Substituted carbazole dyes for efficient molecular photovoltaics: Long electron lifetime and high open circuit voltage performance

Article abstract of DOI:10.1039/b905831a

We designed and synthesized new substituted carbazole dyes, MK-14 and -16, for dye-sensitized solar cells (DSSCs) employing the I^-/I ₃^- redox couple. By the addition of a hexyloxyphenyl substituent to previously reported c

Full text of DOI:10.1039/b905831a

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Substituted carbazole dyes for efficient molecular photovoltaics: long electron
lifetime and high open circuit voltage performance†
Nagatoshi Koumura, a Zhong-Sheng Wang,b Masanori Miyashita,c Yu Uemura,c Hiroki Sekiguchi,d Yan Cui,b
*
d
Atsunori Mori, Shogo Mori and Kohjiro Hara
c
b
*
*
Received 23rd March 2009, Accepted 24th April 2009
First published as an Advance Article on the web 29th May 2009
DOI: 10.1039/b905831a
We designed and synthesized new substituted carbazole dyes, MK-14 and -16, for dye-sensitized solar
ꢀ
cells (DSSCs) employing the Iꢀ/I3 redox couple. By the addition of a hexyloxyphenyl substituent to
previously reported carbazole dyes MK-1 and -2, the electron lifetime and open circuit voltage of the
DSSCs employing these dyes were increased, showing comparable values with those using
a conventional Ru complex dye. This result was achieved by the retardation of the charge
recombination, caused by more effective blocking of the I3ꢀ ion in the electrolyte than that in the cases
of MK-1 and -2. The result shows the importance of the position of alkyl chains attached to the main
framework of dye molecules.
In a previous report, we developed carbazole dyes with an
Introduction
alkyl-functionalized oligothiophene linker to a cyanoacetic acid
moiety as an acceptor (MK-1 and -2, Fig. 1).7 In comparison to
MK-3, which has no alkyl chain, we found that the alkyl chains
on the thiophenes helped to form a blocking layer for I3ꢀ ions to
be kept away from the TiO2 electrode surface, hence increasing
the electron lifetime and open circuit voltage (VOC). To our
knowledge, this is the first example of the addition of a function
to organic dyes that retards charge recombination. Note that it is
not evident that the addition of alkyl chain results in the retar-
dation of charge recombination.8 It is important where the alkyl
chains are attached and the packing density of the adsorbed
dyes.8,9 In a series of coumarin dyes, we have observed that larger
sized dye molecules tend to have a long electron lifetime.5 We
have synthesized large molecules of carbazole dyes having up to
six thiophenes with alkyl chains.9 Despite the expectation, VOC
was not improved. Even incident photon-to-current conversion
efficiency (IPCE) tended to decrease with an increasing number
Dye-sensitized solar cells (DSSCs) have become one of the
promising molecular photovoltaics due to the high photo-to-
current conversion efficiency as compared with amorphous
silicon solar cells and the potential of low-cost production.1,2
Recently, organic dyes have been attracting much attention with
respect to their application to molecular photovoltaics. While
ruthenium complex dyes3 have kept the highest efficiency since
the pioneering study,1 a large number of organic dyes for use as
molecular photovoltaics have been designed and synthesized
because of the potential of organic dyes, such as the facile
structural modification and high absorption coefficient.4 The
highest energy conversion efficiency of DSSCs based on organic
dyes (ꢁ9%), however, is still lower than that based on ruthenium
dyes (ꢁ11%). The reason for the lower efficiency is mostly faster
charge recombination of the injected electron in the nanoporous
TiO2 electrode to a redox species in liquid electrolyte.5 Recent
papers also show that DSSCs employing metal complex dyes
such as porphyrin and phthalocyanine dyes, also suffer from fast
recombination.6 Thus, to improve the efficiency of DSSCs,
a design guide for sensitizing dyes to retard the recombination is
essential.
aPhotonics Research Institute, National Institute of Advanced Industrial
Science and Technology (AIST), 1–1–1 Higashi, Tsukuba, Ibaraki,
305-8565, Japan. E-mail: n-koumura@aist.go.jp; Fax: +81 29 861 6303;
Tel: +81 29 861 6252
bResearch Center for Photovoltaics, AIST, 1–1–1 Higashi, Tsukuba,
Ibaraki, 305-8565, Japan. E-mail: k-hara@aist.go.jp
cDepartment of Fine Materials Engineering, Shinshu University, 3-15-1
Tokida, Ueda, Nagano, 386-8567, Japan. E-mail: shogmori@shinshu-u.
ac.jp
dDepartment of Chemical Science and Engineering, Kobe University, 1-1
Rokkodai, Noda-ku, Kobe, Hyogo, 657-8501, Japan
† Electronic supplementary information (ESI) available: UV-vis spectra
of MK-1 and -2, IPCE action spectra for DSSCs based on MK-1 and
-2, electron diffusion coefficients and lifetime, a plot of VOC vs electron
density in the DSSCs. See DOI: 10.1039/b905831a
Fig. 1 Molecular structures of organic dyes, MK-1, -2, -14 and -16.
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of thiophenes. The problem with the larger dyes here seems to be
undesired aggregation of the dyes on the TiO2 surface,9 causing
a larger space which allows I3ꢀ to penetrate into the dye layer.
To improve the photovoltaic performance of MK dyes, we
designed and synthesized substituted carbazole dyes, MK-14 and
MK-16, which have a hexyloxyphenyl substituent10 on the
carbazole moiety on the opposite side to an oligothiophene
linker, shown in Fig. 1. Our strategy for the molecular design of
these new dyes was based on two concepts: a further retardation
of charge recombination without causing undesired aggregation
by the addition of the substitute normal to the direction to the
alkyl chains of MK-1 and -2, and an extension of absorption
wavelength by increasing the carbazole donor ability. Based on
these dyes, comparable VOC and electron lifetime of DSSCs with
those for Ru dyes were achieved.
Fig. 2 UV-vis spectra of dyes, MK-14 (solid line) and -16 (dotted line) in
20%THF-toluene.
Results and discussion
Oligothiophene moieties were constructed by repeated Suzuki
coupling and bromination. The purification of intermediates was
performed by flash column chromatography and subsequent
HPLC. The molecular structures of the compounds were fully
Synthesis and UV spectra of dyes
Substituted carbazole dyes, MK-14 and -16 were prepared from
3-bromo-9-ethylcarbazole as described in Scheme 1 and 2.
Scheme 1 Synthesis of organic dye MK-14; (a) (i) Mg, 4-n-hexyloxy-1-bromobenzene/THF, (ii) NiCl2(dppp)/THF, (b) NBS/THF, (c) 5,50-dimethyl-2-
(4-n-hexylthiophen-2-yl)-1,3,2-dioxaborinane, Pd(PPh3)4, Na2CO3aq/DME, (d) POCl3-DMF/DMF (e) cyanoacetic acid, piperidine/toluene-acetoni-
trile.
Scheme 2 Synthesis of organic dye MK-16; (a) NBS/THF, (b) 5,50-dimethyl-2-(4-n-hexylthiophen-2-yl)-1,3,2-dioxaborinane, Pd(PPh3)4, Na2CO3aq/
DME, (c) POCl3-DMF/DMF, (d) cyanoacetic acid, piperidine/toluene-acetonitrile.
4830 | J. Mater. Chem., 2009, 19, 4829–4836
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confirmed by 1H NMR, 13C NMR and elemental analysis. Fig. 2
shows that the absorption maxima of the dyes were similar with
those of MK-1 and -2 (480 nm, Fig. S1, ESI).9 The absorption
edge of MK-16 in the red region was observed to be slightly
shifted to a longer wavelength than that of MK-14 because of the
larger number of thiophenes in the p-conjugated linker part. Due
to the broad absorption band around 400 nm in the case of MK-
16, however, an aggregation of dye molecules on the TiO2 surface
was considered to easily occur compared to MK-14.
The photovoltaic performances of the DSSCs employing MK-
14 and -16 with a thin-film TiO2 electrode (4.8 mm) are summa-
rized in Table 1, including the data of MK-2 and N719 (a Ru
complex dye). The VOC values for the DSSCs based on MK-14
and -16 were slightly lower and higher than those with N719
under one sun and one tenth sun conditions, respectively. Fill
factor (FF) of DSSCs with MK-14 and -16 were low under one
sun conditions, but increased under one tenth sun conditions.
After one day storage of the cells, FF was also increased (Table
S2, ESI). Fill factor is mainly influenced by series resistance and
shunt resistance of solar cells. Since the change of recombination
rate is little during one day storage (Fig. S3, ESI), the increase of
FF is mainly related to the decrease of series resistance. The
molecular size of MK dyes is larger than that of N719, and thus,
its influence on the diffusion of the redox couple would be
expected. In order to fabricate highly efficient DSSCs, we
prepared the DSSCs from home-made TiO2 particles, denoted as
b in Table 1. With thicker TiO2 films to absorb more light and
Photovoltaic performances
Fig. 3 shows the action spectra of incident photon-to-current
conversion efficiency (IPCE) for DSSCs with MK-14 and -16. In
comparison to MK-1 and -2 (Fig. S2, ESI), the onset wavelengths
were shifted to longer wavelength.7,9 The onset wavelengths for
MK-16 were around 850 nm while that with MK-2 was around 800
nm, suggesting the increased donor ability of MK-16. IPCE values
more than 70% were observed in the range of 400 to 650 nm with
a maximum value of 83% at 530 nm for the DSSC based on MK-
14, while the maximum values for MK-16 were slightly decreased.
ꢀ
with an electrolyte containing a higher concentration of I3 to
increase the conductivity of the electrolytes, increases of Jsc and
FF were obtained. At this moment, the maximum h value of
8.1% for MK-14 was obtained under AM 1.5 G irradiation (100
mW cmꢀ2) with the electrolyte: 0.6 M DMPImI + 0.1 M LiI + 0.2
M I2 + 0.5 M TBP in acetonitrile, and with an aperture mask and
without antireflection film.
Electron lifetime measurements
Fig. 4 shows the electron lifetime and open circuit voltage of the
DSSCs. The electron lifetime in the DSSCs with MK-14 and -16
were improved from those of with MK-2 and they were the
longest among the all organic dyes we have measured.5b Note
that the difference between the lifetimes in the DSSCs/N719 and
those in the DSSCs/MK-2 were smaller than that in the previ-
ously published paper.5b This is probably due to the higher
packing density of MK-2 on the TiO2 by employing toluene for
the dye solution instead of mixed solvents of AN/tBuOH/
toluene. The effect of solvent and packing density in detail will be
addressed elsewhere. Here, under the conditions of low light
intensity, the effect of the additional alkyl chain was more
prominent, that is, a longer lifetime is seen than that of DSSCs
using N719 (Fig. 4(a) and Fig. S4, ESI). This is consistent with
the higher VOC of DSSCs under low light intensity (Table 1). The
VOC is influenced not only by the charge recombination rate but
also by the shift of the conduction band edge potential (ECB) of
TiO2. Fig. 4(b) shows that the VOC values of the DSSCs were the
same at the matched electron density, regardless of the dyes
examined here, suggesting comparable Ecb among the DSSCs.
The retardation of the charge recombination could be caused
Fig. 3 IPCE action spectra for solar cells based on MK-14 (solid line)
and -16 (dotted line).
Table 1 Solar-cell performance for DSSCsa
b
Dye
w/mm
TiO2
JSC/mA cmꢀ2
VOC/V
FF
Eff./%
MK-14c
MK-14
MK-16c
4.8
4.8
4.7
4.7
4.8
4.8
5.1
6.0
a
a
a
a
a
a
a
b
b
b
b
b
11
1.1
11
1.2
9.5
0.72
0.64
0.72
0.65
0.74
0.63
0.69
0.77
0.79
0.76
0.73
0.71
0.64
0.67
0.60
0.66
0.70
0.69
0.64
0.62
0.77
0.71
0.69
0.71
4.8
4.6
4.7
5.0
4.9
4.3
5.0
6.3
6.3
7.8
7.3
8.1
c d
,
c d
,
MK-16
N719c
N719
c d
,
0.97
11
MK-2c
MK-14c
N719c
13.1
10.3
14.5
14.5
16.0
6.0
MK-14e
MK-16e
MK-14f
12.0
12.0
16.5
ꢀ
ꢀ
by more efficient blocking of I3 and/or the decreased I3
concentrations due to the negatively charged oxygen atom in the
substituent. We measured the electron lifetime in DSSCs with
a decreased amount of adsorbed dyes, where the physical
blocking effect was not expected, and observed large decreases of
the lifetime in the DSSCs using MK-14, and -16 (Fig. S5, ESI),
suggesting the physical block is more significant.
a
Incident light: AM 1.5G (100 mW cmꢀ2) with a mask and without an
b
anti-reflection film. TiO2, a: HPW-18NR, cell area, c.a. 0.16 cm2 with
a mask (0.17 cm2), b: home made TiOc with a scattering layer, cell area
c
c.a. 0.25 cm2 with a mask (0.2354 cm2). Electrolyte: 0.6 M DMPImI +
0.1 M LiI + 0.05 M I2 + 0.5 M TBP in acetonitrile. Under a ND10
d
e
filter. 0.6 M DMPImI + 0.1 M LiI + 0.1 M I2 + 0.5 M TBP in
The cause of the longer electron lifetime with the new dyes
than that with N719 under low light intensity is not clear yet. The
drawback of the new dyes was the low fill factor. This might be
f
acetonitrile. 0.6 M DMPImI + 0.1 M LiI + 0.2 M I2 + 0.5 M TBP in
acetonitrile.
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new alkyl chain of MK-14 and MK-16 normal to the adsorption
site would be more effective to block larger molecule redox
couples11 and/or polymer hole conductors.
Conclusions
We newly synthesized hexyloxyphenyl substituted carbazole dyes
for DSSCs and demonstrated that a hexyloxyphenyl substituent
increased the electron lifetime, and consequently gave a higher
open circuit voltage. The result was achieved by having the
blocking effect not only on the lateral direction with respect to
the TiO2 surface as for MK-1 and -2 but also on the normal
direction as for MK-14 and -16. Our approach shows that two
functions: sensitization of TiO2 and retardation of charge
recombination, can be added separately, and such separated
design would provide a wide selection of molecular design for the
functionalization. In comparison to the case of N719, these dyes
still need to be improved in view of electron lifetime. We consider
the shape of the dyes; spherical for N719 and cylindrical for the
MK series, has an important role on the recombination rate.
Experimental section
General methods
1H NMR spectra were recorded on a Bruker Avance400 (400
MHz). 13C NMR spectra were recorded on a Bruker Avance400
(100 MHz). Chemical shifts are denoted in d-unit (ppm) relative
to CDCl3, THF-d8. The splitting patterns are designated as
follows: s (singlet); d (doublet); t (triplet); q (quartet); m
(multiplet) and br (broad). Elemental analyses were measured by
a CE Instruments EA1110 automatic elemental analyzer.
Column chromatography was performed on silica gel (Kanto,
Silica Gel 60N, spherical, 40–50 mm). Most of the organic
compounds were finally purified by preparative HPLC (YRU-
880 detector from SHIMAMURA Tec.) on silica gel (pre-packed
column, CPS-HS-221-05 or CPS-223L-1 from KUSANO
KAGAKU) The solvents were distilled and dried, if necessary,
by standard methods. Reagents and starting materials were used
as obtained from Aldrich, Wako, Kanto Chemical, TCI, Merck.
Absorption spectra were measured with a SHIMADZU UV-
3101PC.
Fig. 4 Electron lifetimes in the DSSCs employing MK (metal free
organic) and N719 (Ru complex) dyes (a), and open circuit voltage (b) as
a function of electron density in the DSSCs.
caused by the decreased ion mobility in the electrolytes, where
the additional alkyl chain would prevent not only the approach
of I3ꢀ to the TiO2 surface but also the diffusion of electrolytes in
the pore of the TiO2 electrodes. The different light intensity
dependence between the new dyes and the others might be related
to different redox couple concentration profiles under steady
Synthesis
9-Ethyl-3-(4-(n-hexyloxy)phenyl)-9H-carbazole 2. A Grignard
reagent was prepared from 4-n-hexyloxy-1-bromobenzene (1.69
g, 6.57 mmol) and magnesium turnings (176 mg, 7.22 mmol) in
anhydrous THF (30 mL). The resulting mixture was refluxed for
1 h. After cooling, the solution of the Grignard reagent was
added dropwise to an ice-cooled suspension of 9-ethyl-3-bromo-
9H-carbazole (900 mg, 3.28 mmol) and Ni(dppp)Cl2 (18 mg,
0.033 mmol) in THF (30 mL). The reaction mixture was refluxed
overnight. The mixture was carefully quenched with sat. NH4Cl
aqueous solution, and extracted with several portions of EtOAc.
The combined organic layer was washed with H2O and brine,
dried over MgSO4, and evaporated under reduced pressure. The
crude product was purified by flash column chromatography
(hexane/EtOAc ¼ 100/1) and subsequent purification by HPLC
(silica gel, hexane/EtOAc ¼ 25/1) to afford 932 mg (2.40 mmol,
ꢀ
light intensity, that is, I3 ions could not diffuse back to Pt
electrodes effectively, increasing the concentrations of I3ꢀ in the
pore of the electrode. The increased FF with the electrolyte
containing high [I3ꢀ] on Table 1 is consistent with this hypothesis.
ꢀ
The higher [I3ꢀ] is also favorable in view of the Iꢀ/I3 redox
potential, that is, it increases the potential difference between the
conduction band edge of the TiO2 and the Iꢀ/I3ꢀ. On the other
hand, the high [I3ꢀ] increases the charge recombination rate and
the absorption of light by the electrolyte. Thus, fine tuning of the
concentration is needed. The optimization would be more
effective when the optimization of the size and distribution of
pore in the TiO2 electrode occur simultaneously. In addition, the
4832 | J. Mater. Chem., 2009, 19, 4829–4836
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73%) of 9-ethyl-3-(4-(n-hexyloxy)phenyl)-9H-carbazole 2 as
1
139.3, 134.2, 132.1, 127.9, 125.9, 125.0, 124.0, 123.35, 123.27,
123.2, 118.2, 118.0, 117.4, 114.7, 108.65, 108.61, 67.9, 37.4, 31.7,
31.6, 30.7, 30.4, 29.3, 29.1, 25.7, 22.60, 22.57, 14.1, 14.0, 13.6.
Anal. Calcd for C36H43NOS: C, 80.40; H, 8.06; N, 2.60, S, 5.96.
Found. C, 80.19; H, 8.44; N, 2.65, S, 5.84.
a white solid, H NMR (400 MHz, CDCl3) d 8.26 (1H, dd, J ¼
1.8, 0.6 Hz), 8.16 (1H, ddd, J ¼ 7.8, 1.2, 0.8 Hz), 7.69 (1H, dd, J ¼
8.5, 1.5 Hz), 7.65 (2H, d, J ¼ 8.9 Hz), 7.50 (1H, ddd, J ¼ 8.2, 7.0,
1.2 Hz), 7.47–7.42 (2H, m), 7.26 (1H, ddd, J ¼ 7.8, 6.9, 1.0 Hz),
7.03 (2H, d, J ¼ 8.9 Hz), 4.39 (2H, q, J ¼ 7.2 Hz), 4.04 (2H, t, J ¼
6.6 Hz), 1.88–1.81 (2H, m), 1.56–1.50 (2H, m), 1.47 (3H, t, J ¼
7.2 Hz), 1.42–1.36 (4H, m), 0.95 (3H, t, J ¼ 7.1 Hz), 13C NMR
(100 MHz, CDCl3) d 158.0, 140.2, 138.9, 134.4, 131.9, 128.0,
125.6, 124.8, 123.3, 123.0, 120.3, 118.7, 118.2, 114.7, 108.5, 108.4,
67.9, 37.3, 31.6, 29.3, 25.7, 22.6, 14.0, 13.6. Anal. Calcd for
C26H29NO: C, 84.06; H, 7.87; N, 3.77. Found. C, 84.11; H, 7.75;
N, 3.67.
9-Ethyl-3-(4-(n-hexyloxy)phenyl)-6-(5-bromo-4-n-hexylthiophen-2-
yl)-9H-carbazole 5. The bromination of 9-ethyl-3-(4-(n-hexylox-
y)phenyl)-6-(4-n-hexylthiophen-2-yl)-9H-carbazole 4 (239 mg,
0.44 mmol) with N-bromosuccinimide (87 mg, 0.49 mmol) in
THF (5 mL) was carried out in a similar manner to that of 3. The
crude product was purified by column chromatography (hexane/
EtOAc ¼ 25/1) and successive HPLC on silica gel (hexane/EtOAc
¼ 50/1) to obtain bromide 5 (271 mg, 0.44 mml, 99%) as a white
1
3-Bromo-9-ethyl-6-(4-(n-hexyloxy)phenyl)-9H-carbazole 3. To
a solution of 9-ethyl-3-(4-(n-hexyloxy)phenyl)-9H-carbazole 2
(903 mg, 2.33 mmol) in THF (20 mL) was added N-bromo-
succinimide (435 mg, 2.45 mmol). The reaction mixture was
stirred at room temperature for 1 h, and quenched with 10%
aqueous solution of Na2CO3 and extracted with EtOAc three
times. The combined organic layer was washed with H2O and
brine, dried over MgSO4, and evaporated under reduced pres-
sure. The crude product was purified by column chromatography
(hexane/EtOAc ¼ 10/1) and successive HPLC on silica gel
(hexane/EtOAc ¼ 25/1) to obtain bromide 3 (882 mg, 1.98 mml,
84%) as a white solid, 1H NMR (400 MHz, CDCl3) d 8.25 (1H, d,
J ¼ 1.8 Hz), 8.20 (1H, d, J ¼ 1.8 Hz), 7.69 (1H, dd, J ¼ 8.5, 1.8
Hz), 7.61 (2H, d, J ¼ 8.8 Hz), 7.55 (1H, dd, J ¼ 8.7, 1.8 Hz), 7.43
(1H, dd, J ¼ 8.5 Hz), 7.28 (1H, d, J ¼ 8.7 Hz), 7.02 (2H, d, J ¼ 8.8
Hz), 4.34 (2H, q, J ¼ 7.2 Hz), 4.03 (2H, t, J ¼ 6.6 Hz), 1.87–1.80
(2H, m), 1.55–1.47 (2H, m), 1.43 (3H, t, J ¼ 7.2 Hz), 1.40–1.36
(4H, m), 0.94 (3H, t, J ¼ 7.0 Hz), 13C NMR (100 MHz, CDCl3)
d 158.2, 139.3, 138.9, 134.2, 128.3, 128.1, 125.6, 124.8, 123.2,
122.4, 118.5, 114.8, 111.6, 109.9, 108.8, 68.1, 37.7, 31.6, 29.3,
25.8, 22.6, 14.1, 13.8. Anal. Calcd for C26H28BrNO: C, 69.33; H,
6.27; N, 3.11. Found. C, 69.49; H, 6.17; N, 3.04.
solid, H NMR (400 MHz, CDCl3) d 8.28 (1H, d, J ¼ 1.8 Hz),
8.26 (1H, d, J ¼ 1.8 Hz), 7.69 (1H, dd, J ¼ 8.5, 1.8 Hz), 7.64 (2H,
d, J ¼ 8.8 Hz), 7.62 (1H, dd, J ¼ 8.5, 1.8 Hz), 7.43 (1H, d, J ¼ 8.5
Hz), 7.37 (1H, d, J ¼ 8.5 Hz), 7.06 (1H, s), 7.02 (2H, J ¼ 8.8 Hz),
4.36 (2H, q, J ¼ 7.2 Hz), 4.03 (2H, t, J ¼ 6.6 Hz), 2.61 (2H, br t, J
¼ 7.8 Hz), 1.87–1.80 (2H, m), 1.71–1.63 (2H, m), 1.55–1.50 (2H,
m), 1.46 (3H, t, J ¼ 7.2 Hz), 1.42–1.33 (10H, m), 0.94 (3H, t, J ¼
7.0 Hz), 0.93 (3H, t, J ¼ 7.0 Hz), 13C NMR (100 MHz, CDCl3)
d 158.2, 145.0, 143.0, 139.9, 139.5, 134.3, 132.4, 128.1, 125.3,
125.1, 123.8, 123.5, 123.3, 122.8, 118.5, 117.4, 114.8, 108.84,
108.81, 106.5, 68.1, 37.7, 31.7, 31.6, 29.8, 29.7, 29.3, 29.0, 25.8,
22.6, 22.6, 14.11, 14.05, 13.8. Anal. Calcd for C36H42BrNOS: C,
70.11; H, 6.86; N, 2.27, S, 5.20. Found. C, 70.16; H, 7.14; N, 2.27,
S, 5.16.
9-Ethyl-3-(4-(n-hexyloxy)phenyl)-6-(3,40-di-n-hexyl-[2,20]bithio-
phen-5-yl)-9H-carbazole 6. The Suzuki-coupling reaction of
bromide 5 (467 mg, 0.76 mmol) with 4-n-hexylthiophene-2-
boronic acid ester (318 mg, 1.14 mmol) using Pd(PPh3)4 (87 mg,
0.078 mmol) as a catalyst in DME (10 mL) was carried out in
a similar manner to that for 4. The crude product was purified by
column chromatography (hexane/EtOAc ¼ 25/1) and successive
HPLC on silica gel (hexane/EtOAc ¼ 25/1) to obtain bithiophene
6 (457 mg, 0.65 mmol, 86%) as a slightly yellow oil, 1H NMR (400
MHz, CDCl3) d 8.34 (1H, d, J ¼ 1.8 Hz), 8.30 (1H, d, J ¼ 1.8 Hz),
7.72 (1H, dd, J ¼ 8.5, 1.8 Hz), 7.69 (1H, dd, J ¼ 8.5, 1.8 Hz), 7.64
(2H, d, J ¼ 8.8 Hz), 7.44 (1H, d, J ¼ 8.5 Hz), 7.39 (1H, d, J ¼ 8.5
Hz), 7.20 (1H, s), 7.04–7.00 (3H, m), 6.89 (1H, d, J ¼ 1.2 Hz),
4.39 (2H, q, J ¼ 7.2 Hz), 4.03 (2H, t, J ¼ 6.6 Hz), 2.80 (2H, br t, J
¼ 7.8 Hz), 2.63 (2H, br t, J ¼ 7.8 Hz), 1.87–1.79 (2H, m), 1.77–
1.62 (4H, m), 1.47 (3H, t, J ¼ 7.2 Hz), 1.53–1.28 (18H, m), 0.95–
0.89 (9H, m), 13C NMR (100 MHz, CDCl3) d 158.1, 143.5, 142.9,
140.1, 139.7, 139.4, 136.2, 134.2, 132.2, 129.2, 128.0, 126.6, 125.3,
125.1, 124.7, 123.7, 123.4, 123.3, 119.4, 118.3, 117.3, 114.7,
108.72, 108.71, 68.0, 37.5, 31.7, 31.7, 31.6, 30.9, 30.6, 30.5, 30.3,
29.6, 29.33, 29.30, 29.0, 25.7, 22.64, 22.60, 22.60, 14.1, 14.1, 14.0,
13.7. Anal. Calcd for C46H57NOS2: C, 78.47; H, 8.16; N, 1.99, S,
9.11. Found. C, 78.71; H, 8.62; N, 2.01, S, 8.72.
9-Ethyl-3-(4-(n-hexyloxy)phenyl)-6-(4-n-hexylthiophen-2-yl)-
9H-carbazole 4. The mixture of 3-bromo-9-ethyl-6-(4-(n-
hexyloxy)phenyl)-9H-carbazole
3 (328 mg, 0.73 mmol),
4-n-hexylthiophene-2-boronic acid ester (306 mg, 1.09 mmol),
tetrakis(triphenylphosphine)palladium (84 mg, 0.073 mmol) and
0.5 mL of 10% aqueous solution of Na2CO3 in dimethoxyethane
(10 mL) was refluxed for 24 h. After cooling, H2O was added and
the reaction mixture was extracted with EtOAc three times. The
combined organic layer was washed with H2O and brine, dried
over MgSO4, and evaporated under reduced pressure. The crude
product was purified by column chromatography (hexane/EtOAc
¼ 25/1) and successive HPLC on silica gel (hexane/EtOAc ¼ 25/1)
to obtain a monothiophene adduct 4 (255 mg, 0.47 mmol, 65%) as
a white solid, 1H NMR (400 MHz, CDCl3) d 8.35 (1H, d, J ¼ 1.8
Hz), 8.30 (1H, d, J ¼ 1.8 Hz), 7.72 (1H, dd, J ¼ 8.5, 1.8 Hz), 7.68
(1H, dd, J ¼ 8.5, 1.8 Hz), 7.64 (2H, d, J ¼ 8.6 Hz), 7.43 (1H, d, J ¼
8.5 Hz), 7.38 (1H, d, J ¼ 8.5 Hz), 7.21 (1H, d, J ¼ 1.3 Hz), 7.02
(2H, J ¼ 8.6 Hz), 6.85 (1H, d, J ¼ 1.3 Hz), 4.37 (2H, q, J ¼ 7.2 Hz),
4.04 (2H, t, J ¼ 6.6 Hz), 2.66 (2H, br t, J ¼ 7.8 Hz), 1.88–1.80 (2H,
m), 1.74–1.66 (2H, m), 1.55–1.48 (2H, m), 1.46 (3H, t, J ¼ 7.2 Hz),
1.43–1.35 (10H, m), 0.94 (3H, t, J ¼ 7.0 Hz), 0.93 (3H, t, J ¼ 7.0
Hz), 13C NMR (100 MHz, CDCl3) d 158.1, 145.2, 144.1, 139.6,
0
0
9-Ethyl-3-(4-(n-hexyloxy)phenyl)-6-(5 -bromo-3,40-di-n-hexyl-[2,2 ]bithio-
phen-5-yl)-9H-carbazole 7. The bromination of bithiophene 6 (457
mg, 0.65 mmol) with N-bromosuccinimide (121 mg, 0.68 mmol)
in THF (5 mL) was carried out in a similar manner to that of 3.
The crude product was purified by column chromatography
(hexane/EtOAc ¼ 25/1) and successive HPLC on silica gel
This journal is ª The Royal Society of Chemistry 2009
J. Mater. Chem., 2009, 19, 4829–4836 | 4833

View Article Online
(hexane/EtOAc ¼ 25/1) to obtain bromide 7 (497 mg, 0.64 mml,
98%) as a yellow oil, 1H NMR (400 MHz, CDCl3) d 8.33 (1H, d, J
¼ 1.8 Hz), 8.29 (1H, d, J ¼ 1.8 Hz), 7.71 (1H, dd, J ¼ 8.5, 1.8 Hz),
7.69 (1H, dd, J ¼ 8.5, 1.8 Hz), 7.64 (2H, d, J ¼ 8.8 Hz), 7.44 (1H,
d, J ¼ 8.5 Hz), 7.39 (1H, d, J ¼ 8.5 Hz), 7.19 (1H, s), 7.02 (2H, d,
J ¼ 8.8 Hz), 6.86 (1H, s), 4.38 (2H, q, J ¼ 7.2 Hz), 4.03 (2H, t, J ¼
6.6 Hz), 2.76 (2H, br t, J ¼ 7.8 Hz), 2.58 (2H, br t, J ¼ 7.8 Hz),
1.87–1.79 (2H, m), 1.75–1.59 (4H, m), 1.46 (3H, t, J ¼ 7.2 Hz),
1.53–1.30 (18H, m), 0.96–0.89 (9H, m), 13C NMR (100 MHz,
CDCl3) d 158.1, 143.4, 142.3, 140.6, 139.8, 139.3, 136.1, 134.1,
132.2, 128.1, 127.9, 125.9, 125.1, 125.0, 124.6, 123.7, 123.4, 123.2,
118.2, 117.2, 114.7, 108.70, 108.68, 107.9, 67.9, 37.5, 31.7, 31.6,
31.6, 30.6, 29.6, 29.54, 29.50, 29.3, 29.3, 28.9, 25.7, 22.62, 22.60,
22.58, 14.1, 14.1, 14.0, 13.7. Anal. Calcd for C46H56BrNOS2: C,
70.56; H, 7.21; N, 1.79, S, 8.19. Found. C, 70.19; H, 7.30; N, 1.78,
S, 8.31.
8.8 Hz), 7.44 (1H, d, J ¼ 8.5 Hz), 7.40 (1H, d, J ¼ 8.5 Hz), 7.22
(1H, s), 7.05 (1H, s), 7.04 (1H, s), 7.02 (1H, d, J ¼ 8.8 Hz), 4.38
(2H, q, J ¼ 7.2 Hz), 4.03 (2H, t, J ¼ 6.6 Hz), 2.95 (2H, br t, J ¼
7.8 Hz), 2.84 (4H, br t, J ¼ 7.8 Hz), 1.87–1.80 (2H, m), 1.78–1.68
(6H, m), 1.47 (3H, t, J ¼ 7.1 Hz), 1.53–1.31 (24H, m), 0.95–0.89
(12H, m), 13C NMR (100 MHz, CDCl3) d 181.5, 158.2, 153.4,
145.3, 143.9, 142.5, 141.2, 140.0, 139.5, 136.6, 135.9, 134.3, 132.4,
128.9, 128.4, 128.12, 128.08, 127.8, 125.2, 125.1, 125.0, 123.8,
123.5, 123.3, 118.5, 117.5, 114.8, 108.8, 108.8, 68.1, 37.7, 31.68,
31.65, 31.6, 31.5, 31.4, 30.4, 30.1, 29.83, 29.81, 29.33, 29.29,
29.26, 29.0, 28.4, 25.7, 22.63, 22.60, 22.60, 22.5, 14.10, 14.06,
14.0, 14.0, 13.8. Anal. Calcd for C57H71NO2S3: C, 76.21; H, 7.97;
N, 1.56, S, 10.71. Found. C, 76.30; H, 8.17; N, 1.58, S, 10.84.
2-Cyano-3-[500-[9-ethyl-3-(4-(n-hexyloxy)phenyl)-9H-carbazol-
6-yl]-30,300,4-tri-n-hexyl-[2,20,50,200]terthiophen-5-yl]acrylic acid,
MK-14. A mixture of aldehyde 9 (70 mg, 0.078 mmol) with
cyanoacetic acid (13 mg, 0.16 mmol) in dry acetonitrile (2 mL)
and dry toluene (2 mL) was refluxed in the presence of piperidine
(0.5 mL) for 15 h. After cooling the mixture was diluted with
chloroform, and the organic layer was washed with aqueous HCl
(1 N), H2O and brine, dried over Na2SO4, and evaporated under
reduced pressure. The crude product was purified by column
chromatography (CHCl3 / CHCl3/EtOH ¼ 10/1) to obtain
9-Ethyl-3-(4-(n-hexyloxy)phenyl)-6-(3,40,400-tri-n-hexyl-[2,20,50,
200]terthiophen-5-yl)-9H-carbazole 8. The Suzuki-coupling reac-
tion of bromide 7 (417 mg, 0.53 mmol) with 4-n-hexylthiophene-
2-boronic acid ester (224 mg, 0.80 mmol) using Pd(PPh3)4 (62
mg, 0.053 mmol) as a catalyst in DME (10 mL) was carried out in
a similar manner to that of 4. The crude product was purified by
column chromatography (hexane/EtOAc ¼ 25/1) and successive
HPLC on silica gel (hexane/EtOAc ¼ 25/1) to obtain terthio-
phene 8 (394 mg, 0.45 mmol, 85%) as a yellow oil, 1H NMR (400
MHz, CDCl3) d 8.35 (1H, d, J ¼ 1.8 Hz), 8.31 (1H, d, J ¼ 1.8 Hz),
7.73 (1H, dd, J ¼ 8.5, 1.8 Hz), 7.69 (1H, dd, J ¼ 8.5, 1.8 Hz), 7.65
(2H, d, J ¼ 8.8 Hz), 7.44 (1H, d, J ¼ 8.5 Hz), 7.39 (1H, d, J ¼ 8.5
Hz), 7.22 (1H, s), 7.03 (2H, J ¼ 8.8 Hz), 7.02 (1H, s), 7.00 (1H, d,
J ¼ 1.2 Hz), 6.91 (1H, d, J ¼ 1.2 Hz), 4.37 (2H, q, J ¼ 7.2 Hz),
4.04 (2H, t, J ¼ 6.6 Hz), 2.84 (2H, br t, J ¼ 7.8 Hz), 2.79 (2H, br t,
J ¼ 7.8 Hz), 2.64 (2H, br t, J ¼ 7.8 Hz), 1.88–1.80 (2H, m), 1.80–
1.63 (6H, m), 1.47 (3H, t, J ¼ 7.2 Hz), 1.54–1.29 (24H, m), 0.97–
0.88 (12H, m), 13C NMR (100 MHz, CDCl3) d 158.1, 143.5,
143.0, 140.3, 139.8, 139.41, 139.39, 135.7, 134.2, 134.2, 132.2,
130.4, 128.8, 128.0, 127.9, 126.9, 125.2, 125.1, 124.9, 123.7, 123.5,
123.3, 119.7, 118.3, 117.3, 114.7, 108.7, 108.7, 68.0, 37.5, 31.71,
31.67, 31.67, 31.62, 30.54, 30.52, 30.45, 30.34, 29.7, 29.4, 29.31,
29.31, 29.26, 29.0, 25.8, 22.65, 22.61, 22.61, 22.61, 14.11, 14.08,
14.08, 14.04, 13.8. Anal. Calcd for C56H71NOS3: C, 77.28; H,
8.22; N, 1.61, S, 11.05. Found. C, 77.36; H, 8.64; N, 1.61, S,
11.07.
1
a dye MK-14 (61 mg, 0.063 mmol, 81%) as dark-red solids, H
NMR (400 MHz, THF-d8) d 8.47 (1H, br s), 8.41 (1H, s), 8.40
(1H, br s), 7.74 (1H, br d, J ¼ 8.5 Hz), 7.70 (1H, dd, J ¼ 8.5, 1.1
Hz), 7.65 (2H, d, J ¼ 8.8 Hz), 7.53 (1H, d, J ¼ 8.5 Hz), 7.52 (1H,
d, J ¼ 8.5 Hz), 7.36 (1H, s), 7.23 (1H, s), 7.13 (1H, s), 6.99 (2H, d,
J ¼ 8.8 Hz), 4.45 (2H, q, J ¼ 7.0 Hz), 4.01 (2H, t, J ¼ 6.5 Hz),
2.94–2.83 (6H, m), 1.84–1.65 (8H, m), 1.54–1.29 (27H, m), 0.95–
0.90 (12H, m), 13C NMR (100 MHz, CDCl3) d 168.4, 158.2,
156.3, 146.7, 144.4, 144.1, 143.8, 141.6, 140.0, 139.5, 137.7, 134.3,
132.4, 129.3, 128.6, 128.5, 128.2, 128.1, 126.8, 125.3, 125.2, 124.9,
123.8, 123.5, 123.3, 118.5, 117.4, 116.2, 114.8, 108.9, 108.9, 93.3,
68.1, 37.8, 31.75, 31.73, 31.63, 31.55, 31.2, 30.34, 30.31, 30.1,
30.0, 29.4, 29.32, 29.27, 29.1, 29.0, 25.8, 22.7, 22.63, 22.63, 22.57,
14.15, 14.13, 14.06, 14.06, 13.9. Anal. Calcd for C60H72N2O3S3:
C, 74.65; H, 7.52; N, 2.90, S, 9.96. Found. C, 72.68; H, 7.29; N,
2.78, S, 9.64.
9-Ethyl-3-(4-(n-hexyloxy)phenyl)-6-(500-bromo-3,40,400-tri-n-hexyl-
[2,20,50,200]terthiophen-5-yl)-9H-carbazole 10. The bromination of
terthiophene 8 (250 mg, 0.29 mmol) with N-bromosuccinimide
(56 mg, 0.32 mmol) in THF (5 mL) was carried out in a similar
manner to that of 3. The crude product was purified by column
chromatography (hexane/EtOAc ¼ 25/1) and successive HPLC
on silica gel (hexane/EtOAc ¼ 25/1) to obtain bromide 10 (251
mg, 0.26 mml, 92%) as a yellow oil, 1H NMR (400 MHz, CDCl3)
d 8.35 (1H, br s), 8.31 (1H, d, J ¼ 1.8 Hz), 7.73 (1H, dd, J ¼ 8.4,
1.5 Hz), 7.69 (1H, dd, J ¼ 8.5, 1.8 Hz), 7.65 (2H, d, J ¼ 8.7 Hz),
7.43 (1H, d, J ¼ 8.4 Hz), 7.39 (1H, d, J ¼ 8.5 Hz), 7.22 (1H, s),
7.03 (2H, J ¼ 8.7 Hz), 7.02 (1H, s), 6.86 (1H, s), 4.37 (2H, q, J ¼
7.1 Hz), 4.04 (2H, t, J ¼ 6.6 Hz), 2.83 (2H, br t, J ¼ 7.8 Hz), 2.74
(2H, br t, J ¼ 7.8 Hz), 2.59 (2H, br t, J ¼ 7.8 Hz), 1.88–1.80 (2H,
m), 1.78–1.60 (6H, m), 1.47 (3H, t, J ¼ 7.1 Hz), 1.54–1.30 (24H,
m), 0.97–0.90 (12H, m), 13C NMR (100 MHz, CDCl3) d 158.1,
143.2, 142.4, 140.6, 140.0, 139.9, 139.4, 135.5, 134.8, 134.3, 132.3,
128.1, 127.9, 126.4, 125.20, 125.17, 124.9, 123.8, 123.5, 123.3,
500-[9-Ethyl-3-(4-(n-hexyloxy)phenyl)-9H-carbazol-6-yl]-30,300,4-
tri-n-hexyl-[2,20,50,200]terthiophene-5-carbaldehyde 9. To a cold
solution of terthiophene 8 (155 mg, 0.18 mmol) in dry DMF (2
mL) at 0 ꢂC was added a Vilsmeier reagent, which was prepared
with 0.05 mL of POCl3 in DMF (0.2 mL). The mixture was
stirred at 70 ꢂC for 7 h, and quenched with 10% aqueous solution
of NaOAc (10 mL) after cooling, and extracted with EtOAc three
times. The combined organic layer was washed with H2O and
brine, dried over MgSO4, and evaporated under reduced pres-
sure. The crude product was purified by column chromatography
(hexane/EtOAc ¼ 10/1) and successive HPLC on silica gel
(hexane/EtOAc ¼ 10/1) to obtain aldehyde 9 (103 mg, 0.12 mml,
64%) as an orange oil, 1H NMR (400 MHz, CDCl3) d 10.02 (1H,
s), 8.34 (1H, d, J ¼ 1.8 Hz), 8.30 (1H, d, J ¼ 1.8 Hz), 7.72 (1H, dd,
J ¼ 8.5, 1.8 Hz), 7.69 (1H, dd, J ¼ 8.5, 1.8 Hz), 7.64 (1H, d, J ¼
4834 | J. Mater. Chem., 2009, 19, 4829–4836
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118.4, 117.4, 114.8, 108.8, 108.8, 108.4, 68.0, 37.6, 31.71, 31.65,
31.62, 31.61, 30.53, 30.53, 29.7, 29.6, 29.5, 29.34, 29.31, 29.31,
29.23, 28.9, 25.8, 22.65, 22.62, 22.62, 22.59, 14.12, 14.08, 14.08,
14.05, 13.8. Anal. Calcd for C56H70BrNOS3: C, 70.86; H, 7.43;
N, 1.48, S, 10.13. Found. C, 70.34; H, 7.73; N, 1.50, S, 9.51.
29.2, 28.9, 28.3, 25.7, 22.62, 22.59, 22.57, 22.57, 22.5, 14.09,
14.06, 14.02, 13.99, 13.99, 13.8. Anal. Calcd for C67H85NO2S4: C,
75.58; H, 8.05; N, 1.32, S, 12.05. Found. C, 75.10; H, 8.16; N,
1.34, S, 11.56.
2-Cyano-3-[5%-(9-ethyl-3-(4-(n-hexyloxy)phenyl)-9H-carbazol-
6-yl]-30,300,3%,4-tetra-n-hexyl-[2,20,50,200,500,2%]quaterthiophenyl-5-
yl]acrylic acid, MK-16. A mixture of aldehyde 12 (208 mg, 0.20
mmol) with cyanoacetic acid (33 mg, 0.39 mmol) in a mixed
solvent of dry acetonitrile (2 mL) and dry toluene (2 mL) was
refluxed in the presence of piperidine (0.5 mL) for 20 h. After
cooling the mixture was diluted with chloroform, and the organic
layer was washed with aqueous HCl (1 N), H2O and brine, dried
over Na2SO4, and evaporated under reduced pressure. The crude
9-Ethyl-3-(4-(n-hexyloxy)phenyl)-6-(3,40,400,4%-tetra-n-hexyl-[2,2050,
200,500,2%]quaterthiophen-5-yl)-9H-carbazole 11. The Suzuki-
coupling reaction of bromide 10 (251 mg, 0.26 mmol) with 4-n-
hexylthiophene-2-boronic acid ester (148 mg, 0.53 mmol) using
Pd(PPh3)4 (31 mg, 0.026 mmol) as a catalyst in DME (10 mL)
was carried out in a similar manner to that of 4. The crude
product was purified by column chromatography (hexane/
EtOAc ¼ 25/1) and successive HPLC on silica gel (hexane/EtOAc
¼ 25/1) to obtain quaterthiophene 11 (253 mg, 0.24 mmol, 92%)
as an orange oil, 1H NMR (400 MHz, CDCl3) d 8.35 (1H, d, J ¼
1.8 Hz), 8.30 (1H, d, J ¼ 1.8 Hz), 7.73 (1H, dd, J ¼ 8.5, 1.8 Hz),
7.69 (1H, dd, J ¼ 8.5, 1.8 Hz), 7.65 (2H, d, J ¼ 8.8 Hz), 7.44 (1H,
d, J ¼ 8.5 Hz), 7.40 (1H, d, J ¼ 8.5 Hz), 7.21 (1H, s), 7.02 (2H, J
¼ 8.8 Hz), 7.01–6.96 (3H, m), 6.90 (1H, br s), 4.39 (2H, q, J ¼ 7.1
Hz), 4.03 (2H, t, J ¼ 6.6 Hz), 2.86–2.74 (6H, m), 2.62 (2H, br t, J
¼ 7.8 Hz), 1.87–1.79 (2H, m), 1.78–1.61 (8H, m), 1.47 (3H, t, J ¼
7.1 Hz), 1.53–1.32 (30H, m), 0.97–0.88 (15H, m), 13C NMR (100
MHz, CDCl3) d 158.1, 143.6, 143.1, 140.4, 139.8, 139.6 139.5,
139.4, 135.6, 134.3, 134.2, 133.6, 132.3, 130.8, 129.9, 128.8, 128.2,
128.0, 128.0, 127.0, 125.2, 125.1, 124.9, 123.7, 123.5, 123.3, 119.9,
118.4, 117.3, 114.7, 108.8, 108.8, 68.0, 37.6, 31.72, 31.69, 31.67,
31.66, 31.63, 30.55, 30.52, 30.48, 30.46, 30.4, 29.8, 29.5, 29.4,
29.32, 29.28, 29.28, 29.2, 29.0, 25.8, 22.7, 22.64, 22.61, 22.61,
21.61, 14.13, 14.10, 14.08, 14.08, 14.04, 13.8. Anal. Calcd for
C66H85NOS4: C, 76.47; H, 8.26; N, 1.35, S, 12.37. Found. C,
76.00; H, 8.49; N, 1.38, S, 11.54.
product was purified by column chromatography (CHCl3
/
CHCl3/ethanol ¼ 10/1) to obtain a dye MK-16 (209 mg, 0.19
1
mmol, 95%) as a dark-red solid, H NMR (400 MHz, THF-d8)
d 8.46 (1H, br s), 8.41 (1H, s), 8.40 (1H, br s), 7.74 (1H, br d, J ¼
8.5 Hz), 7.69 (1H, dd, J ¼ 8.5, 1.1 Hz), 7.65 (2H, d, J ¼ 8.8 Hz),
7.51 (1H, d, J ¼ 8.5 Hz), 7.50 (1H, d, J ¼ 8.5 Hz), 7.34 (1H, s),
7.24 (1H, s), 7.12 (1H, s), 7.10 (1H, s), 6.99 (2H, d, J ¼ 8.8 Hz),
4.44 (2H, q, J ¼ 7.2 Hz), 4.00 (2H, t, J ¼ 6.5 Hz), 2.93–2.82 (8H,
m), 1.84–1.63 (10H, m), 1.55–1.28 (33H, m), 0.95–0.89 (15H, m),
13C NMR (100 MHz, THF-d8) d 164.6, 159.3, 155.4, 144.7, 144.6,
143.9, 143.5, 141.7, 141.6, 141.1, 140.6, 137.1, 136.3, 135.1, 133.3,
130.8, 130.3, 130.1, 130.0, 129.1, 129.0, 128.6, 128.3, 126.1, 125.9,
125.8, 124.7, 124.42, 124.39, 119.1, 118.1, 116.9, 115.4, 109.9,
109.8, 98.2, 68.6, 38.3, 32.74, 32.69, 32.69, 32.6, 32.5, 32.2, 31.5,
31.4, 31.3, 30.8, 30.6, 30.34, 30.34, 30.30, 30.2, 30.2, 29.9, 29.5,
26.8, 23.58, 23.56, 23.56, 23.54, 23.47, 14.53, 14.50, 14.49, 14.4,
14.4, 14.1. Anal. Calcd for C70H86N2O3S4: C, 74.29; H, 7.66; N,
2.48, S, 11.33. Found. C, 74.42; H, 7.91; N, 2.42, S, 11.56.
5%-[9-Ethyl-3-(4-(n-hexyloxy)phenyl)-9H-carbazol-6-yl]-30,300,3%4-
tetra-n-hexyl-[2,20,50,200,500,2%]quaterthiophene-5-carbaldehyde 12.
To a cold solution of quaterthiophene 11 (253 mg, 0.27 mmol) in
Preparation of dye-sensitized TiO2 electrodes
Nanocrystalline TiO2 photoelectrodes were prepared from
a solution containing TiO2 nano-particles (HPW-18NR, Cata-
lysts & Chemicals Ind. Co., Ltd.). The paste was applied on to
transparent conducting oxide (SnO2:F) by doctor-blading tech-
ꢂ
dry DMF (5 mL) at 0 C was added a Vilsmeier reagent, which
was prepared with 0.1 mL of POCl3 in DMF (0.5 mL). The
mixture was stirred at 70 ꢂC for 7 h, and quenched with 10%
aqueous solution of NaOAc (30 mL) after cooling, and extracted
with dichloromethane three times. The combined organic layer
was washed with H2O and brine, dried over MgSO4, and evap-
orated under reduced pressure. The crude product was purified
ꢂ
niques and annealed at 550 C for 30 min in air.
To fabricate highly efficiency DSSCs, nanocrystalline TiO2
photoelectrodes were prepared by a screen printing using TiO2
nanoparticles and an organic TiO2 paste prepared by methods
reported in a previous paper.12 The TiO2 paste consisted of TiO2
nanoparticles (ca. 20 nm), ethyl cellulose as a binder, and a-
terpineol as a solvent. The TiO2 paste was printed on a glass
substrate coated with transparent conducting oxide and subse-
quently sintered at 500 ꢂC in air for 1 h. The thickness of the TiO2
thin films, was measured with an Alpha-Step 300 profiler
(TENCOR INSTRUMENTS). The TiO2 film electrode consists
a transparent layer (8 or 12.5 mm) and a scattering layer (4 mm),
which contains large TiO2 particles (av. 100 nm) and small
particles (av. 20 nm) at a molar ratio of 4:6. The MK dyes were
dissolved at a concentration of 0.3 mM in toluene (KANTO
CHEMICAL). A Ru complex dye (N719) was obtained from
Peccell Technology and dissolved in a mixed solvents of AN and
tBuOH. The TiO2 films were immersed in the dye solutions and
then kept at 25 ꢂC for more than 12 h to allow the dye to adsorb
to the TiO2 surface, and rinsed with the same solvents. The
by column chromatography (hexane/EtOAc
¼
10/1) and
successive HPLC on silica gel (hexane/EtOAc ¼ 10/1) to obtain
1
aldehyde 12 (208 mg, 0.20 mml, 80%) as a dark-orange oil, H
NMR (400 MHz, CDCl3) d 10.02 (1H, s), 8.35 (1H, d, J ¼ 1.8
Hz), 8.30 (1H, d, J ¼ 1.8 Hz), 7.72 (1H, dd, J ¼ 8.5, 1.8 Hz), 7.69
(1H, dd, J ¼ 8.5, 1.8 Hz), 7.64 (1H, d, J ¼ 8.8 Hz), 7.43 (1H, d, J
¼ 8.5 Hz), 7.39 (1H, d, J ¼ 8.5 Hz), 7.22 (1H, s), 7.05 (1H, s),
7.03–7.01 (4H, m), 4.38 (2H, q, J ¼ 7.2 Hz), 4.03 (2H, t, J ¼ 6.6
Hz), 2.95 (2H, br t, J ¼ 7.8 Hz), 2.86–2.80 (6H, m), 1.87–1.80
(2H, m), 1.79–1.67 (8H, m), 1.47 (3H, t, J ¼ 7.2 Hz), 1.53–1.30
(30H, m), 0.97–0.88 (15H, m), 13C NMR (100 MHz, CDCl3)
d 181.4, 158.1, 153.2, 145.1, 143.3, 142.4, 140.6, 140.4, 139.8,
139.4, 136.0, 135.9, 135.1, 134.2, 132.3, 129.2, 129.1, 128.4, 128.4,
128.0, 127.7, 125.09, 125.07, 124.9, 123.6, 123.4, 123.2, 118.3,
117.3, 114.7, 108.7, 108.7, 68.0, 37.6, 31.7, 31.64, 31.60, 31.58,
31.5, 31.3, 30.4, 30.3, 30.1, 29.8, 29.8, 29.6, 29.3, 29.27, 29.26,
This journal is ª The Royal Society of Chemistry 2009
J. Mater. Chem., 2009, 19, 4829–4836 | 4835

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T. Renouard, S. M. Zakeeruddin, R. Humphry-Baker, P. Comte,
P. Liska, L. Cevey, E. Costa, V. Shklover, L. Spiccia,
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G. B. Deacon, C. A. Bignozzi and M. Gratzel, J. Am. Chem. Soc.,
2001, 123, 1613.
4 (a) A. Forneli, M. Planells, M. A. Sarmentero, E. Martinez-Ferrero,
B. C. O’Regan, P. Ballester and E. Palomares, J. Mater. Chem.,
2008, 18, 1652; (b) K. R. J. Thomas, Y.-C. Hsu, J. T. Lin, K.-
M. Lee, K.-C. Ho, C.-H. Lai, Y.-M. Cheng and P.-T. Chou, Chem.
Mater., 2008, 20, 1830; (c) D. Kuang, S. Uchida, R. Humphry-
electrolyte was 0.6
M 1,2-dimethyl-3-n-propylimidazolium
iodide (DMPImI) + 0.1 M LiI + 0.05 M I2 + 0.5 M 4-tert-
butylpyridine (TBP) in AN. Reagent-grade LiI (WAKO
CHEMICAL) and I2 (WAKO) were used for the electrolyte.
DMPImI was purchased from TOMIYAMA PURE CHEM-
ICAL INDUSTRIES Ltd. A Pt counter electrode were prepared
by sputtering (ca. 200 nm) onto TCO-coated glass substrate.
€
Baker, S. M. Zakeeruddin and M. Gratzel, Angew. Chem., Int. Ed.,
2008, 47, 1923; (d) A. Otsuka, K. Funabiki, N. Sugiyama, H. Mase,
T. Yoshida, H. Minoura and M. Matsui, Chem. Lett., 2008, 37,
176; (e) H. Tian, X. Yang, R. Chen, Y. Pan, L. Li, A. Hagfeldt and
L. Sun, Chem. Commun., 2007, 3741; (f) T. Edvinsson, C. Li,
N. Pschirer, J. Scho1neboom, F. Eickemeyer, R. Sens, G. Boschloo,
A. Herrmann, K. Mu1llen and A. Hagfeldt, J. Phys. Chem. C,
2007, 111, 15137; (g) R. Chen, X. Yang, H. Tian, X. Wang,
A. Hagfeldt and L. Sun, Chem. Mater., 2007, 19, 4007; (h) Z.-
S. Wang, Y. Cui, K. Hara, Y. Dan-oh, C. Kasada and A. Shinpo,
Adv. Mater., 2007, 19, 1138; (i) S. Kim, J. K. Lee, S. O. Kang,
J. Ko, J.-H. Yum, S. Fantacci, F. De Angelis, D. Di Censo,
Photovoltaic measurements of the solar cells
The photovoltaic performance of the solar cells was measured
with a source meter (ADVANTEST, R6246). We employed an
AM 1.5G solar simulator (WACOM, WXS-80C-3) as the light
source. The incident light intensity was calibrated by using
a standard solar cell composed of a crystalline silicon solar cell
and an IR-cut off filter (SCHOTT, KG-5), giving the photo-
response range of amorphous silicon solar cell (produced and
calibrated by Japan Quality Assurance Organization). For highly
efficient DSSCs, we used an aperture mask (0.2354 cm2) attached
onto the top of the cells in the photovoltaic measurements.
Action spectra of the monochromatic incident photon-to-current
conversion efficiency (IPCE) of the solar cell were measured with
a CEP-99W system (BUNKOH-KEIKI Co., Ltd.).
€
Md. K. Nazeeruddin and M. Gratzel, J. Am. Chem. Soc., 2006, 128,
16701; (j) S. Ito, S. M. Zakeeruddin, R. Humphry-Baker, P. Liska,
R. Charvet, P. Comte, Md. K. Nazeeruddin, P. Pechy, M. Takata,
€
H. Miura, S. Uchida and M. Gratzel, Adv. Mater., 2006, 18, 1202;
(k) M. Velusamy, K. R. Justin Thomas, J. T. Lin, Y. C. Hsu and
K. C. Ho, Org. Lett., 2005, 7, 1899; (l) T. Horiuchi, H. Miura,
K. Sumioka and S. Uchida, J. Am. Chem. Soc., 2004, 126, 12218;
(m) T. Kitamura, M. Ikeda, K. Shigaki, T. Inoue, N. A. Anderson,
X. Ai, T. Lian and S. Yanagida, Chem. Mater., 2004, 16, 1806; (n)
K. Hara, T. Sato, R. Katoh, A. Furube, Y. Ohga, A. Shinpo,
S. Suga, K. Sayama, H. Sugihara and H. Arakawa, J. Phys. Chem.
B, 2003, 107, 597.
Transient photovoltage measurements
Electron lifetimes in the DSSCs were obtained by stepped light-
induced transient measurements of photovoltage. The experi-
mental procedure for the measurements is described in detail
elsewhere.13 In short, DSSCs were irradiated by a diode laser
(Coherent, Lablaser, l ¼ 635 nm) and the decay of open circuit
voltage, caused by step-wise decrease of a small fraction of the
laser intensity, was measured. The measurement was repeated
with various initial laser intensities, giving different electron
density in the DSSCs. Electron lifetime (t) was obtained by
fitting an exponential function, exp(-t/t), to the voltage decay.
The electron density was estimated by the charge extraction
method introduced by Peter and co-workers.14 Our experimental
setup is described in a previous paper.15 In short, irradiated laser
light was turned off simultaneously with the switch from open
circuit to short circuit conditions. Then, the induced transient
current was recorded, and then the amount of the charges in the
DSSC at open circuit conditions was obtained by numerical
integration of the current transient. The control of the laser
intensity and circuit conditions was performed by LabVIEW
with a DAQ card (National Instruments).
5 (a) K. Hara, K. Miyamoto, Y. Abe and M. Yanagida, J. Phys. Chem.
B, 2005, 109, 23776; (b) M. Miyashita, K. Sunahara, T. Nishikawa,
Y. Uemura, N. Koumura, K. Hara, A. Mori, T. Abe, E. Suzuki
and S. Mori, J. Am. Chem. Soc., 2008, 130, 17874.
6 (a) B. C. O’Regan, I. Lopez-Duarte, M. V. Martinez-Diaz,
A. Forneli, J. Albero, A. Morandeira, E. Palomares, T. Torres
and J. R. Durrant, J. Am. Chem. Soc., 2008, 130, 2906; (b)
A. J. Mozer, P. Wagner, D. L. Officer, G. G. Wallace,
W. M. Campbell, M. Miyashita, K. Sunahara and S. Mori,
Chem. Commun., 2008, 4741.
7 N. Koumura, Z.-S. Wang, S. Mori, M. Miyashita, E. Suzuki
and K. Hara, J. Am. Chem. Soc., 2006, 128, 14256;
N. Koumura, Z.-S. Wang, S. Mori, M. Miyashita, E. Suzuki
and K. Hara, J. Am. Chem. Soc., 2008, 130, 4202, (Addition
and Correction).
8 S. N. Mori, W. Kubo, T. Kanzaki, N. Masaki, Y. Wada and
S. Yanagida, J. Phys. Chem. C, 2007, 111, 3522.
9 Z.-S. Wang, N. Koumura, Y. Cui, M. Takahashi, H. Sekiguchi,
A. Mori, T. Kubo, A. Furube and K. Hara, Chem. Mater., 2008,
20, 3993.
10 (a) G. Zhang, H. Bala, Y. Cheng, D. Shi, X. Lv, Q. Yu and P. Wang,
Chem. Commun., 2009, 2198; (b) R. Li, X. Lv, D. Shi, D. Zhou,
Y. Cheng, G. Zhang and P. Wang, J. Phys. Chem. C, 2009, 113,
7469; (c) J.-H. Yum, D. P. Hagberg, S.-J. Moon, K. M. Karlsson,
T. Marinado, L. Sun, A. Hagfeldt, M. K. Nazeeruddin and
€
M. Gratzel, Angew. Chem., Int. Ed., 2009, 48, 1576; (d)
D. P. Hagberg, J.-H. Yum, H.-J. Lee, F. D. Angelis, T. Marinado,
K. M. Karlsson, R. Humphry-Baker, L. Sun, A. Hagfeldt,
Acknowledgements
€
M. Gratzel and M. K. Nazeeruddin, J. Am. Chem. Soc., 2008, 130,
6259.
This work was supported by New Energy and Industrial Tech-
nology Development Organization (NEDO) of Japan.
11 S. A. Sapp, C. M. Elliott, C. Contado, S. Caramori and
C. A. Bignozzi, J. Am. Chem. Soc., 2002, 124, 11215.
12 Z.-S. Wang, H. Kawauchi, T. Kashima and H. Arakawa, Coord.
Chem. Rev., 2004, 248, 1381.
13 S. Nakade, T. Kanzaki, Y. Wada and S. Yanagida, Langmuir, 2005,
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4836 | J. Mater. Chem., 2009, 19, 4829–4836
This journal is ª The Royal Society of Chemistry 2009