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C.-G. Wu et al. / Dyes and Pigments 99 (2013) 1091e1100
focuses on the theoretical calculations using density functional
theory (DFT) and time-dependent DFT (TD-DFT), complementing
experiments, to study the structure, electronic absorption spectra,
energy levels of the sensitizers both in solution [19e24] and on TiO2
clusters [25e29]. The results provide useful information to expedite
the development of appropriate dyes for DSSCs.
2.3.1. Synthesis of 3,6-di-tert-butyl-9-9H-carbazole-2-thiophen-
4,4-dimethyl-2H-cyclo-penta[2,1-b;3,4-b0]dithiophene-2-acrylic
acid (W-1)
(W-1) was prepared by refluxing the mixture of 3,6-di-tert-
butyl-9-9H-carbazole-2-thiophen-4,4-dimethyl-2H-cyclopenta
[2,1-b;3,4-b0]di-thiophene-2-car-boxaldehyde (1.0 g, 1.7 mmol, see
ESI), NH4OAc (0.20 g, 2.6 mmol), and CNCH2COOH (0.22 g,
2.6 mmol) in CH3COOH (50 mL) for 6 h under Ar. CHCl3 was used to
extract the product, after recrystallization, W-1 dye was obtained as
a red solid, mp ¼ 285 ꢂC (decomposed). IR (1679 cmꢁ1 (C]O);
2213 cmꢁ1 (C^N), see Figure S2, ESI). 1H NMR (Figure S3 (ESI),
300 MHz, dH/ppm in DMSO-d6): 1.45 (18H, s), 1.60 (6H, s), 7.48 (1H,
d, 3.8 Hz), 7.60 (5H, m), 7.73 (1H, s), 8.10 (1H, s), 8.41 (2H, s), 8.52
(1H, s). 13C NMR (Figure S4 (ESI), 300 MHz, dH/ppm in DMSO-d6):
24.41, 31.75, 34.56, 44.99, 109.53, 116.88, 117.28, 118.81, 123.17,
123.48, 124.14, 125.40, 132.35, 132.96, 134.17, 136.63, 137.53, 139.20,
141.85, 143.71, 146.58, 147.00, 160.63, 164.08, 165.95. MS: m/z 660
([M]ꢃ); HRAB-MS found: m/z 660.3426. Elemental analysis: calcd.
for C39H36N2O2S3.H2O: C, 69.02; H, 5.60; N, 4.13; S, 14.16%. Found: C,
68.48; H, 5.73; N, 4.17; S, 14.10%.
This article reports the photovoltaic performance of a series new
De
part of the conjugated spacer. It was known that dithiophene is
generally used as a linker for high-efficiency De eA photo-
peA organic dyes containing cyclopentadithiophene moiety as a
p
sensitizers. Compared to dithiophene, cyclopentadithiophene
(CPDT) unit has a more rigid conjugation structure, higher absorp-
tion coefficient [30] and better charge mobility [31] as well as facile
structure modification. Therefore CPDT has been generally used as a
monomer for the low band-gap polymer [32e35]. Furthermore,
cyclopentadithiophene moiety may act as a photon absorber where
the charge separation occurs, and migrates to the opposite di-
rections by the presence of the donor and acceptor units at each side,
increasing the separation of the excitons. Nevertheless, cyclo-
pentadithiophene is not generally employed in the high-efficient
organic dyes. Therefore, knowing the parameters which deter-
mine the photovoltaic performance of cyclopentadithiophene-
containing organic dyes is the focus of this article.
2.3.2. Synthesis of 3,6-di-tert-butyl-9-[5-(thiophen-2-yl)thiophen-
2-yl]-9H-carbazole-4,4-dimethyl-2H-cyclopenta[2,1-b;3,4-b0]
dithiophene-2-acrylic acid (W-2)
2. Experimental
The preparation procedures of W-2 dyes are the same as those
for synthesizing W-1 dye except 3,6-di-tert-butyl-9-[5-(thiophen-
2-yl)thiophen-2-yl]-9H-carbazole instead of 3,6-di-tert-butyl-9-
(thiophen-2-yl)-9H-carbazole (2.93 g, 6.8 mmol, see ESI) was used
to react with Me3SnCl (1.5 M, 3 mL). 3,6-di-tert-butyl-9-[5-(thio-
phen-2-yl)thiophen-2-yl]-9H-carbazole was prepared by Stille
coupling between 3,6-di-tert-butyl-9-[5(trimethylstannanyl)-thio-
phen-2-yl]-9H-carbazole and 2-bromothiohene. W-2 dye was iso-
lated as a dark green solid, mp ¼ 300 ꢂC (decomposed). IR
(1679 cmꢁ1 (C]O); 2213 cmꢁ1 (C^N), see Figure S2, ESI). 1H NMR
2.1. Materials
All reagents were obtained from the commercial resources and
used as received unless specified. Solvents were dried over sodium
or CaH2 before use. Unless otherwise specified, all reactions were
performed under an Ar atmosphere using the standard Schlenk
techniques. All chromatographic separations were carried out on
the silica gel (60M, 240e400 mesh) column. The structures of dyes
and their intermediates were identified with 1H NMR spectra. The
structure of the final products was further confirmed by IR, 13C NMR
spectra, FAB-MS and elemental analysis.
spectrum was displayed in Figure S5 (ESI). 1H NMR (300 MHz, dH
/
ppm in DMSO-d6): 1.51 (18H, s), 1.57 (6H, s), 7.50 (8H, m), 7.71 (1H,
s), 8.06 (1H, s), 8.39 (2H, s), 8.47 (1H, s). 13C NMR (Figure S6,
300 MHz, dH/ppm in DMSO-d6): 24.87, 32.21, 35.01, 45.50, 109.99,
117.27, 119.08, 119.18, 123.59, 123.86, 124.63, 125.59, 125.92, 126.03,
130.60, 133.54, 133.91, 135.62, 136.52, 137.69, 137.84, 139.72, 140.93,
144.02, 144.18, 161.05, 165.28, 165.55. MS: m/z 742 ([M]ꢃ); LRFAB-
MS found: m/z 742.2990. Elemental analysis: calcd. for
2.2. Physicochemical studies
1H and 13C NMR spectra were recorded with a Bruker 300 MHz
NMR spectrometer in CDCl3 or [D6]DMSO. FAB-MS spectra were
obtained using the JMS-700 HRMS. UV/Vis spectra of dyes in THF
C43H38N2O2S4.0.5H2O: C, 68.71; H, 5.19; N, 3.72; S, 17.04%. Found: C,
and adsorbed on TiO2 (4
mm thickness) films were measured using a
68.69; H, 5.04; N, 3.27; S, 17.05%.
Cary 300 Bio spectrometer. Photoluminescence spectra (in THF
solutions, Figure S1, ESI) were obtained using a Hitachi F-4500
spectrophotometer in the laboratory atmosphere at room temper-
ature. Cyclic voltammetric measurement was performed in a
single-compartment, three-electrode cell with an ITO glass work-
ing electrode and a Pt wire counter electrode. The reference elec-
trode was Ag/Agþ and the supporting electrolyte was 0.1 M LiClO4
in THF using an Autolab system (PGSTAT 30, Autolab, Eco-Chemie,
the Netherlands), the scan rate is 50 mV sꢁ1 and the ferrocene/
ferrocinium redox couple was used as an external calibration
standard. Elemental analysis was carried out with a Heraeus CHNe
OeS Rapid-F002 analysis system. The thickness of TiO2 film was
measured by a profile-meter (Dektak3, Veeco/Sloan Instruments
Inc., USA).
2.3.3. Synthesis of 3,6-di-tert-butyl-9-(3-octylthiophen-2-yl)-9H-
carbazole-4,4-dimethyl-H-cyclopenta[2,1-b;3,4-b0]di-thiophene-2-
acrylic acid (W-3)
The preparation procedures of W-3 dye is the same as those for
the synthesis of W-1 dye except 2-bromo-3-octylthiophene instead
of 2-bromothiophene was used to react with 3,6-ditert
butylcarbazole. W-3 dye was isolated as a red solid, mp ¼ 240 ꢂC
(decomposed). IR (1679 cmꢁ1 (C]O); 2213 cmꢁ1 (C^N), see
Figure S2, ESI).1H NMR spectrumwas displayed in Figure S7 (ESI).1H
NMR (300 MHz, dH/ppm in DMSO-d6): 0.81 (3H, t, 7.0 Hz),1.08 (10H,
s),1.48 (18H, s),1.51 (8H, s), 2.33 (2H, t, 7.2 Hz), 7.23 (1H, s), 7.26 (1H,
s), 7.59 (3H, m), 7.71 (1H, s), 8.09 (1H, s), 8.38 (2H, s), 851 (1H, s). 13
C
NMR (Figure S8 (ESI), 300 MHz, dH/ppm in DMSO-d6): 14.04, 22.54,
24.94, 27.61, 29.04, 29.08, 29.79, 31.70, 31.99, 34.75, 45.66, 92.65,
109.63, 116.27, 116.70, 117.57, 123.54, 123.89, 124.56, 130.84, 132.59,
133.09, 134.98, 136.43, 140.57, 142.17, 143.55, 144.28, 148.05, 149.53,
161.30, 166.51, 169.01. MS: m/z 772 ([M]ꢃ); LRFAB-MS found: m/z
772.4457. Elemental analysis: calcd. for C47H52N2O2S3.0.5H2O: C,
72.21; H, 6.91; N, 3.59; S,12.29%. Found: C, 72.62; H, 6.86; N, 3.55; S,
12.55%.
2.3. Synthesis of W-series dyes
The detailed synthesis and characterization of all intermediates
and the IR spectra as well as 1H and 13C NMR spectra (Figures S2e
S10) of these four metal free dyes can be found in the electronic
supporting information (ESI).