Review Article Theoretical Studies of Electronic Structure and ...downloads.hindawi.com/journals/jnm/2015/605728.pdf · Theoretical Studies of Electronic Structure and Photophysical

Review ArticleTheoretical Studies of Electronic Structure andPhotophysical Properties of a Series of Indoline Dyes withTriphenylamine Ligand

Xue-Feng Ren1 Jun Zhang1 and Guo-Jun Kang12

1School of Chemical Engineering amp Technology China University of Mining and Technology Xuzhou 221008 China2Low Carbon Energy Institute China University of Mining and Technology Xuzhou 221008 China

Correspondence should be addressed to Guo-Jun Kang gjkangcumteducn

Received 9 March 2015 Accepted 15 April 2015

Academic Editor Ruomeng Yu

Copyright copy 2015 Xue-Feng Ren 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

To design efficient organic sensitizer a series of D-120587-A indoline dyes with different donor parts have been investigated by densityfunctional theory (DFT) and time-dependentDFT (TD-DFT) approachThemolecular geometries frontiermolecular orbitals andabsorption spectra of these dyes have been systematically investigated to provide comprehensive understanding of the structure-property relationships Compared with D149 our designed dyes have proper HOMO and LUMO energy level narrowed HOMO-LUMO energy gap and broadened absorption band by introducing the N(CH

3)2and N(phenyl)

2groups at the donor part

Furthermore the dimeric dyes and dye-(TiO2)6systems have been optimized by DFT method to simulate the intermolecular

interactions as well as interaction between the dyes dimmers and semiconductor interface respectively Through the analysesof absorption energies (119864ads) energy levels of the HOMO and LUMO light harvesting efficiency (LHE) and the driving force ofelectrons injections (Δ119866inject) it is found that the designed dyes should have improved optical properties by importing the N(CH

3)2

group This work is hoped to provide a theoretical guiding role in design of new dyes for dye-sensitized solar cells

1 Introduction

Due to increasing energy demands and concerning globalwarming scientists have paid tremendous effort on devel-oping cheap and easily accessible renewable energy sourcesDye-sensitized solar cells (DSSCs) have been regarded asone of the most promising next-generation photovoltaic cellsdue to their potentially low fabrication costs easy produc-tion and flexibility compared to traditional silicon-basedsolar cells [1] A typical DSSC is constructed with thedye sensitizer dye-absorbed nanocrystalline semiconductoroxide (such as TiO

2or ZnO) electrolyte containing IminusI

3

minus

redox couples and closed circuit Obviously the sensitizerplays a significant role for improving the efficiency of DSSCsTherefore considerable synthetic works have been carriedout on Ru-based sensitizers [2ndash4] and metal-free organicdye sensitizers [5ndash10] Among them indoline dye sensitizers[11] have attracted much attention because of their high

molar extinction coefficient relatively less expensive and lowpollution of environmental Although the significant progresshas been made in the organic dyes the conversion efficiencyof indoline type dyes is still lower than theRu-based sensitizer[12] Therefore the investigation on the organic dye is veryimportant for realizing large-scale commercial production

Except themassive synthesized research theoretical stud-ies have been accepted as extremely powerful and comparablylow-cost tools for revealing the effect of chemical modifi-cations on the optical properties [13ndash18] In spite of out-standing electronic and optical properties of triphenylaminederivatives in solar cell [19ndash22] to our knowledge there isno detailed study on indoline-containing materials coupledwith triphenylamine as donor part Consequently in orderto reveal the role of triphenylamine on the photophysicalproperties and develop more efficient dyes the donor part ofD149 dye is replaced by triphenylamine unitThen triphenyl-amine-containing indoline dyes are designed by introducing

Hindawi Publishing CorporationJournal of NanomaterialsVolume 2015 Article ID 605728 9 pageshttpdxdoiorg1011552015605728

2 Journal of Nanomaterials

NS

O

NS

O

S

R1

R2

Donor (D)

Acceptor (A)

NN

N N ND149

Electron conductor (120587)

N1N2 C1C2

C3C4

CH2COOH

CH3 CH3

CH3

CF3

CF3

CH3D =

D3 R1= R2 =

D1 R1= R2 =

D4 R1= R2 =

D2 R1= R2 =

Figure 1 Sketch map of the studied dyes

the N(CH3)2 N(phenyl)

2 and CF

3at the donor part of D149

in this work (see Figure 1) A systematic comparison andanalysis of the geometries frontier molecular orbitals andabsorption spectra of these dyes are carried out Furthermorethe light harvesting efficiency (LHE) and the driving forceof electrons injections (Δ119866inject) are calculated to estimatethe short-circuit photocurrent density In addition the elec-tron coupling of dimeric dyes and dye-(TiO

2)6systems is

simulated by DFT method to testify the electron injectionefficiency This work is expected to reveal the effect ofchemical modification on the DSSCs efficiency and providevaluable guidance for developing efficiency dyes

2 Computational Details

All calculations were performed with the Gaussian 09 pro-gram package [23] The density functional theory DFT(B3LYP) approach had been successfully used to calculatethe ground geometries in indoline dye sensitizers [13ndash15 24]Therefore in this work the geometries structures of mon-omer and dimer dyes were fully optimized at the DFT level ofB3LYP method [25 26] using the 6-31G(d) basis set Follow-ing the optimized geometry the vibrational frequencies werecalculated and the results confirmed that all the optimizedmonomer geometries were stable geometric structures Theabsorption spectra of these dyes were investigated by TDDFTwith the B3LYP approach associated with the polarizedcontinuum model (PCM) [27 28] in methanol media

To investigate the electronic coupling interaction betweenthese dyes andTiO

2nanoparticles the absorption geometries

of dyes(TiO2)6clusters were calculated by B3LYP method

The 6-31G(d) basis sets were used for C H O N S andF atoms and LANL2DZ for Ti atom Although (TiO

2)6

cluster is a simplistic model it was believed to qualitatively

reproduce the trend of the charge distribution [29] Theabsorption energies (119864ads) of dyes(TiO2)6 were calculated bythe following equation

119864ads = 119864dye + 119864(TiO2)6

minus 119864[dye(TiO

2)6] (1)

The 119864dye 119864(TiO2)6

and 119864[dye(TiO

2)6]were the total energies

of dyes (TiO2)6cluster and dye(TiO

2)6 respectively

The short-circuit current density (119869sc) which is closelyconnected to the energy conversion efficiency (120578) of the solarcell [30] can be determined by the following equation [31]

119869sc = int LHE (120582)Φinject120578collect119889120582 (2)

where LHE(120582) is the light-harvesting efficiency at a givenwavelength [31] Φinject is the electron injection efficiencyto the semiconductor substrate and 120578collect is the electroncollection efficiency 120578collect can be assumed as a constant inthe same DSSCs with sole different dyes [32] As a result theenhancement of 119869sc should focus on improving the LHE(120582)and Φinject The Φinject is related to the driving force Δ119866injectfor the electron injection According to Preatrsquos method [33]the Δ119866inject of electron injections from the excited states ofdyes to semiconductor surface are calculated

The light-harvesting efficiency LHE(120582) can be calculatedwith

LHE (120582) = 1 minus 10minus119891 (3)

where119891 is the oscillator strength of themaximum absorptionspectra of dyes

3 The Molecular Geometries of Dyes

The sketch map and the optimized geometries of D149and D1ndashD4 are shown in Figures 1 and 2 respectively

Journal of Nanomaterials 3

C N F HS

D149

D3D2

D4

D1

1416

14131407

1408

1412324

∘

433∘

293∘

371∘

2526∘

Figure 2 The optimized geometry of the studied dyes together with the important bond length (A) and dihedral angle (∘)

The triphenylamine moiety indoline and rhodanine groupand CH

2COOH act as an electron donor (D) electron

conductor (120587) and acceptor (A) respectively As shown inFigure 2 the dihedral angle of C

4-C3-N2-C2for D149 is

2526∘ D2 and D3 have steric obstruction conformation bygradually adding the N(phenyl)

2groups in D1 For example

the dihedral angle of C4-C3-N2-C2forD1ndashD3 is calculated to

be 293∘ 324∘ and 371∘ respectively Note that the dihedralangle of C

4-C3-N2-C2increases from 371∘ (D3) to 433∘ (D4)

by introducing the CF3group at the end of triphenylamine

Obviously the steric obstruction can be justified by properfunctional group and thus avoids the unfavorable dye aggre-gation on the TiO

2surface Besides the dihedral angle of

C4-C3-N2-C2 the bond length C

1ndashN1between the D and

120587 part increases in the following order D4 (1408 A) lt D3(1412 A) lt D2 (1413 A) lt D1 (1416 A) indicating the bondconjugation ability decreases in the same order This can beexplained by the NBO charges on the C

1and N

1atoms The

NBO charges on N1atom of D2ndashD4 are similar with D1

But for C1atom it decreases dramatically in the following

orderD4 (0148e) gtD3 (0133e) gtD2 (0127e) gtD1 (0117e)suggesting the bond conjugation ability has been enhancedby introducing N(phenyl)

2and CF

3substitutions

31 Frontier Molecular Orbital Analysis The energy levelsof the HOMO and LUMO as well as the HOMO-LUMOgaps are drawn in Figure 3 together with the energy levelsof TiO

2semiconductor conduction band (minus400 eV) [34] and

the redox potential of IminusI3

minus (minus480 eV) [35]

minus1minusminusminusminusminusminusminusminusminusminusminusminusminusminusminusminusminusminusminusminusminusminusminusminus1111111111111111111111111111111111111111111111111111111111111111

Ener

gy (e

V)

0

minus2

minus3

minus4

minus5

minus6

II3minus

minus236

271

minus507

minus217

222

minus439

minus224

228

minus453

minus229

234

minus463

minus245

266

minus511

TiO2

D149 D3D2 D4D1

Figure 3The energy levels and contour plot of HOMO and LUMOas well as HOMO-LUMO energy gap (eV) of D149 andD1ndashD4 Theredox potential of IminusI

3

minus (minus480 eV) and energy level of conductionband (CB) of the TiO

2surface (minus400 eV) are drawn in red line

As drawn in Figure 3 the HOMO and LUMO energy lev-els of D1ndashD3 increase remarkably (minus439 eV and minus217 eV forD1 minus453 eV and minus224 eV forD2 and minus463 eV and minus229 eVfor D3) compared with D149 obtained by us (minus507 eV andminus236 eV) and previous work [24] (minus5009 eV andminus2408 eV)which means that the energy level of molecular orbital canbe greatly changed by introduction of triphenylamine into


300 350 400 450 500 550 600 650 700 750 80000

Abso

rban

ce

Wavelength (nm)

D1D2D3

D4

D149

10 times 105

50 times 104

Figure 4 Simulated absorption spectra for D149 andD1ndashD4 obtained by B3LYP6-31Glowast method in methanol media

the donor part Although the introduction of triphenylamineunit increases the HOMO values relative to D149 the HOMOlevel of D1ndashD3 still approaches the redox potential of IminusI

3

minus

(minus480 eV) The HOMO level of D4 (minus511 eV) decreasesdramatically by importing the CF

3group at the end of

the triphenylamine group which is lower by 031 eV thanIminusI3

minus redox potential This means that the studied dyesensure efficient dye regeneration In addition the LUMOenergy of D1ndashD4 is higher than the conduction band edge ofTiO2 which would provide enough driving force for electron

injection for ultrafast excited-state electron injection [36]Thus it is a good approach to enhance the ability of dyeregeneration by introducing the N(CH

3)2and N(phenyl)

2

substitutions at the donor part especially for CF3group

With the dramatically stabilized HOMO energy the HOMO-LUMO energy gap of these dyes increases in the followingorder D1 (222 eV) lt D2 (228 eV) lt D3 (234 eV) lt D4(266 eV) The energy gaps of our designed dyes D1ndashD3 aremuch smaller than the famous D149 As reported by previouswork [37 38] the sensitizers that have smaller energy gapvalues may show higher efficiency in the DSSCs Thus it canbe inferred that our designed molecules may have improvedlight harvesting ability

As drawn in Figure 3 the electron densities of theHOMOofD149 ismainly located on the donor part and indoline ringthe electron densities of its LUMO are mainly distributedaround the 120587 group It suggests that the HOMO to LUMOtransition is a good charge separated state The electrondistributions of the HOMOs and LUMOs for D1ndashD4 havethe similar features Both the HOMOs and LUMOs of D1ndashD4 possess 120587 and 120587lowast orbital delocalization Therefore it canbe confirmed that the intramolecular charge transfer (ICT)may occur when electron excitation occurs from the HOMOto LUMO in these dyes

32 The Absorption Spectra On the basis of the optimizedground state geometries the absorption spectra of dyesare calculated by TDDFTB3LYP method with PCM inmethanolmediaThe simulated electronic absorption spectra

are depicted in Figure 4 and the corresponding absorptiondata are collected in Table 1

Figure 4 shows the absorption spectrum of D1ndashD3displaying three major absorption bands in their UVVisspectra the lowest energy absorption band (in the regionof 6000ndash8000 nm) lower energy absorption band (in theregion of 4500 to 6000 nm) and higher energy absorptionband (in the region of 3000 to 4500 nm) Compared withD1ndashD3 the absorption spectra of D4 are different in theband locations and intensity due to importing the electron-withdrawing CF

3groups From Figure 4 and Table 1 the low-

est lying distinguishable absorption speak (1198781) of these dyes

exhibits dramatically blue shift tendency D1 (7351 nm) gtD2 (6935 nm) gt D3 (6615 nm) gt D4 (6002 nm) gt D149(5561 nm) which is closely related to the increased HOMO-LUMOenergy gaps of these compounds (see Figure 3) Basedon the analysis of electron density of HOMO and LUMO (seeSection 32) all of the absorption behaviors of the 119878

1can be

ascribed to the intramolecular charge transfer (ICT) charac-ter The maximum absorption speak of D1 andD2 is locatedat 5175 and 5187 nm respectively which is contributed byHOMO-1 rarr LUMO transition The HOMO-1 of D1 andD2is contributed by 231 (D) + 768 (120587) and 534 (D) +426 (120587) respectivelyThus it is reasonable to assign the 5175and 5187 nm for D1 and D2 to ICT character For D3 theabsorption speakwith the largest oscillator strength is locatedat 5157 nm which is contributed by HOMO-2rarr LUMOtransition The HOMO-2 of D3 is focused on 999 (D)therefore the 5157 nm of D3 still displays ICT characterWith respect to D4 the absorption at 4915 (attributed byHOMO-1rarr LUMO) and 3713 nm (attributed by HOMOrarrLUMO+4) are assigned to ICT character The high-energyabsorption speak for D1ndashD4 is located at 3985 3622 3656and 3466 nm respectively which is ascribed to 199 (D) +794 (120587)rarr 982 (120587) 851 (D) + 145 (120587) rarr 208(D) + 579 (120587) + 213 (A) 869 (D) + 131 (120587) rarr 771(D) + 212 (120587) and 587 (D) + 411 (120587) rarr 832 (D) +164 (120587) transitions with the ICT character

From the above calculations it can be seen that all theabsorption speaks of D1ndashD4 are covering the entire visible


Table 1 The calculated absorption wavelength 120582 (nm) excitation energy (eV) oscillator strength (119891 gt 02) major configuration andtransition nature for D149 andD1ndashD4 (H L D 120587 and A denote the HOMO LUMO triphenylamine moiety indoline and rhodanine groupand CH2COOH resp)

120582 (nm) 119864 (eV) 119891 Major configuration Character

D149S1 5561 223 13220 99 H rarr L 3012 (D) + 698 (120587) rarr 955 (120587)S2 4258 291 06637 70 H-1 rarr L 401 (D) + 594 (120587) rarr 955 (120587)S3 4105 302 02097 67 H rarr L + 1 301 (D) + 698 (120587) rarr 518 (D) + 477 (120587)

D1

S1 7351 169 03047 100 H rarr L 872 (D) rarr 982 (120587)S2 5175 240 09613 99 H-1 rarr L 231 (D) + 768 (120587) rarr 982 (120587)S5 3985 311 04368 69 H-3 rarr L 199 (D) + 794 (120587) rarr 982 (120587)S13 3277 378 02404 78 H rarr L + 6 872 (D) rarr 578 (120587) + 391 (A)

D2

S1 6935 179 03812 99 H rarr L 851 (D) + 145 (120587) rarr 909 (120587)S2 5187 239 08282 91 H-1 rarr L 534 (D) + 426 (120587) rarr 909 (120587)S4 4696 264 02039 97 H rarr L + 1 851 (D) + 145 (120587) rarr 928 (120587)S5 4027 308 03328 85 H-3 rarr L 249 (D) + 656 (120587) rarr 909 (120587)S10 3624 342 03017 61 H rarr L + 4 851 (D) + 145 (120587) rarr 208 (D) 579 (120587) + 213 (A)

D3

S1 6615 187 03729 99 H rarr L 869 (D) + 131 (120587) rarr 972 (120587)S2 5157 240 09305 98 H-2 rarr L 999 (D) rarr 972 (120587)S10 3656 339 05877 92 H rarr L + 4 869 (D) + 131 (120587) rarr 771 (D) + 212 (120587)S11 3638 341 02335 57 H-4 rarr L 440 (D) + 553 rarr 972 (120587)S12 3539 350 02481 47 H rarr L + 2 869 (D) + 131 (120587) rarr 962 (D)

D4

S1 6002 207 06676 99 H rarr L 587 (D) + 411 (120587) rarr 964 (120587)S2 4915 252 07025 98 H-1 rarr L 460 (D) + 536 (120587) rarr 964 (120587)S4 4279 290 03875 91 H rarr L + 1 587 (D) + 411 (120587) rarr 892 (120587)S7 3713 334 07061 90 H rarr L + 4 587 (D) + 411 (120587) rarr 996 (D)S12 3571 347 02167 53 H-4 rarr L 999 (120587) rarr 964 (120587)S13 3466 358 02581 64 H rarr L + 6 587 (D) + 411 (120587) rarr 832 (D) + 164 (120587)

region which makes these dyes suitable for the application ofDSSCs The location and intensity of the absorption band ofthese dyes are greatly affected by introducing the N(CH

3)2

N(phenyl)2 and CF

3groups which means the photophysical

properties can be well tuned by proper substitutions All theintense absorption bands of D1ndashD4 correspond to the ICTtransition which will play an important role in conversionefficiencies

33 Photoelectric Conversion Efficiency of Dyes Rapid elec-tron injection from the photoinduced excited states of dyesto the TiO

2is desired for high performance of DSSCs

According to Preatrsquos method [33] the driving force Δ119866injectof electrons injections from the excited states of dyes tosemiconductor surface is calculated and the results are drawnin Figure 5

Figure 5 shows that all theΔ119866inject values are very negative(in the region of minus155ndashminus186 eV) which suggests that thedye excited state lies above the TiO

2conduction band edge

Therefore it is favorable for electron injection from theexcited state dye to the TiO

2conduction band edge Com-

paredwithD149 (minus108 eV)D1ndashD4havemuchmore negativeΔ119866inject values As expected the electron injection ability hasbeen improved by replacing the donor part of D149 by triph-enylamine Furthermore the Δ119866inject values of D2 and D3are minus174 eV and 166 eV respectively which are much morepositive than D1 (minus186 eV) indicating that the introduction

D149D3D2 D4D1

096

094

092

090

088

086

084

082

080

078

20

18

16

14

12

10

minusΔG

inje

ct(e

V)

LHE

(120582)

Figure 5 The calculated minusΔ119866inject (in eV) and LHE(120582) of studiedcomplexes

of diphenylamine at the end of triphenylamine unit resultsin destabilization of the oxidized dye and therefore reducesthe electron injection In addition Δ119866inject value of D4(minus155 eV) is positive than that of D3 indicating it would not


25682623

2448

(a)

Intermolecular CT

HOMO = minus433 eV LUMO = minus229 eV

(b)

Figure 6 (a) The optimized ground geometry of D1 dimer and (b) its HOMO and LUMO orbital The Hsdot sdot sdotO bond length (A) is labeled inthe optimized geometry

be favorable to enhance the electron injection by importingthe CF

3group at the end of phenylamine According to (3)

in Section 2 the LHE(120582) of studied complexes are calculatedand the results are also drawn in Figure 5 As depicted inFigure 5 the D1 has larger LHE(120582) than D2ndashD4 whichmeans that D1 has more efficient light harvesting capabilitythan others As discussed in Section 2 the large values ofΔ119866inject and LHE(120582) are possible approaches to maximize theshort-circuit (119869sc) Consequently it is a promising approachto enhance the efficiency by introducing the N(CH

3)2group

at the donor part

34 Structures and Properties of Dye Dimers The inter-molecular interactions of these dyes dimer are investigatedby B3LYP method to predict the stabilization upon dyeaggregation Figure 6 illustrates the optimized geometries ofD1 dimer Further survey of the HOMO and LUMO orbitalsof D1 dimer is also collected in Figure 6 The propertiesof D2-D3 dimers are given in Figure S1 in the supportinginformation (see Supplementary Material available online athttpdxdoiorg1011552015605728)

As shown in Figure 6 and Figure S1 all these stablemolecules have formed intermolecular Hsdot sdot sdotO hydrogenbonds Take D1 dimer as an example the carboxyl andterminal carbonyl group of thiazolidine form three Hsdot sdot sdotOhydrogen bonds One Hsdot sdot sdotO hydrogen bond is 2568 Awhich is formed by the carboxyl and one terminal H atomsin the ethyl Another two Hsdot sdot sdotO hydrogen bonds are 2623and 2448 A which are formed by the two O atoms in thecarbonyl group of thiazolidines interact with the two Hatoms In addition the HOMOs of dimers are mainly locatedon one monomer while their LUMO are contributed byanother monomeric unit Clearly the intermolecular chargetransfer process between the dyes dimers may occur for allthe dyes Compared with the isolated dye monomer (seeFigure 3) the HOMO energy of D1 dimer slightly increasesby 006 eV while the LUMO energy decreases by 012 eVrespectively Because of the dramatically decreased LUMOenergy the HOMO-LUMO energy gap of D1 dimer becomesnarrowed 018 eV compared with monomer Similarly theHOMO-LUMO energy gap of D2 dimer and D3 dimerdecreases by 014 eV and 018 eV respectively compared withcorresponding monomer Normally the narrowed HOMO-LUMO energy gap favors red shifted of absorption spectra

As reported by Pastore and De Angelis [13] the red-shiftof absorption spectra for indoline dye are due to the dyeaggregation Therefore dye aggregation is expected to beassociated with the HOMO-LUMO energy gap of dye dimerSince there are small differences of HOMO-LUMO energygap of these dimers compared with correspondingmonomerintroducing the N(phenyl)

2substitutions at the donor may

play a slightl effect on avoiding unfavorable dye aggregation

35 Dye-(TiO2)6Complexes For a better understanding of

the effect of the triphenylamine-based donor on the electroncoupling these dyes bound to (TiO

2)6cluster are optimized

by B3LYP method As well accepted there are two commonabsorption models for dyes absorbed on the surface [39 40]One is a single Ti-O monodentate binding mode another isa bidentate chelating structure mode In this work we takeD4 as an example to testify which mode is stable absorptionconfiguration The optimized geometries of D4-(TiO

2)6in

different models are drawn in Figure S2 It can be seenthat the total energy of bidentate-chelating configurationis lower 375 kcalmol than single monodentate mode Thisagrees with the previous work that is the bidentate chelatingstructure mode is usually predicted to be stable [13 41ndash43]Therefore the D149 and D1ndashD3 absorbed on the surface areoptimized under the bidentate chelating structure modeTheoptimized geometry absorption energies (119864ads) and the con-tour plot of theHOMOand LUMOof dye-(TiO

2)6complexes

are depicted in Figure 7The energy level of frontier moleculeorbital (eV) of the dye-(TiO

2)6and the energies differences

between the dye and dye-(TiO2)6are drawn in Figure 8

As shown in Figure 7 the decreased order of119864abs forD149andD1ndashD4 is D149 (2368 kcalmol) gtD1 (2081 kcalmol) gtD2 (1566 kcalmol) gt D3 (1032 kcalmol) gt D4 (285 kcalmol) indicating the interactions between the dye and TiO

2

surface is decreasing in the same order In particular forD4the 119864abs is so small that D4 is difficult to be chemisorbedon the cluster After absorption to the (TiO

2)6cluster the

calculated distances of D1 between the carboxylic oxygenatoms and the (TiO

2)6cluster (TindashO bond lengths) are about

2032 A and 2115 A By introducing the N(phenyl)2and CF

3

groups the two Ti-O bond lengths increase to 2032 A and2116 A for D2 2032 A and 2117 A for D3 and 2032 A and2119 A forD4 It suggests that theN(phenyl)

2andCF

3groups


2031 2032 2032 20322115 2116 2117 21192108

2039

HOMOHOMOHOMOHOMOHOMO

LUMO LUMO LUMO LUMO LUMO

D149 D3D2D1 D4

Eads = 2369kcalmolEads = 2081 kcalmol Eads = 1566kcalmol Eads = 1032kcalmol Eads = 285 kcalmol

Figure 7 Optimized geometries absorption energies (kcalmol) and contour plot of HOMO and LUMO of studied molecule absorbed onthe (TiO

2)6cluster

135

LUMO

LUMO

HOMO

D4D3D2

151137140

Ener

gy (e

V)

145

D1

HOMO

D149minus2

minus4

minus6

minus8 D149 (TiO2)6

D1 (TiO2)6

D2 (TiO2)6

D3 (TiO2)6

D4 (TiO2)6

Figure 8 The energy diagram of frontier molecule orbital (eV) ofthe dye-(TiO

2)6 as well as the HOMO and LUMO energy of dyes

have decreased the electron coupling between the dyes andsurface which is consistent with the analyses of 119864ads

Molecular orbital spatial distribution shows that theHOMO of dye-(TiO

2)6is mainly localized over the donor

part of dyes while the LUMO is focused on the (TiO2)6

part As expected the interfacial electron injection fromthe dye to the TiO

2surface may successively transfer when

the dyes bind on the TiO2film Furthermore compared

with the isolated sensitizer the HOMOs have subtle changes(about 01 eV) when the D149 and D1ndashD4 absorb to (TiO

2)6

cluster The most noticeable difference between the isolateddyes and dye-(TiO

2)6is focused on the LUMO energy The

LUMO energy of (D1ndashD4)-(TiO2)6dramatically decreases

compared with D149-(TiO2)6 suggesting that the LUMOs of

all designed dyes create relative strong electronic couplingwith TiO

2film and as a result further boost the electron

injection In addition the LUMO of D1-(TiO2)6is lower

145 eV than that of D1 While the lower-lying energy LUMO

of D149-(TiO2)6(135 eV) D2-(TiO

2)6(140 eV) and D3-

(TiO2)6(137 eV) becomes smaller than that of D1 indicating

that the electronic coupling to the TiO2surface decreases by

importing the N(phenyl)2

4 Conclusions

The electronic structures absorption spectra and photo-physical properties of triphenylamine-based indoline dyes asphotosensitizers for application in DSSCs were investigatedby density functional theory (DFT) and time-dependentDFT (TD-DFT) The calculated results demonstrated thatthe donor parts had great effect on the structure and opticalproperties Compared with D149D1ndashD3 had proper HOMOand LUMO energy level as well as narrow HOMO-LUMOenergy gap by introducing the N(CH

3)2and N(phenyl)

2

groups at the donor part therefore D1ndashD3 may be goodDSSC sensitizers The absorption speaks of D1ndashD4 coveredthe entire visible region and the intense absorption bands ofthem all corresponded to the intramolecular charge transfertransition which may play an important role in conversionefficiencies The stable molecule of D1ndashD3 dimmers wereformed by intermolecular Hsdot sdot sdotO hydrogen bonds The dataof 119864abs and the LUMO energy level of dye-(TiO

2)6suggested

that D1 had the strongest interactions between the dye andTiO2surface of these dyes Furthermore D1 had larger

Δ119866inject and LHE(120582) values than D2ndashD4 indicating that D1mayhave improved energy conversion efficiency by introduc-ing the N(CH

3)2group at the donor part of triphenylamine

We hope that this work will be helpful for designing theorganic dyes with high efficiency

Conflict of Interests

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


Acknowledgments

Financial supports were received from NSFC (no 21243006and 51304193) the Basic Research Program of JiangsuProvince (no BK20130172) and the Fundamental ResearchFunds for the Central Universities (nos 2013QNA14 and2010QNA10) A Project funded by the Priority AcademicProgram Development of Jiangsu Higher Education Insti-tutions is acknowledged The authors are grateful to theHigh Performance Computing Center of China Universityof Mining and Technology for the award of CPU hours toaccomplish this work

References

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

2filmsrdquo Nature vol

353 pp 737ndash740 1991[2] M Gratzel ldquoSolar energy conversion by dye-sensitized photo-

voltaic cellsrdquo Inorganic Chemistry vol 44 no 20 pp 6841ndash68512005

[3] M K Nazeeruddin A Kay I Rodicio et al ldquoConversion oflight to electricity by cis-X2bis(221015840-bipyridyl-441015840-dicarboxy-late)ruthenium(II) charge-transfer sensitizers (X = Cl- Br- I-CN- and SCN-) on nanocrystalline titanium dioxide elec-trodesrdquo Journal of the American Chemical Society vol 115 no14 pp 6382ndash6390 1993

[4] M K Nazeeruddin P Pechy T Renouard et al ldquoEngineeringof efficient panchromatic sensitizers for nanocrystalline TiO

2-

based solar cellsrdquo Journal of the American Chemical Society vol123 no 8 pp 1613ndash1624 2001

[5] S Chang H Wang L T Lin Lee et al ldquoPanchromatic lightharvesting by N719 with a porphyrin molecule for high-performance dye-sensitized solar cellsrdquo Journal of MaterialsChemistry C vol 2 no 18 pp 3521ndash3526 2014

[6] R K Kanaparthi J Kandhadi and L Giribabu ldquoMetal-freeorganic dyes for dye-sensitized solar cells Recent advancesrdquoTetrahedron vol 68 no 40 pp 8383ndash8393 2012

[7] Y Wu and W Zhu ldquoOrganic sensitizers from Dndash120587ndashA to DndashAndash120587ndashA effect of the internal electron-withdrawing units onmolecular absorption energy levels and photovoltaic perfor-mancesrdquoChemical Society Reviews vol 42 pp 2039ndash2058 2013

[8] B-G Kim K Chung and J Kim ldquoMolecular design principleof all-organic dyes for dye-sensitized solar cellsrdquo Chemistry AEuropean Journal vol 19 no 17 pp 5220ndash5230 2013

[9] G B Consiglio F Pedna C Fornaciari et al ldquoAssessment ofnew gem-silanediols as suitable sensitizers for dye-sensitizedsolar cellsrdquo Journal of Organometallic Chemistry vol 723 pp198ndash206 2013

[10] W H Howie F Claeyssens HMiura and LM Peter ldquoCharac-terization of solid-state dye-sensitized solar cells utilizing highabsorption coefficient metal-free organic dyesrdquo Journal of theAmerican Chemical Society vol 130 no 4 pp 1367ndash1375 2008

[11] S Ito H Miura S Uchida et al ldquoHigh-conversion-efficiencyorganic dye-sensitized solar cells with a novel indoline dyerdquoChemical Communications no 41 pp 5194ndash5196 2008

[12] 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

[13] M Pastore and F De Angelis ldquoAggregation of organic dyeson TiO

2in dye-sensitized solar cells models an Ab initio

investigationrdquo ACS Nano vol 4 no 1 pp 556ndash562 2010[14] H Fukunishi S Nakamura and S Fujieda ldquoInfluence of

conformation on the absorption spectra of flexible organicdyes used in dye-sensitized solar cellsrdquo Computational andTheoretical Chemistry vol 1014 pp 29ndash36 2013

[15] Q Q Li L L Lu C Zhong et al ldquoNew indole-based metal-free organic dyes for dye-sensitized solar cellsrdquo The Journal ofPhysical Chemistry B vol 113 no 44 pp 14588ndash14595 2009

[16] P Liu J-J Fu M-S Guo X Zuo and Y Liao ldquoEffect of thechemical modifications of thiophene-based N3 dyes on theperformance of dye-sensitized solar cells a density functionaltheory studyrdquo Computational and Theoretical Chemistry vol1015 pp 8ndash14 2013

[17] S Meng E Kaxiras M K Nazeeruddin and M GratzelldquoDesign of dye acceptors for photovoltaics from first-principlescalculationsrdquo Journal of Physical Chemistry C vol 115 no 18 pp9276ndash9282 2011

[18] W-L Ding D-MWang Z-Y Geng X-L Zhao and Y-F YanldquoMolecular engineering of indoline-based D-A-120587-A organicsensitizers toward high efficiency performance from first-principles calculationsrdquo Journal of Physical Chemistry C vol 117no 34 pp 17382ndash17398 2013

[19] M Liang and J Chen ldquoArylamine organic dyes for dye-sensitized solar cellsrdquo Chemical Society Reviews vol 42 no 8p 3453 2013

[20] W Xu B Peng J Chen M Liang and F Cai ldquoNew triphenyl-amine-based dyes for dye-sensitized solar cellsrdquo Journal ofPhysical Chemistry C vol 112 no 3 pp 874ndash880 2008

[21] M Liang W Xu F Cai et al ldquoNew triphenylamine-basedorganic dyes for efficient dye-sensitized solar cellsrdquo Journal ofPhysical Chemistry C vol 111 no 11 pp 4465ndash4472 2007

[22] H-Q Xia J Wang F-Q Bai and H-X Zhang ldquoTheo-retical studies of electronic and optical properties of thetriphenylamine-based organic dyes with diketopyrrolopyrrolechromophorerdquo Dyes and Pigments vol 113 pp 87ndash95 2015

[23] M J Frisch G W Trucks H B Schlegel et al Gaussian 09Revision B04 Gaussian Wallingford Conn USA 2009

[24] H W Ham and Y S Kim ldquoTheoretical study of indoline dyesfor dye-sensitized solar cellsrdquo Thin Solid Films vol 518 no 22pp 6558ndash6563 2010

[25] C Lee W Yang and R G Parr ldquoDevelopment of the Colle-Salvetti correlation-energy formula into a functional of theelectron densityrdquo Physical Review B vol 37 no 2 pp 785ndash7891988

[26] A D Becke ldquoDensity-functional thermochemistry IIIThe roleof exact exchangerdquoThe Journal of Chemical Physics vol 98 no7 p 5648 1993

[27] M Cossi G Scalmani N Rega and V Barone ldquoNew devel-opments in the polarizable continuum model for quantummechanical and classical calculations onmolecules in solutionrdquoJournal of Chemical Physics vol 117 no 1 pp 43ndash54 2002

[28] V Barone M Cossi and J Tomasi ldquoA new definition of cavitiesfor the computation of solvation free energies by the polarizablecontinuum modelrdquo Journal of Chemical Physics vol 107 no 8pp 3210ndash3221 1997

[29] R Sanchez-De-Armas J Oviedo Lopez M A San-Miguel JF Sanz P Ordejon and M Pruneda ldquoReal-time TD-DFT sim-ulations in dye sensitized solar cells the electronic absorptionspectrum of alizarin supported on TiO

2nanoclustersrdquo Journal


of Chemical Theory and Computation vol 6 no 9 pp 2856ndash2865 2010

[30] M R Narayan ldquoReview dye sensitized solar cells based onnatural photosensitizersrdquo Renewable and Sustainable EnergyReviews vol 16 no 1 pp 208ndash215 2012

[31] J-Z Zhang H-B Li Y Wu et al ldquoModulation on chargerecombination and light harvesting toward high-performancebenzothiadiazole-based sensitizers in dye-sensitized solar cellsa theoretical investigationrdquo Journal of Power Sources vol 267pp 300ndash308 2014

[32] J Zhang H-B Li S-L Sun Y Geng Y Wu and Z-M SuldquoDensity functional theory characterization and design of high-performance diarylamine-fluorene dyeswith different120587 spacersfor dye-sensitized solar cellsrdquo Journal of Materials Chemistryvol 22 no 2 pp 568ndash576 2012

[33] J Preat C Michaux D Jacquemin and E A PerpeteldquoEnhanced efficiency of organic dye-sensitized solar cells triph-enylamine derivativesrdquo Journal of Physical Chemistry C vol 113no 38 pp 16821ndash16833 2009

[34] M Gratzel ldquoPhotoelectrochemical cellsrdquo Nature vol 414 no6861 pp 338ndash344 2001

[35] D Cahen G Hodes M Gratzel J F Guillemoles and I RiessldquoNature of photovoltaic action in dye-sensitized solar cellsrdquoJournal of Physical Chemistry B vol 104 no 9 pp 2053ndash20592000

[36] S Meng and E Kaxiras ldquoElectron and hole dynamics in dye-sensitized solar cells influencing factors and systematic trendsrdquoNano Letters vol 10 no 4 pp 1238ndash1247 2010

[37] W M Campbell K W Jolley P Wagner et al ldquoHighly efficientporphyrin sensitizers for dye-sensitized solar cellsrdquo Journal ofPhysical Chemistry C vol 111 no 32 pp 11760ndash11762 2007

[38] R Ma P Guo H Cui X Zhang M K Nazeeruddin and MGratzel ldquoSubstituent effect on themeso-substituted porphyrinstheoretical screening of sensitizer candidates for dye-sensitizedsolar cellsrdquoThe Journal of Physical Chemistry A vol 113 no 37pp 10119ndash10124 2009

[39] M Nara H Torii and M Tasumi ldquoCorrelation between thevibrational frequencies of the carboxylate group and the typesof its coordination to a metal ion an ab initio molecular orbitalstudyrdquo Journal of Physical Chemistry vol 100 no 51 pp 19812ndash19817 1996

[40] G B Deacon and R J Phillips ldquoRelationships between thecarbon-oxygen stretching frequencies of carboxylato complexesand the type of carboxylate coordinationrdquo Coordination Chem-istry Reviews vol 33 no 3 pp 227ndash250 1980

[41] P Chen J H Yum F de Angelis et al ldquoHigh open-circuitvoltage solid-state dye-sensitized solar cells with organic dyerdquoNano Letters vol 9 no 6 pp 2487ndash2492 2009

[42] H Tian X Yang R Chen R Zhang A Hagfeldt and L SunldquoEffect of different dye baths and dye-structures on the per-formance of dye-sensitized solar cells based on triphenylaminedyesrdquo Journal of Physical Chemistry C vol 112 no 29 pp 11023ndash11033 2008

[43] M Pastore and F D Angelis ldquoComputational modeling of starkeffects in organic dye-sensitized TiO

2heterointerfacesrdquo The

Journal of Physical Chemistry Letters vol 2 no 11 pp 1261ndash12672011

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


NS

O

NS

O

S

R1

R2

Donor (D)

Acceptor (A)

NN

N N ND149

Electron conductor (120587)

N1N2 C1C2

C3C4

CH2COOH

CH3 CH3

CH3

CF3

CF3

CH3D =

D3 R1= R2 =

D1 R1= R2 =

D4 R1= R2 =

D2 R1= R2 =

Figure 1 Sketch map of the studied dyes

the N(CH3)2 N(phenyl)

2 and CF

3at the donor part of D149

in this work (see Figure 1) A systematic comparison andanalysis of the geometries frontier molecular orbitals andabsorption spectra of these dyes are carried out Furthermorethe light harvesting efficiency (LHE) and the driving forceof electrons injections (Δ119866inject) are calculated to estimatethe short-circuit photocurrent density In addition the elec-tron coupling of dimeric dyes and dye-(TiO

2)6systems is

simulated by DFT method to testify the electron injectionefficiency This work is expected to reveal the effect ofchemical modification on the DSSCs efficiency and providevaluable guidance for developing efficiency dyes

2 Computational Details

All calculations were performed with the Gaussian 09 pro-gram package [23] The density functional theory DFT(B3LYP) approach had been successfully used to calculatethe ground geometries in indoline dye sensitizers [13ndash15 24]Therefore in this work the geometries structures of mon-omer and dimer dyes were fully optimized at the DFT level ofB3LYP method [25 26] using the 6-31G(d) basis set Follow-ing the optimized geometry the vibrational frequencies werecalculated and the results confirmed that all the optimizedmonomer geometries were stable geometric structures Theabsorption spectra of these dyes were investigated by TDDFTwith the B3LYP approach associated with the polarizedcontinuum model (PCM) [27 28] in methanol media

To investigate the electronic coupling interaction betweenthese dyes andTiO

2nanoparticles the absorption geometries

of dyes(TiO2)6clusters were calculated by B3LYP method

The 6-31G(d) basis sets were used for C H O N S andF atoms and LANL2DZ for Ti atom Although (TiO

2)6

cluster is a simplistic model it was believed to qualitatively

reproduce the trend of the charge distribution [29] Theabsorption energies (119864ads) of dyes(TiO2)6 were calculated bythe following equation

119864ads = 119864dye + 119864(TiO2)6

minus 119864[dye(TiO

2)6] (1)

The 119864dye 119864(TiO2)6

and 119864[dye(TiO

2)6]were the total energies

of dyes (TiO2)6cluster and dye(TiO

2)6 respectively

The short-circuit current density (119869sc) which is closelyconnected to the energy conversion efficiency (120578) of the solarcell [30] can be determined by the following equation [31]

119869sc = int LHE (120582)Φinject120578collect119889120582 (2)

where LHE(120582) is the light-harvesting efficiency at a givenwavelength [31] Φinject is the electron injection efficiencyto the semiconductor substrate and 120578collect is the electroncollection efficiency 120578collect can be assumed as a constant inthe same DSSCs with sole different dyes [32] As a result theenhancement of 119869sc should focus on improving the LHE(120582)and Φinject The Φinject is related to the driving force Δ119866injectfor the electron injection According to Preatrsquos method [33]the Δ119866inject of electron injections from the excited states ofdyes to semiconductor surface are calculated

The light-harvesting efficiency LHE(120582) can be calculatedwith

LHE (120582) = 1 minus 10minus119891 (3)

where119891 is the oscillator strength of themaximum absorptionspectra of dyes

3 The Molecular Geometries of Dyes

The sketch map and the optimized geometries of D149and D1ndashD4 are shown in Figures 1 and 2 respectively


C N F HS

D149

D3D2

D4

D1

1416

14131407

1408

1412324

∘

433∘

293∘

371∘

2526∘

















1and N

1atoms The




2and CF

3substitutions






Ener

gy (e

V)

0

minus2

minus3

minus4

minus5

minus6

II3minus

minus236

271

minus507

minus217

222

minus439

minus224

228

minus453

minus229

234

minus463

minus245

266

minus511

TiO2

D149 D3D2 D4D1


3





300 350 400 450 500 550 600 650 700 750 80000

Abso

rban

ce

Wavelength (nm)

D1D2D3

D4

D149

10 times 105

50 times 104



3

minus






3)2and N(phenyl)

2










1can be







D1


D2


D3


D4



3)2

N(phenyl)2 and CF











D149D3D2 D4D1

096

094

092

090

088

086

084

082

080

078

20

18

16

14

12

10

minusΔG

inje

ct(e

V)

LHE

(120582)




25682623

2448

(a)

Intermolecular CT


(b)





3)2group

at the donor part










2)6in


2)6complexes





2


2)6cluster the




3


2andCF

3groups


2031 2032 2032 20322115 2116 2117 21192108

2039



D149 D3D2D1 D4



2)6cluster

135

LUMO

LUMO

HOMO

D4D3D2

151137140

Ener

gy (e

V)

145

D1

HOMO

D149minus2

minus4

minus6

minus8 D149 (TiO2)6

D1 (TiO2)6

D2 (TiO2)6

D3 (TiO2)6

D4 (TiO2)6











2)6









of D149-(TiO2)6(135 eV) D2-(TiO

2)6(140 eV) and D3-




4 Conclusions


3)2and N(phenyl)

2


2)6suggested








Acknowledgments


References







2-























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




C N F HS

D149

D3D2

D4

D1

1416

14131407

1408

1412324

∘

433∘

293∘

371∘

2526∘

















1and N

1atoms The




2and CF

3substitutions






Ener

gy (e

V)

0

minus2

minus3

minus4

minus5

minus6

II3minus

minus236

271

minus507

minus217

222

minus439

minus224

228

minus453

minus229

234

minus463

minus245

266

minus511

TiO2

D149 D3D2 D4D1


3





300 350 400 450 500 550 600 650 700 750 80000

Abso

rban

ce

Wavelength (nm)

D1D2D3

D4

D149

10 times 105

50 times 104



3

minus






3)2and N(phenyl)

2










1can be







D1


D2


D3


D4



3)2

N(phenyl)2 and CF











D149D3D2 D4D1

096

094

092

090

088

086

084

082

080

078

20

18

16

14

12

10

minusΔG

inje

ct(e

V)

LHE

(120582)




25682623

2448

(a)

Intermolecular CT


(b)





3)2group

at the donor part










2)6in


2)6complexes





2


2)6cluster the




3


2andCF

3groups


2031 2032 2032 20322115 2116 2117 21192108

2039



D149 D3D2D1 D4



2)6cluster

135

LUMO

LUMO

HOMO

D4D3D2

151137140

Ener

gy (e

V)

145

D1

HOMO

D149minus2

minus4

minus6

minus8 D149 (TiO2)6

D1 (TiO2)6

D2 (TiO2)6

D3 (TiO2)6

D4 (TiO2)6











2)6









of D149-(TiO2)6(135 eV) D2-(TiO

2)6(140 eV) and D3-




4 Conclusions


3)2and N(phenyl)

2


2)6suggested








Acknowledgments


References







2-























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




300 350 400 450 500 550 600 650 700 750 80000

Abso

rban

ce

Wavelength (nm)

D1D2D3

D4

D149

10 times 105

50 times 104



3

minus






3)2and N(phenyl)

2










1can be







D1


D2


D3


D4



3)2

N(phenyl)2 and CF











D149D3D2 D4D1

096

094

092

090

088

086

084

082

080

078

20

18

16

14

12

10

minusΔG

inje

ct(e

V)

LHE

(120582)




25682623

2448

(a)

Intermolecular CT


(b)





3)2group

at the donor part










2)6in


2)6complexes





2


2)6cluster the




3


2andCF

3groups


2031 2032 2032 20322115 2116 2117 21192108

2039



D149 D3D2D1 D4



2)6cluster

135

LUMO

LUMO

HOMO

D4D3D2

151137140

Ener

gy (e

V)

145

D1

HOMO

D149minus2

minus4

minus6

minus8 D149 (TiO2)6

D1 (TiO2)6

D2 (TiO2)6

D3 (TiO2)6

D4 (TiO2)6











2)6









of D149-(TiO2)6(135 eV) D2-(TiO

2)6(140 eV) and D3-




4 Conclusions


3)2and N(phenyl)

2


2)6suggested








Acknowledgments


References







2-























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials







D1


D2


D3


D4



3)2

N(phenyl)2 and CF











D149D3D2 D4D1

096

094

092

090

088

086

084

082

080

078

20

18

16

14

12

10

minusΔG

inje

ct(e

V)

LHE

(120582)




25682623

2448

(a)

Intermolecular CT


(b)





3)2group

at the donor part










2)6in


2)6complexes





2


2)6cluster the




3


2andCF

3groups


2031 2032 2032 20322115 2116 2117 21192108

2039



D149 D3D2D1 D4



2)6cluster

135

LUMO

LUMO

HOMO

D4D3D2

151137140

Ener

gy (e

V)

145

D1

HOMO

D149minus2

minus4

minus6

minus8 D149 (TiO2)6

D1 (TiO2)6

D2 (TiO2)6

D3 (TiO2)6

D4 (TiO2)6











2)6









of D149-(TiO2)6(135 eV) D2-(TiO

2)6(140 eV) and D3-




4 Conclusions


3)2and N(phenyl)

2


2)6suggested








Acknowledgments


References







2-























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




25682623

2448

(a)

Intermolecular CT


(b)





3)2group

at the donor part










2)6in


2)6complexes





2


2)6cluster the




3


2andCF

3groups


2031 2032 2032 20322115 2116 2117 21192108

2039



D149 D3D2D1 D4



2)6cluster

135

LUMO

LUMO

HOMO

D4D3D2

151137140

Ener

gy (e

V)

145

D1

HOMO

D149minus2

minus4

minus6

minus8 D149 (TiO2)6

D1 (TiO2)6

D2 (TiO2)6

D3 (TiO2)6

D4 (TiO2)6











2)6









of D149-(TiO2)6(135 eV) D2-(TiO

2)6(140 eV) and D3-




4 Conclusions


3)2and N(phenyl)

2


2)6suggested








Acknowledgments


References







2-























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




2031 2032 2032 20322115 2116 2117 21192108

2039



D149 D3D2D1 D4



2)6cluster

135

LUMO

LUMO

HOMO

D4D3D2

151137140

Ener

gy (e

V)

145

D1

HOMO

D149minus2

minus4

minus6

minus8 D149 (TiO2)6

D1 (TiO2)6

D2 (TiO2)6

D3 (TiO2)6

D4 (TiO2)6











2)6









of D149-(TiO2)6(135 eV) D2-(TiO

2)6(140 eV) and D3-




4 Conclusions


3)2and N(phenyl)

2


2)6suggested








Acknowledgments


References







2-























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Acknowledgments


References







2-























































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




























CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials










CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



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Review Article Theoretical Studies of Electronic Structure and ...downloads.hindawi.com/journals/jnm/2015/605728.pdf · Theoretical Studies of Electronic Structure and Photophysical