Spectroscopic properties of monolithic silica gels dotted with axially substituted phthalocyanine of Zr(IV), Hf(IV)

and selected lanthanides.Yuriy Gerasymchuk*, Victor Chernii**, Larisa Tomachynski**, Irina Tretyakova**, Janina Legendziewicz*, Stanisław Radzki***

* Faculty of Chemistry, Wrocław University, 14 F. Joliot-Curie str., 50-383 Wrocław, Poland **V.I.Vernadskii Institute of General and Inorganic Chemistry, 32/34 Palladin ave., Kiev, Ukraine.*** Faculty of Chemistry, Maria Curie-Skłodowska University, 20-031 Lublin, Poland

General properties and applies of phthalocyanine dotted sol-gel materials

For over 30 years phthalocyanine dyes have been extensively studied due to their spectroscopic and photoelectric properties and can be applied in many branches: in the field of physics, in technique, medicine, chemistry and other sciences. Metallophthalocyanine compounds have attracted special attention due to their unique properties such as conductivity electrochromism and variety of catalytic function. Phthalocyanines are characterized by significant absorption in the visible region, large absorption coefficient, and high thermal and photochemical stability. For that reason they are good potential candidates in solar-to-electric energy conversion and as modulators of light energy in laser devices. As model system for phthalocyanine basic solar-to-electric energy converters, optical data carriers, chemical sensors and laser devices we can use sol-gel materials doped by metalloporphyrins and its analogues – metalophthalocyanines. It is a new mixing organic and inorganic hybrid material with unique physical, chemical and optical properties. Sol-gel monolith and sol-gel thin films are very useful to encapsulate various guests such as inorganic clusters, lanthanide complexes, laser dyes etc. Different complexes including metalloporphyrin and metallophthalocyanine based systems have also been encapsulated by sol-gel processing to give hybrid organic-inorganic. Application of the metalroporphyrins and metalophthalocyanines dotted sol-gel materials as catalyst of oxidation of alkenes, aromatic, halogenoorganic and other organic and inorganic compounds have been also reported. Moreover, sol-gel materials have been intensively investigated as host media to encapsulate different spacious biological materials, including enzymes, catalytic antibodies, proteins, polynucleic acids, microbials, animal cells and plants for applications in byocatalysis, immunodiagnostics, bioptical devices and as biosensors or bioimplants.

Types of investigated axially substituted phthalocyanatometal complexes and solubility

M(IV) = Zr, Hf

L = gallic acid; 5-sulfosalicylic acid; oxalic acid, methyl ester of gallic acid

Soluble in water and most of polar organic solvents

Standard method of obtaining of gels, dotted by phthalocyanines of I and II groups of investigated complexes

M(IV) = Zr, Hf

L = 2,4-pentanedione, pirocatecholic acid, citric acid

Soluble in benzene, toluene, pyridine, THF

M(IV) = Dy, Ho, Er, Tm, Yb, Lu

Soluble in pyridine, DMSO, DMF

Group I Group II Group III

nm300 400 500 600 700 800

A

0.0

0.2

0.4

0.6

0.8Before gellingAfter gellingAfter one month dryingAfter one year dryingEtOH solutionH2O solution

DMSO solution

nm300 400 500 600 700 800 900

A

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Cm=2*10-5

Cm=1*10-5

Cm=5*10-6

Cm=2.5*10-6

a)

det= 500nm

[nm]300 350 400 450 500

Rela

tive

in

ten

sit

y

0.0

5.0e+4

1.0e+5

1.5e+5

2.0e+5

2.5e+5Cm = 2.5*10-6

Cm = 5*10-6

Cm = 1*10-5

Cm = 2*10-5

nm300 400 500 600 700

Re

lati

ve

in

ten

sit

y

0

20000

40000

60000

80000

Cm = 2.5*10-6

Cm = 5*10-6

Cm = 1*10-5

Cm = 2*10-5

det= 750-765nm

ex = 400nm

[nm]300 400 500 600 700 800

Re

lati

ve

in

ten

sit

y o

f fl

uo

res

ce

nc

e

0

1e+5

2e+5

3e+5

Cm = 2.5*10-6

Cm = 5*10-6

Cm = 1*10-5

Cm = 2*10-5

Undotted gel

ex = 620nm

[nm]660 680 700 720 740 760 780 800

Rel

ativ

e in

ten

sity

of

flu

ore

scen

ce

0

1e+5

2e+5

3e+5

4e+5

5e+5

6e+5

Cm = 2.5*10-6

Cm = 5*10-6

Cm = 1*10-5

Cm = 2*10-5

[nm]500 600 700 800 900

Re

lati

ve

in

ten

sit

y o

f fl

uo

res

ce

nc

e

0

10000

20000

30000

40000

50000Cm = 2.5*10-6

Cm = 5*10-6

Cm = 1*10-5

Cm = 2*10-5

100nm 100nm

Absorption properties of investigated axially substituted phthalocyanatometal complexes incorporated in silica gels

Excitation and emission properties of investigated phthalocyaine complexes incorporated in silica gels

AFM pictures and computer analysis of surfaces of obtained phthalocyanine dotted silica gels

Preparation of transparent monolithic silica gels, dotted by lanthanide containing axially substituted phthalocyanines

Introduction of substituents to the peripheral position of Pc macrocycle is known to influence significantly the physical and chemical properties of PcM system. Moreover, metallophthalocyanine complexes containing metal in valence higher than two give possibility to bind directly to the metal one or more additional ligands, usually in the so called out of plane position, perpendicular to the N8 moiety. The axial ligands can significantly change the spectral, photophysical and other properties of PcM complexes. The mixed ligand phthalocyanine compounds are also good substrates for the synthesis even more complicated sandwich-type or trinuclear complexes.

The alcogels with various amounts of complexes from group I and II were synthesized by standard method: the sol-gel polymerization of tetraethyl orthosilicate [Si(OC2H5)4 - TEOS]. HCl was used as hydrolysis catalyst and NH3 aq. as a condensation catalyst to synthesize TEOS alcogels. We mixed TEOS (65%) with distilled water (35%) and HCl. After hydrolysis, we added NH3 aq. to the TEOS mixture. Mixture was doped with DMSO solutions of group I complexes [2·10^-4 M/dcm3] and THF/DMSO=1:1 solutions of group II complexes, for achieving of concentration of phthalocyanines in alcogels of the order of 2.5·10^-4 – 4·10^-5 M/dcm^3. We was not added formamide as antycracking reagent to mixture, because DMSO fulfilled the same function. Then, the sol was gelled in disposal polyacrylic cells sealed with parafilm to mesure light absorption before and after gelation. Final gelation was achieved after 3 days. After month parafilm was perforated to allow evaporate pore solvent during monolith drying. The following percent ratio was used: TEOS:H2O=65:35. Amount of DMSO was responded of the amount of added solution of phthalocyanine complexes. Gels with largest DMSO content has a longer time of gelation and drying.

Just after Dried, after month Dried, after year gel formation

The aceto- substituted phthalocyanines of lanthanides have several of negative properties in point of view of dotting of silica gels with using of standard method, described above. First o all, the complexes of lanthanides from Ce to Eu have a very bad solubility in most of organic solvents, used for gel dotting. On the other side, that complexes are demetalized in presence of light alcohols ( such as methanol, ethanol, propanol or izopropanol), that are liberate in time of hydrolysation and poly-condensation of silica gel precursors. But they are relatively stable in butanol (we checked the line of alcohols respectively tu commercial precursors). We evolved a new method of obtaining of transparent monolithic silica gel with using of tetrabutylorthosilicate as pecursor. A solution, mixed in mole ratios, of tetrabutyl orthosilicate (C4H9O)4Si : n-butyl alcohol : water : HCl = 350:150:10:1 was heated and stirred at a temperature of 120° C for three hours, whereby the solution used for a sol-gel method was synthesized. After cooling, the appropriate amount of complex solution in DMSO was added with stirring.

The phthalocyanines encapsulated in silica matrixes shows specific spectral characteristics. However at first glance the absorption characteristic of these complexes in silica gels is similar to that one in solutions, detailed analysis shows many differences. The most important is conclusion that molecules of investigated complexes of phthalocyanines in gels exist not only in solution closed in the micro pores of matrix, but also in the form of extra complexes, formed by direct phthalocyanines bonds with silica matrix. The changes in spectral properties of zirconium and hafnium phthalocyanine complexes depend on the stage of sol to gel to glass pathway. Aggregation processes, and their dependence upon concentration of complexes and stages of forming of silica matrix have been also described.

Comparing the excitation and emission spectra in solution and glassy solid matrix much more differences than in absorption spectra can be notices. This is from the one side result of the stronger phthalocyanine aggregation in the pores of dry gel and dry and concentration quenching effect, from the second side the

Soret band overlaps with strong emission band of silica matrix. The last effect disappears when phthalocyanine in solid are excited by the wavelengths longer than 550 nm.

It must be also emphasised that due to the intensive 700-725 nm emission upon relatively long wavelength excitation the axially substituted zirconium and hafnium phthalocyanines can be considered as

photodynamic therapy agents, which might be selective towards the certain types of tumour cells. The successful incorporation into silica gels proved that fibber optics dotted by investigated phthalocyanines

could be used in photodynamic therapy. This type of fibber optics when providing 630 nm light would excite addition emission about 710 nm. Special fibber can be prepared either in the monolithic form or silica fibber

could be covered by the sol-gel thin film containing investigated phthalocyanines.

The using of computer analysis of AFM pictures, that was registered for silica gels, gives ability to make several basic conclusions:

• The surface of “free” undotted solica gels, that was obtained by hydrolysis and polycondensation of precursors (TEOS, TBOS) is much smooth than non modified surfaces of metals. Their “roughness” is comparable with glass surface.

• The ”smooth” surface of silica gels is the perfect medium for immobilization and visualization (representation on surface) the porphyrine and phthalocyanine molecules by using of AFM method.

• The agglomeration processes of axially substituted phthalocyanine complexes of Zr(IV) and Hf(IV) can be estimated directly from AFM pictures by using the fractal analysis of pictures.