research article theoretical insight into organic dyes...

Research ArticleTheoretical Insight into Organic Dyes IncorporatingTriphenylamine-Based Donors and Binary 120587-ConjugatedBridges for Dye-Sensitized Solar Cells

Shuxian Wei1 Xiaoqing Lu1 Xiaofan Shi1 Zhigang Deng1 Yang Shao1 Lianming Zhao1

Wenyue Guo1 and Chi-Man Lawrence Wu2

1 College of Science China University of Petroleum Qingdao Shandong 266580 China2Department of Physics and Materials Science City University of Hong Kong Kowloon Hong Kong

Correspondence should be addressed to Xiaoqing Lu luxqupceducn and Wenyue Guo wyguoupceducn

Received 8 April 2014 Revised 11 May 2014 Accepted 19 May 2014 Published 11 June 2014

Academic Editor Yen-Lin Chen

Copyright copy 2014 Shuxian Wei et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

The design of light-absorbent sensitizers with sustainable and environment-friendly material is one of the key issues for the futuredevelopment of dye-sensitized solar cells (DSSCs) In this work a series of organic sensitizers incorporating alkoxy-substitutedtriphenylamine (tpa) donors and binary 120587-conjugated bridges were investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT) Molecular geometry electronic structure and optical absorption spectra are analyzed in the gasphase chloroform and dimethylformamide (DMF) solutions Our results show that properly choosing the heteroaromatic atomsandor adding one more alkoxy-substituted tpa group can finely adjust the molecular orbital energy The solvent effect renders theHOMO-LUMO gaps of the tpa-based sensitizers decrease in the sequence of DMF solution lt chloroform solution lt gas phaseThe absorption spectra are assigned to the ligand-to-ligand charge transfer (LLCT) characteristics via transitions mainly from tpa34-ethylenedioxythiophene (edot) and alkyl-substituted dithienosilole (dts) groups to edot dts and cyanoacrylic acid groupsThebinary 120587-conjugated bridges play different roles in balancing the electron transfer and recombination for the different tpa-basedsensitizers The protonationdeprotonation effect has great effect on the HOMO-LUMO gaps and thus has great influence on thebands at the long wavelength region but little influence on the bands at the short wavelength region

1 Introduction

Dye-sensitized solar cells (DSSCs) are currently under activeinvestigation for the solar energy utilization along with thegrowing worldwide demand for environmentally friendlyenergy sources [1ndash7] The relative high performance sim-ple fabrication process and low production costs renderDSSCs as competitive alternative to conventional silicondevices Usually DSSCs are fabricated by sensitizers (dyes)photoanodes (mesoporous TiO

2films) counterelectrodes

and electrolyteshole transporters So far polypyridyl Ru(II)-based complexes are proven to be the most efficient sensitiz-ers employed in DSSCs [8ndash11] such as the tetraprotonatedRu(441015840-dicarboxy-221015840-bipyridine)

2(NCS)

2complex (coded

asN3) [8] and its doubly protonated analog (coded asN719)

[10] Although highly efficient with a high efficiency over121 [12] Ru-based prototypes are facing the problem ofcostly synthesis and undesired environmental issues Metal-free organic sensitizers which are in good agreement withthe trend of the future developments of DSSCs using envi-ronmentally friendly and inexpensivematerials show severaladvantageous features relative to Ru-based complexes (1)diversity of organic molecular structures can ensure morediversity of sensitizers for DSSCs (2) high molar extinctioncoefficients of organic sensitizers can render the use ofthinner semiconductor to promote charge separation (3)more flexibility of organic sensitizers can be beneficial forconstructing semitransparent andor multicolor solar cellsAt present the highest photon-to-electron energy conversion

Hindawi Publishing CorporationInternational Journal of PhotoenergyVolume 2014 Article ID 280196 9 pageshttpdxdoiorg1011552014280196

2 International Journal of Photoenergy

efficiency has exceeded 13 for DSSCs using organic sensi-tizer [13]

From a theoretical point of view a few criteria shouldbe fulfilled for the design of ideal organic sensitizers (1)the molecular orientation should facilitate intramolecularcharge transfer and spatial separation should maintain thephotooxidized donor at a distance from the photoinjectedelectrons diminishing the impact of back electron transferprocesses (2) the energy level of LUMO should be sufficientlyhigh for efficient electron injection into the TiO

2 whereas the

energy level of HOMO should be sufficiently low for efficientregeneration of the oxidized state (3) the absorption bandshould extend from the whole visible region to near infraredrange with strong absorption strength (4) the stability shouldbe good enough for about 108 turnover cycles of exposureto nature [14 15] Based on these requirements the organicsensitizers are usually designed to be of electron donor-conjugated bridge-electron acceptor structure called D-120587-Aarchitecture with TiO

2surface anchoring groups integrated

into the acceptor moiety Arylamines and alkylamines dueto strong electron donating abilities as well as efficientintramolecular charge transfer characteristics are usuallyused as electron donors in the D-120587-A organic sensitizers[16ndash23] Among them DSSC using this metal-free organicsensitizer incorporating the lipophilic triphenylamine aselectron donor and the hydrophilic cyanoacrylic acid aselectron acceptor (coded as C219) has achieved an efficiencyover 10 [24]

However a detailed atomistic characterization of thissensitizer is still not clear enough Such an atomistic char-acterization can not only provide information that comple-ments the experimental work but also help to understand thestructural and the electronic properties for design of novelsensitizers with improved performances [25ndash28] In thiswork we present a theoretical characterization of C219 andits derivatives 1ndash5 Molecular geometry electronic structureand spectral property of the sensitizers are investigated inthe gas phase chloroform and dimethylformamide (DMF)solutions by means of the density functional theory (DFT)and time-dependent DFT (TD-DFT) calculations

2 Computational Methods

All calculations on the tpa-based sensitizers were performedwith DFT and TD-DFT in the Gaussian 09 program package[29] The B3LYP exchange correlation functional in con-junction with the 6-31G(d) basis set which has alreadybeen proved to be an optimal compromise between accuracyand computational cost for such large aromatic molecules[30] was employed in the geometrical optimizations withoutany symmetry constraints for the sensitizers consideredin both gas phase and solutions The solvent effects wereevaluated using the nonequilibrium [31] implementation ofthe conductor-like polarizable continuum model (C-PCM)[32ndash34] This approach provides results very close to thoseobtained by the original dielectric model for high dielectricconstant solvents but is significantly more effective in geom-etry optimizations and less prone to the numerical errors

arising from the small part of the solute electron cloud lyingoutside the cavity [34] TD-DFT calculations were used toinvestigate the optical properties of the sensitizers using theapproximation of 119864

0-0 with the lowest vertical excitationenergy of the system at the ground state geometry whichcan be accurately and efficiently calculated by TD-DFT [35]The 50 lowest spin-allowed singlet-singlet transitions up toan energy of at least sim40 eV were taken into account in thecalculations of the adsorption spectra

3 Results and Discussion

In the following sections we start with the geometricaldescription of C219 and its derivatives followed by thediscussion of electronic structures and molecular orbitalenergy levels and then the analysis of absorption spectrain the real environment of chloroform and DMF solutionsand finally the comparison of the relative light-harvestingefficiency (RLHE) of the tpa-based sensitizers

31 Geometrical Considerations The chemical structures ofC219 and its derivatives 1ndash5 are shown in Figure 1 C219 iscomposed of three parts (1) an alkoxy-substituted tripheny-lamine (tpa) as donor (2) a cyanoacrylic acid as acceptorand anchoring group and (3) a binary 120587-conjugated unitconsisting of 34-ethylenedioxythiophene (edot) and alkyl-substituted dithienosilole (dts) as bridge [24] For compu-tational convenience the C

6H13

+ and C8H17

+ groups of theexperimental C219 sensitizer are replaced by methyl groupsmarked with blue dash-lined ellipses and red dash-linedcircles as shown in Figure 1 Considering that the electrontransfermainly takes place via the high120587-electron conjugatedtpa center to acceptor andor bridge centers the end-onsubstitutions of the C

6H13

+ and C8H17

+ groups by methylgroups have slight influence on the spectral properties of theC219 sensitizer

In fact these substitutions are checked in order not toresult in appreciable changes in the electronic structures aswell as the absorption spectra The S atoms in the conjugatedbridge of the prototype molecule C219 are substituted by thesame electron-rich heteroaromatic O and Se atoms in sen-sitizers 1 and 2 For sensitizers 3 4 and 5 one more alkoxy-substituted tpa group is added to substitute the ethylenedioxygroup in 1 C219 and 2 This structural design is basedon two considerations (1) the heteroaromatic atoms mayadjust the molecular orbital energies appropriately and (2)onemore alkoxy-substituted tpa groupmay not only enhancethe electron-donating ability but also effectively inhibit I

3

minus

from approaching the surface of TiO2by forming a denser

layer at the surface In addition Na+ is used to substitutefor H+ on cyanoacrylic acid groups in order to evaluate theprotonationdeprotonation effect that is 11015840C2191015840 21015840 31015840 41015840and 51015840 as shown in Figure 1

According to the experimental setup of C219 the solventsfor calculations are chloroform (relative dielectric constantEPS = 471) and DMF (EPS = 3722) The spectra recorded indifferent solvents are available thus rendering it conceivableto investigate the solvent effects For all the ground state

International Journal of Photoenergy 3

OO

N

O

O

S iN

O

N

O

OS iN

ON

O

O

C219 R1 = S R2 = H

1 R1 = O R2 = H

2 R1 = Se R2 = H

C219998400 R1 = S R2 = Na

R1 = O R2 = Na

R1 = Se R2 = Na

3 R1

R1

R1

R1R1

R1

R1

= O R2 = H

4 R1 = S R2 = H

5 R1 = Se R2 = H

R1 = O R2 = Na

R1 = S R2 = Na

R1 = Se R2 = Na

R2O

R2O

1998400

2998400

3998400

4998400

5998400

Figure 1 Schematic structures of the tpa-based sensitizersTheC6H13

+ and C8H17

+ groups in the tpa-based sensitizers are replaced bymethylgroups marked with blue dash-lined ellipses and red dash-lined circles

geometries our results show that different solvents have nonoticeable impact because of the difference of the solventpolarity

32 The Frontier Orbitals and Energy Levels The electronicexcitation occurs mainly from the highest occupied molec-ular orbitals (HOMOs) to the lowest unoccupied molecularorbitals (LUMOs) and usually the HOMOs localize on thedonor subunit and LUMOs on the acceptor subunit Theelectronic structure analysis is thus essential to evaluatewhether the molecular orbital contributions facilitate theefficient charge separation or not Considering the similarityof their geometriesC219 andC2191015840 are chosen to exhibit thefrontier molecular orbitals for 1 C219 2 and 11015840 C2191015840 21015840 4and 41015840 are used to show the frontier molecular orbitals for 3ndash5 and 31015840ndash51015840 respectively Figure 2 shows the selected frontiermolecular orbitals of C219 C2191015840 4 and 41015840 calculated at theB3LYP6-31G(d) level in chloroform solution The first sixfrontier molecular orbital energies and the HOMO-LUMOgaps are depicted in Figure 3

It is clear seen from Figure 2 that the first three HOMOs(HOMO HOMO-1 and HOMO-2) of C219 are mainlycomposed of the 120587 combinations of C and N on tpa edotand dts groups Particularly for the HOMO considerablecontribution is from the tpa ligand This point is confirmedas one more tpa ligand is introduced in 4 in which the firsttwo HOMOs show almost entirely tpa-based characteristics

The bridge involved or not in the HOMOs would be of greatdifference for the electron transfer If the binary bridge ofedot and dts is involved in the HOMOs it would facilitatethe direct transfer of electron from the donor to the acceptorsubunit but it is also easy to occur recombinations for thetransferred electrons Otherwise it would prevent electronrecombination effectively but is not beneficial for the electrontransfer The key point for the binary bridge is that spatialseparation should balance the photooxidized donor at adistance from the photoinjected electrons diminishing theimpact of back electron transfer processes [24 36ndash39] Inthis sense the binary bridge of edot and dts in C219 playsa more positive role in promoting electron transfer but amore negative role in diminishing back electron transferthan that in 4 [24] That is the binary 120587-conjugated bridgesplay different roles in balancing the electron transfer andrecombination for the different tpa-based sensitizers

The first three LUMOs of C219 are delocalized throughthe edot dts and cyanoacrylic acid groups as shown inFigure 2 Sizeable contributions are from the cyanoacrylicacid group which would facilitate the excited electronsinjection into the semiconductors directly The 120587lowast orbitalsfrom tpa ligand are almost not involved in the LUMOs Con-sidering that the LUMOs also include the spatial separationit would be favorable for the electron recombination if thebinary bridge of edot and dts is involved in the HOMOsThat is 4 and 41015840 are much better than C219 and C2191015840 for


C219

C219998400

4

LUMO +2 LUMO +1 LUMO HOMO

4998400

HOMO-1 HOMO-2

Figure 2 The frontier molecular orbitals of sensitizers C219 C2191015840 4 and 41015840 Isodensity contour = 002

diminishing the impact of back electron transfer Seen fromFigure 2 substitutions of Na+ for H+ (C219 4 rarr C2191015840 41015840)on cyanoacrylic acid groups havemore effects on the LUMOsthan the HOMOs as mirrored by the alterations of the Na+-associated cyanoacrylic acid orbital shapes Substitutions ofO and Se for S atom on the bridge alter the energy levels ofthe frontier molecular orbitals obviously The energy levelsof both HOMO and LUMO in the same framework are inthe sequence of 5 lt 4 lt 3 and 2 lt C219 lt 1 in the gasphase and solutions as shown in Figure 3 This is due to theelectron donating ability of the heteroatom involved Se gt Sgt O which stabilizes the complexes by lowering their energylevels Similar trend appears for the Na+-substituted analogs

As seen from Figure 3 the HOMO-LUMO gaps of thetpa-based sensitizers decrease in the sequence of DMFsolution lt chloroform solution lt gas phase For instancethe HOMO-LUMO gaps of C219 are 192 197 and 209 eVobtained inDMF chloroform and the gas phase respectivelyThis trend is due to the interactions of the sensitizers andthe surroundings with different relative dielectric constantAs the relative dielectric constant increases that is gas phase(EPS = 000) lt chloroform solution (EPS = 471) lt DMFsolution (EPS = 3722) the interaction between the tpa-based sensitizers and the surroundings increases and thusintramolecular interactions become weak and their energylevels increase [40 41] The tpa-based sensitizers are lessinsensitive to the change of solvent as mirrored by a 005 eVshift when going from chloroform solution to DMF solutionwhile more sensitive to the change when going from thegas phase to the solutions Besides substitutions of Na+for H+ on cyanoacrylic acid groups have great effect on

the HOMO-LUMO gaps As shown in Figure 3 the valuesincrease by 028 and 031 eV when going from C219 and 4 toC2191015840 and 41015840 respectively This is ascribed to the fact thatthese substitutions destabilize the LUMOs greater than theHOMOs and thus enlarge the HOMO-LUMO gaps in goodconsistencywith the alteration trend of the frontiermolecularorbital distributions

33 Electronic Excitations and Absorption Spectra Theabsorption spectra of the tpa-based sensitizers are shown inFigure 4 in which H+- and Na+-contained sensitizers aredepicted in Figures 4(a) and 4(b) respectively Overall theband line shapes obtained in the gas phase and solutions agreewell with each other but the spectra obtained in solutionsare shifted toward the long wavelength region with respectto those obtained in the gas phase [42 43] Comparison ofthe results gained in two solutions shows that the spectra inDMF solution are slightly red-shifted with respect to thosein chloroform solution This trend is in good agreementwith the sequence of the HOMO-LUMO gaps obtained intwo solutions As for the protonationdeprotonation effectsubstitutions of Na+ for H+ render the spectra toward theshort wavelength region as shown in Figures 4(a) and 4(b)This trend agrees well with the enlarged HOMO-LUMOgaps of tpa-based sensitizers caused by these substitutions Inview of the real environment of DSSCs and the experimentalsetups the results obtained in chloroform solution are usedfor the discussion of spectral properties as follows Table 1 liststhe selected excitation energies (119864 nm) oscillator strength(119891) and relative orbital contributions to the optical transi-tions between 350 and 800 nm of the absorption spectra inchloroform solution


E (e

V)

DMF solutionChloroform solutionGas phase

4321 C219 5 4321 C219 5 4321 C219 5

182184190 187189195 198200206 188192204 201205215 192197209

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

(a)

211215225 218223233 232236236 213218229 231236246 220225237


E (e

V)

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

1998400 C219998400 2998400 3998400 4998400 5998400 1998400 C219998400 2998400 3998400 4998400 5998400 1998400 C219998400 2998400 3998400 4998400 5998400

(b)

Figure 3 Energy levels and HOMO-LUMO gaps of the tpa-based sensitizers

For C219 in chloroform solution four separated absorp-tion bands are found to center at sim360 sim439 sim529 and sim714 nm At sim360 nm the band is composed of two peaks at3564 and 3633 nm originated from the starting orbitals ofthe HOMOHOMO-1 combinations to the arriving orbitalsof LUMO+1LUMO+2 (see Table 1) Frontier orbital analysisshows that this band has the interligand and intraligandligand-to-ligand charge transfer (LLCT) characteristics thatis transitions occur from tpa edot and dts groups toedot dts and cyanoacrylic acid groups Similarly the bandsat sim439 sim529 and sim714 nm also show interligand LLCTcharacteristics It is quite different from the metal-centeredcomplexes in previous investigations [25ndash28] in which spec-tra at the short wavelengths of the visible region showmainlythe LLCT characteristic while those at the long wavelengthsof the visible region show mixed characteristics of metal-to-ligand charge transfer (MLCT) and LLCT For C219 there isan increasing trend of oscillator strength (which is regardedas the measure of the intensity of the absorption peaks [3744]) along with the shift of the absorption band towardthe long wavelength region that is the stronger oscillator

strength appears in the band at the longer wavelength regionThe lowest vertical excitation for C219 occurs at 7131 nmwith the oscillator strength of 1281 originated from the 100HOMO rarr LUMO transition This transition occurs fromtpa edot and dts groups to edot dts and cyanoacrylic acidgroups a mixed LLCT characteristic Similar spectra andelectronic excitation trends also appear for the O- and Se-substituted sensitizers 1 and 2 as shown in Figure 4(a)

The spectra tend to shift toward the short wavelengthregionwhen substitutingNa+ forH+ as shown in Figure 4(b)For C2191015840 in chloroform solution four separated absorp-tion bands are found to center at sim350 sim424 sim488 andsim630 nm Compared with the corresponding bands of C219the substitution of Na+ for H+ has little effect on the bandsat the short wavelength region (sim360 and sim439 nm versussim350 and sim424 nm) but has great effect on the bands atthe long wavelength region (sim529 and sim714 nm versus sim488and sim630 nm) However the increasing trend of oscillatorstrength in 11015840 C2191015840 and 21015840 is still the same as thatin C219 along with the absorption band toward the long


400 500 600 700 800

0

4

8

12

16

DMF solution

Chloroform solution

Gas phaseIn

tens

ity (a

u)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

C21912

345

Wavelength (nm)

(a)

400 500 600 700 800

0

4

8

12

16

DMF solution

Chloroform solution

Gas phase

Inte

nsity

(au

)400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

Wavelength (nm)

1998400

C219998400

2998400

3998400

4998400

5998400

(b)

Figure 4 Simulated absorption spectra of H+- (a) and Na+- (b) contained tpa-based sensitizers

wavelength region The lowest vertical excitation for C2191015840occurs at 6300 nm with the stronger oscillator strength of1456 than the corresponding value of C219 In the energyrange investigated the band calculated at sim630 nm for C2191015840is in good agreement with the experimental result of 584 nmmore consistent than C219 at sim714 nm [24] This means thespectra of the tpa-based organic sensitizers as well as theenergy levels and the HOMO-LUMO gaps are sensitive tothe protonationdeprotonation effect

The introduction of one more alkoxy-substituted tpagroup alters the spectra significantly as shown in Figure 4For 4 in chloroform solution the oscillator strength ofbands becomes weaker at the long wavelength region of600ndash800 nm while stronger at middle wavelength regionof 500ndash600 nm than the corresponding values of C219

With respect to oscillator strength it will be affected bythe electron-donating capability from 120587-conjugation andheteroaromatic groups in sensitizers [27 44 45] Similartrends occur for the O- and Se-substituted sensitizers 3 5and their Na+-substituted sensitizers 31015840 41015840 and 51015840 For 4 atsim532 nm the band results from the 98HOMO-2 rarr LUMOtransition with the oscillator strength of 0967 (see Table 1)This transition shows the interligand and intraligand LLCTcharacteristic from tpa edot dts and even cyanoacrylic acidgroups to edot dts and cyanoacrylic acid groups The lowestvertical excitation for 4 occurs at 7543 nm with the oscillatorstrength of 0487 originated from the 100 HOMO rarrLUMO transition Obviously this transition has interligandLLCTcharacteristic that is transition occurs fromdouble tpagroups to edot dts and cyanoacrylic acid groups


Table 1 Selected excitation energies (119864 nm) oscillator strength (119891) and relative orbital contributions to the optical transitions between 350and 800 nm of the absorption spectra of tpa-based sensitizers in chloroform solutiona

119864 119891 Composition 119864 119891 CompositionC219 C2191015840

7131 1281 H minus 0 rarr L + 0 (100) 6300 1456 H minus 0 rarr L + 0 (99)5304 0616 H minus 1 rarr L + 0 (97) 4874 0409 H minus 1 rarr L + 0 (97)4385 0281 H minus 0 rarr L + 1 (88) 4230 0292 H minus 0 rarr L + 1 (91)

3873 0023 H minus 3 rarr L + 0 (72)H minus 1 rarr L + 1 (14) 3545 0085 H minus 0 rarr L + 2 (67)

H minus 1 rarr L + 1 (24)3633 0212 H minus 0 rarr L + 2 (86) 3505 0023 H minus 0 rarr L + 3 (90)3564 0152 H minus 1 rarr L + 1 (68)

4 41015840

7543 0487 H minus 0 rarr L + 0 (100) 6351 0699 H minus 0 rarr L + 0 (99)6582 0286 H minus 1 rarr L + 0 (99) 5597 0314 H minus 1 rarr L + 0 (98)5323 0967 H minus 2 rarr L + 0 (98) 4905 0713 H minus 2 rarr L + 0 (97)4505 0137 H minus 0 rarr L + 1 (94) 4295 0201 H minus 0 rarr L + 1 (93)





3522 0029 H minus 0 rarr L + 3 (88)3491 0201 H minus 1 rarr L + 2 (90)aOnly oscillator strength 119891 gt 002 and orbital percentage gt 10 are reported where H = HOMO and L = LUMO

Table 2TheHOMO and LUMO energies HOMO-LUMO gaps lowest vertical excitation energies (119864119860) oscillator strengths (119891) and relative

LHE (RLHE) for all sensitizersa

Solutions Sensitizers LUMO HOMO HOMO-LUMO 119864119860

119891 RLHE

Chloroform

1 minus251 minus456 205 182 1150 0980C219 minus270 minus467 197 174 1281 10002 minus273 minus465 192 170 1435 10163 minus256 minus456 200 176 0614 11234 minus276 minus465 189 165 0487 10005 minus281 minus464 184 160 0524 1040

DMF


aAll energies are in eV

34 Light-Harvesting Efficiency (LHE) Light-harvesting effi-ciency (LHE) as a good indicator of the incident photon-to-electron conversion efficiency (IPCE) characterizes the abil-ity of dyes in harvesting lightThe LHE can be approximatelyexpressed as [46]

LHE = 1 minus 10minus119860 = 1 minus 10minus119891 (1)

where 119860(119891) is the absorption (oscillator strength) of the dyeassociated with the 120582max that is the lowest vertical excitationenergy (119864A) Table 2 lists the HOMO and LUMO energiesHOMO-LUMOgaps lowest vertical excitation energies (119864

119860)

oscillator strengths (119891) and relative LHE (RLHE) of allsensitizers calculated in chloroform and DMF solutionsAccording to the structural and spectral properties therelative LHE (RLHE) is evaluated by comparing sensitizers


1 C219 and 2 with C219 sensitizers 3 4 and 5 with 4 Theinfluence of solutions on LHE is negligible due to the littledifference in 119864A and119891 for sensitizers in different solutions asshown in Table 2 For 1 C219 and 2 in chloroform solution2 owns the highest RLHE of 1016 followed by C219 with1000 and 1 of 0980 This trend is in good agreement withthe sequence of electron donating ability of heteroatomsinvolved Se gt S gt O For 3 4 and 5 in chloroform solution3 shows the highest RLHE of 1123 followed by 5 of 1040and 4 of 1000This indicates that the adjustment on the LHEvia the heteroatoms would not be of much help after greatlyenhancing the electron-donating group such as another tpadonor involved

4 Conclusions

In this work we have presented a theoretical investigation onorganic sensitizers incorporating alkoxy-substituted triph-enylamine donors and binary 120587-conjugated bridges basedon DFTTD-DFT calculations in the gas phase chloroformand DMF solutions Our results show that properly choosingthe heteroaromatic atoms and adding one more alkoxy-substituted tpa group can finely adjust the molecular orbitalenergies Frontier orbital analysis shows that the three highestHOMOs are mainly composed of the 120587 combinations on tpaedot and dts groups for C219-like sensitizers but only tpagroup for 4-like analogs The three LUMOs are delocalizedthrough the edot dts and cyanoacrylic acid groups for alltpa-based sensitizers The HOMO-LUMO gaps of the tpa-based sensitizers decrease in the sequence of DMF solutionlt chloroform solution lt gas phase according well to theincrease of relative dielectric constant of gas phase lt chlo-roform solution lt DMF solution The spectra are assigned tothe LLCT characteristics which are originated mainly fromtransitions of tpa edot and dts groups to edot dts andcyanoacrylic acid groups The binary 120587-conjugated bridgeplays a dual role in balancing the electron transfer andrecombination for C219-like sensitizers but an active rolein diminishing the impact of back electron transfer for 4-like analogs The protonationdeprotonation effect enlargesthe HOMO-LUMO gaps and thus has great influence on thebands at the long wavelength region but little influence onthe bands at the short wavelength region

Conflict of Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

This work was supported by NSFC (21303266) ShandongProvinceNatural Science Foundation (ZR2011EMZ002) Pro-motive Research Fund for Excellent Young andMiddle-AgedScientists of Shandong Province (BS2013CL031) PetroChinaInnovation Foundation (2013D-5006-0406) and the Fun-damental Research Funds for the Central Universities(13CX05004A 13CX05020A and 13CX02025A)

References

[1] B ORegan and M Gratzel ldquoA low-cost high-efficiency solarcell based on dye-sensitized colloidal TiO

2filmsrdquo Nature vol

353 no 6346 pp 737ndash740 1991[2] AHagfeldt andMGratzel ldquoMolecular photovoltaicsrdquoAccounts

of Chemical Research vol 33 no 5 pp 269ndash277 2000[3] M Gratzel ldquoPhotoelectrochemical cellsrdquo Nature vol 414 no

6861 pp 338ndash344 2001[4] M Gratzel ldquoDye-sensitized solar cellsrdquo Journal of Photochem-

istry and Photobiology C Photochemistry Reviews vol 4 no 2pp 145ndash153 2003

[5] M Gratzel ldquoApplied physics solar cells to dye forrdquo Nature vol421 no 6923 pp 586ndash587 2003

[6] M Gratzel ldquoSolar energy conversion by dye-sensitized photo-voltaic cellsrdquo Inorganic Chemistry vol 44 no 20 pp 6841ndash68512005

[7] L M Goncalves V de Zea Bermudez H A Ribeiro and A MMendes ldquoDye-sensitized solar cells a safe bet for the futurerdquoEnergy amp Environmental Science vol 1 no 6 pp 655ndash667 2008

[8] M K Nazeeruddin A Kay I Rodicio et al ldquoConver-sion of light to electricity by cis-X

2bis(221015840-bipyridyl-441015840-

dicarboxylate)ruthenium(II) charge-transfer sensitizers (X =Cl- Br- I- CN- and SCN-) on nanocrystalline TiO

2elec-

trodesrdquo Journal of the American Chemical Society vol 115 no14 pp 6382ndash6390 1993

[9] P Wang S M Zakeeruddin J E Moser et al ldquoStable newsensitizer with improved light harvesting for nanocrystallinedye-sensitized solar cellsrdquo Advanced Materials vol 16 no 20pp 1806ndash1811 2004

[10] M K Nazeeruddin F de Angelis S Fantacci et al ldquoCom-bined experimental and DFT-TDDFT computational study ofphotoelectrochemical cell ruthenium sensitizersrdquo Journal of theAmerican Chemical Society vol 127 no 48 pp 16835ndash168472005

[11] Y Chiba A Islam Y Watanabe R Komiya N Koide and LHan ldquoDye-sensitized solar cells with conversion efficiency of111rdquo Japanese Journal of Applied Physics vol 45 no 25 pp638ndash640 2006

[12] Q J Yu Y H Wang Z H Yi et al ldquoHigh-efficiency dye-sensitized solar cells the influence of lithium ions on excitondissociation charge recombination and surface statesrdquo ACSNano vol 4 no 10 pp 6032ndash6038 2010

[13] SMathew A Yella P Gao et al ldquoDye-sensitized solar cells with13 efficiency achieved through the molecular engineering ofporphyrin sensitizersrdquo Nature Chemistry vol 6 no 3 pp 242ndash247 2014

[14] M Gratzel ldquoConversion of sunlight to electric power bynanocrystalline dye-sensitized solar cellsrdquo Journal of Photo-chemistry and Photobiology A Chemistry vol 164 no 1ndash3 pp3ndash14 2004

[15] N Robertson ldquoOptimizing dyes for dye-sensitized solar cellsrdquoAngewandte ChemiemdashInternational Edition vol 45 no 15 pp2338ndash2345 2006

[16] T Horiuchi H Miura K Sumioka and S Uchida ldquoHighefficiency of dye-sensitized solar cells based on metal-freeindoline dyesrdquo Journal of the American Chemical Society vol126 no 39 pp 12218ndash12219 2004

[17] K Hara T Sato R Katoh et al ldquoNovel conjugated organic dyesfor efficient dye-sensitized solar cellsrdquo Advanced FunctionalMaterials vol 15 no 2 pp 246ndash252 2005


[18] D P Hagberg T Edvinsson T Marinado G Boschloo AHagfeldt and L Sun ldquoA novel organic chromophore for dye-sensitized nanostructured solar cellsrdquo Chemical Communica-tions no 21 pp 2245ndash2247 2006

[19] N Koumura Z-S Wang S Mori M Miyashita E Suzukiand K Hara ldquoAlkyl-functionalized organic dyes for efficientmolecular photovoltaicsrdquo Journal of the American ChemicalSociety vol 128 no 44 pp 14256ndash14257 2006

[20] S Kim J K Lee S O Kang et al ldquoMolecular engineeringof organic sensitizers for solar cell applicationsrdquo Journal of theAmerican Chemical Society vol 128 no 51 pp 16701ndash167072006

[21] H Choi J K Lee K Song S O Kang and J KoldquoNovel organic dyes containing bis-dimethylfluorenyl aminobenzo[b]thiophene for highly efficient dye-sensitized solar cellrdquoTetrahedron vol 63 no 15 pp 3115ndash3121 2007

[22] Z J Ning and H Tian ldquoTriarylamine a promising core unit forefficient photovoltaicmaterialsrdquoChemical Communications no37 pp 5483ndash5495 2009

[23] Z JNingQ ZhangHC Pei et al ldquoPhotovoltage improvementfor dye-sensitized solar cells via cone-shaped structural designrdquoThe Journal of Physical Chemistry C vol 113 no 23 pp 10307ndash10313 2009

[24] W D Zeng Y M Cao Y Bai et al ldquoEfficient dye-sensitizedsolar cells with an organic photosensitizer featuring orderlyconjugated ethylenedioxythiophene and dithienosilole blocksrdquoChemistry of Materials vol 22 no 5 pp 1915ndash1925 2010

[25] X Q Lu S X Wei C-M Lawrence Wu W Y Guo andL M Zhao ldquoTheoretical characterization of ruthenium com-plexes containing functionalized bithiophene ligands for dye-sensitized solar cellsrdquo Journal of Organometallic Chemistry vol696 no 8 pp 1632ndash1639 2011

[26] X Q Lu C-M Lawrence Wu S X Wei and W Y GuoldquoDFTTD-DFT investigation of electronic structures and spec-tra properties of Cu-based dye sensitizersrdquo The Journal ofPhysical Chemistry A vol 114 no 2 pp 1178ndash1184 2010

[27] X Q Lu S XWei C-M LawrenceWu S R Li andW Y GuoldquoCan polypyridyl Cu(I)-based complexes provide promisingsensitizers for dye-sensitized solar cells A theoretical insightinto Cu(I) versus Ru(II) sensitizersrdquo The Journal of PhysicalChemistry C vol 115 no 9 pp 3753ndash3761 2011

[28] X Q Lu S X Wei C-M Lawrence Wu et al ldquoTheoreticalinsight into the spectral characteristics of Fe(II)-based com-plexes for dye-sensitized solar cells-Part I Polypyridyl ancillaryligandsrdquo International Journal of Photoenergy vol 2011 ArticleID 316952 11 pages 2011

[29] M J Frisch G W Trucks H B Schlegel et al Gaussian 09Revision A1 Gaussian Wallingford Conn USA 2009

[30] C Angeli M Pastore and R Cimiraglia ldquoNew perspectives inmultireference perturbation theory the n-electron valence stateapproachrdquo Theoretical Chemistry Accounts vol 117 no 5-6 pp743ndash754 2007

[31] M Cossi and V Barone ldquoTime-dependent density functionaltheory for molecules in liquid solutionsrdquoThe Journal of Chemi-cal Physics vol 115 no 10 pp 4708ndash4717 2001

[32] S Mierts E Scrocco and J Tomasi ldquoElectrostatic interactionof a solute with a continuum A direct utilizaion of ABinitio molecular potentials for the prevision of solvent effectsrdquoChemical Physics vol 55 no 1 pp 117ndash129 1981

[33] M Cossi V Barone R Cammi and J Tomasi ldquoAb initio studyof solvated molecules a new implementation of the polarizable

continuum modelrdquo Chemical Physics Letters vol 255 no 4ndash6pp 327ndash335 1996

[34] V Barone and M Cossi ldquoQuantum calculation of molecularenergies and energy gradients in solution by a conductor solventmodelrdquoThe Journal of Physical Chemistry A vol 102 no 11 pp1995ndash2001 1998

[35] F D Angelis S Fantacci and A Selloni ldquoAlignment of the dyesmolecular levels with the TiO

2band edges in dye-sensitized

solar cells a DFT-TDDFT studyrdquo Nanotechnology vol 19 no42 Article ID 424002 2008

[36] J Feng Y Jiao W Ma M K Nazeeruddin M Gratzel and SMeng ldquoFirst principles design of dye molecules with ullazinedonor for dye sensitized solar cellsrdquo The Journal of PhysicalChemistry C vol 117 no 8 pp 3772ndash3778 2013

[37] W J Fan D Z Tan and W-Q Deng ldquoAcene-modified triph-enylamine dyes for dye-sensitized solar cells a computationalstudyrdquo ChemPhysChem vol 13 no 8 pp 2051ndash2060 2012

[38] K P Guo K Y Yan X Q Lu et al ldquoDithiafulvenyl unit as a newdonor for high-efficiency dye-sensitized solar cells synthesisand demonstration of a family ofmetal-free organic sensitizersrdquoOrganic Letters vol 14 no 9 pp 2214ndash2217 2012

[39] G L Zhang H Bala Y M Cheng et al ldquoHigh efficiency andstable dye-sensitized solar cells with an organic chromophorefeaturing a binary 120587-conjugated spacerrdquo Chemical Communica-tions no 16 pp 2198ndash2200 2009

[40] M Pastore E Mosconi F de Angelis and M Gratzel ldquoAcomputational investigation of organic dyes for dye-sensitizedsolar cells benchmark strategies and open issuesrdquoThe Journalof Physical Chemistry C vol 114 no 15 pp 7205ndash7212 2010

[41] J Preat C Michaux D Jacquemin and E A PerpeteldquoEnhanced efficiency of organic dye-sensitized solar cells triph-enylamine derivativesrdquoThe Journal of Physical Chemistry C vol113 no 38 pp 16821ndash16833 2009



[44] N Santhanamoorthi C-M Lo and J-C Jiang ldquoMolecu-lar design of porphyrins for dye-sensitized solar cells aDFTTDDFT studyrdquo The Journal of Physical Chemistry Lettersvol 4 no 3 pp 524ndash530 2013

[45] C-Y Chen M Wang J-Y Li et al ldquoHighly efficient light-harvesting ruthenium sensitizer for thin-film dye-sensitizedsolar cellsrdquo ACS Nano vol 3 no 10 pp 3103ndash3109 2009

[46] H S Nalwa Handbook of Advanced Electronic and PhotonicMaterials and Devices Conducting Polymers Academic PressSan Diego Calif USA 2001

Submit your manuscripts athttpwwwhindawicom

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Inorganic ChemistryInternational Journal of

Hindawi Publishing Corporation httpwwwhindawicom Volume 2014

International Journal ofPhotoenergy


Carbohydrate Chemistry

International Journal of


Journal of

Chemistry


Advances in

Physical Chemistry

Hindawi Publishing Corporationhttpwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2014

Bioinorganic Chemistry and ApplicationsHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

SpectroscopyInternational Journal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Medicinal ChemistryInternational Journal of


Chromatography Research International


Applied ChemistryJournal of



Theoretical ChemistryJournal of


Journal of

Spectroscopy

Analytical ChemistryInternational Journal of


Journal of


Quantum Chemistry


Organic Chemistry International

ElectrochemistryInternational Journal of



CatalystsJournal of


efficiency has exceeded 13 for DSSCs using organic sensi-tizer [13]

From a theoretical point of view a few criteria shouldbe fulfilled for the design of ideal organic sensitizers (1)the molecular orientation should facilitate intramolecularcharge transfer and spatial separation should maintain thephotooxidized donor at a distance from the photoinjectedelectrons diminishing the impact of back electron transferprocesses (2) the energy level of LUMO should be sufficientlyhigh for efficient electron injection into the TiO

2 whereas the

energy level of HOMO should be sufficiently low for efficientregeneration of the oxidized state (3) the absorption bandshould extend from the whole visible region to near infraredrange with strong absorption strength (4) the stability shouldbe good enough for about 108 turnover cycles of exposureto nature [14 15] Based on these requirements the organicsensitizers are usually designed to be of electron donor-conjugated bridge-electron acceptor structure called D-120587-Aarchitecture with TiO

2surface anchoring groups integrated

into the acceptor moiety Arylamines and alkylamines dueto strong electron donating abilities as well as efficientintramolecular charge transfer characteristics are usuallyused as electron donors in the D-120587-A organic sensitizers[16ndash23] Among them DSSC using this metal-free organicsensitizer incorporating the lipophilic triphenylamine aselectron donor and the hydrophilic cyanoacrylic acid aselectron acceptor (coded as C219) has achieved an efficiencyover 10 [24]

However a detailed atomistic characterization of thissensitizer is still not clear enough Such an atomistic char-acterization can not only provide information that comple-ments the experimental work but also help to understand thestructural and the electronic properties for design of novelsensitizers with improved performances [25ndash28] In thiswork we present a theoretical characterization of C219 andits derivatives 1ndash5 Molecular geometry electronic structureand spectral property of the sensitizers are investigated inthe gas phase chloroform and dimethylformamide (DMF)solutions by means of the density functional theory (DFT)and time-dependent DFT (TD-DFT) calculations

2 Computational Methods

All calculations on the tpa-based sensitizers were performedwith DFT and TD-DFT in the Gaussian 09 program package[29] The B3LYP exchange correlation functional in con-junction with the 6-31G(d) basis set which has alreadybeen proved to be an optimal compromise between accuracyand computational cost for such large aromatic molecules[30] was employed in the geometrical optimizations withoutany symmetry constraints for the sensitizers consideredin both gas phase and solutions The solvent effects wereevaluated using the nonequilibrium [31] implementation ofthe conductor-like polarizable continuum model (C-PCM)[32ndash34] This approach provides results very close to thoseobtained by the original dielectric model for high dielectricconstant solvents but is significantly more effective in geom-etry optimizations and less prone to the numerical errors

arising from the small part of the solute electron cloud lyingoutside the cavity [34] TD-DFT calculations were used toinvestigate the optical properties of the sensitizers using theapproximation of 119864

0-0 with the lowest vertical excitationenergy of the system at the ground state geometry whichcan be accurately and efficiently calculated by TD-DFT [35]The 50 lowest spin-allowed singlet-singlet transitions up toan energy of at least sim40 eV were taken into account in thecalculations of the adsorption spectra

3 Results and Discussion

In the following sections we start with the geometricaldescription of C219 and its derivatives followed by thediscussion of electronic structures and molecular orbitalenergy levels and then the analysis of absorption spectrain the real environment of chloroform and DMF solutionsand finally the comparison of the relative light-harvestingefficiency (RLHE) of the tpa-based sensitizers

31 Geometrical Considerations The chemical structures ofC219 and its derivatives 1ndash5 are shown in Figure 1 C219 iscomposed of three parts (1) an alkoxy-substituted tripheny-lamine (tpa) as donor (2) a cyanoacrylic acid as acceptorand anchoring group and (3) a binary 120587-conjugated unitconsisting of 34-ethylenedioxythiophene (edot) and alkyl-substituted dithienosilole (dts) as bridge [24] For compu-tational convenience the C

6H13

+ and C8H17

+ groups of theexperimental C219 sensitizer are replaced by methyl groupsmarked with blue dash-lined ellipses and red dash-linedcircles as shown in Figure 1 Considering that the electrontransfermainly takes place via the high120587-electron conjugatedtpa center to acceptor andor bridge centers the end-onsubstitutions of the C

6H13

+ and C8H17

+ groups by methylgroups have slight influence on the spectral properties of theC219 sensitizer

In fact these substitutions are checked in order not toresult in appreciable changes in the electronic structures aswell as the absorption spectra The S atoms in the conjugatedbridge of the prototype molecule C219 are substituted by thesame electron-rich heteroaromatic O and Se atoms in sen-sitizers 1 and 2 For sensitizers 3 4 and 5 one more alkoxy-substituted tpa group is added to substitute the ethylenedioxygroup in 1 C219 and 2 This structural design is basedon two considerations (1) the heteroaromatic atoms mayadjust the molecular orbital energies appropriately and (2)onemore alkoxy-substituted tpa groupmay not only enhancethe electron-donating ability but also effectively inhibit I

3

minus

from approaching the surface of TiO2by forming a denser

layer at the surface In addition Na+ is used to substitutefor H+ on cyanoacrylic acid groups in order to evaluate theprotonationdeprotonation effect that is 11015840C2191015840 21015840 31015840 41015840and 51015840 as shown in Figure 1

According to the experimental setup of C219 the solventsfor calculations are chloroform (relative dielectric constantEPS = 471) and DMF (EPS = 3722) The spectra recorded indifferent solvents are available thus rendering it conceivableto investigate the solvent effects For all the ground state


OO

N

O

O

S iN

O

N

O

OS iN

ON

O

O

C219 R1 = S R2 = H

1 R1 = O R2 = H

2 R1 = Se R2 = H

C219998400 R1 = S R2 = Na

R1 = O R2 = Na

R1 = Se R2 = Na

3 R1

R1

R1

R1R1

R1

R1

= O R2 = H

4 R1 = S R2 = H

5 R1 = Se R2 = H

R1 = O R2 = Na

R1 = S R2 = Na

R1 = Se R2 = Na

R2O

R2O

1998400

2998400

3998400

4998400

5998400


+ and C8H17








C219

C219998400

4


4998400

HOMO-1 HOMO-2







E (e

V)


4321 C219 5 4321 C219 5 4321 C219 5

182184190 187189195 198200206 188192204 201205215 192197209

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

(a)

211215225 218223233 232236236 213218229 231236246 220225237


E (e

V)

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

1998400 C219998400 2998400 3998400 4998400 5998400 1998400 C219998400 2998400 3998400 4998400 5998400 1998400 C219998400 2998400 3998400 4998400 5998400

(b)






400 500 600 700 800

0

4

8

12

16

DMF solution

Chloroform solution

Gas phaseIn

tens

ity (a

u)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

C21912

345

Wavelength (nm)

(a)

400 500 600 700 800

0

4

8

12

16

DMF solution

Chloroform solution

Gas phase

Inte

nsity

(au

)400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

Wavelength (nm)

1998400

C219998400

2998400

3998400

4998400

5998400

(b)











4 41015840










119891 RLHE

Chloroform


DMF






119860)




4 Conclusions




Acknowledgments


References











2bis(221015840-bipyridyl-441015840-


2elec-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


OO

N

O

O

S iN

O

N

O

OS iN

ON

O

O

C219 R1 = S R2 = H

1 R1 = O R2 = H

2 R1 = Se R2 = H

C219998400 R1 = S R2 = Na

R1 = O R2 = Na

R1 = Se R2 = Na

3 R1

R1

R1

R1R1

R1

R1

= O R2 = H

4 R1 = S R2 = H

5 R1 = Se R2 = H

R1 = O R2 = Na

R1 = S R2 = Na

R1 = Se R2 = Na

R2O

R2O

1998400

2998400

3998400

4998400

5998400


+ and C8H17








C219

C219998400

4


4998400

HOMO-1 HOMO-2







E (e

V)


4321 C219 5 4321 C219 5 4321 C219 5

182184190 187189195 198200206 188192204 201205215 192197209

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

(a)

211215225 218223233 232236236 213218229 231236246 220225237


E (e

V)

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

1998400 C219998400 2998400 3998400 4998400 5998400 1998400 C219998400 2998400 3998400 4998400 5998400 1998400 C219998400 2998400 3998400 4998400 5998400

(b)






400 500 600 700 800

0

4

8

12

16

DMF solution

Chloroform solution

Gas phaseIn

tens

ity (a

u)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

C21912

345

Wavelength (nm)

(a)

400 500 600 700 800

0

4

8

12

16

DMF solution

Chloroform solution

Gas phase

Inte

nsity

(au

)400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

Wavelength (nm)

1998400

C219998400

2998400

3998400

4998400

5998400

(b)











4 41015840










119891 RLHE

Chloroform


DMF






119860)




4 Conclusions




Acknowledgments


References











2bis(221015840-bipyridyl-441015840-


2elec-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


C219

C219998400

4


4998400

HOMO-1 HOMO-2







E (e

V)


4321 C219 5 4321 C219 5 4321 C219 5

182184190 187189195 198200206 188192204 201205215 192197209

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

(a)

211215225 218223233 232236236 213218229 231236246 220225237


E (e

V)

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

1998400 C219998400 2998400 3998400 4998400 5998400 1998400 C219998400 2998400 3998400 4998400 5998400 1998400 C219998400 2998400 3998400 4998400 5998400

(b)






400 500 600 700 800

0

4

8

12

16

DMF solution

Chloroform solution

Gas phaseIn

tens

ity (a

u)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

C21912

345

Wavelength (nm)

(a)

400 500 600 700 800

0

4

8

12

16

DMF solution

Chloroform solution

Gas phase

Inte

nsity

(au

)400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

Wavelength (nm)

1998400

C219998400

2998400

3998400

4998400

5998400

(b)











4 41015840










119891 RLHE

Chloroform


DMF






119860)




4 Conclusions




Acknowledgments


References











2bis(221015840-bipyridyl-441015840-


2elec-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


E (e

V)


4321 C219 5 4321 C219 5 4321 C219 5

182184190 187189195 198200206 188192204 201205215 192197209

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

(a)

211215225 218223233 232236236 213218229 231236246 220225237


E (e

V)

minus7

minus6

minus5

minus4

minus3

minus2

minus1

0

1998400 C219998400 2998400 3998400 4998400 5998400 1998400 C219998400 2998400 3998400 4998400 5998400 1998400 C219998400 2998400 3998400 4998400 5998400

(b)






400 500 600 700 800

0

4

8

12

16

DMF solution

Chloroform solution

Gas phaseIn

tens

ity (a

u)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

C21912

345

Wavelength (nm)

(a)

400 500 600 700 800

0

4

8

12

16

DMF solution

Chloroform solution

Gas phase

Inte

nsity

(au

)400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

Wavelength (nm)

1998400

C219998400

2998400

3998400

4998400

5998400

(b)











4 41015840










119891 RLHE

Chloroform


DMF






119860)




4 Conclusions




Acknowledgments


References











2bis(221015840-bipyridyl-441015840-


2elec-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of


400 500 600 700 800

0

4

8

12

16

DMF solution

Chloroform solution

Gas phaseIn

tens

ity (a

u)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

C21912

345

Wavelength (nm)

(a)

400 500 600 700 800

0

4

8

12

16

DMF solution

Chloroform solution

Gas phase

Inte

nsity

(au

)400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

400 500 600 700 800

0

4

8

12

16

Inte

nsity

(au

)

Wavelength (nm)

1998400

C219998400

2998400

3998400

4998400

5998400

(b)











4 41015840










119891 RLHE

Chloroform


DMF






119860)




4 Conclusions




Acknowledgments


References











2bis(221015840-bipyridyl-441015840-


2elec-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of







4 41015840










119891 RLHE

Chloroform


DMF






119860)




4 Conclusions




Acknowledgments


References











2bis(221015840-bipyridyl-441015840-


2elec-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of



4 Conclusions




Acknowledgments


References











2bis(221015840-bipyridyl-441015840-


2elec-





















































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of











































Journal of

Chemistry


Advances in

Physical Chemistry



Journal of

Volume 2014














Journal of

Spectroscopy



Journal of


Quantum Chemistry






CatalystsJournal of

research article theoretical insight into organic dyes...

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