New D-π-A system dye based on dithienosilole and carbazole: Synthesis, photo-electrochemical properties and dye-sensitized solar cell performance

Article abstract of DOI:10.1016/j.jphotochem.2014.07.021

New donor-linker-acceptor pattern organic dye containing a dithienosilole unit as a π-conjugated system, a carbazole moiety as an electron donor, and a cyanoacrylic acid unit as an electron acceptor was synthesized for application in dye-sensitized solar cell (DSSC). Its photophysical and electrochemical properties were investigated, the dithienosilole unit could dramatically lower the lowest unoccupied molecular orbital (LUMO) level and energy gap. Its performances as sensitizers in solar cells were measured, and possessed a power conversion efficiency of 4.80%.

Full text of DOI:10.1016/j.jphotochem.2014.07.021

Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 54–61
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
New D–␲-A system dye based on dithienosilole and carbazole:
Synthesis, photo-electrochemical properties and dye-sensitized solar
cell performance
Jie Liua, Xiang Suna, Zhifang Lib, Bin Jina, Guoqiao Laib, Haiying Lic, Chengyun Wanga,∗
,
Yongjia Shena, Jianli Huaa
a Key Laboratory for Advanced Materials and Institute of Fine Chemicals, East China University of Science and Technology, 130 Meilong Road, Shanghai,
200237, China
b Key Laboratory of Organosilicon Chemistry and Material Technology of Ministry of Education, Hangzhou Normal University, Hangzhou 310012, China
c Key Laboratory for Advanced Materials and Department of Chemistry, East China University of Science and Technology, 130 Meilong Road, Shanghai,
200237, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 8 April 2014
Received in revised form 24 June 2014
Accepted 24 July 2014
Available online 2 August 2014
New donor–linker–acceptor pattern organic dye containing a dithienosilole unit as a ␲-conjugated sys-
tem, a carbazole moiety as an electron donor, and a cyanoacrylic acid unit as an electron acceptor was
synthesized for application in dye-sensitized solar cell (DSSC). Its photophysical and electrochemical
properties were investigated, the dithienosilole unit could dramatically lower the lowest unoccupied
molecular orbital (LUMO) level and energy gap. Its performances as sensitizers in solar cells were mea-
sured, and possessed a power conversion efficiency of 4.80%.
Keywords:
Carbazole
© 2014 Elsevier B.V. All rights reserved.
Dithienosilole
␲-Conjugated system
Power conversion efficiency
Dye-sensitized solar cell
1. Introduction
co-workers reported a sensitizer C219 with dihexyl-substituted
dithienosilole and 3,4-ethylenedioxythiophene unit as the binary
Photovoltaic cell is of great significance in energy territory for
its clean and recyclable characteristics. Although inorganic solar
cell still currently dominates the photovoltaic field, it is greatly
limited by either costly or hazardous materials involved in the tech-
nologies. In contrast, dye-sensitized solar cell (DSSC) draws many
attentions for its low-cost, versatile, energy-saving, and environ-
mental friendly performance.
Dye sensitizer is the key part of DSSC. Generally speaking,
sensitizer in high performance should have wide and strong
absorption in the visible region, good solubility, appropriate low-
est unoccupied molecular orbital (LUMO) and highest occupied
molecular orbital (HUMO) level for effective electron-injection to
the semiconductor’s conduction band and dye regeneration [1].
Recently, researched interesting has been focused on the Donor–␲-
Acceptor (D–␲-A) system owing to its effective photo-induced
intra-molecular charge-transfer characteristics [2]. Wang and
␲-conjugated spacer between alkoxy-substituted triphenylamine
electron donor and cyanoacrylic acid electron acceptor, exhibiting
promising photovoltaic property [3].
Arylamine-based moieties are employed as the electron donor
(D) frequently for their strong electron-donating nature [4]. As
arylamine derivative, carbazole shares its strong electron-giving
capacity and has been studied for different applications [5,6].
Castellano and co-workers synthesized carbazole or bithiophene
bridged sensitizers and obtained a conversion efficiency of 2.70%
[7]. Koumura and co-workers researched on a series of sensitiz-
ers with carbazole as the D unit, repeating thiophenes as the ␲
moiety and cyanoacrylate as the electron-drawing part, and the
DSSC reached a high power conversion efficiency [8,9]. Li and
co-workers researched indole-based carbazole and got a conver-
sion efficiency of 4.31%, and a pyrrole-containing carbazole with
a conversion efficiency of 4.62% [10]. Roncali and co-workers
researched similar substituted triarylamine donors and got a con-
version efficiency of 1.92% [11]. These reports encouraged us to
explore the application of carbazole as the electron donor for
the D–␲-A pattern dye. Besides, carbazole has good thermo and
∗
Corresponding author. Tel.: +86 021 64252967; fax: +86 021 64252967.
E-mail address: cywang@ecust.edu.cn (C. Wang).
http://dx.doi.org/10.1016/j.jphotochem.2014.07.021
1010-6030/© 2014 Elsevier B.V. All rights reserved.

J. Liu et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 54–61
55
chemical stability, which is favorable for the long lifetime of
DSSC.
1 h at −78 ◦C, the solution resulted in a white suspension. Then
a solution of dichlorodioctylsilane (963 mg, 2.96 mmol) in THF
(10 mL) was added dropwise. The mixture was stirred for another
5 h at −78 ◦C, warmed to room temperature, and stirred overnight.
The reaction was quenched by saturated aqueous NH4Cl solution
(30 mL).The aqueous layer was extracted with dichloromethane
(3 × 15 mL). The combined organic layers were washed with water,
dried over anhydrous MgSO4, filtrated, evaporated in vacuum to
remove the solvent. Then the crude product was purified by col-
umn chromatography with petroleum ether as eluent to yield a
light green oil (210 mg, 20%). 1H NMR (CDCl3, 400 MHz): ı 7.18 (d,
J = 4.7 Hz, 2H, SCH), 7.04 (d, J = 4.7 Hz, 2H, SCCH), 1.40–1.19 (m, 24H),
0.92–0.82 (m, 10H).
In this paper, we reported the design, synthesis and proper-
ties of a new dye sensitizer in D–␲-A pattern. A binary ␲ moiety
comprising thiophene and 4,4-dioctyl dithienosilole (DODTS) was
employed in the system. Thiophene and DODTS are linked by
ethynyl, which can broaden the ␲-conjugation of the dye molecule.
The synthesis, properties and applications of siloles have been
widely studied for many years [12]. As a derivative of silole,
DODTS shows low LUMO energy level characteristic and has good
coplanarity as well as electron-transfer capacity [13,14]. So the
incorporation of DODTS as one of the binary ␲ moieties will facili-
tate the electron-transfer process and lower the LUMO level of the
dye. Carbazole is used as the D unit for its outstanding electron-
donating ability and thermo stability. Cyanoacrylic acid works
as the electron acceptor. Its strong electron-drawing ability con-
tributes to the intra-molecular charge transfer, and carboxyl helps
the dye to adsorb on the TiO2 particles. Therefore, it may have
promising prospects in the field of DSSC.
4,4-Dioctyl-dithieno[3,2-b:2ꢀ,3ꢀ-d]silole-2-carbaldehyde (4):
To
a stirring solution of 3 (300 mg, 0.72 mmol) and N,N-
dimethylformamide (63 mg, 0.86 mmol) in dry 1,2-dichloroethane
(20 mL) was added dropwise phosphorus-oxychloride (442 mg,
2.88 mmol) at 0 ◦C. The reaction mixture was then heated to
70 ◦C and stirred for 4 h. After being cooled to room tempera-
ture, the reaction mixture was quenched with saturated sodium
acetate aqueous solution (20 mL) and extracted with ethyl acetate
(15 × 3 mL). The combined organic layers were washed with
brine, dried over anhydrous magnesium sulfate, filtered and
evaporated in vacuum to remove the solvent. The crude prod-
uct was purified by column chromatography on silica gel with
dichloromethane/petroleum ether (v/v, 1:1) as eluent to afford 4
as a yellow oil (259 mg, 81%). 1H NMR (CDCl3, 400 MHz): ı 9.86 (s,
1H, CHO), 7.71 (s, 1H, SCCH), 7.39 (d, J = 4.7 Hz, 1H, SCH), 7.12 (d,
J = 4.7 Hz, 1H, SCCH), 1.39–1.21 (m, 24H), 0.89–0.84 (m, 10H).
4,4-Dioctyl-6-bromo-dithieno[3,2-b:2ꢀ,3ꢀ-d]silole-2-
carbaldehyde (5): To a stirring solution of 4 (200 mg, 0.45 mmol)
in chloroform (25 mL) was added dropwise N-bromosuccinimide
(96 mg, 0.54 mmol)) in dichloromethane (10 mL) at 0 ◦C. The reac-
tion mixture was then warmed to room temperature and stirred
for 12 h. The mixture was poured into water and extracted with
diethyl ether. The combined extracts were washed with brine,
dried over anhydrous sodium sulfate, filtered, and evaporated in
vacuum to remove the solvent. The crude product was purified by
a short silica gel column with dichloromethane/petroleum ether
(v/v, 1:1) as eluent to afford 5 as a yellow solid (212 mg, 90%). 1H
NMR (CDCl3, 400 MHz): ı 9.87 (s, 1H, CHO), 7.70 (s, 1H, SCCH), 7.08
(s, 1H, SCBrCH), 1.41–1.21 (m, 24H), 0.94–0.85 (m, 10H).
2. Experimental section
2.1. Materials and measurements
Unless otherwise stated, all solvents and reagents were
chemical pure or analytical pure and used as received from
commercial sources without further purification. Solvents for
chemical synthesis such as tetrahydrofuran (THF), triethylamine,
1,2-dichloroethane were purified by dehydration and distilled with
standard methods. Lithium diisopropylamide (LDA) was prepared
[15] and used soon after its preparation. Pd(PPh3)2Cl2 was syn-
thesized according to Ref. [16] and stored in dry container. The
nuclear magnetic resonance (NMR) spectra were obtained from a
Bruker Avance III 400 (in CDCl3). Mass spectra were obtained using
Micromass LCTTM (HREI-TOF). The UV–vis spectra were recorded
by a Varian Cary00 UV–vis Spectrometer (THF as solvent). Fluores-
cence spectra were recorded by a Varian Cary Eclipse Fluorescence
Spectrometer (THF as solvent).
2.2. Synthetic procedures and characterizations
3,3ꢀ-Dibromo-2,2ꢀ-bithiophene (2): In a 250 mL three neck
flask, 3-bromothiophene (4.0 g, 24.54 mmol) was solved in anhy-
drous THF (50 mL). The solution was cooled to −78 ◦C and LDA
solution was added dropwise over 20 min. Then the solution
was stirred for 1 h at the same temperature and CuCl2 (6.56 g,
49.08 mmol) was added in one portion. After being stirred for 1 h at
−78 ◦C, the mixture was warmed to room temperature and stirred
for another 5 h. The reaction was quenched with water. The crude
compound was extracted with dichloromethane and washed by
distilled water, dried over anhydrous MgSO4, and evaporated in
vacuum. The residue was purified by silica gel column chromatog-
raphy (eluent: petroleum ether). Compound 2 was obtained as
a white solid (1.7 g, 42%). 1H NMR (CDCl3, 400 MHz): ı 7.41 (d,
J = 5.4 Hz, 2H, SCH), 7.08 (d, J = 5.4 Hz, 2H, SCCH).
9-(Thiophen-2-yl)-9H-carbazole (7): A mixture of CuI (0.68 g,
3.6 mmol), 18-Crown-6 (0.48 g, 1.8 mmol), K2CO3 (8.3 g, 60 mmol),
carbazole (6.00 g, 35.88 mmol), 2-bromothiophene (5.85 g,
35.88 mmol) and N,N-dimethyl formamide (DMF) (100 mL)
was heated at 170 ◦C for 24 h under nitrogen. After cooling to
room temperature, the mixture was quenched with 1 M HCl
solution. The Precipitate was filtered and washed with NH3·H2O
and water. The gray crude product was purified by a short silica
gel column with dichloromethane/petroleum ether (v/v, 1:10) as
eluent to afford 7 as a light yellow solid (2.77 g, 31%). 1H NMR
(CDCl3, 400 MHz): ı 8.12 (d, J = 7.8 Hz, 2H, C12H8N), 7.49–7.45 (m,
4H, C12H8N), 7.41–7.38 (d, J = 4.0 Hz, 1H, SCH), 7.35–7.30 (m, 2H,
C12H8N), 7.22–7.19 (m, 2H, SCCH).
9-(5-Bromothiophen-2-yl)-9H-carbazole (8): To
a stirring
LDA solution was prepared with n-BuLi and diisopropylamine by
following method [15]: Diisopropylamine (3.0 g, 29.45 mmol) was
solved in THF (10 mL), and cooled to −78 ◦C, then n-BuLi (1.6 M solu-
tion, 19 mL) was added and stirred for 1 h, therefore LDA solution
was obtained and used soon after its preparation.
solution of 7 (800 mg, 3.21 mmol) in dichloromethane (50 mL)
was dropwise added N-bromosuccinimide (685 mg, 3.85 mmol) in
dichloromethane/acetic acid (25/25 mL) at 0 ◦C. The reaction mix-
ture was then warmed to room temperature and stirred for 12 h.
The mixture was poured into water and extracted with diethyl
ether. The combined extracts were washed with brine, dried over
anhydrous sodium sulfate, filtered, and evaporated in vacuum to
remove the solvent. The crude product was purified by a short sil-
ica gel column with dichloromethane/petroleum ether (v/v, 1:1) as
eluent to afford 8 as a yellow solid (948 mg, 90%). 1H NMR (400 MHz,
4,4-Dioctyl-dithieno[3,2-b:2ꢀ,3ꢀ-d]silole (3):
A mixture of
1.6 M n-BuLi in hexane (3.7 mL, 5.92 mmol), anhydrous THF (40 mL)
in a round-bottom flask was cooled to −78 ◦C, then a solution of 2
(800 mg, 2.47 mmol) in anhydrous THF (10 mL) was added drop-
wise over 15 min under vigorous stirring. After being stirred for

56
J. Liu et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 54–61
CDCl3): ı 8.09 (d, J = 7.8 Hz, 2H, C12H8N), 7.45–7.42 (m, 4H, C12H8N),
7.33–7.28 (m, 2H, C12H8N), 7.16 (d, J = 3.9 Hz, 1H, SCCH), 6.98 (d,
J = 3.9 Hz, 1H, SCCH).
condensation reaction between compound 4 and cyanoacetic acid.
The concrete operations were similar to the synthesis of CTDTSCA
from compound 11. 1H NMR (400 MHz, CDCl3): ı 8.37 (s, 1H,
4-(5-(9H-carbazol-9-yl)thiophen-2-yl)-2-methylbut-3-yn-2-
ol (9): To a stirring solution of compound 8 (900 mg, 2.74 mmol)
in triethylamine (60 mL) were added Pd(PPh3)2Cl2 (96 mg,
0.14 mmol), PPh3 (72 mg, 0.27 mmol), CuI (52 mg, 0.27 mmol)
under Argon. Then 2-methyl-3-butyn-2-ol (690 mg, 8.22 mmol)
was added dropwise to the stirring mixture. The reaction mixture
was stirred at room temperature for 6 h. The solvent was removed
by evaporating in vacuum. The crude product was purified by a
short silica gel column with dichloromethane/petroleum ether
(v/v, 1:2) as eluent to afford 9 as an orange oil (745 mg, 82%). 1H
NMR (400 MHz, CDCl3):ı 8.06 (d, J = 7.7 Hz, 2H, C12H8N), 7.48–7.38
(m, 4H, C12H8N), 7.30–7.26 (m, 2H, C12H8N), 7.21 (d, J = 3.9 Hz, 1H,
SCCH), 7.02 (d, J = 3.9 Hz, 1H, SCCH), 1.63 (s, 6H, 2CH3).
C CH), 7.74 (s, 1H, SCCH), 7.46 (d, J = 4.5 Hz, 1H, SCH), 7.14 (d,
J = 4.6 Hz, 1H, SCCH), 1.34–1.22 (m, 24H), 0.90–0.82 (m, 10H).
HRMS (ESI, m/z): [M]+ calcd for C28H38NO2S2Si, 513.2191; found,
513.2145. IR (KBr, cm−1): 2967, 2921, 2848, 2215, 1711, 1574,
1470, 1380, 1261, 1100, 1019, 804, 709, 615.
3-(5-(9H-carbazol-9-yl) thiophen-2-yl)-2-cyanoacrylic acid
(CTCA): CTCA was prepared through a Vilsmeier–Haack reaction
and a Knoevenagel condensation reaction from compound 7. The
Vilsmeier–Haack reaction of compound 7 was similar to that of
compound 3, the Knoevenagel condensation reaction of compound
12 and cyanoacetic acid was similar to that of compound 11.
1H NMR (400 MHz, CDCl3): ı 8.39 (s, 1H, C CH), 8.10 (d, J = 7.7,
2H, C12H8N), 7.93–7.88(m, 1H, SCCH), 7.71–7.66 (m, 2H, C12H8N),
7.51–7.45 (m, 2H, C12H8N), 7.39–7.34 (m, 3H, C12H8N & SCCH).
HRMS (ESI, m/z): [M]+ calcd for C20H11N2O2S, 344.0619; found,
344.0629. IR (KBr, cm−1): 2924, 2850, 2200, 1621, 1519, 1394, 1077,
727.
9-(5-Ethynylthiophen-2-yl)-9H-carbazole (10): A mixture of
compound 9 (400 mg, 1.21 mmol), potassium hydroxide (135 mg,
2.42 mmol) in isopropanol was heated to 70 ◦C under argon atmo-
sphere. After being stirred for 8 h at 70 ◦C, the reaction mixture was
added by water and extracted by dichloromethane. The combined
extracts were washed with brine, dried over anhydrous sodium
sulfate, filtered, and evaporated in vacuum to remove the solvent.
The residue was purified by column chromatography on a silica
gel column with petroleum/dichloromethane (v/v, 10/1) as elu-
2.3. Cyclic voltammetry
The cyclic voltammograms of the dyes adsorbed on the TiO2
film was measured with a Versastat II electrochemical workstation
(Princeton Applied Research) using 0.1 M TBAPF6 (Aldrich) as the
supporting electrolyte, the sensitizer attached to a nanocrystalline
TiO2 film deposited on the conducting FTO glass as the working
electrode, a platinum wire as the counter electrode, and a reg-
ular calomel electrode in saturated KCl solution as the reference
ent. Compound 10 was obtained as a white solid (240 mg, 73%). 1
H
NMR (400 MHz, CDCl3): ı 8.06 (d, J = 7.7 Hz, 2H, C12H8N), 7.52–7.42
(m, 4H, C12H8N), 7.36 (d, J = 3.9 Hz, 1H, SCCH), 7.34–7.30 (m, 2H,
C12H8N), 7.08 (d, J = 3.9 Hz, 1H, SCCH), 3.40 (s, 1H, C CH).
6-(1-(2-(Carbazol-9-yl)-thiophen-5-yl)-ethynyl)-4,4-dioctyl-
dithieo[3,2-b:2ꢀ,3ꢀ-d]silole-2-carbaldehyde (11): To a stirring
solution of compound 5 (100 mg, 0.19 mmol) in triethylamine
(30 mL) were added Pd(PPh3)2Cl2(14 mg, 0.02 mmol), CuI (7 mg,
0.04 mmol) under Argon. Then compound 10 (104 mg, 0.38 mmol)
in triethylamine (10 mL) was added dropwise to the stirring mix-
ture. The reaction mixture was stirred for 6 h at 80 ◦C. The solvent
was removed by evaporating in vacuum. The crude product was
purified by a silica gel column with dichloromethane/petroleum
ether (v/v, 1:2) as eluent to afford 11 as an orange-red oil (55 mg,
40%). 1H NMR (400 MHz, CDCl3): ı 9.88 (s, 1H, CHO), 8.11 (d,
J = 7.7 Hz, 2H, C12H8N), 7.72 (s, 1H, SCCH), 7.55 (d, J = 8.2 Hz, 2H,
electrode. The scan rate was 100 mV s−1
.
2.4. Fabrication of dye-sensitized solar cells
A screen–printed double layer of titania particles were used
as the photoelectrode. A 10 ␮m layer of 13 nm TiO2 nanoparticles
was first printed on the clean FTO conducting glass plates. After
the film was dried at 125 ◦C over 6 min, another 4 ␮m layer of
400 nm light-scattering anatase particles was coated on. Then the
electrodes were gradually sintered in a muffle furnace at 275 ◦C
for 5 min, at 325 ◦C for 5 min, at 375 ◦C for 5 min, at 450 ◦C for
15 min and at 500 ◦C for 15 min, respectively. The size of the TiO2
film was 0.25 cm2. These films were immersed into a 40 mM aque-
ous TiCl4 solution at room temperature for 12 h, then washed
with water and ethanol. The films were then heated at 450 ◦C for
30 min. After cooling, the TiO2 electrodes were immersed into the
dye solutions of 1 mM in dichloromethane at room temperature
for 12 h. Counter electrodes of the DSSC were prepared by spin-
coating three drops of 0.02 M H2PtCl6 in 2-propanol on the FTO
glass plates followed by annealing treatment at 400 ◦C for 15 min.
The dye-anchored TiO2 working electrode and the counter elec-
trode were assembled into a sealed DSSC cell with a hot-melt gasket
between them. A drop of electrolyte solution was injected into the
cell through a drilled hole. The electrolyte solution was consisted
of 0.5 M 1-butyl-3-methylimidazolium iodide (BM II), 0.1 M 1,2-
dimethyl-3-propylimidazolium iodide (DMP II), 0.03 M I2, 0.05 M
LiI, 0.5 M 4-tert-butylpyridine (tBP) and 0.1 M guanidinium thio-
cyanate (GT) in acetonitrile-valeronitrile(85:15, v/v). Finally, the
hole was sealed using a UV-melt gum and a cover glass.
C12H8N), 7.46 (dd, J1 = 8.2 Hz, J2 = 7.2 Hz, 2H, C12H8N), 7.35–7.30
(dd, J1 = 7.7 Hz, J2 = 7.2 Hz, 2H, C12H8N), 7.27 (d, J = 3.8 Hz, 1H,
SCCH),7.22 (s, 1H, SCCH), 7.14 (d, J = 3.8 Hz, 1H, SCCH), 1.34–1.22
(m, 24H), 0.90–0.83 (m, 10H).
3-(6-(1-(2-(Carbazol-9-yl)-thiophen-5-yl)-ethynyl)-4,4-
dioctyl-dithieo[3,2-b:2ꢀ,3ꢀ-d]silole-2-yl-)-2-cyanoacrylic
acid
a stirred solution of compound 11 (100 mg,
(CTDTSCA): To
0.14 mmol) and cyanoacetic acid (48 mg, 0.56 mmol) in chloroform
(30 mL) was added piperidine (0.1 mL). The reaction mixture was
refluxed for 12 h and then acidified with 2 M hydrochloric acid
aqueous solution (20 mL). The crude product was extracted into
chloroform, washed with water, and dried over anhydrous sodium
sulfate. After removing solvent under reduced pressure, the residue
was purified by flash chromatography with dichloromethane and
methanol/dichlormehane (v/v, 1:10) in turn as eluent to yield a
red solid (77 mg, 70%). 1H NMR (400 MHz, CDCl3): ı 8.34 (s, 1H,
C
CH), 8.11 (d, J = 7.7 Hz, 2H, C12H8N), 7.74 (s, 1H, SCCH), 7.55 (d,
J = 8.2 Hz, 2H, C12H8N), 7.46 (dd, J1 = 8.2, J2 = 7.2, 2H, C12H8N), 7.38
(d, J = 3.7 Hz, 1H, SCCH), 7.35–7.32 (m, 3H, C12H8N & SCCH), 7.14
(d, J = 3.8 Hz, 1H, SCCH), 1.34–1.22 (m, 24H), 0.90–0.82 (m, 10H).
HRMS (ESI, m/z): [M]+ calcd for C46H47N2O2S3Si, 784.2647; found,
784.2579. IR (KBr, cm−1): 2959, 2921, 2848, 2211, 1729, 1638,
1613, 1462, 1385, 1264, 1098, 1024, 805, 620.
2.5. Photovoltaic measurements
Photovoltaic measurements employed an AM 1.5 solar simula-
tor equipped with a 300 W xenon lamp (model no. 91160, Oriel).
The power of the simulated light was calibrated to 100 mW cm−2
using a Newport Oriel PV reference cell system (model 91150 V).
3-(4,4-Dioctyl-dithieo[3,2-b:2ꢀ,3ꢀ-d]silole-2yl-)-2-
cyanoacrylic acid (DTSCA): DTSCA was prepared by a Knoevenagel

J. Liu et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 54–61
57
Scheme 1. Synthetic routes of CTDTSCA, DTSCA and CTCA. Reagents and conditions: (i) −78 ◦C, LDA, THF, CuCl2; (ii) −78 ◦C, nBuLi, dichlorodioctylsilane; (iii) 80 ◦C, POCl3,
DMF, 1, 2-dichloroethane; (iv) rt., NBS, chloroform; (v) 170 ◦C, 2-bromothiophene, CuI, 18-Crown-6, K2CO3; (vi) rt., NBS, dichloromethane/acetic acid; (vii) rt., Pd(PPh3)2Cl2,
PPh3, CuI, 2-methyl-3-butyn-2-ol, triethylamine; (viii) refluxed, KOH, isopropanol; (ix) 70 ◦C, compound 5, Pd(PPh3)2Cl2, PPh3, CuI, triethylamine; (x) 70 ◦C, cyanoacetic acid,
piperidine, chloroform; (xi) 80 ◦C, POCl3, DMF, 1, 2-dichloroethane; (xii) 70 ◦C, cyanoacetic acid, piperidine, chloroform; (xiii) 70 ◦C, cyanoacetic acid, piperidine, chloroform.
Current density–voltage (J–V) curves were obtained by applying an
external bias to the cell and measuring the generated photocurrent
with a model 2400 source meter (Keithley Instruments Inc. USA).
The voltage step and delay time of the photocurrent were 10 mV
and 40 ms, respectively. Action spectra of the incident monochro-
matic photon-to-electron conversion efficiency (IPCE) for the solar
cells were measured on a Newport-74125 system (Newport Instru-
ments). The intensity of monochromatic light was measured with
a Si detector (Newport-71640). The electrochemical impedance
spectroscopy (EIS) measurements of all the DSSC were performed
using a Zahner IM6e Impedance Analyzer (Zahner-Elektrik GmbH &
CoKG, Kronach, Germany). The frequency range is 0.1 Hz–100 kHz.
The magnitude of the alternative signal is 10 mV.
of compound 2 and dichlorodioctylsilane [19]. Compound 4, pre-
pared in a high yield of 81% through selective monoformylation of
3 by controlling the dosage of DMF and POCl3 [20], was bromi-
nated by N-bromosuccinimide (NBS) in chloroform to afford 5
[21]. Chloroform used as solvent in the bromination step avoided
the inconvenience of using hard-removed DMF [22]. The elec-
tron donor unit was synthesized in several steps with carbazole
and 2-bromothiophene as original materials. Carbazole and 2-
bromothiophene were refluxed in a mixture of CuI, 18-Crown-6,
K2CO3 in DMF to afford 7 in 31% yield [23]. Compound 8, prepared
by monobromination of 7, was reacted with 2-methylbut-3-yn-2-ol
under the catalysis of Pd(PPh3)2Cl2, PPh3, CuI in argon protec-
tion to afford 9 in 82% yield [24]. The terminal acetylene 10
was synthesized in 74% yield by refluxing of 9 in potassium
hydroxide/isopropanol solution [25]. After synthesizing 11 through
Sonogashira reaction of 10 and 5, the final dye CTDTSCA was
obtained via Knoevenagel condensation reaction of the aldehyde
11 and cyanoacetic acid in the presence of piperidine catalyst in
70% yield [26]. The synthetic methods of dye CTCA and DTSCA
were similar to but much simpler than that of CTDTSCA. CTCA was
obtained by the treatment of 9-(thiophen-2-yl)-9H-carbazole with
Vilsmeier–Haack reaction and Knoevenagel condensation. DTSCA
was obtained by the Knoevenagel condensation reaction of 4 and
cyanoacetic acid in presence of piperidine.
2.6. Theoretical calculations
Theoretical calculations based on density functional theory
method have been performed with Gaussian 09 program [17]. The
calculations were performed with the B3LYP exchange correlation
functional under 6–31G (d) basis.
3. Results and discussion
3.1. Synthesis
CTDTSCA was obtained by several steps according to the syn-
thetic routes shown in Scheme 1. Starting from the coupling of
3-bromothiophene in the presence of LDA and CuCl2, [18] 4,4ꢀ-
dioctyl-dithieo[3,2-b:2ꢀ,3ꢀ-d]silole (3) was obtained by the reaction
3.2. UV–vis absorption and emission spectra
The UV–vis absorption spectra of the organic dyes in THF are
shown in Fig. 1. The CTDTSCA has an intense absorption spectrum

58
J. Liu et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 54–61
Fig. 1. UV–vis absorption spectra of CTDTSCA, CTCA, DTSCA.
Fig. 3. Absorption spectra of CTDTSCA, CTCA and DTSCA anchoring on the 10 ␮m
porous TiO2 nanoparticle films.
centerd at 450 nm (ε = 4.2 × 104 M−1 cm−1). It shows obvious red-
the HOMO level of CTDTSCA (−5.14 eV) is lower than the redox
potential of I−/I3− couple (−4.60 eV) [28,29], allowing the oxidized
sensitizer to accept electrons from I− to regenerate CTDTSCA and
avoid the charge recombination between the oxidized dyes and
photo-injected electrons in the TiO2 film. For comparison, the cyclic
voltammetry curves of CTCA and DTSCA were also measured.
As shown in Table 1, CTDTSCA possesses a higher HOMO level
than DTSCA, it may be due to effective electron-donating function
of carbazole unit and the broadened ␲ conjugation with thiophene-
ethynyl-DODTS. DTSCA shows the lowest LUMO level among the
three dyes, and CTDTSCA has a lower LUMO level than CTCA, indi-
cating that the incorporation of DODTS decrease the LUMO level
remarkably.
shift in contrast to the maximum absorption wavelength (ꢀmax
)
of CTCA (400 nm) and DTSCA (409 nm), demonstrating remarkable
effect of DODTS unit in narrowing the energy gap and the effective
electron-donating function of carbazole unit. The emission spectra
of the organic dyes in THF are shown in Fig. 2. The emission band
of CTDTSCA was centerd at 554 nm when excited on its maximum
absorption.
Absorption spectra of CTDTSCA, CTCA and DTSCA anchoring on
the 10 ␮m porous TiO2 nanoparticle films are shown in Fig. 3, the
ꢀmax of CTDTSCA exhibits slightly blue-shifted behaviour in com-
parison with that in THF solution. It may attribute to the weaker
electron drawing effect of carboxylate–TiO2 unit compared to car-
boxylic acid.
3.4. Theoretical calculations
3.3. Electrochemical properties
As replacing the octyl chains linked to silicon with methyl won’t
make obvious difference in energy or molecular topology of the
frontier orbitals [32], the density functional theory (DFT) calcula-
tions of dimethyl substituted silicon CTDTSCA, CTCA and DTSCA
were performed. The isodensity surface plots of HOMO and LUMO
of dimethyl substituted silicon CTDTSCA, CTCA and DTSCA were
presented in Fig. 5.
HOMO and LUMO level of dimethyl-substituted CTDTSCA, CTCA
and DTSCA calculated by Guassian 09 are −5.35 eV and −2.90 eV,
−5.81 eV and −2.75 eV, −5.71 eV and −2.69 eV, respectively. The
The first ground-state oxidation potential (Eox), which is cor-
responding to the HOMO level of dye, was measured by cyclic
voltammetry (CV) with 0.1 M tetrabutylammonium hexafluo-
rophosphate (TBAPF6) in acetonitrile solution, the results are
represented in Fig. 4 and Table 1. The LUMO levels of sensitizers
were calculated by the values of HOMO and the zero-zero excita-
tion energy (E0–0), and the latter was estimated from the absorption
onset. The energy offset of LUMO (−3.14 eV for CTDTSCA) with
respect to the TiO2 conduction band edge (−4.00 eV) [27] provides
an effective driving force for the electron-injection process. Besides,
Fig. 2. Emission spectra of CTDTSCA, CTCA, DTSCA.
Fig. 4. Cyclic voltammograms of CTDTSCA, CTCA, and DTSCA anchored on TiO2.

J. Liu et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 54–61
59
Table 1
Photophysical and electrochemical data for dyes.
a
b
c
d
Dye
ꢀonset (nm)
Eg (eV)
Eonset (eV)
EHOMO (eV)
ELUMO (eV)
ox
CTDTSCA
CTCA
DTSCA
550
490
503
2.24
2.53
2.46
0.98
1.10
1.35
−5.38
−5.50
−5.75
−3.14
−2.97
−s3.29
a
Absorption spectra of dyes on TiO2 were obtained through measuring the dye adsorbed on TiO2 nanoparticle film in CH2Cl2 solution.
b
c
The optical gap Eg was estimated from the onset point of the absorption spectra: Eg = 1240/ꢀonset
.
The oxidation potentials of dye anchored on TiO2 were measured with 0.1 M tetrabutylammonium hexaflurophosohate (TBAPF6) as electrolyte, HOMO was estimated
from EHOMO = −(4.4 + Eonsetox) eV [30,31].
d
ELUMO = EHUMO + Eg.
Fig. 5. Frontier molecular orbital of dimetyl-substituted CTDTSCA, CTCA and DTSCA.
energy gaps are 2.45 eV, 3.06 eV, 3.02 eV, respectively. These results
are close to the data from CV. The slight difference of the theoretical
calculations and experimental data can be attributed to the neglect
of solvent effect in theory calculation, the tendency of DFT to over-
estimate ␲-conjugation and the replacement of octyl with methyl
[33].
3.5. Photovoltaic performances
The incident monochromatic photon-to-current conversion
efficiency (IPCE) spectra of DSSC sensitized by CTDTSCA, CTCA and
DTSCA are shown in Fig. 6. The IPCE of CTDTSCA exceeds 60% from
364 nm to 500 nm, reaching its maxima of nearly 70%. The IPCE
spectrum of CTDTSCA is higher and greatly wider than that of CTCA,
as can be expected from the absorption spectra. It may be attributed
to good electron-transferring capacity and effective function in nar-
rowing the energy gap of DODTS unit. The IPCE of CTCA exceeds
50% from 370 nm to 510 nm and reaches its peak of nearly 65%,
while the IPCE of DTSCA almost stays below 20%. It implicates that
DODTS unit plays little role in electron-donating and N-substituted
carbazole displays strong electron-donating effect in the CTDTSCA
molecule.
The reason of the improved performance of CTDTSCA can also be
proved by theoretical calculation (Fig. 5). As shown in Fig. 5, HOMO
of dimethyl-substituted CTDTSCA is delocalized through the whole
molecule. LUMO of dimethyl-substituted CTDTSCA was popu-
lated over thiophene, ethynyl, dimethyl-substituted dithienosilole
(DMDTS) and cyanoacrylic acid fragments with sizable contribu-
tion from DMDTS and cyanoacrylic acid fragments. This spatially
directed separation of HOMO and LUMO is an ideal condition for
Fig. 6. IPCE spectra of DSSC based on CTDTSCA, CTCA and DTSCA.
dye-sensitized solar cell, which facilitates ultrafast interfacial elec-
tron injection from excited dyes to TiO2.
Additionally, the hole location on the carbazole unit facilities
the electron donor to approach, promoting the dye regeneration.
Furthermore, HOMO and LUMO exhibit overlapping extension to
the thiophene, ethyne and DMDTS spacers, strengthening the elec-
tronic coupling parallel to the transition dipole moment between
the two electronic states, which in turn increases the strength
between the two states. It’s worthy to mention that ꢁ*–␲* hyper-
conjugation, characteristic of the silole ring, was not inspected
from the LUMO orbital plot, probably arising from the energetic

60
J. Liu et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 54–61
Table 2
Photovoltaic performance of DSSC sensitized by CTDTSCA, CTCA, DTSCAa.
Dye
Jsc (mA cm−2
)
Voc (V)
FF
Á (%)
CTDTSCA
CTCA
DTSCA
10.54
6.48
1.64
0.68
0.62
0.52
0.67
0.71
0.67
4.80
2.83
0.57
a
Under AM 1.5 illumination (power 100 mW cm−2
) with an active area of
0.25 cm2.
Fig. 8. EIS Nyquist plots (i.e., minus imaginary part of the impedance −Zꢀꢀ vs the real
part of the impedance Zꢀ when sweeping the frequency) for DSSC based on CTDTSCA
and CTCA dyes.
Fig. 7. Photocurrent density vs voltage for DSSC based on CTDTSCA, CTCA and DTSCA
under AM 1.5 G simulated solar light (100 mW cm−2).
stabilization of carbon-backbone-based ␲*-orbital by the strong
electron-withdrawing cyanoacrylic fragment.
The photovoltaic parameters of DSSC sensitized by CTDTSCA,
CTCA and DTSCA are listed in Table 2. Fig. 7 shows the current
density–voltage (J–V) curves of the DSSC sensitized by the above
dyes under standard global AM 1.5G solar irradiation. The short-
circuit photocurrent density (Jsc), open-circuit voltage (Voc), and fill
factor (FF) of the solar cell based on CTDTSCA are 10.54 mA cm−2
,
0.67 V, and 0.67, respectively, yielding an overall power conversion
efficiency (␩) of 4.80%. Under the same condition, the devices based
on CTCA and DTSCA obtained much lower conversion efficiencies
of 2.83% and 0.57%, respectively. These differences in photovoltaic
properties were consistent with the IPCE-␭ spectra, in which the
curve of CTDTSCA is higher and broader than that of CTCA and
DTSCA. It indicates that the introduction of DODTS can effectively
improve the performance of dye sensitizer. The poor performance
of DSSC sensitized by DTSCA presumably owed to the lack of
rich-electron group, for example, carbazole. DSSC sensitized by
CTDTSCA and CTCA both got a medium or higher power conversion
efficiency, these results reflect effective electron-donating function
of N-substituted carbazole.
The electrochemical impedance spectroscopy (EIS) was carried
on in the dark. The EIS analysis provides information about inter-
facial charge transfer process. Fig. 8 shows the typical Nyquist
plots of both electrodes at an applied bias of −0.70 V. In both
cells, a larger semicircle occurs in the lower frequency range and
a smaller semicircle occurs in the higher frequency range. The
larger semicircle corresponds to the charge-transfer process at
the TiO2/dye/electrolyte interface, while the smaller semicircle
corresponds to the charge-transfer process at the Pt/electrolyte
interface. The difference in smaller semicircles at higher frequen-
cies is small, but the difference in larger semicircles is significant.
The much larger radii of the lower frequency semicircles of the
CTDTSCA cell indicates a stronger charge-transfer resistance at the
TiO2/dye/electrolyte interface.
Fig. 9. EIS Bode plots (i.e., the phase of the impedance vs the frequency) for DSSC
based on CTDTSCA and CTCA dyes.
the charge transfer at the Pt/electrolyte interface and the one at
lower frequency corresponds to the charge-transfer process at the
TiO2/dye/electrolyte interface. The characteristic frequency of the
lower frequency peak in the Bode plot is related to the charge
recombination rate, and its reciprocal is associated with the elec-
tron lifetime [34,35]. The lower frequency peak of the CTDTSCA
cell shifts to a lower frequency compared to the CTCA cell, indicat-
ing less charge recombination and longer electron lifetime at the
TiO2/dye/electrolyte interface. Both the EIS Nyquist and Bode plots
suggest that the insert of DODTS unit in the dye molecule greatly
improves the charge-transfer ability at the TiO2/dye/electrolyte
interface. We deduce that the long octyl chains may partly act as
the blocking units between TiO2 surface and electrolyte, preventing
−
I3 ions approaching the TiO2 surface.
4. Conclusion
To summarize, we had successfully synthesized a novel D–␲-
A pattern organic dye sensitizer CTDTSCA, in which dithienosilole
unit acted as ␲-conjugated system, carbazole moiety acted as elec-
tron donor, and cyanoacrylic acid unit acted as electron acceptor.
The DSSC sensitized by it reached a medium-high power conver-
sion efficiency of 4.80%. It indicated that the dye with N-substituted
Fig. 9 shows the EIS Bode plots of the DSSC based on CTDTSCA
and CTCA. The peak feature at higher frequency corresponds to

J. Liu et al. / Journal of Photochemistry and Photobiology A: Chemistry 294 (2014) 54–61
61
carbazole utilized as the electron donor can obtain promising pho-
toelectric property. CTDTSCA possesses larger absorption maxima
and narrower energy gap than that of CTCA (in which thiophene
acted as ␲-conjugated system), leading to DSSC sensitized by
CTDTSCA possesses better photovoltaic performances than DSSC
sensitized by CTCA. It may be attributed to the incorporation of
DODTS unit, which can broaden the ␲-conjugation and effectively
reduce the LUMO level. These results revealed the potential value
of DODTS unit in designing ideal organic dye sensitizer.
[9] N. Koumura, Z.S. Wang, S. Mori, M. Miyashita, E. Suzuki, K.A. Hara, J. Am. Chem.
Soc. 128 (2006) 14256–14257.
[10] (a) Q.Q. Li, L.L. Lu, C. Zhong, J. Shi, Q. Huang, X.B. Jin, T.Y. Peng, J.G. Qin, Z. Li, J.
Phys. Chem. B 113 (2009) 14588–14595;
(b) Q.Q. Li, L.L. Lu, C. Zhong, J. Huang, Q. Huang, J. Shi, X.B. Jin, T.Y. Peng, J.G. Qin,
Z. Li, Chem. Eur. J. 15 (2009) 9664–9668.
[11] V. Jeux, D. Demeter, P. Leriche, J. Roncali, RSC Adv. 3 (2013) 5811–5814.
[12] (a) A.J. Qin, J.W.Y. Lam, B.Z. Tang, Prog. Polym. Sci. 37 (2012) 182–209;
(b) S.C. Yin, J. Zhang, H.K. Feng, Z.J. Zhao, L.W. Xu, H.Y. Qiu, B.Z. Tang, Dyes Pig-
ments 95 (2012) 174–179;
(c) W.F. Shu, C.W. Guan, W.H. Guo, C.Y. Wang, Y.J. Shen, J. Mater. Chem. 22
(2012) 3075–3081;
(d) J. Liu, C.X. Yan, S.S. Li, C.Y. Wang, Y.J. Shen, Chin. J. Chem. 30 (2012)
2861–2868.
[13] K.H. Lee, J. Ohshita, A. Kunai, Organometallics 23 (2004) 5481–5487.
[14] J. Ohshita, M. Nodono, T. Watanabe, Y. Ueno, A. Kunai, Y. Harima, K. Yamashita,
J. Organomet. Chem. 553 (1998) 487–491.
Acknowledgements
The authors are grateful to financial support from the National
Natural Science Foundation of China (No. 20872035, 21076078),
Hangzhou Normal University, and the East China University of Sci-
ence and Technology.
[15] D. Enders, R. Pieter, B. Renger, D. Seebach, Org. Synth. 6 (1988) 542.
[16] N. Miyaura, A. Suzuki, Org. Synth. 8 (1993) 532.
[17] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino, G. Zheng, J.L. Sonnenberg, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M.
Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R. Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M.
Cossi, N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C.
Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth,
P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman,
J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, Revision A. 01, Gaussian, Inc.,
Wallingford, CT, 2009.
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.jphotochem.
2014.07.021.
References
[18] S. Mishra, A. Palai, R. Srivastava, M. Kamalasanan, M. Patr, J. Polym. Sci., A:
Polym. Chem. 47 (2009) 6514–6525.
[19] G. Lu, H. Usta, C. Risko, L. Wang, A. Facchetti, M.A. Ratner, T.J. Marks, J. Am.
Chem. Soc. 130 (2008) 7670–7685.
[20] L.Y. Lin, C.H. Tsai, K.T. Wong, T.W. Huang, L. Hsieh, S.H. Liu, H.W. Lin, C.C. Wu,
S.H. Chou, S.H. Chen, A. Tsa, J. Org. Chem. 75 (2010) 4778–4785.
[21] P.M. Beaujuge, W. Pisula, H.K. Tsao, S. Ellinger, K. Müllen, J.R. Reynolds, J. Am.
Chem. Soc. 131 (2009) 7514–7515.
[1] R. Faccio, W.L. Fernández, H. Pardo, A.W. Mombrú, Recent Pat. Nanotechnol. 5
(2011) 46–62.
[2] (a) S. Ito, S.M. Zakeeruddin, B.R. Humphry, P. Liska, R. Charvet, P. Comte, M.K.
Nazeeruddin, P. Pechy, M. Takata, H. Miura, S. Uchida, M. Gra˘tzel, Adv. Mater.
18 (2006) 1202–1205;
(b) S. Ito, H. Miura, S. Uchida, M. Takata, K. Sumioka, P. Liska, P. Comte, P. Pechy,
M. Gra˘tzel, Chem. Commun. 41 (2008) 5194–5196;
(c) G. Zhang, H. Bala, Y. Cheng, D. Shi, X. Lv, Q. Yu, P. Wang, Chem. Commun. 16
(2009) 2198–2200;
(d) H. Im, S. Kim, C. Park, S.H. Jang, C.J. Kim, K. Kim, N.G. Park, C. Kim, Chem.
Commun. 46 (2010) 1335–1337.
[22] R.H. Mitchell, Y.H. Lai, R.V. Williams, J. Org. Chem. 44 (1979) 4733–4735.
[23] Q. Zhang, J.S. Chen, Y.X. Cheng, L.X. Wang, D.G. Ma, X.B. Jing, F.S. Wang, Mater.
Chem. 14 (2004) 895–900.
[24] R.A. Batey, M. Shen, A.J. Lough, Org. Lett. 4 (2002) 1411–1414.
[25] A.O. King, N. Yasuda, Organomet. Chem. 6 (2004) 205–245.
[26] K. Do, D. Kim, N. Cho, S. Paek, K. Song, J. Ko, Org. Lett. 14 (2012) 222–225.
[27] G. Zhang, Y. Bai, R. Li, D. Shi, S. Wenger, S.M. Zakeeruddin, M. Gra˘tzel, P. Wang,
Energy Environ. Sci. 2 (2009) 92–95.
[3] W. Zeng, Y. Cao, Y. Bai, Y. Wang, Y. Shi, M. Zhang, F. Wang, C. Pan, P. Wang,
Chem. Mater. 22 (2010) 1915–1925.
[4] (a) S.G. Awuah, J. Polreis, J. Prakash, Q.Q. Qiao, Y.J. You, J. Photochem. Photobiol.
A 224 (2011) 116–122;
(b) W.Y. Wong, G.J. Zhou, X.M. Yu, H.S. Kwok, B.Z. Tang, Adv. Funct. Mater. 16
(2006) 838–846;
[28] A. Hagfeldf, M. Gra˘tzel, Chem. Rev. 95 (1995) 49–68.
[29] M. Gra˘tzel, Nature 414 (2001) 338–344.
(c) G. Zhou, W.Y. Wong, B. Yao, Z. Xie, L. Wang, Angew. Chem. Int. Ed. 46 (2007)
1149–1151.
[5] R. Tarsang, V. Promarak, T. Sudyoadsuk, S. Namuangruk, S. Jungsuttiwong, J.
Photochem. Photobiol. A 273 (2014) 8–16.
[6] Y. Ooyama, Y. Shimada, A. Ishii, G. Ito, Y. Kagawa, I. Imae, K. Komaguchi, Y.
Harima, J. Photochem. Photobiol. A 203 (2009) 177–185.
[7] A.C. Onicha, K. Panthi, T.H. Kinstle, F.N. Castellano, J. Photochem. Photobiol. A
223 (2011) 57–64.
[30] A.K. Agrawal, S.A. Jenekhe, Chem. Mater. 8 (1996) 579–589.
[31] Y.F. Li, Y. Cao, J. Gao, D.L. Wang, G. Yu, A.J. Heeger, Synth. Met. 99 (1999)
243–248.
[32] H. Huang, J. Youn, R.P. Ortiz, Y. Zheng, A. Facchetti, T. Marks, Chem. Mater. 23
(2011) 2185–2200.
[33] J.R. Reimers, Z.L. Cai, A. Bilic, N.S. Hush, Ann. N.Y. Acad. Sci. 1006 (2003)
235–251.
[34] M. Adachi, M. Sakamoto, J. Jiu, Y. Ogata, S. Isoda, J. Phys. Chem. B 110 (2006)
[8] Z.S. Wang, N. Koumura, Y. Cui, M. Takahashi, H. Sekiguchi, A. Mori, T. Kubo, A.
Furube, K. Hara, Chem. Mater. 20 (2008) 3993–4003.
13872–13880.
[35] Q. Wang, J. Moser, M. Gra˘tzel, J. Phys. Chem. B 109 (2005) 14945–14953.