

at the perylene bay region, through ether and ethynyl linkages, extended the maximum

absorbance wavelength from 525 nm for nitroxides 98 and 90 to 536 nm and 560 nm

for nitroxides 118 and 116 respectively. Accordingly the wavelength of maximum

fluorescence emission was extended from 535 nm for nitroxides 98 and 90 to 566 nm

and 582 nm for nitroxides 118 and 116 respectively (Table 1). This fluorescence shift

can be justified by the extended conjugation system contained within perylene

compounds substituted at the bay region. A comparison of the fluorescence emission


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from the nitroxides (118, 116, 98 and 90) and their corresponding methoxyamine

adducts (117, 114, 99 and 92) showed a significant fluorescence suppression arising

from the presence of the nitroxide moiety.

Figure 32: Fluorescence spectra of perylene-based probes 114 (—), 116 (---) and 115 (···), 1 μM in

chloroform, following excitation at 525 nm.

This fluorescence suppression effect was most pronounced (~23 fold) in di-nitroxide

116 where fluorescence quantum yields of 0.0044 and 0.1 where obtained for 116 and

methoxyamine 114 respectively (Table 1). The mono-nitroxide analogue 115 still

demonstrated strongly suppressed fluorescence (ΦF = 0.009) even by a single nitroxide

group (Figure 32).

Perylene diimides typically exhibit high fluorescence quantum yields (close to

unity)125 and Wille et al. have previously reported a comparable fluorescence quantum

yield for perylene nitroxide 131 trapped with a 2-cyanoprop-2-yl radical to be 0.95 in

DCM.123 However, in this study, a significant decrease in the fluorescence quantum


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efficiencies of the perylene methoxyamines 117, 114, 99 and 92 was observed, as

demonstrated by the obtained fluorescence quantum yield values of 0.295, 9.96 × 10-

2, 0.508 and 0.42 respectively (Table 1). To investigate whether the alkyl R-group of

the alkoxyamine may influence the quantum yield, a different alkoxyamine adduct was

prepared through reaction of nitroxide 118 with radicals derived from the reaction of

ethyl 2-bromoisobutyrate with copper catalyst. However, the fluorescence quantum

efficiency of the resulting alkoxyamine adduct was similar to that of methoxyamine

117 (data not shown). The isoindoline heterocyclic ring component of the

methoxyamines may lead to the observed decrease in fluorescence quantum yield, as

1,7-dipyrrolidino based perylene diimides exhibit lowered quantum yields due to

significant amino-to-perylene diimide quadrupolar charge-transfer character.164, 182-183

To test this, an analogue (130) of methoxyamine 117 was prepared where the

isoindoline rings at positions 1 and 7 on the perylene unit were replaced with phenoxy

groups. For160 this compound, a higher value of 0.7619 for the fluorescence quantum

yield was obtained. This supports the hypothesis that the low fluorescence quantum

yields arise from charge-transfer processes between the N lone pair of the isoindoline

ring and the π-system of the perylene unit.

Preliminary assessment of the photostability of the newly synthesised profluorescent

nitroxides was achieved by comparing the relative photostability of the methoxyamine

adducts (104, 106, 117 and 114) against 9,10-bis(phenylethynyl)anthracene (the

fluorescent core which features in the current state-of-art profluorescent probe 29) and

N,N′-bis(2,5-di-tert-butylphenyl)-1,7-dibromo-3,4,9,10-perylene dicarboximide 113.

Profluorescent nitroxide 23 displays significant fluorescence suppression (>20 fold)

and has been shown to have considerable thermal stability98, 100 yet its performance

under photo-oxidative conditions has not been reported. To obtain a clear picture of


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the relative stability of the fluorphores involved, the non-radical methoxyamine

analogues were analyzed. This removes any complications arising from the stabilizing

effect of the nitroxide antioxidant. Thus the photostabilities of compounds 104, 106,

113, 117, 114 and 9,10-bis(phenylethynyl)anthracene 29 study were assessed by

irradiating samples in cyclohexane in a Heraeus Suntest CPS+ device operating at an

irradiation level of approximately 765 Wm-2 and held at 40ºC. Methoxyamines 99 and

92 could not examined due to their limited solubility in cyclohexane. The fluorescence

intensity at the λmax value for each compound was recorded periodically and the

percentage loss of fluorescence for each compound is shown in Figure 33. The least

stable fluorophore in this environment was 9,10-bis(phenylethynyl)anthracene (29)

which displayed a 50% decrease in fluorescence after only ~2 hours of photo-

irradiation. The fluorescence performance of the naphthalimide fluorophores 104 and

106 was much more robust, giving a 50% emission reduction after ~8 and ~20 hours

photo-irradiation respectively. The bay-region brominated perylene 113 showed a

photo-stability similar to the napthalimide fluorophore 106. The fluorescence from the

perylene fluorophores 117 and 114, however demonstrated substantial stability with a

reduction to 50% emission not being reached until 50 and 80 hours respectively. There

was also a trend showing that substitution at the bay-region of perylene with an alkyne

linker produced a more photostable compound than substitution with an ether linkage.

These results demonstrate the increased photostability of the bay-region substituted

perylene compounds 117 and 114 over the napthalimide or 9,10-

bis(phenylethynyl)anthracene based fluorophores. The rapid loss of fluorescence from

9,10-bis(phenylethynyl)anthracene is not surprising as photodegradation of this

fluorophore is known to proceed by the addition of photogenerated singlet oxygen to

the anthracene core to form a 9,10-endoperoxide.184 This highlights the limited value


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of this fluorophore as a profluorescent probe to monitor photo-oxidative damage in

materials. Based on these results, bay-substituted perylene systems on the other hand

show considerably more potential in this regard.

Figure 33: Fluorescence loss (calculated as a percentage from the fluorescence intensity at λmax) for

cyclohexane solutions of 9,10-bis(phenylethynyl)anthracene 29 (-♦-, λmax = 470 nm), 104 (-■-, λmax = 408

nm), 106 (-Δ-, λmax = 407 nm), 113 (-x-, λmax = 534 nm), 117 (-●-, λmax = 522 nm) and 114 (-+-, λmax = 557 nm)

following photo-irradiation at 765 Wm-2 and 40ºC.

3.4. Conclusions

Novel profluorescent mono- and bis-isoindoline nitroxides containing napthalimide

and perylene diimide structural cores and their respective methoxyamine adducts were

synthesised. The methoxyamine derivatives of the napthalimide-based probes (104

and 106) were prepared by nucleophilic substitution and palladium-catalysed

Sonogashira coupling reactions from the corresponding aryl bromides in high yield

(84 and 90%). Subsequent deprotection gave the desired nitroxides (105 and 107) in


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good yield. The bay region substituted bis-methoxyamine adducts of the perylene-

based probes (117 and 114) were prepared in a similar fashion in moderate-high yield

(52 and 87%) with deprotection again yielding the bis-nitroxides (118 and 116) in

excellent yield. Selective removal of a single methoxyamine group from the bis-

methoxymine 114 was also achieved with stoichiometric control of m-CPBA to give

mono-nitroxide 115 in moderate yield (55%). Unsymmetrical perylene-based probes

(98 and 90) bearing an imide linked nitroxide and an imide linked solubilizing group

were prepared in one pot from 3,4,9,10-perylenetetracarboxylic dianhydride and a

mixture of the corresponding aryl amines in modest yield (26% and 22%). The

corresponding methoxyamines (99 and 92) were accessed by subsequent reaction of

the nitroxides (98 and 90) with methyl radicals. The prepared profluorescent

compounds demonstrated strongly suppressed fluorescence emission even though the

measured fluorescence quantum yields for the corresponding methoxyamine

derivatives were lower than typical perylenes. Assessment of the photostability of the

newly prepared compounds revealed that the bay-region substituted perylene

compounds 117 and 114 displayed enhanced photostability over the napthalimide

compounds (104 and 106), bay-region brominated perylene 15 and 9,10-

bis(phenylethynyl)anthracene 29. These results suggest that perylene-based

profluorescent nitroxides (118, 116 and 115) may provide a sensitive technique for

assessing the early stages of photo-oxidative polymer degradation.

3.5. Experimental Section

3.5.1. General procedures

All starting materials and reagents were purchased from Sigma Aldrich. All reactions

were monitored using Merck Silica Gel 60 F254 TLC plates and visualized with UV


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light. Column chromatography was performed using silica gel 60 Å (230 - 400 mesh).

1H NMR spectra were run at 400 MHz and 13C NMR spectra at 100 MHz. Chemical

shifts (δ) for 1H and 13C NMR spectra run in CDCl3 are reported in ppm relative to the

solvent residual peak: proton (δ = 7.26 ppm) and carbon (δ= 77.2 ppm). Multiplicity

is indicated as follows: s (singlet); d (doublet); t (triplet); m (multiplet); dd (doublet of

doublet); br s (broad singlet). Coupling constants are reported in Hertz (Hz). Mass

spectra were recorded using either electrospray or electron impact (where specified)

as the ionization technique in positive ion mode. All MS analysis samples were

prepared as solutions in methanol. Infrared spectra were recorded as neat samples

using a Nicolet 870 Nexus Fourier Transform infrared spectrometer equipped with a

DTGS TEC detector and an Attenuated Total Reflectance (ATR) accessory. Analytical

HPLC was performed on a Hewlett Packard 1100 series HPLC, using an Agilent prep-

C18 scalar column (10 μm, 4.6 × 150 mm) at a flow rate of 1 mL/min. All UV/Vis

spectra were recorded on a single beam Varian Cary 50 UV-Vis spectrophotometer.

Fluorescence measurements were performed on a Varian Cary 54 Eclipse fluorescence

spectrophotometer equipped with a standard multicell Peltier thermostatted sample

holder. Melting points were measured on a Gallenkamp Variable Temperature

Apparatus by the capillary method and are uncorrected. EPR spectroscopy was carried

out on a Magnettech MiniScope EPR spectrometer using a suitable nonpolar solvent

at room temperature. All air-sensitive reactions were carried out under ultra-high

purity argon. Diethyl ether and toluene were dried by storing over sodium wire. THF

was freshly distilled from sodium benzophenone ketal, acetonitrile from calcium

hydride and DMF from 4Å molecular sieves.

Tetrakis(triphenylphosphine)palladium(0) was freshly prepared according to literature

procedures.163 N-(2,5-Di-tert-butylphenyl)-4-bromo-1,8-naphthalimide 103 was


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prepared in 2 steps using literature procedures from commercially available 1,8-

naphthalic anhydride.157, 185 N,N′-Bis(2,5-di-tert-butylphenyl)-1,7-dibromo-3,4,9,10-

perylene dicarboximide 113 was prepared in 2 steps from perylene-3,4,9,10-

tetracarboxylic dianhydride using established methods.[16] 2-Methoxy-5-nitro-1,1,3,3-

tetramethylisoindoline 61[14] and 5-ethynyl-2-methoxy-1,1,3,3-tetramethylisoindoline

81105 were prepared using established literature protocols.145

3.5.2. 5-Hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline 64

A solution of 5-diazonium-2-methoxy-1,1,3,3-tetramethylisoindoline

tetrafluoroborate 63 (84.1 mg, 2.64 × 10-4 mol) in deionised water (25 mL) was heated

at reflux for 5 hr. The solution was cooled and extracted with DCM (5 × 10 mL). The

combined DCM layers were washed with water (1 × 10 mL) and dried over sodium

sulphate. The organic layer was concentrated in vacuo to yield 64 as a pale yellow

crystalline solid. The aqueous layer was heated at reflux overnight and worked up

using the above procedure to yield a second portion of product (43 mg, 81%). M.p.

134-136°C. 1H NMR (400 MHz, CDCl3, 25°C, TMS): δ=1.40 (s, 12H, CH3-C), 2.84

(s, 3H, NH2), 3.77 (s, 3H, CH3-O), 6.56 (d, J = 1.91 Hz, 1H, Ar-H), 6.69 (dd, J = 8.07,

1.91 Hz, 1H, Ar-H), 6.97 (d, J = 8.07 Hz, 1H, Ar-H). 13C NMR (100 MHz, CDCl3,

25°C, TMS): δ= 65.4, 66.7, 67.0, 108.4, 114.5, 122.5, 137.5, 146.9, 155.0. HRMS

(ESI): m/z (%) = 222.1649 (10) [M+H]+; calcd. for C13H20NO2 [M+H]+ 222.1494.

3.5.3. N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-

tetramethylisoindolin-5-yloxy)-1,8-naphthalimide 104

N-(2,5-Di-tert-butylphenyl)-4-bromo-1,8-naphthalimide 103 (31.478 mg, 6.778 × 10-

5 mol) and 5-hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline 64 (15 mg, 6.778 ×


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10-5 mol) were dissolved in freshly distilled DMF (10 mL). Potassium hydroxide (4

mg, 6.778 × 10-5 mol) was added and the stirring solution was heated at 100°C for 24

hrs. The mixture was allowed to cool to room temperature and then diluted slowly with

2 M NaOH (10 mL) with stirring. The precipitate was collected and washed with water

(3 × 5 mL) until the filtrate ran clear. It was then dissolved in DCM (50 mL) and

washed further with water (10 mL), dried over sodium sulphate and concentrated in

vacuo. Purification by silica gel column chromatography in chloroform yielded 104 as

a yellow solid (34.4 mg, 84%). M.p. 122-125°C. 1H NMR (400 MHz, CDCl3, 25°C,

TMS): δ=1.29 (s, 9H, CH3); 1.32 (s, 9H, CH3); 1.46 (s, 6H, CH3); 1.49 (s, 6H, CH3);

3.81 (s, 3H, O-CH3); 6.95-7 (m, 3H, Ar-H); 7.07 (dd, 1H, J = 8.22, 1.96 Hz, Ar-H);

7.20 (d, 1H, J = 8.22 Hz, Ar-H); 7.44 (dd, 1H, J = 8.61, 2.35 Hz, Ar-H); 7.57 (d, 1H,

J = 8.7 Hz, Ar-H); 7.82 (dd, 1H, J = 7.78, 7.30 Hz, Ar-H); 8.52 (d, 1H, J = 8.22 Hz,

Ar-H); 8.71 (dd, 1H, J = 7.23, 1.49 Hz, Ar-H); 8.77 (dd, 1H, J = 8.50, 1.38 Hz, Ar-H).

13C NMR (100 MHz, CDCl3, 25°C, TMS): δ=15.3, 31.2, 31.7, 34.2, 34.8, 50.8, 65.5,

67.2, 110.3, 114.1, 116.7, 119.8, 122.9, 123.4, 124.0, 126.1, 126.5, 127.8, 128.7, 128.8,

130.1, 132.3, 133.0, 133.3, 142.6, 143.8, 147.9, 150.0, 154.0, 160.4, 164.8, 165.4. IR

(ATR) νmax 781 (=C-H), 1050 (C-O), 1352 (R3N), 1484 (aryl C-C), 1664 (C=O), 2961

cm-1 (alkyl CH3). HRMS (ESI): m/z (%) = 627.3095 (34) [M+Na]+; calcd. for

C39H44N2O4Na [M+Na]+ 627.3199.


tetramethylisoindolin-2-yloxyl-5-yloxy)-1,8-naphthalimide

105

mCBPA (6.12 mg, 2.84 x 10-5 mol) was added to an ice-cold solution of N-(2,5-di-tert-

butylphenyl)-4-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-1,8-


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naphthalimide 104 (8.6 mg, 1.42 x 10-5 mol) in DCM (20 mL). The solution was stirred

for an hour at room temperature and then chilled in an ice-bath and treated with 2 M

aqueous NaOH until the solution was basic. The resulting solution was extracted with

DCM (3 × 10 mL) and the combined organic layers were washed with base (5 × 10

mL) and water (1 × 30 mL). The organic phase was dried over sodium sulphate and

concentrated in vacuo. Purification by silica gel column chromography (chloroform)

gave 105 as a yellow solid (7.3 mg, 78%). M.p 150-152°C. 1H NMR (400 MHz,

CDCl3, 25°C, TMS): δ=1.30 (s, 9H, 3 × CH3); 1.33 (s, 9H, 3 × CH3); 7.1 (s, 1H, Ar-

H); 7.46 (d, 1H, J = 8.73 Hz, Ar-H); 7.60 (d, 1H, J = 8.73 Hz, Ar-H); 7.87 (br s, 1H,

Ar-H); 8.59 (br s, 1H, Ar-H); 8.75 (d, 1H, J = 5.97 Hz, Ar-H); 8.80 (br s, 1H , Ar-H).

IR (ATR) νmax 782 (=C-H), 1138 (C-O), 1375 (R3N), 1487 (aryl C-C), 1667 (C=O),

2968 cm-1 (alkyl CH3). HRMS (ESI): m/z (%) = 612.2855 (35) [M+Na]+, calcd. for

C38H41N2O4Na [M+Na]+ 612.2964. EPR: g = 2.0058, aN = 1.429 mT.

3.5.5. 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline 62

2-Methoxy-5-nitro-1,1,3,3-tetramethylisoindoline 61 (78 mg, 3.12 x 10-4 mol) was

dissolved in methanol (10 mL) and palladium on carbon (10% wt. loading, 24 mg)

added. The solution was placed in a Parr hydrogenator under an atmosphere of

hydrogen (40 psi) with shaking for 3 hours. The resulting suspension was filtered

through celite and the celite washed thoroughly with methanol. The combined filtrates

were concentrated at reduced pressure to give 62 as a cream solid in quantitative yield.

M.p. 52-54°C. 1H NMR (400 MHz, CDCl3, 25ºC, TMS): δ=1.41 (s, 12H, 4 x CH3),

2.84 (s, 2H, NH2), 3.77 (s, 3H, O-CH3), 6.35 (d, J = 2.35 Hz, 1H, Ar-H), 6.52 (dd, J =

8.22, 2.35 Hz, 1H, Ar-H), 6.92 (d, J = 8.22 Hz, 1H, Ar-H). 13C NMR (100 MHz,

CDCl3, 25°C, TMS): δ= 65.4, 66.7, 67.0, 108.2, 114.5, 122.2, 135.5, 145.7, 146.4.


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HRMS (ESI): m/z (%) = 221.1792 (10) [M+H]+, calcd. for C13H21N2O [M+H]+

221.1654.

3.5.6. 5-Diazonium-2-methoxy-1,1,3,3-tetramethylisoindoline

tetrafluoroborate 63

A solution of 5-amino-2-methoxy-1,1,3,3-tetramethylisoindoline 62 (117 mg, 5.3135

× 10-4 mol) in dry acetonitrile (0.5 mL) was added dropwise to a stirring solution of

nitrosyl tetrafluoroborate (124.1 mg, 10.628 × 10-4 mol) in dry acetonitrile (1 mL) at

-30 °C (dry ice/acetonitrile bath). Once the addition was complete, the reaction was

left to warm to room temperature for 30 min. Dry diethyl ether (3 mL) with added

dropwise to the reaction and the mixture was left to stir to ensure precipitation. The

white precipitate of 63 was collected by filtration, washed with dry diethyl ether and

stored under argon in the freezer (165.4 mg, 98 %). M.p. 138-140°C. 1H NMR (400

MHz, CDCl3, 25°C, TMS): δ= 1.45 (s, 12H, 4 × CH3), 3.73 (s, 3H, CH3-O), 7.93 (d, J

= 9 Hz, 1H, Ar-H), 8.60 (d, J = 4.3 Hz, 1H, Ar-H), 8.62 (s, 1H, Ar-H). 13C NMR (100

MHz, CDCl3, 25°C, TMS): δ= 65.4, 65.8, 68.3, 108.4, 115.0, 122.8, 125.6, 127.0,

133.5, 148.1, 159.0. IR (ATR) νmax 2200 cm-1 (N≡N). HRMS (ESI): m/z (%) =

322.1624 (45) [M+3H]3+, calcd. for C13H18BF4N3O [M+3H]3+ 322.1714.


tetramethylisoindoline-5-ethynyl)-1,8-naphthalimide 106

N-(2,5-Di-tert-butylphenyl)-4-bromo-1,8-naphthalimide 103 (16 mg, 0.0349 mmol),

triethylamine (1.4 mL), copper (I) iodide (3.32 mg, 3.49 × 10-6 mol) and Pd(PPh3)4 (4

mg, 3.46 × 10-6 mol) were dissolved in dry THF (1.4 mL). The mixture was submitted

to 4 freeze-pump-thaw cycles. A solution of 5-ethynyl-2-methoxy-1,1,3,3-


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tetramethylisoindoline 81 (20 mg, 0.0872 mmol) in dry THF (0.5 mL) was added to

the mixture and the tube was sealed under argon and heated at 80°C for 24 hours. The

reaction mixture diluted with DCM (5 mL) and washed with 2 M aqueous HCl (3 × 5

mL). The organic phase was run through basic alumina and then purified by silica gel

column chromatography in diethyl ether/DCM 1:3 to give 106 as a yellow solid (19.4

mg, 90 %). M.p. 150°C (dec). 1H NMR (400 MHz, CDCl3, 25°C, TMS): δ= 1.29 (s,

9H, 3 × CH3); 1.32 (s, 9H, 3 × CH3); 1.49 (s, 12H, 4 × CH3); 3.81 (s, 3H, O-CH3); 6.99

(d, 1H, J = 1.8 Hz, Ar-H); 7.18 (d, 1H, J = 8.11 Hz, Ar-H); 7.43 (s, 1H, Ar-H); 7.45

(dd, 1H, J = 8.26, 1.8 Hz, Ar-H); 7.58 (s, 1H, Ar-H); 7.59 (dd, 1H, J = 7.67, 2.41 Hz,

Ar-H); 7.89 (t, 1H, J = 7.97 Hz, Ar-H); 7.99 (d, 1H, J = 7.66 Hz, Ar-H); 8.61 (d, 1H,

J = 7.67 Hz, Ar-H); 8.70 (d, 1H, J = 7.36 Hz, Ar-H); 8.82 (d, 1H, J = 8.41 Hz, Ar-

H).13C NMR (100 MHz, CDCl3, 25°C, TMS): δ= 14.2, 21.5, 22.7, 29.4, 29.7, 31.2,

31.7, 32.0, 35.0, 34.3, 35.5, 65.6, 67.1, 67.3, 85.78, 99.7, 121.0, 122.0, 122.4, 123.4,

125.2, 126.3, 127.5, 127.8, 128.1, 128.8, 130.8, 130.9, 131.3, 132.1, 132.8, 132.8,

143.8, 146.0, 147.1, 150.1, 164.8, 165.0. IR (ATR) νmax 782 (=C-H), 1050 (C-O), 1237

(Ar-O-C), 1356 (R3N), 1709 (C=O), 2206 (C≡C), 2958 cm-1 (alkyl CH3).


tetramethylisoindolin-2-yloxyl-5-ethynyl)-1,8-

naphthalimide 107

N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-tetramethylisoindoline-5-ethynyl-

1,8-naphthalimide 106 (11.6 mg, 0.0189 mmol) was dissolved in DCM (25 mL) and

m-CPBA (7 mg, 2.84 x10-5 mol) was added slowly to the stirring solution. After 10

minutes, the reaction was complete following analysis by TLC (DCM) and 2 M NaOH

was added (25 mL) and the resulting mixture was washed with water (5 x 10 mL).


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Purification by silica gel column chromatography (DCM) gave 107 as a yellow oil

(11.2 mg, 99%). M.p 165-170°C. IR (ATR) νmax 782 (=C-H), 1064 (C-O), 1236 (Ar-

O-C), 1356 (R3N), 1709 (C=O), 2205 (C≡C), 2968 cm-1 (alkyl CH3). EPR: g = 2.0064,

aN = 1.402 mT.

3.5.9. N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-

tetramethylisoindolin-5-yloxy)-perylene-3,4,9,10-

tetracarboxy diimide 117

Anhydrous K2CO3 (1.5 mg, 1.13 × 10-4 mol) and 5-hydroxy-2-methoxy-1,1,3,3-

tetramethylisoindoline 64 (10 mg, 4.52 × 10-5 mol) were added to an NMP (20 mL)

solution of 1,7-dibromoperylene dianhydride 113 (20.89 mg, 2.26 × 10-5 mol). The

mixture was stirred at 120°C for 8 hr under an atmosphere of argon, cooled to room

temperature and then treated with aqueous 1 M HCl (~20 mL) to precipitate the

product. The precipitate was collected by filtration and washed with water until

neutrality. The resulting solid was dissolved in DCM, dried over sodium sulphate and

concentrated in vacuo. The product was purified by silica gel chromatography (DCM)

to yield a yellow solid (23.8 mg, 87.4%). M.p: 196-199°C. Analysis by 1H NMR

spectroscopy revealed a 1:4 mixture of 1,7 and 1,6 regioisomers. N,N-Di-(2,5-di-tert-

butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy) perylene-

3,4,9,10-tetracarboxy diimide 117: 1H NMR (400 MHz, CDCl3, 25°C, TMS): δ=1.25

(s, 18H, CH3); 1.26 (s, 18H, CH3); 1.43 (s, 24H, CH3); 3.77 (s, 6H, O-CH3); 6.95 (m,

6H, Ar-H); 7.13 (dd, 2H, J = 1.95, 8.25 Hz, Ar-H); 7.42 (dd, 2H, J = 1.96, 8.68, Hz,

Ar-H); 7.55 (d, 2H, J = 8.68 Hz, Ar-H); 8.40 (d, 2H, J = 1.74 Hz, Ar-H); 8.68 (dd, 2H,

J = 1.3, 8.46 Hz, Ar-H); 9.65 (dd, 2H, J = 5.64, 8.68 Hz, Ar-H). N,N-Di-(2,5-di-tert-

butylphenyl)-1,6-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy) perylene-


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3,4,9,10-tetracarboxy diimide: 1H NMR (400 MHz, CDCl3, 25°C, TMS): δ=1.25 (s,

18H, CH3); 1.26 (s, 18H, CH3); 1.43 (s, 24H, CH3); 3.77 (s, 6H, O-CH3); 6.95 (m, 6H,

Ar); 7.13 (dd, 2H, J = 1.95, 8.25 Hz, Ar); 7.42 (dd, 2H, J = 1.96, 8.68 Hz, Ar); 7.55 (d,

2H, J = 8.68 Hz, Ar); 8.32 (d, 2H, J = 1.74 Hz, Ar); 8.75 (dd, 2H, J = 1.3, 8.46 Hz,

Ar); 9.60 (dd, 2H, J = 5.64, 8.68 Hz, Ar). 13C NMR (100 MHz, CDCl3, 25°C, TMS):

δ=30.4, 31.4, 31.7, 34.2, 35.5, 65.5, 67.0, 67.2, 113.1, 118.5, 118.5, 122.6, 123.6,

124.2, 125.5, 126.4, 127.5, 127.7, 128.8, 129.0, 129.7, 130.6, 131.7, 132.4, 133.8,

133.79, 142.2, 143.7, 148.0, 150.1, 154.3, 154.4, 155.6, 156.6, 163.7, 163.9, 164.4,

264.6. IR (ATR) νmax 753 (=C-H), 1050 (C-O), 1258 (Ar-O-C), 1336 (R3N), 1707

(C=O), 2958 cm-1 (alkyl CH3).

3.5.10. N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-3,4,9,10-


mCBPA (7.46 mg, 4.33 x 10-5 mol) was added to an ice-cooled solution of N,N-di-(2,5-

di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)

perylene-3,4,9,10-tetracarboxy diimide 117 (26 mg, 2.16x10-5 mol) in DCM (25 mL).

The solution was stirred for an hour at room temperature and then cooled in an ice bath

and quenched with 2 M aqueous NaOH until the solution was basic. The aqueous phase

was extracted with DCM until the organic layer was colourless and the combined

organic layers washed with 2 M NaOH (5 × 10 mL) and water (2 × 10 mL) and then

dried over sodium sulphate and concentrated in vacuo. The product was purified by

silica gel column chromatography (5% diethyl ether in DCM) to yield a 118 as a purple

solid (22 mg, 87%). The isomers were not separated. M.p 196-200°C. IR (ATR) νmax


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752 (=C-H), 1113 (C-O), 1261 (Ar-O-C), 1337 (R3N), 1706 (C=O), 2962 cm-1 (alkyl

CH3). EPR: g = 2.0064, aN = 1.406 mT.

3.5.11. N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-

tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-


1,7-Dibromoperylene diimide 113 (16.1 mg, 0.0174 mmol), triethylamine (1 mL),

copper (I) iodide (1.66 mg, 0.0872 mmol) and Pd(PPh3)4 (2 mg, 0.00174 mmol) were

dissolved in dry THF (1 mL). The mixture was submitted to 4 freeze-pump-thaw

cycles. A solution of 5-ethynyl-2-methoxy-1,1,3,3-tetramethylisoindoline 81 (20 mg,

0.0872 mmol) in a small amount of dry THF (0.5 mL) was added to the mixture and

the tube was sealed under argon and heated at 80°C for 48 hours The reaction mixture

was dissolved in DMC (50 mL) and washed with 2 M HCl (3 × 10 mL), run through

basic alumina and then purified by silica gel column chromatography (20% hexane in

DCM) to give 114 as a red solid (7.59 mg, 36%). M.p. 163-170°C. 1H NMR (400

MHz, CDCl3, 25°C, TMS): δ=1.32 (s, 18H, CH3); 1.34 (s, 18H, CH3); 1.48 (s, 12H,

CH3); 1.50 (s, 12H, CH3); 3.80 (s, 3H, O-CH3); 7.04 (s, 2H, Ar-H); 7.22 (d, 2H, J =

8.59 Hz, Ar-H); 7.44 (s, 2H, Ar-H); 7.49 (m, 2H, Ar-H); 7.59 (dd, 2H, J = 1.2, 7.68

Hz, Ar-H); 7.62 (d, 2H, J = 1.2, 7.68 Hz, Ar-H); 8.81 (m, 2H, Ar-H); 8.98 (s, 2H, Ar-

H); 10.40 (d, 2H, J = 8.59 Hz, Ar-H). IR (ATR) νmax 752 (=C-H), 1050 (C-O), 1262

(Ar-O-C), 1346 (R3N), 1707 (C=O), 2188 (C≡C), 2958 cm-1 (alkyl CH3).


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tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-

3,4,9,10-tetracarboxy diimide 116

m-CPBA (5.4 mg, 3.77 x10-5 mol) was added slowly to an ice-cooled solution of N,N-

(2,5-di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-ethynyl)

perylene-3,4,9,10-tetracarboxy diimide 114 (23 mg, 1.88 x10-5 mol) was dissolved in

ice-cooled DCM (50 mL). The solution was stirred for an hour at room temperature

and then cooled in an ice bath and quenched with 2 M aqueous NaOH. The aqueous

phase was extracted with DCM until the organic level was colourless and the combined

organic layers washed with water (5 × 10 mL), dried over sodium sulphate and

concentrated in vacuo. The compound was purified by column chromatography (10%

diethyl ether in DCM) to yield a 114 as a red solid (22 mg, 99%). M.p. 162-167°C. 1H

NMR (400 MHz, CDCl3, 25°C, TMS): δ=1.32 (s, 18H, CH3); 1.34 (s, 18H, CH3); 7.00

(s, 2H, Ar-H); 7.50 (d, 2H, J = 5.38 Hz, Ar-H); 7.61 (d, 2H, J = 5.38 Hz, Ar-H); 8.56

(br s, 2H, Ar-H); 8.84 (br s, 2H, Ar-H); 8.98 (br s, 2H, Ar-H); 10.44 (br s, 2H, Ar-H).

IR (ATR) νmax 752 (=C-H), 1068 (C-O), 1223 (Ar-O-C), 1325 (R3N), 1708 (C=O),

2192 (C≡C), 2961 cm-1 (alkyl CH3). EPR: g = 2.0064, aN = 1.443 mT.

3.5.13. N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-ethynyl)-7-(2-methoxy-

1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-


N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-

ethynyl) perylene-3,4,9,10-tetracarboxy diimide 114 (18.9 mg, 1.55 x10-5 mol) was


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dissolved in ice-cooled DCM (40 mL) and m-CPBA (2.7 mg, 1.55 x10-5 mol) was

added slowly to the stirring solution. The reaction was allowed to warm to room

temperature and after 1 hr, 2 M aqueous NaOH (10 mL) was added. The resulting

solution was washed with water (2 × 20 mL), dried (anhydrous Na2SO4) and

concentrated in vacuo. Purification of the obtained residue by column chromatography

(DCM) gave 115 as a red solid (8.8 mg, 47%). M.p. 202-206°C. 1H NMR (400 MHz,

CDCl3, 25°C, TMS): δ=1.32 (s, 18H, CH3); 1.33 (s, 18H, CH3); 3.84 (s, 1.5H, O-CH3)

6.99 (s, 2H, Ar-H TB); 7.47 (d, 2H, J = 11.86 Hz, Ar-H); 7.61 (d, 2H, J = 8.21 Hz, Ar-

H); 8.55 (b, 2H, Ar-H TB); 8.80 (b, 2H, Ar-H P); 8.97 (b, 2H, Ar-H P); 10.42 (b, 2H,

Ar-H). EPR: g = 2.0066, aN = 1.414 mT.

3.5.14. General procedure for the synthesis of compounds 98 and

90

Perylene-3,4,9,10-tetracarboxylic dianhydride 42 (1 equiv.), aniline derivative (1.2

equiv.), amino-1,1,3,3-tetramethylisoindolin-2-yloxyl 57 (1.2 equiv.), zinc acetate

(0.75 equiv.) and imidazole (2 g) were combined and heated at 130°C for 6 hrs under

an argon atmosphere. The mixture was allowed to cool and 2 M aqueous HCl was

added to dissolve the imidazole. The resulting solution was extracted with chloroform

and the combined organic layers washed with water, brine and dried with anhydrous

magnesium sulphate. The solvent was removed under reduced pressure and

purification by silica gel column chromatography (in mixtures of methanol and

chloroform) gave the target compounds.


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3.5.15. N-(Octylphenyl)-N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-

perylene-3,4,9,10-tetracarboxyl-diimide 98

The general procedure detailed above was employed using N-octylaniline (29.7 mg,

0.144 mmol). Purification using column chromatography (3% methanol/chloroform)

gave 98 as a red solid (24 mg, 26%). M.p. >300°C (dec.) 1H NMR (400 MHz, CDCl3,

25ºC, TMS): δ=0.6- 0.8 (m, 3H, CH3), 1.2-1.4 (m, 12H, CH2), 1.7 (s, 6H, 2 × CH3),2.71

(br s, 2H, CH2-Ar), 7.34 (br s, 1H, J = 8.06 Hz, Ar-H), 8.55 (br s, 4H, Ar-H), 8.71 (br

s, 4H, Ar-H). Not all 1H NMR signals were observed due to paramagnetic broadening

by the nitroxide radical. IR (ATR) νmax 750 (=C-H), 1259 (Ar-O-C), 1362 (R3N), 1725

(C=O), 2923 cm-1 (alkyl CH3). EPR: g = 2.0058, aN = 1.408 mT.

3.5.16. N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-

tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-

tetracarboxyl-diimide 90

The general procedure detailed above was employed using 2,5-di-tert-butylaniline (16

mg, 0.078 mmol). Purification using column chromatography (1%

methanol/chloroform) gave 90 as a red solid (11 mg, 22%). M.p. >300°C (dec.) 1H

NMR (400 MHz, CDCl3, 25ºC, TMS): δ=1.55 (s, 18H, 6 × CH3), 7.08 (br s, 1H, Ar-

H), 7.49 (d, 1H, J = 8.23 Hz, Ar), 7.61 (d, 1H, J = 7.88 Hz, Ar-H), 8.70 (d, 4H, J =

5.78 Hz, Ar-H), 8.79 (d, 4H, J = 7.02 Hz, Ar-H). Not all 1H NMR signals were

observed due to paramagnetic broadening by the nitroxide radical. IR (ATR) νmax 745

(=C-H), 1072 (C-O), 1257 (Ar-O-C), 1358 (R3N), 1703 (C=O), 2961 cm-1 (alkyl CH3).

EPR: g = 2.0055, aN = 1.44 mT.


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3.5.17. General procedure for the synthesis of compounds 99 and

92

Hydrogen peroxide solution (30%, 5 equiv.) was added dropwise to an ice-cooled

solution of perylene-based nitroxide (1 equiv.) and iron(II) sulphate heptahydrate (2.5

equiv.) in a solution of minimal DMSO. The resulting solution was stirred at room

temperature for 30 minutes and then poured onto ice-cold sodium hydroxide (1 M

aqueous solution). The mixture was extracted with chloroform and washed with water

several times to remove the DMSO. The organic phase was dried over anhydrous

sodium sulphate and concentrated in vacuo. Purification by silica gel column

chromatography (3% methanol/chloroform) gave the target compounds.

3.5.18. N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-

tetramethylisoindolin-2-yl)-perylene-3,4,9,10-


The general procedure detailed above was employed using N-(octylphenyl)-

N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide

98 to give the desired compound 99 as a red solid (12 mg, 12%). M. p. >300°C (dec.)

1H NMR (400 MHz, CDCl3, 25°C, TMS): δ= 0.6- 0.8 (m, 3H, CH3), 1.2-1.6 (m, 12H,

CH2), 1.48 (s, 6H, 2 × CH3), 1.51 (s, 6H, 2 × CH3), 2.71 (t, 2H, J = 7.74 Hz, CH2-Ar),

3.81 (s, 3H, CH3-O), 7.09 (d, 1H, J = 1.61 Hz, Ar-H), 7.20 (dd, 1H, J = 7.74, 1.94 Hz,

Ar-H), 7.26 (d, 1H, J = 8.06 Hz, Ar-H), 7.28 (d, 1H, J = 8.71, Ar-H), 7.38 (d, 1H, J =

8.06 Hz, Ar-H), 8.67 (d, 4H, J = 8.06, Ar-H), 8.75 (dd, 4H, J = 7.74, 2.28 Hz, Ar-H).

13C NMR (100 MHz, CDCl3, 25°C, TMS): δ=13.1, 21.7, 28.5, 28.7, 30.9, 64.5, 66.2,


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120.9, 122.3, 122.5, 127.2, 128.5, 130.8, 133.8, 133.9, 162.6. IR (ATR) νmax 750 (=C-

H), 1073 (C-O), 1276 (Ar-O-C), 1379 (R3N), 1723 (C=O), 2924 cm-1 (alkyl CH3).

3.5.19. N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-1,1,3,3-

tetramethylisoindolin-2-yl)-perylene-3,4,9,10-


The general procedure detailed above was employed using N-(2,5-di-tert-

butylphenyl)-N’-(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-

tetracarboxyl-diimide 90 to give the desired compound 92 as a red solid (10 mg, 7 %).

M. p. >300°C (dec.) 1H NMR (400 MHz, CDCl3, 25ºC, TMS): δ=1.25 (s, 9H, 3 ×

CH3), 1.34 (s, 9H, 3 × CH3), 1.51 (s, 12H, 4 × CH3), 3.81 (s, 3H, CH3-O), 7.04 (d, 1H,

J = 1.44 Hz, Ar-H), 7.08 (d, 1H, J = 1.44 Hz, Ar-H), 7.2 (dd, 1H, J = 8.2, 1.93, Ar-H),

7.29 (d, 1H, J = 8.68 Hz, Ar-H), 7.48 (d, 1H, J = 8.68 Hz, Ar-H), 7.61 (dd, 1H, J = 8.2,

1.93 Hz, Ar-H), 8.72 (m, 8H, Ar-H). 13C NMR (100 MHz, CDCl3, 25°C, TMS): δ=

14.3, 22.9, 29.1, 29.6, 29.9, 29.9, 32.1, 38.9, 65.7, 67.35, 122.1, 122.8, 123.5, 123.7,

124.4, 126.7, 127.5, 129.8, 131.9, 134.1, 134.9, 146.0, 146.8, 163.7, 182.1. IR (ATR)

νmax 800 (=C-H), 1019 (C-O), 1257 (Ar-O-C), 1346 (R3N), 1704 (C=O), 2974 cm-1

(alkyl CH3).

3.5.20. N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-perylene-

3,4,9,10-tetracarboxy diimide 130

Anhydrous K2CO3 (1.5 mg, 1.13 x10-4 mol) and phenol (10 mg, 4.52 x10-5 mol) were

added to a solution of 1,7-dibromoperylene dianhydride 113 (20.89 mg, 2.26 x10-5

mol) in NMP (20 mL). The mixture was stirred at 120°C overnight under an

atmosphere of argon, then cooled to room temperature and the product was


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precipitated by the addition of aqueous 1 M HCl (20 mL). The precipitate collected by

filtration and washed with water until neutrality. The solid was then dissolved in DCM

(50 mL), dried over sodium sulphate and concentrated in vacuo. Purification by silica

gel chromatography (DCM) gave 130 as a red solid (19.3 mg, 91%). Analysis by 1H

NMR spectroscopy revealed a 2:1 mixture of 1,7 and 1,6 regioisomers. N,N’-(2,5-Di-

tert-butylphenyl)-1,7-di-(phenoxy)-perylene-3,4,9,10-tetracarboxy diimide 27: 1H

NMR (400 MHz, CDCl3, 25ºC, TMS): δ=1.26 (s, 18H, CH3); 1.28 (s, 18H, CH3); 1.43

(s, 24H, CH3); 6.96 (m, 2H, Ar-H); 7.19 (d, 4H, J = 7.89 Hz, Ar-H); 7.45 (m, 6H, Ar-

H); 7.57 (dd, 2H, J = 8.15, 1.45 Hz, Ar-H); 8.41 (d, 2H, J = 1.4 Hz, Ar-H); 8.69 (dd,

2H, J = 8.14, 1.08 Hz, Ar-H); 9.66 (dd, 2H, J = 8.66, 6.16 Hz, Ar-H). N,N’-(2,5-Di-

tert-butylphenyl)-1,6-di-(phenoxy)-perylene-3,4,9,10-tetracarboxy diimide: 1H NMR

(400 MHz, CDCl3, 25ºC, TMS): δ=1.26 (s, 18H, CH3); 1.28 (s, 18H, CH3); 1.43 (s,

24H, CH3); 6.96 (m, 2H, Ar); 7.19 (d, 4H, J = 7.89 Hz, Ar-H); 7.45 (m, 6H, Ar-H);

7.57 (dd, 2H, J = 8.15, 1.45 Hz, Ar-H); 8.33 (d, 2H, J = 1.55 Hz, Ar-H); 8.75 (dd, 2H,

J = 8.2, 1.08 Hz, Ar-H); 9.60 (dd, 2H, J = 8.67, 5.88 Hz, Ar-H).

3.5.21. Photostability study

Separate solutions of 9,10-bis(phenylethynyl)anthracene and compounds 104, 106,

113, 117 and 114 were prepared in freshly distilled cyclohexane such that each gave a

UV absorbance reading of 0.2 (~10 μM). The 6 solutions were each stored in a screw

cap sealed quartz cell and were irradiated in a Heraeus Suntest CPS+ device operating

at an irradiation level of approximately 765 W/m2. The temperature of the chamber

was monitored by thermocouple and held at 40°C. The cells were held in location at

180°, perpendicular to the lamps. The solutions were analysed periodically (hours) by

both UV/vis spectroscopy (200-700 nm) and fluorimetry. Fluorescence loss was


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monitored at the following wavelengths: 9,10-bis(phenylethynyl)anthracene (λmax =

470 nm), 104 (λmax = 408 nm), 106 (λmax = 407 nm), 113 (λmax = 534 nm), 117

(λmax = 522 nm) and 114 (λmax = 557 nm).

3.5.22. Quantum yield and extinction coefficient calculations

Quantum yield efficiencies of fluorescence for compounds 103, 104, 105, 106, 107,

113, 117, 118, 114, 116, 115, 90, 92, 98 and 99 were obtained from measurements at

five different concentrations in cyclohexane or chloroform using the following

equation:

ФF sample = ФF standard × (Absstandard/Abssample) × (Σ[Fsample]/ Σ[Fstandard])

where Abs and F denote the absorbance and fluorescence intensity, respectively, and

Σ[F] denotes the peak area of the fluorescence spectra, calculated by summation of the

fluorescence intensity. Anthracene (ФF = 0.36) and N,N′-bis(2,5-di-tert-butylphenyl)-

3,4,9,10-perylenedicarboximide (ФF = 0.99) were used as standards. Extinction

coefficients were calculated from the obtained absorbance spectra.

3.6. Acknowledgements

We gratefully acknowledge financial support for this work from the Australian

Research Council Centre of Excellence for Free Radical Chemistry and Biotechnology

(CEO 0561607), the Defence Materials Technology Centre, which was established and

is supported by the Australian Government’s Defence Future Capability Technology

Centre (DFCTC) initiative and Queensland University of Technology.

Keywords: nitroxides • fluorescence • radicals • photooxidation


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C H A P T E R F O U R

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4. PROFLUORESCENT NITROXIDE SENSORS FOR

MONITORING PHOTO-INDUCED DEGRADATION

IN POLYMER FILMS

The authors listed below have certified* that:


conception, execution, or interpretation, of at least that part of the publication













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Profluorescent nitroxide sensors for monitoring photo-induced degradation in

polymer films

Sensors and Actuators B: Chemical.

Published: 19 September 2016






John M. Colwell Overall supervision of the project, guided during

experimental design and assisted with manuscript design

and final data analysis


Smith

Overall supervision of the project, guided during







Name Signature Date



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Profluorescent nitroxide sensors for monitoring photo-induced degradation in

polymer films

Vanessa C. Lussini,a,b John M. Colwell,a,b Kathryn E. Fairfull-Smitha and Steven E.

Bottle*[a,b]

Received: 9 June 2916

Published Online: 19 September 2016

DOI: j.snb.2016.09.104

aARC Centre of Excellence for Free Radical Chemistry and Biotechnology. School of

Chemistry, Physics and Mechanical Engineering, Science and Engineering Faculty,

Queensland University of Technology (QUT), GPO Box 2434, Brisbane, QLD 4001,

Australia

bDefence Materials Technology Centre, School of Chemistry, Physics and Mechanical

Engineering, Science and Engineering Faculty, Queensland University of Technology (QUT),

GPO Box 2434, Brisbane, QLD 4001, Australia

E-mail: [email protected]



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4.1. Abstract

A range of profluorescent nitroxides (PFNs) were tested as probes to monitor photo-

induced radical-mediated damage in polymer materials. The most stable and sensitive

probe of the PFNs tested was an alkyne-linked perylenediimide PFN, 116, with

napthalimide and 9,10-bis(phenylethnyl)anthranene-based versions giving lower

stability and sensitivity. Results from photo-ageing of poly(1-trimethylsilyl)-1-

propyne (PTMSP) and the ethylene norbornene copolymer (TOPAS®) films doped

with PFN probes demonstrated that sensors employing these support materials deliver

significantly enhanced sensitivity compared to traditional techniques used to monitor

photo-oxidative degradation of polymers, such as infrared spectroscopy. This

enhanced sensitivity for detecting polymer damage improved methods for the

determination of the serviceable application lifetime of polymers.

4.2. Key words

Profluorescent nitroxide, TOPAS, PTMSP, Fluorescence, Degradation

4.3. Introduction

The application lifetimes of polymer materials are strongly influenced by the

environmental factors to which they are exposed. For many materials, oxidation is a

key influence on service lifetimes, with this degradation process being controlled by

temperature, oxygen concentration and other local factors such as reactive

contaminants that may affect oxidation rates. Laboratory-based studies can be used to

assess environmental effects on polymer degradation. However, it is often difficult to

translate the data generated in the laboratory to methods for actual service lifetime


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prediction. This is, in part, due to the broad range of differing environments to which

polymer materials may be exposed. By combining laboratory-generated ageing data

and a number of field sensors (e.g., temperature, oxygen, chemical), in-service lifetime

predictions may be possible. However, to implement effective systems with sufficient

sensors would be costly and require significant analytical effort. As an alternative to a

suite of sensors, we have developed a simple, sensitive, profluorescent additive that

can be used as an oxidative environment sensor. The validity of this approach has been

successfully demonstrated 98, 186, however photo-stability and the phase distribution of

the probe are factors that control sensor performance. To address some of these issues

we have synthesised components with higher photo-stability.187

The sensor approach described herein is based on the use of profluorescent nitroxides

(PFNs) as free-radical probes. PFNs combine a paramagnetic nitroxide covalently

linked to a fluorophore where the nitroxide acts to quench the fluorescence of the

fluorophore. When the nitroxide radical is removed via radical-radical coupling, the

fluorescence is restored (Figure 34).66, 68 Radical-radical coupling of nitroxides with

transient carbon-centred radicals that are key intermediates in autooxidation reactions

allows PFNs to act as integrating sensors for the degradation process through the

formation of stable alkoxyamine adducts that build up over time.56, 118 PFNs can also

show high fluorescence suppression (over 300-fold 53), which can deliver higher

sensitivity for detecting free-radical polymer degradation than many other common

degradation monitoring techniques.188

By combining the sensitivity of PFNs with an oxidisable substrate, oxidative

environment sensors may be produced. Such sensors can be used to assess

environmental conditions that affect polymer degradation, and therefore give early


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warning of the failure of the material. Previously described PFN-based sensors for

oxidative environment monitoring 98, 186 used an ethylene norbornene copolymer

(TOPAS®) as a relatively inert carrier and polyisoprene (PIP) as the oxidisable

substrate. It was found that the phase structure of this ternary system limited the sensor

response at temperatures below the glass transition of the inert carrier and, therefore,

further development of these materials as sensors was required.

Figure 34: Tethering of a fluorophore to a nitroxide to form a PFN probe

Although the PFN-based sensors described above performed well under thermal

ageing conditions, they were found to be less useful for monitoring photo-oxidative

degradation due to the limited photo-stability of the 9,10-

bis(phenylethynyl)anthracene-based PFN.101 More robust PFNs, based on

naphthalimide and perylenediimide fluorophores (Figure 36), were therefore

developed with these fluorophores providing considerably enhanced photo-oxidative

stability.189

Recently, a perylenediimide-based isoindoline profluorescent nitroxide was used to

monitor the degradation of melamine-formaldehyde crosslinked polyesters under

accelerated weathering conditions.123 This PFN probe was used to assess the impact of

both temperature and UV radiation on the degradation of two commercial polyesters.

The focus of this study, however, was limited to a single PFN. In the work described

herein, we have assessed the resistance of a new range of perylenediimide and


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naphthalimide PFNs in two commercially-available polymers: poly(1-trimethylsilyl)-

1-propyne (PTMSP), and the ethylene norbornene copolymer, TOPAS® (8007x10

grade). These polymers can be used to produce easily handled films via solvent

casting, which readily allows incorporation of the PFNs under mild conditions. The

structures of the polymers studied (Figure 35), allows them to act as model substrates

for a range of other polymer materials such as polyethylene (TOPAS® as a model)

and unsaturated polymers such as polyisoprene (PTMSP as a model).

Figure 35: The structures of the polymers used in this study, PTMSP and TOPAS®

Both PTMSP 190-192 and TOPAS® 193 degrade when exposed to heat or UV light in air

through radical-mediated mechanisms and therefore, in combination with PFNs, they

can be used as sensitive oxidative environment sensors. Here, we describe the use of

perylenediimide and naphthalimide PFNs in PTMSP and TOPAS® matrices as photo-

oxidative environment sensors and highlight the most effective PFN based on the

photo-oxidative stability of these novel systems in the polymer studied.


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Figure 36: Nitroxides used in this study and their non-radical (fluorescent) methoxyamine derivatives

4.4. Experimental

4.4.1. Materials

TOPAS® 8007x10 was a gift from Ciba Speciality Chemicals. PTMSP was purchased

from ABCR GmbH. Cyclohexane was purified using a literature procedure194 where

it was washed with concentrated sulphuric acid until the wash was colourless. The

organic layer was then washed with water, aq. Na2CO3 and again with water until the


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wash solution was at a neutral pH. The washed cyclohexane was then distilled over

calcium hydride. PFNs 23, 105, 107, 118, and 116 along with the methoxyamine, non-

radical analogues, 104, 106, 117 and 114 were synthesised as described previously.53,

187 All other materials and reagents were of analytical reagent grade purity, or higher

and were purchased from Sigma Aldrich, Australia.

4.4.2. PTMSP sample preparation

Each of the compounds shown in Figure 36 (1.94 x10-7 mol) was dissolved in freshly

distilled cyclohexane (7.45 mL) in a 25x75 mm soda glass vial. PTMSP (293 mg) was

then added to each solution and the vials sealed and stirred for 48 hours in the dark.

Each solution was then poured into a Petri dish and the solvent allowed to evaporate

slowly over two days in the dark. Once the films were dry to the touch, they were

placed under vacuum until they reached a constant weight (24 h).

4.4.3. TOPAS® sample preparation

Each of the compounds shown in Figure 36 (4.3610-7 mol) was dissolved in freshly

distilled cyclohexane (16.94 mL) in a 2575 mm soda glass vial. TOPAS® pellets

(660 mg) were then added to each solution and the vials sealed and stirred for 4 hours

in the dark. Each solution was then poured into a Petri dish and the solvent allowed to

evaporate slowly over two days in the dark. Once the films were dry to the touch, they

were placed under vacuum until they reached a constant weight (24 h).

4.4.4. Photo-oxidation of films

Film samples were irradiated in an Heraeus Suntest CPS+ device delivering 250 W/m2.

The temperature in the chamber was set to 40°C. The films were oriented in parallel


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to the lamp. Samples were removed periodically and analysed using UV-Vis,

Fluorescence and FTIR-ATR spectroscopy.

4.4.5. Thermo-oxidation of films

Films were placed in an oven at 70°C on metal racks, and separated by a 5 mm gap.

4.4.6. Characterisation

4.4.6.1. FTIR-ATR Spectroscopy

Infrared spectra were recorded as neat samples using a Nicolet 5700 Nexus Fourier

Transform infrared spectrometer equipped with a DTGS TEC detector and a Smart

Endurance single reflection ATR accessory equipped with a composite diamond IRE

with a 0.75 mm2 sampling surface and a ZnSe focussing element (Nicolet Instrument

Corp., Madison, WI). An Optical Path Difference (OPD) velocity of 0.6329 cm s-1 and

a gain of 8 were used. Spectra were collected over the range 4000-525 cm-1 using 32

scans at 4 cm-1 resolution. Oxidation indices were calculated by taking the ratio of the

maximum peak height in the carbonyl stretching region (1700-1715 cm-1) to the area

under the C-H deformation band (1400-1500 cm-1).

4.4.6.2. UV-Vis Spectroscopy

UV-Vis spectra were recorded on a Varian Cary 50 UV-Vis spectrophotometer.

Spectra were collected from 200-700 nm at a scan rate of 600 nm min-1. All spectra

were corrected to give an absorbance of zero at 700 nm.


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4.4.6.3. Fluorescence Spectroscopy

Fluorescence spectroscopy was undertaken using a Varian Cary Eclipse fluorescence

spectrophotometer. Samples were loaded into a custom-made holding device and

excited at an angle of 45° to the surface, with the emission recorded from the back face

of the sample in order to minimise scattering effects. The excitation wavelength used

changed according to the compound present in the sample: 29; 383 nm, 23; 383 nm,

104; 362 nm, 105; 360 nm, 106; 378 nm, 107; 374 nm, 117; 540 nm, 118; 536 nm,

114; 568 nm, 116; 564 nm. Spectra were collected from 5 nm past the excitation

wavelength up to 700 nm at a scan rate of 600 nm min-1.


4.5.1. Film Preparation

PTMSP and TOPAS® films were prepared by solvent casting, which allowed the

PFNs to be evenly dispersed into the films at well-defined concentrations, without the

need for heating. Previous studies using PFNs and polymer systems have typically

relied on solution swelling of PFNs or melt processing, each of which lead to

limitations in precisely controlling the concentration of dopant. For melt processing,

thermal reactions at high temperature can consume some of the nitroxide before

degradation monitoring can be undertaken.99, 101 The mass of the PFN added to the

films (0.025 wt%) was kept low to reduce aggregation of the PFNs within the film.

There was no evidence of any bathochromic shifts in the bands or any obvious

fluorescence quenching that might arise from aggregation, shown in Figure 37.123, 195-

197


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Figure 37: UV-Vis absorbance (dotted lines) and fluorescence emission (solid lines) spectra of perylene

fluorophore 114 in TOPAS® at various concentrations ranging from 0.025 to 0.0025 w%, showing no

evidence of any bathochromic shifts in the bands or any obvious fluorescence quenching that might arise

from aggregation.

4.5.2. PTSMP films

4.5.2.1. Photo-oxidative degradation

PTMSP has the highest gas permeability of all known synthetic polymers 192, 198-199

due to it being a loosely packed polymer with 20-34% free volume.198 As a result,

oxygen permeability is not limited through this glassy material and PTMSP is therefore

a good model for situations where diffusion-limited oxidation is not dominant.

PTMSP films were aged in an Heraeus Suntest xenon-arc solar simulator delivering

an irradiance of 250 W/m2 (21.6 MJ/m2/d), which corresponds to the approximate

average daily terrestrial irradiance received during the 2014-2015 summer in Brisbane,

Australia (21.4 MJ/m2/d).200 Films were periodically monitored by fluorescence, UV-

Vis and FTIR-ATR spectroscopy. The films doped with PFNs were compared to films


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doped with the structurally-related non-radical methoxyamine analogues. Analysis in

this way provides insight into the rate of fluorescence switch-on from the PFN as

compared to the degradation rate of the parent fluorophore, as shown by the decrease

in fluorescence emission intensity for the non-radical adducts (29, 104, 106, 117 and

114) during ageing of the PTMSP-doped films.

Figure 38: Change in fluorescence emission of PTMSP films doped either with 29, 1 (-■-/left axis) or the

nitroxide analogue, 23 (-♦-/right axis) with respect to UV ageing time (hours).

The non-radical fluorophore 9,10-bis(phenylethynyl)anthracene, BPEA (29), shown

in Figure 38, started to degrade within two hours of UV exposure and its fluorescence

emission had decreased to 50% after 4 hours. BPEA 29 is known for its thermal

stability and its PFN analogue 29 has been used successfully for detecting alkyl

radicals with a high trapping ability.98 However, it is also known to have limited photo-

stability due to the reactivity of its anthracene core.201-202 Despite the rapid

photobleaching of the fluorophore, the BPEA-based nitroxide (23) still showed a

fluorescence emission increase of ~2.5 fold after ~1 hour of irradiation. It is likely that


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degradation of the fluorophore and photobleaching occurs predominantly after the

conversion of most of the nitroxide free radicals, which act as stabilising antioxidants.

However the degradation of the fluorophore, (as shown in Figure 38 by the loss of

fluorescence emission from the BPEA parent compound, 29 after 3 hours) is at least

as large as the fluorescence increase generated by the PFN 23. Therefore, this PFN has

limited value as a sensor for photo-oxidative damage.

Figure 39: Change in fluorescence emission of PTMSP films doped either with ether-linked naphthalimide

fluorophore 104 (-■-/left axis) or the nitroxides analogue 105 (-♦-/right axis) with respect to UV ageing time

(hours).


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Figure 40: Change in fluorescence emission of PTMSP films doped either with alkyne-linked

naphthalimide fluorophore 106 (-■-/left axis) or the nitroxides analogue 107 (-♦-/right axis) with respect to

ageing time (hours).

Both naphthalimide-based compounds (ether-linked, 104/105 (Figure 39) and alkyne-

linked, 106/107 (Figure 40)) showed comparable changes in fluorescence emission

during ageing. The non-radical analogues began to show photobleaching after 3 hours

and their fluorescence emission had decreased by a factor of two after 7-8 hours of

irradiation. This indicated that these structures were more photo-stable than the

anthracene-based fluorophores; 29 and 23. Both naphthalimide nitroxides showed

significant fluorescence switch-on under irradiation, with the ether-linked compound

105 reaching ~3-4-fold levels of increased fluorescence emission and the alkyne-

linked compound 107 peaking at a 3-fold increase in fluorescence emission. However,

degradation of the fluorophore (the rate of which is demonstrated by the

photobleaching of the methoxy amine) resulted in a 50% decrease in fluorescence

emission intensity after 7 hours of irradiation, indicating that photo-degradation

remains a significant factor in determining the probe response.


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Figure 41: Change in fluorescence emission of the PTMSP films doped with either ether-linked

perylenediimide fluorophore 117 (-■-/left axis) or the nitroxides analogue 118 (-♦-/right axis) with respect

to ageing time (hours).

Figure 42: Change in fluorescence emission of the PTMSP films doped with either alkyne-linked

perylenediimide fluorophore 114 (-■-/left axis) or the nitroxides analogue 116 (-♦-/right axis) with respect

to ageing time (hours).


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The perylenediimide-based compounds on the other hand, both the ether-linked,

117/118 (Figure 41) and the alkyne-linked, 114/116 (Figure 42) showed superior

photo-oxidative stability. Both of the non-radical analogues showed a lower rate of

photobleaching than the other chromophores studied and both of the nitroxides

continued to display increasing florescence emission during the ageing studies.

Figure 43: Changes in the fluorescence emission of PTMSP films doped with non-radical analogues, 29 (-■-

, λmax = 470 nm), 104 (-▲-, λmax = 410 nm), 106 (-●-, λmax = 430 nm), 117 (-▬-, λmax = 560 nm) and 114 (-♦-,

λmax = 615 nm) following photo-irradiation at 250 Wm-2 and 40ºC for up to 6 h. Note: data collection was

stopped at 6 hours as discolouration gave higher intensities than I0.


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Figure 44: Changes the fluorescence emission of PTMSP films doped with the nitroxides, 23 (-■-, λmax = 470

nm), 154 (-▲-, λmax = 408 nm), 107 (-●-, λmax = 428 nm), 118 (-▬-, λmax = 550 nm) and 116 (-♦-, λmax = 610

nm) following photo-irradiation at 250 Wm-2 and 40ºC for up to 10 h.

When comparing the non-radical analogues (29, 104, 106, 117 and 114), Figure 43,

there is a clear distinction between the photo-oxidative stability of the fluorophores.

Perylenediimides were the most stable compounds, showing no decrease in

fluorescence emission over 10 hours of ageing. Their PFN analogues showed

continuing increases in fluorescence emission intensity with increasing irradiation

time. However, the alkyne-linked PFN 116 displayed the highest fluorescence

emission increase (40-fold) compared to the ether-linked 118 (10-fold), as shown in

Figure 44.

It has previously been demonstrated that both nitroxide radical need to be removed

before complete fluorescence switch-on is apparent for PFNs comprising 2 nitroxide

moieties 187. This results in a different rate of fluorescence switch-on between

difunctional perylenediimide-based PFNs and the monofunctional napthalimide-based


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PFNs. However, this is not always apparent with the competing nature of

photobleaching of the fluorophore. Fluorescence data for the aged PTMSP-doped

films are summarised in Table 2.

Table 2: Summary of PFN fluorescence changes in PTMSP films doped with PFNs or their non-radical

analogues during ageing.

Time to reach maximum

fluorescence emission (h)

Relative fluorescence

increase from time zero

Non-radical

analogue

stability (h)[a]

Relative

fluorescence

achieved (%)[b]

23 3 2.7 3.5 49

105 5 3.5 7 73

107 4 3.0 7 23

118 >10 11 (10 h) >10 32

116 >10 42 (10 h) >10 49

[a] time at which the non-radical analogue was reduced to 50% fluorescence intensity compared to an

unaged sample.

[b] Fluorescence increase achieved relative to the maximum fluorescence emission from the

corresponding non-radical analogue.


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Figure 45: Change of the fluorescence emission for the PFN 116 in PTMSP from 0-10 h ageing compared

to its non-radical analogue, 114 at time zero in PTMSP, showing that the 116 has not achieved complete

switch-on after 10 h ageing.

The pure PTMSP films degraded rapidly under the photo-oxidation conditions

delivered by the Heraeus Suntest CPS+ to the point of becoming too brittle to handle

after 10 hours of irradiation. PTMSP is known to degrade through a chain scission

mechanism to form low molecular weight products that contain carbonyl and hydroxy

groups.192, 203 Infrared spectroscopy can be used to follow the degradation process.

Here, FTIR-ATR was used and it was found that variations in the contact of the

degrading films with the ATR internal reflection element surface showed a large

variation across each of the samples (even after normalisation of the data referenced

to the total peak area from 1600-650 cm-1). Although FTIR-ATR analysis was unable

to provide a reproducible measure of the levels of oxidation of the samples, it did

confirm oxidative degradation was occurring. Along with FTIR-ATR data, evidence

of oxidation was provided through noticeable yellowing and enhanced film brittleness

after 6 hours irradiation. The films became too brittle to handle after 10 hours of


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irradiation, independent of the additive present in the samples, with all films breaking

apart under the pressure from the anvil used in measuring the FTIR-ATR spectra.

4.5.2.2. Thermal Degradation

PTMSP films that did not contain a stabilising nitroxide radical, but retained the

fluorescent unit (29, 104, 106, 117 and 114) were thermally aged in the dark in an oven

at 70°C. This was done to ensure that the fluorophores were not affected by the

temperatures experienced during testing in the solar simulator. Thermally-aged films

showed no visible degradation, such as brittleness or loss in fluorescence emission

(Figure 46), which indicates that the fluorophores and the polymer used in this study

are thermally stable under the conditions used.

Figure 46: Change in fluorescence emission from PTMSP films doped with PFN non-radical analogues (29,

105, 106, 117 and 114) over time at 70°C in the dark.


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Figure 47: UV-Vis spectra from undoped (blank) PTMSP (-) and TOPAS® (-) films.

4.5.3. TOPAS® Films

4.5.3.1. TOPAS® Photo-oxidative degradation

TOPAS® is within the family of cyclic olefin copolymers.193 It has high transparency,

high chemical resistance, low density, high thermal stability, low shrinkage, low

moisture absorption, and low birefringence.204-205 TOPAS®, like PTMSP, undergoes

radical induced degradation when exposed to photo-oxidative environments 193,

however at a more controlled rate.

PTMSP absorbs UV (Figure 47) which limits the amount of information that can be

collected regarding the fluorophore and its stability. In contrast, TOPAS® has the

advantage of being an optically transparent material (see Figure 47), which allows UV-

Vis spectra from doped samples to be monitored in parallel with fluorescence emission

during photo-oxidation of the films. UV-Vis spectroscopy can be used to give insight


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into the stability of the fluorophore of the PFN and has been included in the analysis

below.


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Figure 48: Change in the fluorescence emission from TOPAS® films doped with PFNs (■, Right axes),

relative change in UV-Vis absorbance of PFNs (♦, Left axes) and relative change in UV-Vis absorbance of

the non-radical analogues (●, Left axes) during photo-ageing. (a) 104/105 (b) 106/107 (c) 117/118 (d)

114/116

The PFNs survived longer in TOPAS® than they did in PTMSP due to the higher

overall stability of the film after photo-oxidative conditions. The alkyne-linked

naphthalimide probe 107 appeared to be the least stable of the tested PFNs, with its


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UV-Vis absorbance decreasing by a factor of 2 after 50 hours of ageing. The ether-

linked naphthalimide, 105 was more stable with the fluorophore withstanding 96 hours

of irradiation before a loss of 50% of the fluorophore UV-Vis absorbance. The 105

PFN also gave a 20-fold fluorescence emission response up to 96 hours of irradiation.

Both of the perylenediimide PFNs on the other hand demonstrated significant stability,

requiring 504 and 168 hours for the ether-linked, 118 and alkyne-linked, 116

compounds respectively (Figure 48), at which time the fluorophores had lost half of

their absorbance compared to time zero. The free-radical containing PFNs tested

displayed enhanced stability compared to their non-radical analogues, showing that

the presence of the nitroxide induced a degree of protection, most likely through the

recognised antioxidant capabilities of this functional group.

Even though the ether-linked perylenediimide PFN 118 had a higher stability than the

alkyne-linked PFN 116, the alkyne-linked PFN showed a higher level of fluorescence

emission switch-on (40-fold), Figure 49. PFN 116 also showed significant

fluorescence change during ageing in the PTMSP films, allowing easier detection of

radical formation within the films. All of the absorbance and fluorescence data for the

aged TOPAS®-doped films are summarised in Table 3.

All TOPAS®-doped films were further tested to ensure films did not experience

thermal degradation in the photo-oxidative environment. The TOPAS®-doped films

were subjected to a dark oven at 70°C for an extended period of time. Like PTMSP,

the TOPAS® films demonstrated thermal stability with no evidence of spectrographic

change or changes in physical properties.

Table 3: Summary of PFN sensor performance and stability in TOPAS® films following photo-oxidative

degradation.


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Time to reach

maximum

fluorescence

emission (h)

Fluorescence

increase from

time zero ()

PFN

stability[a]

Non-

radical

analogue

stability

(h)[a]

Relative

fluorescence

achieved

(%)[b]

105 144 20 96 70 33

107 72 6 50 20 7.2

118 264 3.2 504 90 11

116 504 40 168 100 3.7

[a] Time at which the fluorophore had lost half of its maximum absorbance compared to time zero.

[b] Fluorescence increase achieved relative to the maximum fluorescence emission from the

corresponding non-radical analogue.

Figure 49: Change of the fluorescence emission for the PFN 116 in TOPAS® from 0-504 h ageing

compared to its non-radical analogue, 114 at time zero in TOPAS®, showing that the PFN 116 has only

achieved a small fraction of complete switch-on after 504 h ageing.


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As in PTMSP, TOPAS® also degrades through a mechanism that involves the

formation of reactive free radicals. The alkyl groups are oxidized to alkene and other

conjugated systems, which results in the normally transparent films becoming

yellow.205-206 This yellowing is observed in the UV-Vis, Figure 50. However, this

yellowing can be difficult to detect in PFN-doped samples due to the absorbance of

the PFN chromophores. Therefore, only the undoped TOPAS® film could be directly

monitored for yellowing during ageing.

Figure 50: UV-Vis absorbance at 250 nm (subtracted from UV-Vis absorbance at 400 nm) for the blank

(undoped) TOPAS® film with respect to time in the suntest (left axis, ■) and the oxidation index calculated

from ATR-IR data from the blank (undoped) TOPAS® film with respect to time in the suntest (right axis,

♦)

Analysis of IR spectra from the undoped, irradiated TOPAS® film showed the

formation of carbonyl bands due to oxidation at a similar rate to the yellowing at 250

nm detected in the UV-Vis. The correlation between the oxidation of alkyl groups and

the formation of carbonyl products during the degradation of film allowed IR to be

used as a monitor for photo-oxidative degradation in the presence of the PFN


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chromophore. However, as the irradiation time increased, the uncertainty in the

oxidation index measurements became larger which is a recognised limitation of IR

monitoring.

There is no convincing evidence of yellowing and/or carbonyl formation in the aged

TOPAS® film until ~240 h, Figure 50 which is consistent with an oxidation induction

period. Studies have demonstrated that the useful lifetime of a polyolefin does not

extend much past this period.98, 188 These results indicate that PFNs detect radical

formation from time zero through increases in fluorescence intensity. This

demonstrates the usefulness of PFNs as sensitive probes to detect degradation caused

from radical formation within the oxidation induction period, where previous

techniques have limited success.

4.6. Conclusions

The aim of this study was to test the photo-oxidative stability of a unique group of

additives that probe the nature of degradation of two types of polymer materials,

PTMSP and TOPAS®. The nitroxide probe’s ability to switch on and report damage

occurring in PTMSP was demonstrated. However, degradation in the Heraeus Suntest

instrument was too severe, which caused rapid embrittlement of the polymer.

TOPAS® was more stable than PTMSP under the testing conditions and its

transparency allowed analysis by UV-Vis spectroscopy in parallel with fluorescence

spectroscopy, which gave insight into the stability of the fluorophores tested. It was

determined that perylenediimide-incorporated PFNs are more photo-stable than

naphthalimide PFNs in both the PTMSP and TOPAS® films. It was also determined

that the nitroxide-containing compounds have higher stability in the photo-oxidative

environment over their non-radical analogues. The alkyne-linked perylenediimide


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PFN, 116 has an impressive switch on ability when exposed to photo-induced radicals,

and it is the most effective PFN probe of the group tested. UV-Vis and IR gave little

information about the early stages of the film’s degree of degradation, confirming the

value of the PFN technique as a tool to give insight into the oxidation induction period

and to predict the overall serviceable lifetime of the polymer. With improved photo-

stability, PFNs can now provide a sensitive and simple technique to monitor changes

during the induction period of the photo-oxidative degradation of polymers.


We gratefully acknowledge financial support for this work from the Australian

Research Council Centre of Excellence for Free Radical Chemistry and Biotechnology

(CEO 0561607), the Defence Materials Technology Centre, which was established and

is supported by the Australian Government’s Defence Future Capability Technology

Centre (DFCTC) initiative and Queensland University of Technology.

C H A P T E R F I V E

P a g e | 186

5. PROFLUORESCENT NITROXIDE SENSORS FOR

MONITORING THE NATURAL AGING OF

POLYMER MATERIALS

The Authors listed below have certified* that:


conception, execution , or interpretation, of at least that part of the publication













P a g e | 187

Profluorescent nitroxide sensors for monitoring the natural aging of polymer

materials

Drafted for Polymer Degradation and Stability






John M. Colwell Overall supervision of the project, guided during

experimental design and assisted with manuscript design

and final data analysis

James Blinco Overall supervision of the project, guided during



Smith

Overall supervision of the project, guided during







Name Signature Date



P a g e | 188

Profluorescent nitroxide sensors for monitoring the natural aging of polymer

materials

Vanessa C. Lussini,a,b John M. Colwell,b James P. Blinco,a Kathryn E. Fairfull-Smitha

and Steven E. Bottle*a,b

[a] ARC Centre of Excellence for Free Radical Chemistry and Biotechnology. School

of Chemistry, Physics and Mechanical Engineering, Faculty of Science and

Engineering, Queensland University of Technology (QUT), GPO Box 2434, Brisbane,

QLD 4001, Australia

[b] Defence Materials Technology Centre, School of Chemistry, Physics and

Mechanical Engineering, Faculty of Science and Engineering, Queensland University

of Technology (QUT), GPO Box 2434, Brisbane, QLD 4001, Australia

E-mail: [email protected] ; Fax: +61 7 3138 1804; Tel: +61 7 3138 1356



P a g e | 189

5.1. Abstract

The utility of profluorescent nitroxides (PFNs) as sensitive probes to detect early stage

photo-oxidative degradation in a cyclic olefin copolymer, TOPAS®, during both

natural aging and accelerated aging under laboratory conditions is reported. PFN

additives in TOPAS® capture radicals to form fluorescent adducts as the material

degrades. The levels of fluorescence detectable from the polymer reflect the degree of

free-radical degradation in the material. PFN probes deliver enhanced sensitivity over

traditional analytical methods for the detection of photo-oxidative degradation of

TOPAS®. The probes are able to highlight polymer degradation occurring within the

oxidation “induction” period, where little change can be observed using infrared

spectroscopy; however, their efficacy does not extend far beyond this period. The

effective probe lifetime however can be significantly extended through the use of

common additives such as the UV absorber (Tinuvin P) and a hindered amine stabiliser

analogue (1,1,3,3-tetramethylisoindol-2-yloxyl, TMIO).

5.2. Key words

Perylenediimide, Photo-oxidative degradation, Profluorescent nitroxide, Sensor,

TOPAS, Weathering.

5.3. Introduction

Natural aging of polymer materials is complicated by many interconnected variables

207-208, with measurements over an extended period (>2 years) typically required to

ensure good reproducibility 209. The long timeframes required for testing are

influenced by typically slow rates of degradation and commonly observed degradation


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“induction” periods, where there are no apparent changes in properties for extended

periods of time 186, 207, 210-214. Accelerated aging is often used to provide a rapid

assessment of degradation behaviour and serviceable lifetimes. However, relating

laboratory-based aging experiments to lifetimes arising from natural exposure is

difficult due to the many variables experienced during in-use conditions 209, 215-219.

Accelerated weathering devices often do not accurately emulate elements of the

environment that may influence the rate of degradation, such as morning dew,

pollution (acid rain) and temperature fluctuations throughout the day 24, 215. To

overcome both the time limitations on testing outdoors and the limitations of

accelerated weathering devices for emulating complex outdoor conditions, the

development of more sensitive methods that can detect changes in the degradation

induction period during outdoor exposure are required.

It has been shown 188, 220-222 that the length of the apparent degradation induction period

is dependent on the sensitivity of the analysis technique used for the measurement of

property changes. For many materials, early-stage degradation may be linked to the

formation of transient, carbon-centred free-radicals 1, 188, 223. Disruption of polymer

degradation by trapping carbon-centred free-radicals forms the basis of a range of

polymer stabilisation processes, including the use of Hindered Amine Stabilisers

(HAS) 21, 35, 224-225. In the mechanism of stabilisation by HAS, nitroxide free-radicals

are formed and these can scavenge carbon-centred free-radicals to give stable adducts

188. Based on this chemistry, sensitive profluorescent nitroxide probes have been

developed that can detect the extent, and even location of polymer damage during the

degradation induction period, with greater sensitivity than other reported methods 35,

64, 101.


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Figure 51: Tethering of a fluorophore to a nitroxide to form a profluorescent nitroxide (PFN), and

trapping of carbon-centred free-radicals (formed during polymer degradation), causing the PFN to switch

from a non-fluorescent to a fluorescent state.

Profluorescent nitroxides (PFNs) are a group of compounds that contain a stable

nitroxide free radical linked to a fluorophore (Figure 51). They display low

fluorescence, but when they react with the alkyl radicals generated during polymer

degradation they form adducts that are fully fluorescent. This allows visualisation of

both the location and the degree of degradation that has occurred within a polymer 64.

The very low fluorescence quantum yield of PFNs compared to their alkoxyamine

adducts 53, 105-106, 118, 123, 145, 187, 226 makes them very sensitive probes for carbon-centred

free radical production during the very early stages of polymer degradation and good

candidates for monitoring degradation during the degradation induction period 35.

However, to act as probes during this period, the PFNs must be stable to the radical

environments within the polymer matrix and other external environmental factors,

such as direct UV exposure. Early studies using PFNs as probes for the photo-oxidative

degradation of polymers revealed limitations with the stability of some of the

fluorophores employed 186. To improve photo-stability, other more photo-stable PFNs

have been developed 187, 227. Initial testing of these PFNs using accelerated weathering

in laboratory tests showed that PFNs based on perylenediimide fluorophores (shown

in Figure 52) were the most photo-stable probes produced to-date. These


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perylenediimide-based probes with improved photo-stability are the focus of the work

described herein.

Figure 52: Fluorescent and profluorescent probes used in this study. The fully fluorescent non-radical

analogue 114 is used as an indicator for the potential response from the profluorescent probes 115 and 116.

To assess the efficacy of PFNs to report polymer degradation, polymers that are known

to degrade via a free-radical process are required, as the PFN fluorescent response

arises from scavenging these species. The well-studied, free-radical-based degradation

behaviour of polyolefins therefore makes this ubiquitous class of polymers excellent

candidates to highlight the capability of PFN probes as reporters of this degradation.

TOPAS®, a simple cyclic olefin copolymer 193 (Figure 53) was used as a model

material due to its structural similarities to other polyolefins and the ability to prepare

solution-cast, optically transparent thin films, with controlled levels of additives, on a

small scale.

Typically, formulated plastics contain a range of stabilisers to increase service lifetime.

To determine if the PFN-technique still allows a record of early lifetime degradation

when such stabilisers are present, 1,1,3,3-tetramethylisoindol-2-yloxyl (TMIO, 55; a

HAS analogue) and Tinuvin P (1; a common UV absorber) (Figure 53) were added to


P a g e | 193

the TOPAS® films as representative photostabilisers in addition to the PFN-based

compounds shown in Figure 52. The stability and degradation-monitoring ability of

the PFN probes were assessed using both environmental and laboratory aging

conditions to determine their effectiveness as probes for free-radical damage in the

presence of common stabilisers.

Figure 53: Structure of TOPAS® (the cyclic olefin copolymer used in this study), TMIO (55; a HALS

analogue) and Tinuvin P (1; a common UV absorber).

1. Experimental

5.4. Materials

TOPAS® 8007X10 and Tinuvin P (1) were received as gifts from Ciba Speciality

Chemicals and were used without further purification. Cyclohexane was purified using

a literature procedure 194, where it was washed with concentrated sulphuric acid until

the wash was colourless. The organic layer was then washed with water, followed by

aq. Na2CO3 and washed again with water until the wash solution reached neutral pH.

The washed cyclohexane was then distilled over calcium hydride. Compounds 114 187,

115 187, 116 187 and 55 58 were synthesised as described previously. All other materials

and reagents were of analytical reagent grade purity, or higher and were purchased

from Sigma Aldrich, Australia.


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5.5. Sample preparation

5.5.1. Doped TOPAS® sample preparation

Each of the compounds shown in Figure 52 (6.078 10-8 mol) were dissolved in

freshly distilled cyclohexane (4.57 mL) in glass vials. TOPAS® pellets (293 mg) were

then added to each solution to give a PFN concentration of ~0.025 wt%, and the vials

were sealed and stirred for 4 hours in the dark. The additives, TMIO (55) and Tinuvin

P (1), were then added in a range of concentrations (), and the mixtures allowed to stir

for a further 1 hour to ensure even dispersion. Each solution was then poured into an

individual Petri dish and the solvent was allowed to evaporate slowly over 2 days, in

the dark. Once the films were touch-dry, they were put under vacuum until their mass

was constant (~24 h). Final film thicknesses were approximately 100 µm. Samples for

outdoor weathering and laboratory ageing were then cut from the same film batches to

avoid differences in concentrations or physical characteristics.

5.5.2. Outdoor weathering

Outdoor weathering experiments were carried out in Brisbane, Australia at a latitude

and longitude of 27°28'38.7"S and 153°01'37.8"E, respectively, on the un-shaded,

fully exposed rooftop of a 14-storey building. Samples were placed in aluminium-

backed holders over a wooden support, at an angle of 180° to the sun for the period

from 18 December, 2014 to 28 January, 2015 (summer). Samples were removed

periodically and analysed using UV-Vis, Fluorescence and FTIR-ATR spectroscopy.

Values for precipitation, solar exposure and temperature were obtained from the

Australian Government Bureau of Meteorology, with the data summarised in Table 4.


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The data were obtained from a weather station that was in close proximity to the aging

site: latitude 27°48'S, longitude 153°04'E, altitude 8 m 200.

5.5.3. Laboratory aging

Film samples were aged in an Heraeus Suntest CPS+ device (Atlas) at temperature of

35°C and an irradiance of 250 W/m2. The samples were oriented parallel to the lamp

and were removed periodically for analysis using UV-Vis, Fluorescence and FTIR-

ATR spectroscopy.

5.6. Analysis methods

5.6.1. FTIR-ATR spectroscopy

Infrared spectra were recorded as neat samples using a Nicolet 5700 Nexus Fourier

Transform infrared spectrometer equipped with a DTGS TEC detector and a Smart

Endurance single reflection ATR accessory. The ATR accessory contained a

composite diamond IRE with a 0.75 mm2 sampling surface and a ZnSe focussing

element (Nicolet Instrument Corp., Madison, WI). An Optical Path Difference (OPD)

velocity of 0.6329 cm s-1 and a gain of 8 were used. Spectra were collected in the range

4000-650 cm-1 using 32 scans at 4 cm-1 resolution. All films were examined in

triplicate. The data was processed using Grams/32 AI software and Microsoft Excel.

Oxidation indices were calculated by taking the ratio of the maximum peak height in

the carbonyl stretching region (1700-1715 cm-1) to the area under the C-H deformation

band (1400-1500 cm-1), using a baseline over the range, 1700-1400 cm-1.


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5.6.2. UV-Vis spectroscopy

All UV-Vis spectra were recorded on a Varian Cary 50 UV-Vis spectrophotometer.

Spectra were collected in the range from 200-700 nm at a scan rate of 600 nm min-1.

All films were examined in triplicate. The spectra were baseline-corrected using a

linear offset to give an absorbance of zero at 600 nm and were further processed using

Microsoft Excel. The data are presented as the fractional change in maximum

absorbance between 500-600 nm compared to un-aged samples.

5.6.3. Fluorescence Spectroscopy





changed according to the compound present in the sample: 114: 568 nm, 115: 564 nm,

116: 564 nm. Spectra were collected from 5 nm past the excitation wavelength to 700

nm. All films were examined in triplicate. The data were processed using Microsoft

Excel and are presented either as peak emission values or as the fractional change in

the maximum intensity between 600-650 nm compared to an un-aged sample.

5.7. Results and discussion

5.7.1. Film preparation

The solubility characteristics of perylenediimide-based compounds and the formation

of aggregates can be affected by solvent/matrix combinations and concentrations used.

We have previously shown via UV-Vis and fluorescence spectroscopy that the


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perylenediimide-based compounds 114, 115 and 116 used here, do not aggregate when

solvent-cast from cyclohexane into TOPAS® at a concentration of 0.025 wt% 227. The

processing of TOPAS® films by solvent-casting allowed for uniform distribution of

additives and avoided the use of high temperatures that can cause some switch-on of

the PFN probe prior to testing 220.

5.7.2. Aging conditions of the TOPAS® films

To evaluate differences between natural weathering and laboratory exposure, film

samples were exposed to natural weathering conditions on the rooftop of a 14-storey

building during the 2014-2015 Brisbane, sub-tropical summer in Australia, and were

also aged in an Heraeus Suntest CPS+ xenon-arc solar simulator operating at an

irradiance of 250 W/m2 and 35°C. The radiant exposure conditions in the laboratory

aging experiments were selected to mirror the outdoor exposure conditions (Table 4).

The rates of oxidation for un-doped TOPAS® films aged in the laboratory were

comparable to the natural weathering conditions (Figure 54).

Table 4: Solar exposure, temperature and rainfall conditions for rooftop weathering and laboratory aging.

Aging conditions

Average daily

solar exposure

(MJ/m2)

Average

maximum daily

temperature

Total

rainfall

(mm)

Suntest laboratory

aging

21.6 35 0

Rooftop natural

exposure

21.34 30.8 338.4


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FTIR-ATR analysis of the aged TOPAS® films showed strong bands corresponding

to oxidation products that have been reported previously for UV-exposed TOPAS®

228. There were four main bands in the carbonyl stretching region of the FTIR spectra:

a lactone band at 1780 cm-1; a vinyl band at 1650 cm-1; an unresolved ester band at

1740 cm-1; and a band at 1720 cm-1, representative of carboxylic acids and ketones.

For both aging environments, there was very little increase in the oxidation index

below 250 MJ/m2 of radiant exposure, Figure 54. This apparent induction period to

oxidation provides scope for using PFN sensors to monitor degradation of the

TOPAS® films, since PFNs have been previously shown to signal degradation before

oxidation can be observed using FTIR 35, 56, 64, 98-101, 106, 123, 186.

Figure 54: Oxidation indices as determined by FTIR-ATR for TOPAS® films aged in the laboratory

(Suntest) and outdoors (data of weather comparisons are summarised in ).


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5.7.3. Using PFNs as sensors of photo-oxidation degradation

Many of the PFNs used in previously reported photo-degradation studies were not

stable under photo-oxidative ageing conditions 186, 227. The photo-stabilities of a

number of novel PFNs were recently compared and their ability to detect polymer

degradation in the early stages of the degradation induction period during laboratory

aging was assessed 227, 229. It was found that, within the group of compounds tested,

the alkyne-linked perylenediimide PFN (116) was the most stable PFN developed.

Therefore PFN 116, the mono-nitroxide analogue (115), and the non-radical, fully

fluorescent methoxyamine analogue (114) were used to monitor degradation during

weathering of films with, and without other additives commonly used in formulated

plastics.

The data shown in Figure 55 demonstrates the sensitivity achievable for perylene-

based PFN probes for the detection of the oxidative degradation of TOPAS®. The

mono-nitroxide PFN, 115 is able to detect the formation of carbon-centred free-

radicals in TOPAS® exposed to laboratory aging conditions well before oxidation can

be observed using FTIR-ATR. Indeed, the large uncertainty in the oxidation index

values shown in Figure 55 results from the very weak signals provided by FTIR-ATR,

reflecting the small number of carbonyl-containing oxidation products produced at

early degradation times. The sampling volume is also small, making heterogeneity

within the sample more prominent.


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Figure 55: Fluorescence emission and oxidation indices of a laboratory-aged PFN (115)-containing

TOPAS® film.

5.7.4. Suitability of mono vs difunctional PFNs as probes for

polymer degradation

The sensitivity of PFNs for the detection of polymer degradation by fluorescence is

dependent on the number of nitroxide free radicals present in the PFN probe. In

solution studies, we have shown 229 that there is only a modest fluorescence increase

when one nitroxide radical reacts in a probe that has two nitroxides within its structure.

In the case of the perylenediimide based PFNs 115 and 116, one nitroxide compared

to two gives an increase in fluorescence quantum yield of 0.00944 and 0.00436

respectively. However, when one nitroxide in PFN 115 or both nitroxides in PFN 116

are converted to non-radical moieties, the fluorescence quantum yield for each rises

significantly. In this context, the non-radical PFN-analogue (114) has a 10-fold higher

fluorescence quantum yield (0.0996) over PFN 115 and more than 20-fold increase

over PFN 116 suggesting the latter would provide the greatest detectable response.


P a g e | 201

Figure 56: Fluorescence emission during natural weathering on the rooftop for TOPAS® films doped with

compounds 115 and 116 (0.025 wt%).

For TOPAS® films doped with either PFN 115 or PFN 116, carbon-centred radical

production can be detected as the films were aged as indicated by an increase in

fluorescence emission (Figure 56). However, PFN 115 produces a significantly

stronger signal than 116. The difunctional PFN 116 must react with two carbon-

centred radicals to deliver similar fluorescence emission as the monofunctional PFN

115 reacting with only one radical. This leads to different degrees of fluorescence

emission increase for each of these probes. Notably, the difunctional PFN 3, would be

expected to show limited mobility within the degrading polymer. After scavenging one

polymer radical, this PFN would become bound to the polymer backbone. This would

therefore limit this probe’s ability to undertake further trapping reactions, restricting it

to radicals formed in close proximity to the site of the first reaction. However, linking

polymer chains would off-set decreases in molecular weight arising from degradation

and this could potentially deliver enhanced application lifetimes for materials

containing this probe.


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5.7.5. PFN Stability

Although the perylenediimide PFNs studied were found to be the most stable of those

tested to date 227, they still undergo some degree of transformation as demonstrated by

decreases in their UV-Vis absorbance over time. While less sensitive than

fluorescence, monitoring using UV-Vis spectroscopy is useful as it provides a total

signal arising from both the probe and probe adducts, independent of the presence of

nitroxide spin. The UV-Vis data shown in Figure 57 indicate that there is a slow loss

of, or at least chemical change in, the chromophore driven by irradiation, such that no

significant absorbance from the original chromophore can be detected after 400 MJ/m2

of irradiation. Notably, the fully fluorescent dimethoxy amine adduct (114), with no

nitroxide, shows the fastest rate of photo-bleaching. The mono-nitroxide PFN 115,

displays similar chromophore stability however the PFN 116 with two free nitroxides

shows a lower rate of bleaching.

Figure 57: Relative change in UV-Vis absorbance for TOPAS® films doped with compounds 114, 115 and

116 (0.025 wt%) during natural exposure on the rooftop.


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The loss of fluorescence emission for the probes under irradiation (Figure 56) is most

evident when the rate of adduct formation becomes slower than the rate of photo-

bleaching. This is likely to happen as the concentration of PFN decreases (through

scavenging). Photo-bleaching is expected to correlate with the generation of singlet

oxygen which arises from reaction of the chromophore excited state with molecular

oxygen. Many molecules that absorb light can generate singlet oxygen 230-234 and such

photosensitizers generally possess high absorption coefficients, high quantum yields

and have excited triplet states at appropriate energy levels and lifetimes 234.

Perylenediimides are known to produce singlet oxygen during UV irradiation 235-238,

and this can lead to fluorophore bleaching. However, when the quantum yield of

fluorescence is low, such as with the PFN probes, there is less energy absorbed to

produce singlet oxygen. However, when the PFNs trap carbon-centred radicals and the

nitroxide spin is removed, their quantum yield of fluorescence increases substantially.

This makes these PFN adducts detectable by fluorescence spectroscopy, but also

increases pathways involving the production of reactive oxygen species such as singlet

oxygen. The higher stability of PFN 116 might be expected to arise from a combination

of the ability of this compound to remove a larger number of radicals from the

degrading polymer system, and its relatively low fluorescence quantum yield after

being singly-bound to a polymer chain by the trapping of a carbon-centred radical.

There is also the potential for excited state quenching for mono-adducts, which could

lead to an increase in the photo-stability for this molecule. The combination of these

factors would decrease the likelihood of singlet oxygen production and oxidative

attack on the fluorophore for PFN 116 which off-sets the decreased emission levels

over PFN 115.


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Figure 58: Relative change in fluorescence emission during natural weathering for TOPAS® films doped

with compounds 114 (fully fluorescent non-radical PFN analogue), 115 (mononitroxide) and 116

(dinitroxide) at 0.025 wt%.

Whatever the cause and control of the bleaching process, its effects are manifested in

lower than expected peak fluorescence emission from the aged films, as shown by the

data in Figure 58. When doped into TOPAS® and aged under natural conditions, films

containing PFN 115 reached a maximum of ~50% of the theoretical “maximum”

fluorescence generated from un-aged films containing the fully fluorescent PFN-

analogue 114 at the same concentration. Films containing PFN 116 on the other hand,

reached only ~10% of the maximum potential fluorescence emission intensity and this

peak arises following considerably more irradiation (345 MJ/m2 versus 95 MJ/m2).

The lower peak fluorescence for PFN 116 is more likely to be due to degradation of

the fluorophore rather than the formation of still pro-fluorescent, single polymer chain

PFN 116 adducts. Despite the low fluorescence maxima detected in films employing

116, this PFN has more sensor potential because the fluorescent response takes longer

to be engendered and is more persistent.


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5.7.6. PFN antioxidant effects

Oxidation indices from FTIR-ATR analyses were used to compare the degree of

degradation of blank TOPAS® films (without PFN) to the films containing PFN and

related additives (Figure 59). The data shows that PFN 116 acts as an antioxidant,

which is evident by the formation of IR-detectable oxidation products at a slower rate

than for un-doped films, although the levels are low and are at the limit of detection

by this technique. Notably, there are no obvious signs of degradation at this stage and

the IR indices do not exceed ~0.08. In our hands, IR detection is most reliable for IR

indices above 0.100 and blank TOPAS® films do not physically embrittle, or

significantly discolour, until IR indices reach ~0.300. In contrast, in films containing

114 and 115, there is evidence of low levels of IR-detectable oxidation products in

these TOPAS® films compared to an un-doped film. Although the loss of fluorescence

signal may be related to photo-bleaching and chromophore oxidation that does not

necessarily impact on the bulk polymer matrix, the detection of even small levels of

extra oxidation suggests some link to the degradation of the PFN-adducts formed in

the polymer. As discussed previously, conversion of the probe to the fluorescent (non-

radical, alkoxyamine) adducts may be expected, under further irradiation, to allow

some production of reactive oxygen species from the excited state fluorophore. In this

context, polymer degradation via singlet oxygen is well established 239-240. Small levels

of oxygenated species produced by irradiation of the fluorophore present in the

nitroxide-adducts generated by radical trapping would therefore be expected to

contribute to some extent to increased levels of degradation of the TOPAS® substrate

and these would be expected to rise as the nitroxide is consumed.


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Figure 59: Oxidation indices as determined by FTIR-ATR for rooftop-exposed TOPAS® films doped with

compounds 114, 115 and 116 (0.025 wt%) and an additive-free control sample.

Although the fully fluorescent PFN-analogue 114 is an alkoxyamine, which would

reflect the fluorescence expected of PFN-polymer adducts, it is unlikely to perform

well as a HAS, as the methoxy group oxidatively unstable 147. Therefore, a degree of

degradation somewhat higher than that of the blank is expected for TOPAS® films

containing PFN 114. The PFN probe 115, as it is an antioxidant nitroxide, would be

expected to act as a stabiliser by trapping of carbon-centred radicals. However, as

shown in Figure 59, the oxidation of PFN 115-containing TOPAS® films was similar

to TOPAS® films containing the non-radical, PFN derivative 114. This enhanced

degradation, although small, is important as it indicates a potential impact on the long-

term stability of films containing this PFN. Notably, as seen in Figure 57 the rate of

chromophore loss for PFN 115 TOPAS® films matches that of PFN 114 films after

~95 MJ/m2 of radiant exposure.


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Figure 60: Oxidation indices as determined by FTIR-ATR (left) and relative change in UV-Vis

absorbance (right) for TOPAS® films doped with compound 114, 115 and 116 (0.025 wt%) during

aging in the laboratory (Suntest) and outdoors weathering (other data for rooftop and suntest

comparisons are summarised in ).

There were slight differences when comparing the oxidation indices of films doped

with compounds 114, 115 and 116 when aged by true weathering conditions, compared

to laboratory aging conditions in the Suntest, Figure 60 (left column). Films doped

with PFN derivative 114 and PFN 115 were found to oxidise faster on the rooftop

compared to exposure in the Suntest apparatus. This may also be related to singlet

oxygen production, as the rooftop samples were exposed to weathering elements that


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are not present in the Suntest, such as environmental contaminants that have been

shown to lead to singlet oxygen production 88, 241. Importantly, there is no evidence for

increased radical formation in the films aged on the rooftop compared to the Suntest,

which would be shown by an increase in fluorescence emission from the PFNs, Figure

SI 138. However, as discussed above, very weak signals and small sampling volume

leads to large uncertainty in the oxidation index values. Therefore, rooftop and suntest

data could be improved by higher sampling volume to lower error bars.

Fluorophore stability using laboratory aging conditions was similar to true weathering

conditions, Figure 60 (right column). PFN 116 was also found to be the most stable

PFN when exposed to laboratory aging conditions in the Suntest. Notably, there was

an induction period, perhaps attributable to temperature variations, before UV-Vis

absorbance could be used to detect degradation of the fluorophore for films that were

naturally aged in the environment (rooftop exposure) compared to the laboratory-aged

samples. After ~100 MJ/m2 irradiation, the rates of fluorophore degradation were

comparable. A summary of all the data comparisons, including PFN-analogue 114,

PFN 115 and PFN 116 are provided in the .

5.7.7. The effect of additives on the stability of PFNs in TOPAS®

films

Common additives such as the UV absorber Tinuvin P (1) and hindered amine

stabilisers of which TMIO (1,1,3,3-tetramethylisoindol-2-yloxyl, 55) is an analogue

are often added to formulated plastics to increase service lifetime. When these

compounds were added to TOPAS® films that contained the alkoxyamine PFN-

derivative 114 an increase in stability of the fluorophore was observed.


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Figure 61: Relative change in UV-Vis absorbance of aged TOPAS® films doped with PFN-analogue 114

(0.025 w%); compared to TOPAS® films containing PFN-analogue 114 + TMIO (1, 2 and 4 eqv. of 114)

with respect to radiant exposure (MJ/m2) on the rooftop.

With increasing concentration of 55, the fluorophore’s UV-Vis signal retained longer

during photoirradiation (Figure 61). This is due to 55 acting as a radical trap in the

degrading polymer system, which reduces the likelihood of radical attack on the

fluorophore. An increase in stability in the film with the addition of 55 was also

observed as an overall decrease in the rate of oxidation detected by ATR-IR, Figure SI

139a.


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(0.025 w%); compared to TOPAS® films containing PFN-analogue 114 + Tinuvin P (0.1, 0.3 and 0.5 wt%)

with respect to radiant exposure (MJ/m2) on the rooftop.

The UV absorber, Tinuvin P (1) provides ultraviolet protection through absorption of

radiation between the wavelength range from 300-400 nm, and it is relatively photo-

stable over long periods of exposure 242. When the concentration of 1 was increased

from 0.1, to 0.3 and then 0.5 wt% in TOPAS® films containing PFN-derivative 114,

the lifetime of the PFN-alkoxyamine derivative increased (Figure 62). As expected,

there was also an increase in the stability of the TOPAS® films with the addition of 5,

as shown by a decrease in the oxidation rate with increasing amounts of 1, Figure SI

139b.

There appeared to be a limiting effective concentration of 5 as there was only a small

difference in stability between films that contained 0.3 wt% of 1 and 0.5 wt% of 1, so

0.3 wt% of 1 was used in further studies. Similarly, there was only a small difference

in stability for films containing 2 equivalents of 55, compared to films with 4

equivalents of 55, so 2 equivalents of 55 were subsequently used.


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(0.025 w%); compared to TOPAS® film containing PFN analogue 114 + Tinuvin P (0.3 wt%), TOPAS®

film containing PFN-analogue 114 + TMIO (2 eqv. of 114) and TOPAS® film containing PFN-analogue

114 + both Tinuvin P (0.3 wt%) and TMIO (2 eqv. of 114) with respect to radiant exposure (MJ/m2) on the

rooftop.

The combination of both the radical trap, TMIO (55) and UV absorber, Tinuvin P (1),

showed a combined antioxidant effect on the PFN’s fluorophore, Figure 63. This effect

has been shown for combinations of UV absorbers and free radical scavengers in

polymer systems, where lifetimes can be significantly increased 243-246. This synergy

is due each additive working through different mechanisms of stabilisation. This

increase of stability was further investigated with films containing PFNs 115 and 116.

It needs to be established that addition of stabilisers has no affect the detection of

photo-oxidative degradation of the TOPAS® films.

5.7.8. The effect of additives on PFNs in TOPAS® films

As previously discussed, the stability of the PFNs is related to the ability to remove

radicals and its lowered quantum yield, which reduces singlet oxygen production.


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Therefore, addition of stabilisers shows the same positive effect of PFN 115 as shown

in PFN-analogue 114, Figure 64.

Figure 64: Relative change in UV-Vis absorbance of aged TOPAS® films doped with PFN 115 (0.025 w%);

compared to TOPAS® film containing PFN 115 + Tinuvin P (0.3 wt%), TOPAS® film containing PFN 115

+ TMIO (2 eqv. of 115) and TOPAS® film containing PFN 115 + both Tinuvin P (0.3 wt%) and TMIO (2

eqv. of 115) with respect to radiant exposure (MJ/m2) on the rooftop.

Like with PFN-analogue 114, enhanced stability is shown as the equivalents of TMIO

(55) is increased, see Figure SI 140a. Addition of 55 removes excess radicals from the

degrading polymer system, therefore reducing radical attack on the fluorophore.

Addition of 1 also reduces radical attack on the fluorophore via ultraviolet protection

of the film. This effect was previously discussed and is shown in Figure 62 with films

doped with PFN- analogue 114. As the weight percentage of 1 increased, there is an

improved stability of PFN 115, see Figure SI 140b. This results in a combined

protective antioxidant effect to the fluorophore of PFN 115 with addition of both 55

and 1, Figure 64.


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Figure 65: Oxidation indices as determined by FTIR-ATR for aged TOPAS® films doped with PFN 115

(0.025 w%); compared to TOPAS® film containing PFN 115 + Tinuvin P (0.3 wt%), TOPAS® film

containing PFN 115 + TMIO (2 eqv. of 115) and TOPAS® film containing PFN 115 + both Tinuvin P (0.3

wt%) and TMIO (2 eqv. of 115) with respect to radiant exposure (MJ/m2) on the rooftop.

The added stability of additives is also shown by an increase of stability in the film.

Addition of 55 serves to remove carbon-centred free-radicals from the degrading

TOPAS® films, retarding the auto-catalytic degradation reactions, which reduces the

number of oxidation products in the film. Addition of 1 decreases the production of

radicals by protecting film through absorption of radiation between the wavelength

range from 300-400 nm. The combined protection of the film is shown in Figure 65.


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Figure 66: Fluorescence maximum trace of aged TOPAS® films doped with PFN 115 (0.025 w%);




The decrease of film degradation can be detected by a rate change in fluorescence

production by the addition of a PFN. However, the non-fluorescent nitroxide TMIO

(55) possesses the same nitroxide structural moiety as is present in PFNs 115 and 116,

so it is able to compete with the PFNs to trap carbon-centred free-radicals. The

outcome of this competition is shown in Figure 66. Addition of 2 equivalents of

compound 55 delayed the fluorescence switch-on from PFN 115. This suggests that

fewer radicals were trapped by the PFN at early aging times and reflects the carbon-

centred free-radical trapping efficiency of 55. Addition of the UV absorber 1 at 0.3

wt% resulted in a delay in the generation of fluorescent adducts as well as decreasing

the value and the time when peak fluorescence emission was detected. This is likely

due to an overall reduction in the rate of film degradation due to the presence of the

UV absorber. Combining the 2 additives (55 and 1) further reduced the degree of

fluorescence switch on. The overall delayed fluorescence switch-on, therefore reduced


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the quantum yield of the film. This thereby decreases the production of singlet oxygen

and subsequent degradation of the PFN chromophore, which is reflected in the more

persistent UV-Vis spectra. However, the addition of additives reduces the fluorescence

response of the PFN. This is due to the degradation of the fluorophore. PFN 115

reached a maximum fluorescence after 95 MJ/m2 of radiant exposure, and at that point

only 20% of the total UV-Vis absorbance has been lost. However, when 2 equivalents

of TMIO (55) is added to the film containing PFN 115, the maximum fluorescence is

reached after 240 MJ/m2 of radiant exposure. At 240 MJ/m2 only 40% of the UV-Vis

absorbance is present. This gives explanation of the poor maximum fluorescence.

There is less of an effect when dditives are added to films containing PFN 116,

compared to when PFN 115 was used. This is due to PFN 116 having an extra nitroxide

moiety per molecule compared to PFN 115, which results in the need to remove two

nitroxide groups per molecule to observe a significant increase in fluorescence, rather

than one (for PFN 2). If the nitroxide moiety is still present, addition of TMIO (55)

does not increase the stability of the fluorophore or the film substrate. Similarly,

addition of UV absorber (Tinuvin P, 1) had only a minor effect on the rate of

fluorescence increase for PFN 116. This is due to the already lowered fluorescence

quantum yield, Figure 67.


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Figure 67: Fluorescence maximum trace of aged TOPAS® films doped with PFN 116 (0.025 w%);




However, when focusing on Figure 67, addition of additives, 55 and 1 still allowed

fluorescent detection of radicals formed in the photo-oxidative degradation of

TOPAS®. The stabilisers not only reduce degradation of the TOPAS® film while

working in synergy, they reduced degradation of the PFN fluorophore. Although

maximum fluorescence was not seen in the film containing both additives, PFN was

still present, indicating fluorescence would continue to grow, allowing substantial

detection of photo-oxidative radical degradation.

5.8. Conclusion

This study has shown that PFNs are sensitive probes for the early stages of photo-

oxidative degradation of polymer materials. The PFN’s reporting lifetimes can be

extended with the addition of a radical trap (55). Their lifetime can also be improved

by addition of nitroxide moieties to the PFN structure, but this affects the PFN’s


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sensitivity. The addition of a UV absorber (1) was also shown to affect the reporting

lifetime of the PFNs via a decrease in the rate of degradation of TOPAS® film

substrates, which also reduced consumption of the PFNs and led to a lower overall

fluorescence signal.

The sensitivity of PFNs to the detection of free-radicals allowed photodegradation to

be observed during the apparent induction period seen using infrared spectroscopy. By

signalling degradation within this induction period, these PFN probes may be able to

provide a sensitive, rapid method for determining relative lifetimes of materials during

natural exposure, thus reducing the time required for outdoor exposure studies.


We gratefully acknowledge financial support for this work from Queensland

University of Technology (QUT), the Australian Research Council Centre of

Excellence for Free Radical Chemistry and Biotechnology (CEO 0561607), and the

Defence Materials Technology Centre, which was established and is supported by the

Australian Government’s Defence Future Capability Technology Centre (DFCTC)

initiative.

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6. THE SYNTHESIS AND STABILITY OF FERRARI

RED- TYPE COMPOUNDS

6.1. Introduction

Corrosion is recognised as a major global financial issue, estimated to cost US$2.5

trillion, which is equivalent to 3.4% of global Gross Domestic Product (GDP).247-248

In the same NACE study, it was estimated that 15-35% of this cost could be prevented

using current control practises. One control method is the use of protective coats, such

as polymers. However, during exposure to sunlight and other weather effects,

polymers undergo degradation and can result in a loss of its structural integrity. This

may result in the development of surface cracks which allows oxygen and moisture to

react with the metal surface.249 Many techniques have been developed to minimise the

chance of this happening by monitoring and re painting systematically. This process

can be time consuming and expensive.

As mentioned in previous chapters, monitoring polymer degradation can lack

sensitivity using current techniques. However, profluorescent nitroxides have shown

the ability to locate and detect polymer damage by trapping the radicals formed during

the initiation stage. 35, 56, 64, 98-101, 106, 123, 186 The challenge has proven to be creating a

PFN stable enough to withstand the harsh environment of radical mediated polymer

degradation.64,35

It has been previously shown that using a photo-stable fluorophore, that PFN’s stability

can be lengthened. Ferrari Red based PFNs have been developed herein, based off the

photo-stable 3,6-diaryl-2,5-dihydro-1,4-dioxopyrrolo[3,4-c]pyrroles (DPP) pigment.

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The DPP pigment is known for its outstanding performance to withstand, heat, light

and weathering effects250-252. It was solubilised using a swallow tail (131) to test it as

a dye compared to its known pigment. However, there is no measurable technique for

testing the photo-stability of a certain compound due to the large number of variables.

In this experiment the Ferrari Red compounds will be compared against the previously

studied 9,10-bis(phenylethynyl)anthracene (29) which is known for its thermal

stability. It will also be tested against the most successful photo-stable PFN to date,

alkyne perylene diimide (116)

Figure 68: Compounds used in this study

The novel PFNs were exposed to photo-oxidative environment in two films, to test

their photo-oxidative stability in a solid model using PTMSP and TOPAS®, as they

were used in previous chapters. Like the previous study, the films were also exposed

to a thermo-oxidative environment to confirm the degradation pathway.

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Figure 69: Polymer films used in photo-oxidative degradation experiment

The methoxy amine derivatives were synthesised to avoid complication with the

antioxidant effect of the nitroxide. This process would simplify the degradation

analysis so only comments on the stability of the fluorophore can be made.

6.2. Experimental

6.2.1. Materials

TOPAS® 8007x10 was a gift from Ciba Speciality Chemicals. PTMSP was purchased

from ABCR GmbH. Cyclohexane was purified using a literature procedure194 where

it was washed with concentrated sulphuric acid until the wash was colourless. The

organic layer was then washed with water, aq. Na2CO3 and again with water until the

wash solution was at a neutral pH. The washed cyclohexane was then distilled over

calcium hydride. PFN 116 along with the methoxyamine, non-radical analogues, 114

were synthesised as described previously.53, 187. All other materials and reagents were

of analytical reagent grade purity, or higher and were purchased from Sigma Aldrich,

Australia.

6.2.1. PTMSP sample preparation

Each of the compounds shown in Figure 68 (1.94 x10-7 mol) was dissolved in freshly

distilled cyclohexane (7.45 mL) in a 25x75 mm soda glass vial. PTMSP (293 mg) was

then added to each solution and the vials sealed and stirred for 48 hours in the dark.

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Each solution was then poured into a Petri dish and the solvent allowed to evaporate

slowly over two days in the dark. Once the films were dry to the touch, they were

placed under vacuum until they reached a constant weight (24 h).

6.2.2. TOPAS® sample preparation

Each of the compounds shown in Figure 68 (4.3610-7 mol) was dissolved in freshly

distilled cyclohexane (16.94 mL) in a 2575 mm soda glass vial. TOPAS® pellets

(660 mg) were then added to each solution and the vials sealed and stirred for 4 hours

in the dark. Each solution was then poured into a Petri dish and the solvent allowed to

evaporate slowly over two days in the dark. Once the films were dry to the touch, they

were placed under vacuum until they reached a constant weight (24 h).

6.2.3. Photo-oxidation of films

Film samples were irradiated in an Heraeus Suntest CPS+ device delivering 250 W/m2.

The temperature in the chamber was set to 40°C. The films were oriented in parallel

to the lamp. Samples were removed periodically and analysed using UV-Vis,

Fluorescence and FTIR-ATR spectroscopy.

6.2.4. Thermo-oxidation of films

Films were placed in an oven at 70°C on metal racks, and separated by a 5 mm gap.

6.2.5. Characterisation

6.2.5.1. Fluorescence Spectroscopy



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changed according to the compound present in the sample: 29; 383 nm, 131, 465 nm,

114, 568 nm, 116; 564 nm. Spectra were collected from 5 nm past the excitation

wavelength up to 700 nm at a scan rate of 600 nm min-1. All films were examined in

triplicate. The data were processed using Microsoft Excel and are presented as the

fractional change in the maximum intensity between 600-650 nm compared to an un-

aged sample.

6.2.6. Synthesis of Ferrari Red based products

Scheme 49: Synthesis of 2,5-bis(2-octyl-1-dodecyl)-3,6-diphenylpyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dion (131)

6.2.6.1. 2,5-dihydro-1,4-dioxo-3,6-diphenylpyrrolo[3,4-c]pyrrole (135)

A mixture of t-BuOK (252 mg, 2.25x10-3 mol, 2.3 equiv.) and benzonitrile 134 (100

mg, 9.697x10-4 mol, 1 equiv.) in 2-methyl-2-butanol (620 µL) was heated at 110 °C.

At this temperature and under vigorous stirring, dimethyl succinate (64 µL, 4.85x10-4

mol, 0.5 equiv.) was added and stirred for a 2 h at 110 °C, the mixture was cooled at

50 °C and treated with methanol (1.34 mL) and AcOH (0.17 mL). After cooling at

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room temperature, the precipitate was collected by filtration and washed repeatedly

with methanol to give 135 (7.7%).1H NMR (400 MHz, DMSO) δ 5.74 (s, 2H, NH);

7.56 (m, 6H, Ar); 8.47 (m, 4H, Ar).

6.2.6.2. 2,5-bis(2-octyl-1-dodecyl)-3,6-diphenylpyrrolo[3,4-c]pyrrole-

1,4(2H,5H)-dion (131)

135 (15 mg, 5.2 x 10-5 mol) and anhydrous K2CO3 (21.6 g, 1.56 -4 mol, 3 equiv.) were

added to a dry round bottom flask and kept it under vaccum at 50 °C for one hour then

anhydrous N, N-dimethylformamide (DMF) (1 mL) was added under argon to the

above mixture. This mixture was then heated to 120°C under argon for 1h. 2-Octyl-1-

dodecylbromide (65.14 mg, 1.56 -4 mol, 3 equiv.) was added drop-wise, and the

reaction mixture was further stirred overnight at 130°C. The reaction mixture was

allowed to cool down to room temperature and poured into water (600 mL) and stirred

for 30 min. The product was extracted with chloroform, washed with DI water, and

dried over anhydrous MgSO4. Removal of the solvent afforded the crude product

which was further purified using column chromatography on silica gel (1:1

Chloroform/Hexane) to gave the product as an orange oil (5%).

1H NMR (400 MHz, CDCl3) δ 0.88 (t, 12H, J = 3.66 Hz, CH3); 1.05- 1.31 (m, 58H,

CH2); 3.73 (d, 4H, J = 7.76 Hz, CH2); 7.49 (m, 6H, Ar); 7.75 (m, 4H, Ar). IR (ATR)

νmax 7.92 (=C-H), 1093 (C-O), 1238 (R3N), 1465 (aryl C-C), 1673 (C=O), 2852 and

2921 cm-1 (alkyl CH3). 253

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Scheme 50: The synthetic route to 2,5-bis(2-octyl-1-dodecyl)-3,6-di(2-methoxy-1,1,3,3-

tetramethylisoindoline)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dion, 133

6.2.6.3. 5-Cyano-1,1,3,3-tetramethylisoindoline (82)

5-Bromo-1,1,3,3- tetramethylisoindoline (65) (250 mg, 9.84 x 10-4 mol),

K4[Fe9CN)6].3H2O (103.25 mg, 0.25 eqv., 2.4 x 10-4 mol), CuI (22.5 mg, 0.1 eqv., 11.8

x10-4 mol), 1-butylimidazole (412 uL, 2eqv.,1.89 x 10-3 mol) and o-xylene (5 mL) as

the solvent were all added to a schlenk and heated to 180 °C for 4 days. Ethyl acetate

was poured into the tube once cooled and it was washed with 2M NaOH. Solids were

removed by filtration and solvent removed by vacuum. A short ethyl acetate column

was performed and everything to collected with the solvent, yielded a yellow oil with

assumed impurities. 1H-NMR (CHCl3, 400MHz): δ= 1.45 (s, 12H, CH3-C), 7.20 (d,

1H, Ar-H), 7.40 (s, 1H, Ar-H), 7.54 (dd, 1H, Ar-H).144

6.2.6.4. 5-Cyano-1,1,3,3-tetramethylisoindolin-2-yloxyl (83)

5-Cyano-1,1,3,3-tetramethylisoindoline (82) was dissolved in DCM and cooled in an

ice bath before m-CPBA was added slowly. Once addition was complete, the ice bath

was removed and allowed to return to RT and stirred for a further 6 hours. The solution

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turned a bright yellow colour and the reaction was basified with 2M NaOH, washed

with water (3x 20 mL) and purified by column chromatography (DCM). To yield a

crystalline yellow solid. (76 % over the 2 steps). IR (ATR) νmax 760 (=C-H), 833 (N-

O), 1372 (R3N), 2227 (C≡N), 2978 cm-1 (alkyl CH3). HRMS (ESI): m/z (%) =

217.2710 (30) [M+1]+, calcd for C13H16N2O• [M+1]+ 216.1263.144

6.2.6.5. 5-Cyano-2-methoxy-1,1,3,3-tetramethylisoindoline (84)

5-Cyano-1,1,3,3-tetramethylisoindolin-2-yloxyl (83) (150 mg, 6.968 x10-4 mol) and

FeSO4.7H2O (484 mg, 2.5eqv., 1.74 x 10-3 mol) were dissolved in DMSO and cooled

in an ice bath while H2O2 was added dropwise. Once the addition was complete, the

reaction was stirred at RT for 30 minutes. Once complete the mixture was poured into

2M NaOH, and extracted with ether (3 x 20 mL) then washed with water (3 x 10 mL).

Solvent was removed by vacuum and purified by column chromatography (10% ether

in hexane) to yield a colourless low melting solid.1H-NMR (CHCl3, 400MHz): δ= 1.43

(s, 12H, CH3-C), 3.77 (s, 3H, CH3-O), 7.19 (d, 1H, J = 7.88 Hz, Ar-H), 7.37 (s, 1H,

Ar-H), 7.52 (dd, 1H, J = 8.1 & 1.07 Hz, Ar-H). HRMS (ESI): m/z (%) = 231.1638 (15)

[M]+ 253.1453 (25) [M+Na] calcd. for C14H19N2O (M) 231.15.

6.2.6.6. 2,5-dihydro-1,4-dioxo-3,6-di(2-methoxy-1,1,3,3-

tetramethylisoindoline)pyrrolo[3,4-c]pyrrole (132)

A mixture of t-BuOK (252 mg, 2.25x10-3 mol) and 84 (223.3 mg, 9.697x10-4 mol) in

2-methyl-2-butanol (620 µL) was heated at 110 °C. At this temperature and under

vigorous stirring, dimethyl succinate (64 µL, 4.85x10-4 mol) was added and stirred for

2 h at 110 °C, the mixture was cooled at 50 °C and treated with methanol (1.34 mL)

and AcOH (0.17 mL). After cooling at room temperature, the precipitate was collected

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by filtration and washed repeatedly with methanol to give 132 (11.2%).250 1H NMR

(400 MHz, DMSO) δ 5.74 (s, 2H, NH); 7.56 (m, 6H, Ar); 8.47 (m, 4H, Ar).250

6.2.6.7. 2,5-bis(2-octyl-1-dodecyl)-3,6-di(2-methoxy-1,1,3,3-

tetramethylisoindoline)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dion (133)

132 (19 mg, 6.625x10-5 mol) and anhydrous K2CO3 (28 mg, 1.988x10-4 mol) were

added to a dry round bottom flask and kept under vacuum at 50 °C for one hour then

anhydrous N, N-dimethylformamide (DMF) (1.34 mL) was added under argon to the

above mixture. This mixture was then heated to 120°C under argon for 1 h. 2-Octyl-

1-dodecylbromide (1.988x10-4 mol, 90 µL) was added drop-wise, and the reaction

mixture was further stirred overnight at 130°C. The reaction mixture was allowed to

cool down to room temperature next day and poured into water (600 mL) and stirred

for 30 min. The product was extracted with chloroform (3 x 10 mL), washed with DI

water (20 mL), and dried over anhydrous MgSO4. Removal of the solvent afforded the

crude product which was further purified using column chromatography on silica gel

(1:1 Chloroform/Hexane) to give the product as an orange oil. 1H NMR (400 MHz,

CDCl3) δ 0.88 (t, 12H, J = 3.66 Hz, CH3); 1.05- 1.31 (m, 58H, CH2); 3.73 (d, 4H, J =

7.76 Hz, CH2); 7.49 (m, 6H, Ar); 7.75 (m, 4H, Ar). IR (ATR) νmax 7.92 (=C-H), 1093

(C-O), 1238 (R3N), 1465 (aryl C-C), 1673 (C=O), 2852 and 2921 cm-1 (alkyl CH3).


6.3.1. Film Preparation

Ferrari red is initially a pigment, however to allow solution testing it was solubilised

using a long swallow tail. Swallow tail Ferrari red was dissolved in cyclohexane, and

the same solvent casting procedure from the previous chapters was used. Solvent

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casting is used to reduce the use of elevated temperatures to remove solvent, and it

also allows easy distribution of the compounds in low concentration.

6.3.2. PTMSP

PTMSP film was used in this study; its popularity is due to the increasing need for

high-performance separation membranes. Due to PTMSPs bulky substituents on its

polymer chain, it produced the most permeable non-porous polymer membrane among

the existing polymers. 254 PTMSP exhibits long-term stability when stored at room

temperature in the dark under vacuum but the material noticeably degrades when

exposed to heat, light or air.190 It is known to degrade through a radical mediated

mechanism which has been previously shown to be perfect for PFN detection.191

6.3.2.1. Photo-oxidative Degradation of PTMSP films


PTMSP films doped either with 29 (-■-, λmax = 383 nm), 131(-▲-, λmax = 465 nm) or 114 (-♦- λmax = 568 nm)

with respect to UV ageing time (hours).

The films were exposed to the synthetic photo-oxidative environment by the Heraeus

Suntest. PTMSP has shown previously to produce radicals at a high rate over other

C H A P T E R S I X

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films tested. Compounds with high fluorescence quantum yields are known to form

singlet oxygen which aids degradation of their own fluorophore, although it is not as

competitive as the radical attack from the degrading polymer system. This is shown in

Figure 70 by the loss of fluorescence during irradiation. Comparing the loss of

fluorescence can be used as a comparison tool to look at relative photo-oxidative

stability. Using this method, compound 114 has higher photo-oxidative stability over

29, due to 114 fluorescence loss being slower which shown in preceding chapters.

However, Ferrari red dye (131) performed poorly compared to both 29 and 114. This

was a surprising outcome due to the positive published literature.

6.3.2.2. Thermo-Oxidative Degradation of PTMSP Films


PTMSP films doped either with 29 (-■-, λmax = 383 nm), 131(-▲-, λmax = 465 nm) or 114 (-♦- λmax = 568 nm)

with respect to ageing time (hours) at 70°C.

PTMSP films were thermally aged in the dark in an oven at 70°C. This was done to

ensure that the fluorophores were not affected by the temperatures experienced during

testing in the solar simulator. Thermally-aged films showed no visible degradation,

such as brittleness or loss in fluorescence emission Figure 71, which indicates that the

C H A P T E R S I X

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fluorophores and the polymer used in this study are thermally stable under the

conditions used.


PTMSP films doped with 116 with respect to UV (-■-) or thermal (-♦-) ageing time (hours).

The number of radicals produced by the degrading system can be detected by

fluorescence given off by a PFN. PFN 116 was used to compare the radical production

in both environments, UV exposure and thermal due to its proven stability. It shows

there are fewer radicals produced when the films were exposed to thermal-oxidative

degradation environments compared to photo-oxidative. As irradiation continues in

the photo-oxidative environment, fluorescence reaches a maximum before tapering

off. As discussed this is due to degradation of the fluorophore. This degradation can

be caused by the high concentration of radicals within the polymer system.

6.3.3. TOPAS®

TOPAS® was the second film to be used in this photo-degradation study. It is within

the family of cyclic olefin copolymers.193 Cyclic copolymers have attractive properties

such as high transparency, low density, high thermal stability, low shrinkage, low

C H A P T E R S I X

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moisture absorption, and low birefringence which allow them to be extremely

attractive for a range of applications.204

6.3.3.1. Photo-Oxidative Degradation of TOPAS® Films


TOPAS® films doped either with 29 (-■-, λmax = 383 nm), 131(-▲-, λmax = 465 nm) or 114 (-♦- λmax = 568

nm) with respect to UV ageing time (hours).

As shown in previous chapters, TOPAS® degrades at a slower rate in a photo-

oxidative environment compared to PTMSP. This results in fewer radials attacking the

compound’s fluorophore that therefore results in a longer survival rate for the PFNs in

C H A P T E R S I X

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TOPAS®. However, as shown by the loss of fluorescence in Figure 73, 131 still has a

poor performance in the photo-oxidative environment compared to 114.

Figure 74: Fluorescence loss (calculated as a percentage from the fluorescence intensity at λmax) of 116

doped in PTMSP (-■-) or TOPAS (-♦-) films with respect to UV ageing time (hours)

The radical production of PTMSP in a photo-oxidative environment is compared

against TOPAS® by the films being doped with PFN 116. PFN 116 is used to detect

the number of radicals produced by each degrading system by an increase of

fluorescence. This increase of fluorescence is shown in Figure 74. There is a rapid

increase of fluorescence by PFN 116 doped in PTMSP films compared TOPAS® film.

This confirms that the larger radical production within the polymer films results in

poorer preforming PFNs as shown by the fast fluorescence switch on followed by the

fluorescence drop off.

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6.3.3.2. Thermo-Oxidative Degradation of TOPAS® Films


TOPAS® films doped either with 29 (-■-, λmax = 383 nm), 131(-▲-, λmax = 465 nm) or 114 (-♦- λmax = 568

nm) with respect to ageing time (hours) at 70°C.

When the films were exposed to a dark 70°C oven, they showed no signs of

degradation. Like PTMSP, it is because the TOPAS® films are more stable in this

environment and therefore there is less radical attack on the fluorophore.

6.4. Conclusion

The focus of this study was to synthesise a new group of photo-stable PFNs using a

Ferrari red pigment base. Although all literature appeared promising, the perylene

diimide based PFN was found to still be the more photo-stable in comparison. While

not proven, it was suspected that solubilising this pigment may have decreased its

stability due to the introduction of the weaker amide bond. Unfortunately, due to

previous testing methods, solubility of PFNs is needed for consistency throughout the

testing and this group of compounds were not investigated further.

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7. CONCLUSIONS AND FUTURE WORK

7.1. Conclusions

This PhD project has advanced knowledge in the area of photo-stable profluorescent

nitroxides. With particular focus on the detection of photo-oxidative induced

degradation via radical mediation using photo-stable profluorescent nitroxides.

Although the thesis did not focus only on the synthesis of the novel PFNs, it was the

most challenging aspect of the project. The difficultly came from the limited solubility

of the perylene diimide (PDI) core, therefore purification was tedious and generally

unsuccessful. Unsymmetrical perylene diimide were achieved via one pot mixed

synthesis, the maximum yield could only be statistical. Synthesis of the corresponding

methoxyamines was also challenging, with the perylene diimide PFN only being

selectively soluble in DMSO. Therefore, the deprotection of the methyl group to

liberate the nitroxide moiety was groundbreaking. Synthesis was moved away from

PDI PFNs with developments in bay region substitution. This resulted in dramatic

solubility in most organic solvents and these perylene diimide and naphthalimide

based PFN were then the focus for the rest of this thesis.

The attention then moved to the stability of these newly synthesised PFNs. The liquid

model photo-degradation experiment by the Hereus Suntest in cyclohexane was the

first evidence that all these novel PFNs were more photo-stable than the successful

BPEA PFN. PFNs doped in the polymer material, PTMSP showed the nitroxide

probe’s ability to switch on and report damage occurring in the degrading film.

However, degradation in the Heraeus Suntest instrument was too severe. This resulted

in TOPAS® being used due to its higher stability under the testing conditions and its


P a g e | 234

transparency. The stability of the TOPAS® films resulted in higher stability of the

PFNs due to there being less radical attack on the fluorophores of the PFNs. It was

determined that perylenediimide-incorporated PFNs are more photo-stable than

naphthalimide PFNs in both the PTMSP and TOPAS® films. It was also determined

that the nitroxide-containing compounds have higher stability in the photo-oxidative

environment over their non-radical analogues. The alkyne-linked perylenediimide

PFN has an impressive switch on ability when exposed to photo-induced radicals, and

it is the most effective PFN probe of the group tested.

Accelerated weathering in the laboratory experiments proved to yield similar trends to

true weathering effects in a Brisbane summer. As previously shown, the radical

production of the degrading polymer system is the major effect on the serviceable

lifetime of the PFN. As the most successful PFN, the alkyne-linked perylenediimide

PFN indicated that TOPAS® degradation via radical production is only affected by

UV exposure. However, other effects were shown by ATR on the rooftop samples

which weren’t seen on the films by Suntest exposure. Which indicate that PFN probes

cannot be used as an absolute probe for polymer degradation. However, the PFN

appears to degrade at a similar rate if the UV exposure is kept the same.

It was concluded that the mechanism of the PFN is not affected by the addition of

radical trappers or UV absorbers which are often present in paint samples. Addition of

additives made the serviceable lifetime of the PFN tuneable depending on

concentration. Higher stability on the degrading film resulted in higher stability of the

PFN. The nitroxide moiety on the PFN was not only an antioxidant to its own

fluorophore but it was an antioxidant to the TOPAS® film too. However, once the


P a g e | 235

nitroxide moiety was removed, the trapped PFN became a prodegradant via the

production of singlet oxygen.

FTIR-ATR is a well-known technique to detect polymer degradation. However, when

used in this thesis, it lacked sensitivity at the early stages of degradation and it was not

reproducible. It highlighted the benefit of PFN technology due to their sensitivity and

reproducibly as a probe for early detection of polymer degradation. With synthesis of

these novel photo-stable profluorescent nitroxide probes, we now can detect

degradation in harsh environments, such as photo-oxidative environments without the

probe failure.

7.2. Future Work

This project fragments into two distinct areas, synthesis and analysis. When focusing

on the synthesis, there are three distinct focuses; changing of the nitroxide; changing

the location of the nitroxide; and changing of the linker, which joins the nitroxide to

the fluorophore. This would allow several other elements of the PFN to be tested.


P a g e | 236

Figure 76: Synthetic targets for varying the perylene diimide PFN

At the start of the project, the focus was addition of the nitroxide through the imide

bond but there were complications with low and variable yields, difficult purification,

and low solubility. Structure 136 continues the focus of the imide formation but with

addition of solubilising groups to the bay region. Due to the perylene diimide structure,

there are multiple points for addition around the bay region. With four solubilising

groups, compound 137, would have increased solubility, with potential for appealing

physical properties such as an increased quantum yield.


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Figure 77: Different potential nitroxides for perylene diimide PFNs

All PFNs synthesised throughout the project used TMIO as its nitroxide. There are

several known stable nitroxides which could be feasible. Using the ethyl nitroxide,

TEIO could make the more sensitive probe, compound 138. This would allow only

small radicals to be trapped over longer reactive polymer chains. TEMPO derivatives

139 also have many benefits such as Denisov mechanism, which would add to the

antioxidant effect of the nitroxide on the PFN during polymer degradation.


P a g e | 238

Figure 78: Potential synthetic goals for photo-stable PFNs

The final aspect would be changing the linker. It was found that the alkyne linked

nitroxide was the most successful PFN, however this still has aspects which could be

improved. For example, the alkyne linker could be improved by coupling through a

Suzuki reaction, compound 140. Decreasing the distance between the nitroxide moiety

and the fluorophore is known to increase quenching character of the PFN. This linker

would also remove the reactivity of the alkyne to a more rigid carbon framework, 141.

This could be done by building the nitroxide moiety into the perylene frame. A similar

compound was synthesised by Blinco et al. using a naphthalene fluorophore, resulting

a successful azaphenalene PFN.106 Jiang et al. published a one pot Suzuki cross-


P a g e | 239

coupling reaction and subsequent light-promoted cyclization to yield two regiospecific

pyridyl annelated bismides, 142.255 The product has a quantum yield of near one,

which would be beneficial for PFN quenching. The challenge would be in the synthesis

of the boronic acid nitroxide. Coronene, 143 are also shown to have high quantum

yields, Choi et al. showed the simple one pot reaction with similar conditions used in

a Suzuki-coupling which spontaneously cyclized to afford a coronene chromophore.256

The coronene reaction could be easily done, with all reagents being successfully made

and/or published. A graphene like perylene diimide compounds,144 was successfully

synthesised by Quin et al.257 With focus leaning towards nitroxide grafted carbon

fibre258 this will complement the current research nicely.258


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Figure 79: Synthetic route for potential new perylene diimide PFNs

The first generation of perylene diimide PFNs were abandoned due to poor solubility

and poor yields. The literature development of mild removal of the methoxy protecting


P a g e | 241

group could improve the synthetic pathway. The pathway would include two extra

steps, however the low yielding methylation step in DMSO could be performed on the

smaller precursor molecule. Since PDI have high solubility in DCM, there is an

expected yield improvement and possible increase in selectivity which was seen during

formation of 115.

Only two factors were focussed on when determining the success of the PFNs

produced, high UV exposure and high temperature. When focusing on aircraft coatings

other factors must be considered, altitude, ranging pressures and, of course cooling

temperature. All of which can change the degradation pathway of the polymer and the

overall functionality of the material. However, this technology is not only limited to

aircraft coating, there should be a focus on all coatings which as exposed to the natural

elements, such as bridges and submarines. This would be interesting to detect all of

the effects of salt water and bacteria growth.

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C H A P T E R N I N E

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9. APPENDIX

9.1. Supplementary Information for Polyaromatic Profluorescent

Nitroxide Probes with Enhanced Photostability (Chapter 3)

V. C. Lussini,[a][b] J. P. Blinco,[a] K. E. Fairfull-Smith*[a] and S. E. Bottle*[a][b]

[a] ARC Centre of Excellence for Free Radical Chemistry and Biotechnology. School of

Chemistry, Physics and Mechanical Engineering, Faculty of Science and Engineering,

Queensland University of Technology (QUT), GPO Box 2434, Brisbane, QLD 4001, Australia

[b] Defence Materials Technology Centre, School of Chemistry, Physics and Mechanical

Engineering, Faculty of Science and Engineering, Queensland University of Technology

(QUT), GPO Box 2434, Brisbane, QLD 4001, Australia

*Corresponding author: E-mail: [email protected] ; Fax: +61 7 3138 1804; Tel: +61 7 3138

1356



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9.1.1. 5-Hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline (64)

02 VL 74B (26 02 13).001.esp

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5

Chemical Shift (ppm)

0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

No

rma

lize

d I

nte

nsity

12.102.930.940.930.99

1.4

0

3.7

7

6.5

66.5

7

6.7

0

6.9

46

.96

Figure 80: 1H NMR spectrum of 5-Hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline (64)


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02VL76_C_110605_CARBON_CDCL3_20150611_01

168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

No

rma

lize

d I

nte

nsity

65

.41

66

.69

67

.01

76

.6876

.99

77

.31

10

8.3

6

11

4.2

912

2.5

1

13

7.4

9

14

6.8

7

15

4.9

5

Figure 81: 13C NMR spectrum of 5-Hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline (64)

Figure 82: HPLC (70% MeOH/ Water) chromatogram of 5-Hydroxy-2-methoxy-1,1,3,3-tetramethylisoindoline (64)


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tetramethylisoindolin-5-yloxy)-1,8-naphthalimide (104)

PROTON_CDCL3_01

8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

No

rma

lize

d I

nte

nsity

17.3511.862.892.810.990.971.020.961.050.992.01

1.2

81

.31

1.4

61

.49

3.8

1

6.9

46

.96

6.9

66

.99

6.9

97

.08

7.1

97

.21

7.4

57

.56

7.5

87

.80

7.8

27

.84

8.5

08

.52

8.7

28

.72

8.7

8

Figure 83: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-1,8-

naphthalimide (104)


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CARBON_CDCL3_01

168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

No

rma

lize

d I

nte

nsity

15

.26

29

.69

31

.20

31

.70

34

.20

35

.48

50

.84

65

.54

66

.98

67

.15

76

.71

77

.03

77

.34

11

0.2

7

11

4.1

2

11

6.6

7

11

9.8

0

12

2.9

31

23

.41

12

4.0

11

26

.1112

6.5

11

27

.77

12

8.6

81

30

.10

13

2.3

31

33

.30

14

2.6

31

43

.76

14

7.8

8

14

9.9

6

15

4.0

0

16

0.4

0

16

4.7

61

65

.42

Figure 84: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-yloxy)-

1,8-naphthalimide (104)

Figure 85: HPLC (70% MeOH/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-

tetramethylisoindolin-5-yloxy)-1,8-naphthalimide (104)


P a g e | 266

9.1.3. N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-2-

yloxyl-5-yloxy)-1,8-naphthalimide (105)

PROTON_CDCL3_01

8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

No

rma

lize

d I

nte

nsity

17.571.231.040.960.991.021.99

1.3

11

.33

7.0

1

7.2

67

.457.4

77.5

97

.61

7.8

7

8.5

98.7

58

.76

8.8

0

Figure 86: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yloxy)-1,8-

naphthalimide (105)


P a g e | 267

Figure 87: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-

2-yloxyl-5-yloxy)-1,8-naphthalimide (105)

Figure 88: EPR (DCM) spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-yloxy)-



P a g e | 268

Figure 89: Quantum Yield of fluorescence calculations for 104 and 105

9.1.4. 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline (62)


P a g e | 269

02VL46-_120615_PROTON_CDCL3_20150612_01

7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

No

rma

lize

d I

nte

nsity

11.512.820.920.971.00

1.4

1

3.7

83

.86

6.4

36

.44

6.5

76

.58

6.8

86

.90

Figure 90: 1H NMR spectrum of 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline (62)

02VL46_C_120615_CARBON_CDCL3_20150612_01

160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

No

rma

lize

d I

nte

nsity

65

.40

66

.65

67

.02

76

.79

77

.11

77

.43

10

8.1

5

11

4.4

7

12

2.2

3

13

5.4

9

14

5.7

11

46

.35

Figure 91: 13C NMR spectrum of 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline (62)


P a g e | 270

Figure 92: HPLC (70% MeOH/ Water) chromatogram of 5-Amino-2-methoxy-1,1,3,3-tetramethylisoindoline (62)

9.1.5. 5-Diazonium-2-methoxy-1,1,3,3-tetramethylisoindoline

tetrafluoroborate (63)


P a g e | 271

PROTON_DMSO_01

14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 -1 -2


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

No

rma

lize

d I

nte

nsity

12.743.361.132.00

Water

1.4

3

2.4

8

3.7

1

7.9

07

.92

8.5

88

.60

8.6

0

Figure 93: 1H NMR spectrum of 5-Diazonium-2-methoxy-1,1,3,3-tetramethylisoindoline tetrafluoroborate (63)

CARBON_DMSO_01

160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

No

rma

lize

d I

nte

nsity

39

.33

39

.54

39

.75

39

.95

40

.17

40

.37

40

.58

65

.38

65

.73

68

.2510

8.4

2

11

5.0

1

12

2.7

5

12

5.5

81

27

.00

13

3.4

5

14

8.0

9

15

9.0

0

Figure 94: 13C NMR spectrum of 5-Diazonium-2-methoxy-1,1,3,3-tetramethylisoindoline tetrafluoroborate (63)


P a g e | 272


tetramethylisoindoline-5-ethynyl)-1,8-naphthalimide (106)

PROTON_CDCL3_01

9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

No

rma

lize

d I

nte

nsity

18.1910.543.011.121.072.001.961.080.980.970.981.00

1.2

81

.32

1.4

9

6.9

97

.17

7.1

97

.26

7.4

27

.46

7.5

77

.59

7.8

97

.98

8.0

0

8.6

08

.62

8.6

98

.71

8.8

08

.83

Figure 95: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-tetramethylisoindoline-5-ethynyl)-



P a g e | 273

02VL121_240615_CARBON_CDCL3_20150625_01

168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8 0


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

No

rma

lize

d I

nte

nsity

21

.44

31

.21

31

.70

34

.22

35

.50

65

.54

67

.08

67

.24

76

.68

77

.00

77

.32

85

.74

99

.69

12

0.9

6

12

1.9

5

12

2.3

1

12

5.1

21

27

.48

12

7.7

31

28

.72

13

0.7

31

30

.83

13

1.2

11

32

.03

13

2.7

1

13

4.1

3

14

3.7

51

45

.93

14

7.0

815

0.0

3

16

4.7

41

65

.01

Figure 96: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-tetramethylisoindoline-5-ethynyl)-


Figure 97: HPLC (75% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-4-(2-methoxy-1,1,3,3-

tetramethylisoindoline-5-ethynyl)-1,8-naphthalimide (106)


P a g e | 274

9.1.7. N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-2-

yloxyl-5-ethynyl)-1,8-naphthalimide (107)

PROTON_CDCL3_01

9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

No

rma

lize

d I

nte

nsity

15.180.970.910.972.050.941.040.99

1.2

91

.32

7.0

0

7.3

6

7.4

77.5

87

.60

7.9

17

.99

8.7

28

.73

8.8

3

Figure 98: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-1,8-

naphthalimide (107)


P a g e | 275

Figure 99: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-

2-yloxyl-5-ethynyl)-1,8-naphthalimide (107)

Figure 100: EPR (DCM) spectrum of N-(2,5-Di-tert-butylphenyl)-4-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-

ethynyl)-1,8-naphthalimide (107)


P a g e | 276

Figure 101: Quantum yield of fluorescence calculations for 106 and 107

9.1.8. N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-

tetramethylisoindolin-5-yloxy)-perylene-3,4,9,10-tetracarboxy

diimide (117)


P a g e | 277

PROTON_CDCL3_01

9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

No

rma

lize

d I

nte

nsity

38.6822.956.035.562.002.041.710.671.271.380.840.951.53

1.2

31

.25

1.2

61

.27

1.4

3

3.7

7

6.9

46

.956.9

66

.96

7.1

27

.14

7.2

47

.43

7.4

47.5

47

.56

8.3

28

.32

8.4

08

.41

8.6

78

.67

8.6

98

.74

8.7

6

9.5

89

.59

9.6

09.6

49

.65

9.6

69

.67

Figure 102: 1H NMR spectrum of N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-

yloxy)-perylene-3,4,9,10-tetracarboxy diimide (117)

CARBON_CDCL3_01

200 192 184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

No

rma

lize

d I

nte

nsity

1.0

2

29

.69

30

.93

31

.18

31

.70

34

.22

35

.48

65

.50

66

.98

67

.18

76

.69

77

.00

77

.32

11

3.1

31

18

.51

12

2.5

91

23

.56

12

4.1

11

24

.17

12

6.3

51

27

.51

12

8.7

61

28

.99

12

9.6

51

30

.63

13

2.4

21

33

.79

14

3.6

51

48

.03

15

0.1

11

54

.36

15

5.5

61

56

.63

16

3.7

41

63

.93

16

4.3

71

64

.6120

6.9

8

Figure 103: 13C NMR spectrum of N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-

5-yloxy)-perylene-3,4,9,10-tetracarboxy diimide (117)


P a g e | 278

Figure 104: HPLC (75% THF/ Water) chromatogram of N,N-Di-(2,5-di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-

tetramethylisoindolin-5-yloxy)-perylene-3,4,9,10-tetracarboxy diimide (117)


tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-3,4,9,10-



P a g e | 279

PROTON_CDCL3_01

10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5


0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

No

rma

lize

d I

nte

nsity

1.2

61

.29

6.9

7

7.4

37

.55

8.7

3

9.6

6

Figure 105: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-


Figure 106: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-yloxy)-perylene-3,4,9,10-tetracarboxy diimide (118)


P a g e | 280

Figure 107: EPR (DCM) spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-




P a g e | 281

9.1.10. N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-

tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy

diimide (114)

PROTON_CDCL3_01

10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

No

rma

lize

d I

nte

nsity

71.2420.232.912.522.085.364.416.951.451.94

1.2

51

.48

1.5

0

3.8

0

7.0

37

.04

7.0

47

.26

7.4

47

.477.5

07

.61

7.6

37

.63

8.7

58.7

78

.79

8.8

28

.98

10

.39

10

.41

Figure 109: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-

ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (114)


P a g e | 282

CARBON_CDCL3_01

168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

0.75

0.80

0.85

0.90

0.95

1.00

No

rma

lize

d I

nte

nsity

Figure 110: 13C NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-


Figure 111: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(2-methoxy-1,1,3,3-

tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (114)


P a g e | 283


tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-3,4,9,10-


PROTON_CDCL3_01

10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

No

rma

lize

d I

nte

nsity

22.712.212.321.982.164.162.03

1.2

21

.26

1.3

4

7.0

0

7.4

8

7.6

3

8.5

6

8.8

58

.98

10

.42

Figure 112: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-



P a g e | 284

Figure 113: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (116)

Figure 114: EPR (DCM) spectrum of N,N-(2,5-Di-tert-butylphenyl)-1,7-di-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-



P a g e | 285

9.1.12. N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-tetramethylisoindolin-2-

yloxyl-5-ethynyl)-7-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-


PROTON_CDCL3_01

10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5


0

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

No

rma

lize

d I

nte

nsity

21.571.492.021.981.99

1.3

21

.33

3.8

4

6.9

97

.01

7.4

57

.49

7.6

07

.62

8.5

5

8.8

0

8.9

7

10

.42

Figure 115: 1H NMR spectrum of N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-ethynyl)-

7-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (115)


P a g e | 286

Figure 116: EPR (DCM) spectrum of N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-tetramethylisoindolin-2-yloxyl-5-

ethynyl)-7-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-tetracarboxy diimide (115)

Figure 117: HPLC (75% THF/ Water) chromatogram of N,N-(2,5-Di-tert-butylphenyl)-1-(1,1,3,3-

tetramethylisoindolin-2-yloxyl-5-ethynyl)-7-(2-methoxy-1,1,3,3-tetramethylisoindolin-5-ethynyl)-perylene-3,4,9,10-



P a g e | 287

Figure 118: Quantum yield of fluorescence calculations for 114, 116 and 115

9.1.13. N-(Octylphenyl)-N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-

perylene-3,4,9,10-tetracarboxyl-diimide (98)


P a g e | 288

02 VL 44- 2ND FRAC.001.esp

11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -0.5 -1.0


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

No

rma

lize

d I

nte

nsity

1.791.838.03

1.3

2

1.5

61

.71

2.7

2

7.4

0

8.5

58

.71

Figure 119: 1H NMR spectrum of N-(Octylphenyl)-N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-

tetracarboxyl-diimide (98)

Figure 120: HPLC (70% THF/ Water) chromatogram of N-(Octylphenyl)-N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-



P a g e | 289

Figure 121: EPR (DCM) spectrum of N-(Octylphenyl)-N’(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-

tetracarboxyl-diimide (98)



P a g e | 290

9.1.14. N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-tetramethylisoindolin-2-

yl)-perylene-3,4,9,10-tetracarboxyl-diimide (99)


P a g e | 291

02 VL 44- METRAP.001.esp

9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0


0

0.05

0.10

0.15

0.20

0.25

No

rma

lize

d I

nte

nsity

12.181.962.980.910.942.197.99

1.3

0

1.4

81

.52

2.6

92.7

12

.73

3.8

1

7.0

9

7.2

17

.27

7.3

87

.40

8.6

68

.68

8.7

48

.76

Figure 123: 1H NMR spectrum of N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-tetramethylisoindolin-2-yl)-perylene-

3,4,9,10-tetracarboxyl-diimide (99)

CARBON_CDCL3_01

200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 -10


-0.01

0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

0.14

No

rma

lize

d I

nte

nsity

0.0

0

13

.11

21

.68

28

.28

28

.69

30

.91

64

.50

66

.17

12

2.2

9

12

7.1

51

28

.4513

0.7

6

13

3.8

2

16

2.5

8

Figure 124: 13C NMR spectrum of N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-tetramethylisoindolin-2-yl)-perylene-



P a g e | 292

Figure 125: HPLC (70% THF/ Water) chromatogram of N-(Octylphenyl)-N’(2-methoxy-1,1,3,3-

tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-diimide (99)

9.1.15. N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-tetramethylisoindolin-2-

yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide (90)


P a g e | 293

02 VL 33 (170611).001.esp

11.0 10.5 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0 -0.5 -1.0


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

No

rma

lize

d I

nte

nsity

19.581.020.960.917.96

1.2

61

.31

1.3

4

7.0

8

7.4

87

.50

7.6

07

.62

8.7

18

.78

Figure 126: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-


02 VL 33- 2ND FRAC 13C.001.esp

200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 -10 -20


0

0.005

0.010

0.015

0.020

0.025

0.030

0.035

0.040

0.045

0.050

0.055

0.060

0.065

0.070

0.075

0.080

0.085

0.090

0.095

No

rma

lize

d I

nte

nsity

1.2

3

14

.33

22

.91

29

.58

29

.91

32

.14

38

.94

65

.74

67

.35

12

2.7

81

23

.47

12

3.7

1

12

7.5

41

29

.7713

1.8

81

34

.07

13

4.9

4

14

5.9

71

46

.77

16

3.7

4

Figure 127: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-tetramethylisoindolin-2-yloxyl)-perylene-



P a g e | 294

Figure 128: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-

tetramethylisoindolin-2-yloxyl)-perylene-3,4,9,10-tetracarboxyl-diimide (90)

Figure 129: EPR (DCM) spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(1,1,3,3-tetramethylisoindolin-2-yloxyl)-



P a g e | 295


9.1.16. N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-1,1,3,3-

tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-

diimide (92)


P a g e | 296

02 VL 33-METRAP (170611).001.esp

8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

No

rma

lize

d I

nte

nsity

19.4112.123.841.011.091.050.551.171.147.99

1.3

11

.34

1.4

9

3.8

1

7.0

47

.08

7.1

97

.21

7.2

87

.30

7.4

77

.49

7.6

07

.62

8.4

78

.49

8.5

98

.618.7

18

.73

8.7

78

.82

Figure 131: 1H NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-1,1,3,3-tetramethylisoindolin-2-yl)-


CARBON_CDCL3_01

200 190 180 170 160 150 140 130 120 110 100 90 80 70 60 50 40 30 20 10 0 -10


0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

0.14

0.15

0.16

0.17

0.18

0.19

No

rma

lize

d I

nte

nsity

TMS

13

.11

21

.68

28

.35

28

.69

30

.21

30

.73

30

.91

64

.52

66

.14

12

0.8

11

21

.58

12

2.2

91

25

.39

12

6.3

21

26

.69

12

7.8

21

30

.88

13

3.9

5

16

2.6

71

63

.38

Figure 132: 13C NMR spectrum of N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-1,1,3,3-tetramethylisoindolin-2-yl)-



P a g e | 297

Figure 133: HPLC (70% THF/ Water) chromatogram of N-(2,5-Di-tert-butylphenyl)-N’-(2-methoxy-1,1,3,3-

tetramethylisoindolin-2-yl)-perylene-3,4,9,10-tetracarboxyl-diimide (92)

9.1.17. N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-perylene-3,4,9,10-


1H NMR spectrum N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-perylene-3,4,9,10-tetracarboxy diimide (130)


P a g e | 298

02VL136_210615_PROTON_CDCL3_20150623_01

10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

No

rma

lize

d I

nte

nsity

31.852.003.214.982.011.831.951.97

1.2

51

.26

1.2

61

.28

1.3

01

.31

1.3

1

1.5

7

6.9

26

.93

6.9

66

.97

7.0

07

.187.2

07

.26

7.2

77

.43

7.4

5

7.5

67

.58

7.6

0

8.3

38

.33

8.4

18

.68

8.6

88

.70

8.7

08

.74

8.7

68

.76

9.5

99

.60

9.6

19

.64

9.6

69

.66

9.6

8

Figure 134: 1H NMR spectrum of N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-perylene-3,4,9,10-tetracarboxy

diimide (130)

02VL136_210615_CARBON_CDCL3_20150624_01

184 176 168 160 152 144 136 128 120 112 104 96 88 80 72 64 56 48 40 32 24 16 8 0


0

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

No

rma

lize

d I

nte

nsity

31

.18

31

.74

34

.22

35

.52

76

.68

76

.99

77

.31

11

9.3

61

19

.49

12

7.4

81

28

.79

12

9.6

41

30

.57

13

0.6

01

30

.73

13

1.6

91

33

.68

14

3.7

3

15

0.0

91

50

.11

15

5.0

51

55

.12

15

6.1

5

16

3.8

31

64

.36

Figure 135: 13C NMR spectrum of N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-perylene-3,4,9,10-tetracarboxy

diimide (130)


P a g e | 299

Figure 136: HPLC (80% THF/ Water) chromatogram of N,N’-(2,5-Di-tert-butylphenyl)-1,7-di-(phenoxy)-perylene-




P a g e | 300

9.2. Supplementary Information for Profluorescent nitroxide

sensors for monitoring the natural aging of polymer materials

(Chapter 5)

Vanessa C. Lussini,a,b John M. Colwell,a,b James P. Blinco,a Kathryn E. Fairfull-Smitha and

Steven E. Bottle*a,b

[a] ARC Centre of Excellence for Free Radical Chemistry and Biotechnology. School of

Chemistry, Physics and Mechanical Engineering, Faculty of Science and Engineering,

Queensland University of Technology (QUT), GPO Box 2434, Brisbane, QLD 4001, Australia

[b] Defence Materials Technology Centre, School of Chemistry, Physics and Mechanical

Engineering, Faculty of Science and Engineering, Queensland University of Technology

(QUT), GPO Box 2434, Brisbane, QLD 4001, Australia

*Corresponding author: E-mail: [email protected] ; Fax: +61 7 3138 1804; Tel: +61 7 3138

1356



P a g e | 301

Figure SI 138: Fluorescence maximum trace of aged TOPAS® films doped with PFN 116 (0.025 w%) during aging in

the laboratory (Suntest) and outdoors weathering.


P a g e | 302

Figure SI 139: Oxidation indices as determined by FTIR-ATR for aged TOPAS® films doped with PFN-analogue 114

(0.025 wt%) with respect to radiant exposure (MJ/m2) on the rooftop.

(a) Compared to TOPAS® films containing PFN-analogue 114 + TMIO (1, 2 and 4 eqv. of 114)

(b) Compared to TOPAS® films containing PFN-analogue 1 + Tinuvin P (0.1, 0.3 and 0.5 wt%)


P a g e | 303

Figure SI 140: Relative change in UV-Vis absorbance for aged TOPAS® films doped with PFN 115 (0.025 wt%) with

respect to radiant exposure (MJ/m2) on the rooftop.

(a) Compared to TOPAS® films containing PFN-analogue 115 + TMIO (1, 2 and 4 eqv. of 115)

(b) Compared to TOPAS® films containing PFN-analogue 155 + Tinuvin P (0.1, 0.3 and 0.5 wt%)

[Type text] C H A P T E R N I N E [Type text]

P a g e | 304

Table SI 5: Summary of aged TOPAS® films doped with PFNs (0.025 wt%) and varying concentrations of

55 and 1 aged in the Suntest and aged on the rooftop.

Compou

nd # used

TMI

O

(55)*

Tinuvi

n P

(1),

wt%

Radiant

exposure

leading to

50% loss of

UV-Vis

absorbance

(MJ/m2)

Radiant

exposure

leading to an

oxidation

index above

0.003 (MJ/m2)

Radiant

exposure

leading to

maximum

fluorescence

emission

(MJ/m2)

Sunte

st

Roofto

p

Sunte

st

Roofto

p

Sunte

st

Rooftop

- 0 220 325

- 1 >800 330

- 2 >800 >800

- 4 >800 >800

- 0.1 >800 520

- 0.3 496.8 660

- 0.5 496.8 485

- 2 0.3 >800 >800

114 0 80 130 260 80

114 1 160 250 520 350

114 2 220 260 660 390

114 4 230 340 >800 460

114 0.1 140 170 360 310

[Type text] C H A P T E R N I N E [Type text]

P a g e | 305

114 0.3 230 270 340 445

114 0.5 170 320 370 470

114 2 0.3 220 520 300 690

115 0 100 100 300 95 110 100

115 1

150 140 430 120 170

Damag

ed

115 2 180 200 610 470 240 100

115 4 220 300 640 240 280 100

115 0.1 120 220 360 515 130 200

115 0.3 180 320 380 480 110 360

115 0.5 170 460 430 510 200 360

115 2 0.3 350 520 >800 600 280 430

116 0 150 260 350 465 350 330

116 1 220 360 500 500 430 370

116 2 260 430 610 490 500 360

116 4 300 480 680 420 540 300

116 0.1 360 460 680 440 >800 720

116 0.3 400 640 640 550 >800 750

116 0.5 320 640 750 520 >800 790

116 2 0.3 430 640 650 600 >800 >800

*mole equivalents relative to compound used

the synthesis and evaluation of polyaromatic ... · vanessa lussini, john colwell, james blinco,...

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