Organic dyes containing a coplanar indacenodithiophene bridge for high-performance dye-sensitized solar cells

Article abstract of DOI:10.1021/jo201730a

A series of new organic dyes exploiting coplanar indacenodithiophene as the central π-spacer of the classical donor-(π-spacer)-acceptor configuration were synthesized and characterized for dye-sensitized solar cells. The coplanarity of the indacenodithiophene core facilitates efficient donor to acceptor charge transfer, imparting the new organic dyes significant bathochromic shifts and remarkable power conversion efficiencies of up to 6.7% (DTInDT) under AM 1.5G radiation.

Full text of DOI:10.1021/jo201730a

Article
pubs.acs.org/joc
Organic Dyes Containing a Coplanar Indacenodithiophene Bridge for
High-Performance Dye-Sensitized Solar Cells
Jia-Hung Chen,† Chih-Hung Tsai,‡ Shao-An Wang,† Ya-Yan Lin,† Tsung-Wei Huang,‡ Shih-Feng Chiu,†
Chung-Chih Wu,*,‡ and Ken-Tsung Wong*,†
†Department of Chemistry, National Taiwan University, Taipei 106, Taiwan
‡Department of Electrical Engineering, Graduate Institute of Photonics and Optoelectronics, and Graduate Institute of Electronics
Engineering, National Taiwan University, Taipei 10617, Taiwan
S
* Supporting Information
ABSTRACT: A series of new organic dyes exploiting coplanar indacenodithiophene as
the central π-spacer of the classical donor−(π-spacer)−acceptor configuration were
synthesized and characterized for dye-sensitized solar cells. The coplanarity of the
indacenodithiophene core facilitates efficient donor to acceptor charge transfer,
imparting the new organic dyes significant bathochromic shifts and remarkable power
conversion efficiencies of up to 6.7% (DTInDT) under AM 1.5G radiation.
bathochromic shifts and thus to yield panchromatic light
harvesting.
ye-sensitized solar cells (DSSCs), greatly improved by
1
DGratzel since 1991,
are currently one of the most
̈
promising next-generation photovoltaic technologies because of
their high efficiency, simplicity of device structures, and cost-
effective production. In addition to the more costly ruthenium-
based sensitizers,2 metal-free organic dyes are also being
exploited in DSSCs for their relatively lower cost and flexibility
in tailoring molecular structures for manipulation of electronic
and photophysical characteristics.3 Among molecular designs of
organic dyes for efficient DSSCs, donor−(π-spacer)−acceptor
(D−π−A) structures stemming from the push−pull concept of
the photoinduced intramolecular charge transfer are mostly
employed to tune the molecular absorption to match solar
radiation for efficient light harvesting.4 In this context, in
addition to the common adoption of a π-electron donor such as
diarylamine and a π-electron acceptor such as cyanoacrylic acid
bearing an anchoring group toward the TiO2 surface, the
modification on the π-spacer is also essential and substantial in
the manipulation of the electronic structures and properties of
the organic dyes. As such, various chromophores previously
utilized in organic optoelectronic devices had been introduced
as effective π-spacers for DSSC dyes, including oligoene,5
coumarin,6 oligothiophene,7 fluorene,8 spirobifluorene,9 and
phenoxazine.10 Recently, organic dyes making use of varied
intrinsic electronic characteristics of the π-spacers were also
reported. The introduction of heteroarenes such as furan,11
selenophene,12 pyrrole,13 quinoline,14 pyrimidine,15 isoxazole,16
and thiazole17 into the π-spacers was shown to enhance
On the other hand, instead of the endless search for
innumerable heteroarenes for use in DSSC dyes, better π-
conjugation can also be readily achieved by increasing the
coplanarity of bridged π-systems.18 For instance, indacenodi-
thiophene, comprising alternate thiophene-phenylene-thio-
phene aromatics through sp3−carbon bridges, showed a great
improvement in terms of both coplanarity and π-conjugation19
and also had been widely exploited as a crucial building block
for polymer solar cells.20 Therefore, we envision that the
utilization of the indacenodithiophene core as a π-spacer of
D−π−A systems may yield new organic dyes for efficient
DSSCs. We report a series of organic D−π−A dyes with
diarylamino as the donor, cyanoacrylic acid as the acceptor, and
coplanar indacenodithiophene as the bridging spacer (Figure
1). The modulation of the donor units allows us to tailor the
molecular energy levels and the absorption edge. In addition,
the central indacenodithiophene π-spacer is functionalized with
4-(n-hexoxy)phenyl groups on the sp3−carbon bridges, which
not only retains the brilliant photophysical properties of the
core but also can potentially suppress undesirable aggregation
of dyes and charge recombination between the electrolyte and
the TiO2 electrode. These new organic D−π−A dyes,
Received: August 18, 2011
Published: October 4, 2011
© 2011 American Chemical Society
8977
dx.doi.org/10.1021/jo201730a|J. Org. Chem. 2011, 76, 8977−8985

The Journal of Organic Chemistry
Article
LDA deprotonation, followed by the subsequent quenching
with chlorotrimethylsilane to give 1,4-bis(5-trimethylsilylthio-
phen-2-yl)-2,5-benzenedicarbonate 2. The TMS groups are
intentionally introduced to facilitate the later intramolecular
cyclization reactions. The addition of an excess of aryllithium,
which was prepared in advance from the corresponding aryl
bromide with n-BuLi, to the ester groups of 2 gave the
corresponding triaryl alcohol intermediate, which was directly
subjected to acid-catalyzed intramolecular annulation without
further purification to afford the coplanar indacenodithiophene
3 in an 82% yield in two steps. The selective bromination of 3
with N-bromosuccinimide (NBS) in CH2Cl2 furnished
monobrominated intermediate 4 in a moderate yield. The
installation of an electronic donor on the indacenodithiophene
core was achieved by palladium-catalyzed C−N bond formation
of 4 with various diaryl amines, giving amine derivatives 5a−c
in high yields. Compounds 5a−c were readily converted into
their corresponding carbaldehydes, 6a−c, respectively, via
Vilsmeier−Haack reaction. In the final step, aldehydes 6a−c
underwent Knoevenagel condensation with cyanoacetic acid in
̈
Figure 1. Structure of the indacenodithiophene-bridged organic dye.
refluxing acetic acid in the presence of ammonium acetate,
giving the corresponding target DSSC sensitizers DPInDT,
DTInDT, and DMPInDT, respectively.
The UV−vis absorption and photoluminescence spectra of
the organic dyes in THF are depicted in Figure 2, and the
corresponding photophysical data are summarized in Table 1.
In the electronic absorption spectra, all three dyes exhibit a
single prominent band with the absorption maximum around
490−520 nm and an extinction coefficient higher than 2.5 ×
104 M−1 cm−1. Such absorption characteristics can be ascribed
combining essential characteristics of a DSSC dye, are thought
to be useful for highly efficient organic photovoltaics.
Scheme 1 depicts the synthetic route for the new organic
dyes. The synthesis of the coplanar indacenodithiophene core
structure was generally based on our previously established
method.19a With a starting compound of diethyl 1,4-bis-
(thiophen-2-yl)-2,5-benzenedicarbonate 1, the trimethylsilyl
(TMS) group was introduced onto the α-thienyl positions by
Scheme 1. Synthesis of Organic Dyes DPInDT, DTInDT, and DMPInDT
8978
dx.doi.org/10.1021/jo201730a|J. Org. Chem. 2011, 76, 8977−8985

The Journal of Organic Chemistry
Article
Figure 3. Absorption spectra of dyes DPInDT, DTInDT, and
DMPInDT anchored to a 7 μm porous TiO2 nanoparticle film.
Figure 2. Normalized UV−vis absorption (−·−) and photo-
luminescence () spectra of organic dyes DPInDT, DTInDT, and
DMPInDT in THF at 25 °C.
the Supporting Information). HOMOs are mainly populated
from the diarylamino donor to the indacenodithiophene π-
spacer, whereas LUMOs are mainly populated from the π-
spacer to the cyanoacetic acid moiety. This result suggests an
effective intramolecular charge transfer between the diary-
lamino donor and the cyanoacetic acid acceptor would occur
during electronic transitions of these dyes. Such electronic
population can facilitate injection of the electron from
photoexcited dyes to the TiO2 electrode. The calculation also
reveals the coplanarity of the indacenodithiophene core as well
as the contribution of methyl and methoxy groups to the
HOMO distributions in DTInDT and DMPInDT, which is
consistent with their stronger electron-donating nature and the
observed red-shifted absorption.
Cyclic voltammetry (CV) was used to probe the electro-
chemical properties of DPInDT, DTInDT, and DMPInDT.
Two oxidation waves were observed on the voltammograms.
The first oxidation waves at lower oxidation potentials were
generally from the contribution of diarylamine, whereas the
second ones, with higher oxidation potentials and quasi-
reversible behaviors, were from the indacenodithiophene π-
spacer. Meanwhile, the lower oxidation potentials of DTInDT
and DMPInDT as compared to that of DPInDT clearly
indicate the HOMO raising effect upon the introduction of
stronger donors in DTInDT and DMPInDT, which is in
accord with the calculation showing the methyl and methoxy
groups’ significant contribution to the HOMO distributions
(Figure S1 of the Supporting Information). On the other hand,
for the reduction waves, these three dyes showed one quasi-
reversible peak. The reduction potentials did not vary
significantly with the variation of the donor moieties, which
is also consistent with the calculations, in which the LUMOs
are less influenced by the diarylamino donors. The zero−zero
to the π−π* transition of the whole D−π−A conjugation
backbone. Apparently, the absorption spectra of DTInDT
(λmax = 500 nm) and DMPInDT (λmax = 520 nm) show
considerable bathochromic shifts as compared with that of
DPInDT (λmax = 490 nm). This result clearly indicates that the
modulation of the optical band-gaps and energy levels of D−π−
A dyes can be feasibly achieved by altering the electronic nature
of diarylamino donors. Similarly, the charge transfer emission
maximum shifts from 628 nm for DPInDT to 660 nm for
DMPInDT. Besides the major emission peak, a shoulder
around 550 nm, which is assigned as emission from the local
excited state, was also detected for three dyes, yet with a much
higher intensity in DPInDT than in DTInDT and DMPInDT.
This result suggests that DTInDT and DMPInDT, the dyes
incorporating stronger donors, possess stronger photoinduced
intramolecular charge transfer ability over the π-conjugation
backbone, leading to larger red shifts in absorption and
emission. Figure 3 depicts the absorption spectra of the organic
dyes once they are anchored to the 7 μm porous TiO2
nanoparticle film. The absorption maxima of these three dyes
were slightly blue-shifted compared to those observed in the
THF solution. It is mainly that the deprotonation of carboxylic
acid upon anchoring to the TiO2 surface leads to the
consequent carboxylate−TiO2 unit which is in general a weaker
acceptor compared to the corresponding carboxylic acid.21 On
the other hand, no peak broadening effect was observed in the
film absorption, indicating that the intermolecular aggregation
between dyes can be significantly suppressed by the pendant
side chains on sp3−carbon bridges, which is advantageous for
constructing a highly efficient organic DSSC dye.
The frontier molecular orbitals of these new dyes were
calculated with density functional theory (DFT) (Figure S1 of
Table 1. Physical Properties of Organic Dyes DPInDT, DTInDT, and DMPInDT
a
a
a
b
c
d
dye
λabs (nm)
ε
(M−1 cm−1
)
λem (nm)
Eox (V)
E0−0 (V)
Eox* (V)
DPInDT
DTInDT
DMPInDT
490
500
520
29622
27866
25268
628
648
660
0.82
0.77
0.71
2.28
2.17
2.11
−1.46
−1.40
−1.40
a
b
The absorption spectra were measured in a THF solution (10−5 M). The oxidation potentials of the dyes were measured in CH2Cl2 with 0.1 M
tetrabutylammonium hexafluorophosphate (TBAPF6) as the electrolyte [working electrode, glassy carbon; reference electrode, Ag/Ag+; calibrated
with ferrocene/ferrocenium (Fc/Fc+) as an internal reference and converted to NHE by addition of 630 mV,22 counter electrode, Pt]. E0−0 was
c
d
determined from the intersection of the absorption and emission spectra in THF. Eox* was calculated as Eox − E0−0
.
8979
dx.doi.org/10.1021/jo201730a|J. Org. Chem. 2011, 76, 8977−8985

The Journal of Organic Chemistry
Article
excitation energy (E0−0) estimated from the onset of the
absorption spectra together with the ground-state oxidation
potential (Eox) was used to calculate the excited-state oxidation
potential [Eox* = Eox − E0−0 (Table 1)]. The thus obtained Eox*
values for three dyes are more negative than the conduction
band edge of TiO2 (−0.5 V vs NHE),23 indicating injection of
the electron from excited-state dyes onto the TiO2 electrode
would be energetically favorable. These dyes also exhibit more
positive ground-state oxidation potentials to ensure facile dye
regeneration through the iodide/triiodide coupled electrolyte
(0.4 V vs NHE) and to prevent the undesirable charge
recombination between the oxidized dyes and photoinjected
electrons on the TiO2 electrode.
Figure 5. IPCE spectra of DSSCs based on organic dyes DPInDT,
DTInDT, and DMPInDT.
Figure 4. Cyclic voltammograms of DPInDT (black), DTInDT
(blue), and DMPInDT (red). TBAPF6 (0.1 M) (oxidation) in CH2Cl2
and TBAP (0.1 M) (reduction) in THF were used as supporting
electrolytes. A glassy carbon electrode was used as the working
electrode.
Figure 6. Photocurrent density vs voltage for DSSCs based on
DPInDT, DTInDT, and DMPInDT organic dyes under AM 1.5G
simulated solar light (100 mW/cm2).
The photovoltaic characteristics of DPInDT, DTInDT, and
DMPInDT as the sensitizers for DSSCs were evaluated using a
sandwich-type DSSC cell comprising 0.6 M 1-butyl-3-
methylimidazolium iodide (BMII), 0.05 M LiI, 0.03 M I2, 0.5
M 4-tert-butylpyridine, and 0.1 M guanidinium thiocyanate in a
mixture of acetonitrile and valeronitrile (85/15, v/v), as the
redox electrolyte. Also, considering the spatial interruption
between dyes provided by the pendant side chains on sp3−
carbon bridges, no co-absorbent was required in the fabrication
of the devices (details of the preparation and characterization of
the device are given in Experimental Section). The incident
monochromatic photon-to-current conversion efficiency
(IPCE) spectra of the DSSCs are shown in Figure 5. The
IPCE of the device using the DPInDT sensitizer exceeds 70%
in the spectral region ranging from 400 to 554 nm and reaches
a maximum of 87% at 476 nm, whereas DTInDT and
DMPInDT, bearing stronger π-electron donors, have shown
IPCE values exceeding 70% in a more red-shifted region from
400−439 to 590 nm and maxima of 86% at 500 nm and 83% at
509 nm, respectively. Such broader spectral responses of
DTInDT and DMPInDT are consistent with the trend in the
absorption spectra, implying their better light harvesting ability
for longer-wavelength visible lights. Intriguingly, though the
IPCE of DMPInDT extends to wavelengths of nearly 700 nm,
this broadened absorption does not reflect higher JSC values (vs
DTInDT) (Figure 6). This perhaps is associated with its
intrinsically smaller extinction coefficient compared to those of
the other two. Via integration of IPCE spectra with the AM
1.5G solar spectrum, indeed DTInDT gives the highest value,
confirming that the DTInDT dye with both a broader
absorption spectrum (vs DPInDT) and a higher extinction
coefficient (vs DMPInDT) would give the highest short-circuit
current density (JSC) as shown in Figure 6.
Figure 6 shows the current−voltage (J−V) curves of the
DSSCs under standard global AM 1.5G solar irradiation. The
DSSCs based on DPInDT, DTInDT, and DMPInDT dyes
showed similar open-circuit voltage and fill factors. The short-
circuit photocurrent density and overall conversion efficiency of
the three dyes were in the following order: DTInDT >
DMPInDT > DPInDT. The DTInDT-based cell exhibited the
highest JSC value, which is consistent with the better sunlight
harvesting ability of DTInDT as discussed above. For the solar
cell based on DTInDT, the short-circuit photocurrent density
(JSC) was 13.54 mA/cm2, the open-circuit voltage (VOC) was
0.69 V, and the fill factor (FF) was 0.71, yielding an overall
conversion efficiency (η) of 6.67%. With relatively lower JSC
values, devices based on DPInDT and DMPInDT show
inferior conversion efficiencies of 6.04 and 6.33%, respectively
(see Table 2). For a fair comparison, the N719-sensitized
DSSC was also fabricated under the same conditions. The
8980
dx.doi.org/10.1021/jo201730a|J. Org. Chem. 2011, 76, 8977−8985

The Journal of Organic Chemistry
Article
electrolyte interface) in the Nyquist plot decreased in the
following order: DPInDT > DMPInDT > DTInDT. The
decrease in the lower-frequency semicircle width with the
increase in DSSC efficiency and the smallest width observed in
the highest-efficiency DTInDT cell indicate the most efficient
electron generation and thus larger electron population at its
TiO2−dye−electrolyte interface.7d Thus, the EIS results are in
good agreement with results of the short-circuit currents and
the overall power conversion efficiencies of the DSSCs.
In summary, we successfully synthesized a series of metal-free
organic DSSC sensitizers by exploiting indacenodithiophene as
an essential π-spacer in the D−π−A structure. Their physical
properties and device performances were examined and
evaluated. Via incorporation of the conventional diarylamine
donor and cyanoacetic acid acceptor, and the indacenodithio-
phene π-spacer with its remarkable coplanar conformation and
charge transfer ability, these new dyes were able to extend the
absorption maxima over 500 nm and exhibited IPCE values of
>80%. Furthermore, the peripheral n-hexoxyphenyl side chains
on the sp3−carbon bridge of the core could serve as a spatial
hindrance to mitigate undesirable dye aggregation. With the
proper adjustment of the electron donating power of the π-
donors, the level of the bathochromic shift could be enhanced.
As the result, all the dyes in this series gave promising DSSC
efficiencies of >6%. Among them, DTInDT, the dye with the
relatively broader absorption and higher extinction coefficient,
showed the highest JSC of 13.54 mA/cm2 and highest
conversion efficiency of 6.67%, which is ∼82% of the efficiency
of the ruthenium dye N719-based reference cell under the same
condition. We believe these results are sufficiently indicative for
the further development of highly efficient metal-free organic
dyes.
Table 2. DSSC Performance Parameters Based on DPInDT,
DTInDT, DMPInDT, and N719 Dyes
a
dye
JSC (mA/cm2)
VOC (V)
FF
η (%)
DPInDT
DTInDT
DMPInDT
N719
12.59
13.54
13.12
15.59
0.68
0.69
0.68
0.75
0.71
0.71
0.71
0.70
6.04
6.67
6.33
8.16
a
Performances of DSSCs were measured with a 0.125 cm2 working
area. Irradiating light was AM 1.5G light (100 mW/cm2).
efficiency of the DTInDT cell reached 82% of that of the N719
cell.
Electrochemical impedance spectroscopy (EIS) is a useful
tool for characterizing important interfacial charge transfer
processes in DSSCs, such as the charge recombination at the
TiO2−dye−electrolyte interface, electron transport in the TiO2
−
electrode, electron transfer at the counter electrode, and I3
transport in the electrolyte. In this study, impedance spectros-
copy of the cells based on DPInDT, DTInDT, and DMPInDT
dyes was used to investigate mechanisms at the internal
interfaces of the DSSCs. This examination was conducted by
subjecting the cells to constant AM 1.5G 100 mW/cm2
illumination and to bias at the open-circuit voltage (VOC) of
the cells (namely, under the condition of no dc electric
current).
Figure 7 shows the EIS Nyquist plots (i.e., minus the
imaginary part of the impedance, −Z′′, vs the real part of the
EXPERIMENTAL SECTION
■
Diethyl 1,4-Bis(5-trimethylsilylthiophen-2-yl)-2,5-benzene-
dicarbonate (2). To a solution of dry diisopropylamine (9.5 mL,
67.4 mmol) in THF (100 mL) at −78 °C was added n-BuLi (1.6 M
solution in n-hexane, 40.4 mL, 64.7 mmol). The reaction mixture was
kept at −78 °C for 1 h, and the solution of diethyl 1,4-bis(thiophen-2-
yl)-2,5-benzenedicarboxylate (10 g, 25.9 mmol) in THF (100 mL) was
added dropwise via an addition funnel. The resulting mixture was
stirred at −78 °C for 1 h, and then chlorotrimethylsilane (8.4 mL, 68.0
mmol) was added dropwise via a syringe. The mixture was warmed to
room temperature and stirred for 1 h. Then, it was poured into water
and extracted with diethyl ether. The combined extracts were dried
over anhydrous magnesium sulfate and filtered, and the solvent was
evaporated. The resulting crude solid was washed with ethanol to
Figure 7. Electrochemical impedance spectroscopy Nyquist plots for
DSSCs based on DPInDT, DTInDT, and DMPInDT organic dyes.
1
afford 2 as a white solid (11.2 g, 82%): mp 96−97 °C; H NMR
(CDCl3, 400 MHz) δ 7.81 (s, 2H), 7.18 (d, J = 3.6 Hz, 2H), 7.14 (d, J
= 3.6 Hz, 2H), 4.21 (q, J = 7.2 Hz, 4H), 1.14 (t, J = 7.0 Hz, 6H), 0.35
(s, 18H); 13C NMR (CDCl3, 100 MHz) δ 167.6, 145.5, 141.7, 134.0,
133.6, 133.2, 131.5, 128.0, 61.6, 13.9, 0.1; IR (KBr) ν 3049, 2957,
1717, 1379, 1230, 841 cm−1.
impedance, Z′, when sweeping the frequency) for DSSCs based
on DPInDT, DTInDT, and DMPInDT dyes. For the
frequency range investigated (20 Hz to 1 MHz), a larger
semicircle occurs in the lower-frequency range (∼20 Hz to 1
kHz) and a smaller semicircle occurs in the higher-frequency
range. With the bias illumination and voltage applied, the larger
semicircle at lower frequencies corresponded to the charge
transfer processes at the TiO2−dye−electrolyte interface, while
the smaller semicircle at higher frequencies corresponded to the
charge transfer processes at the Pt−electrolyte interface. The
three cells showed minimal differences in the smaller
semicircles at higher frequencies; however, the difference
between the cells in the larger semicircles at lower frequencies
was significant. The width of the lower-frequency semicircle
(corresponding to charge transfer resistance at the TiO2−dye−
4,9-Dihydro-4,4,9,9-(p-hexoxyphenyl)-s-indaceno[1,2-b:5,6-
b′]dithiophene (3). To a solution of 1-bromo-4-(n-hexoxy)benzene
(23.0 g, 90.0 mmol) in THF (30 mL) at −78 °C was added n-BuLi
(1.6 M solution in n-hexane, 56.0 mL, 90.0 mmol). The mixture was
warmed to −50 °C and stirred for 1 h, and then a solution of 2 (5.3 g,
10.0 mmol) in THF (20 mL) was added dropwise via an addition
funnel. The mixture was warmed to room temperature and stirred for
12 h, and the reaction was quenched with deionized water and the
mixture extracted with dichloromethane. The combined organic
extracts were dried over anhydrous magnesium sulfate and filtered,
and the solvent was evaporated. The resulting solid was washed with
hexanes to afford a white solid crude intermediate. The white
intermediate was then directly dissolved in acetic acid and heated to 80
8981
dx.doi.org/10.1021/jo201730a|J. Org. Chem. 2011, 76, 8977−8985

The Journal of Organic Chemistry
Article
°C, and 1 mL of concentrated hydrochloric acid was added to the
solution. The mixture was stirred at 80 °C for 2 h, and a solid
precipitated. The suspension was cooled, and the solid was filtered out.
The resulting solid was washed consecutively with water (2 × 50 mL),
an aqueous sodium carbonate solution, and methanol (30 mL) to
1H), 7.30 (d, J = 4.9 Hz, 1H), 7.26 (s, 1H), 6.92−7.18 (m, 17H),
6.75−6.82 (m, 8H), 6.58 (s, 1H), 3.86−3.96 (m, 8H), 2.32 (s, 6H),
1.76−1.82 (m, 8H), 1.31−1.52 (m, 24H), 0.88−0.98 (m, 12H); 13C
NMR (CD2Cl2, 100 MHz) δ 158.2, 155.9, 155.2, 153.9, 152.6, 145.4,
141.1, 136.7, 136.6, 135.9, 134.1, 133.1, 133.0, 129.8, 128.9, 128.8,
127.5, 122.9, 116.9, 116.2, 115.1, 114.2, 68.0, 62.9, 62.0, 31.6, 29.3,
15.7, 22.6, 20.5, 13.9; IR (KBr) ν 2948, 2926, 2855, 1642, 1607, 1507,
1246, 1177, 823 cm−1; MS (m/z, FAB+) 808 (6), 986 (13), 1166 (7);
HRMS (m/z, FAB+) calcd for C78H87NO4S2 1165.6077, found
1165.6072.
1
afford 3 as a white solid (7.9 g, 82%): mp 165 °C (DSC); H NMR
(CDCl3, 400 MHz) δ 7.39 (s, 2H), 7.24 (d, J = 5.2 Hz, 2H), 7.15 (d, d,
J = 6.8 Hz, 8H), 6.97 (d, J = 4.8 Hz, 2H), 6.76 (d, J = 6.8 Hz, 8H),
3.90 (t, J = 6.6 Hz, 8H), 1.75 (m, 8H), 1.44 (m, 8H), 1.34−1.30 (m,
16H), 0.90 (t, J = 6.4 Hz, 12H); 13C NMR (CDCl3, 100 MHz) δ
157.7, 155.9, 153.5, 140.8, 136.5, 134.8, 128.8, 127.4, 122.8, 117.1,
114.0, 67.9, 61.9, 31.7, 29.3, 25.9, 22.7, 14.2; IR (KBr) ν 3031, 2932,
2858, 1606, 1507, 1467, 1245, 1175, 821 cm−1; HRMS (m/z, FAB+)
calcd for C64H74O4S2 970.5029, found 970.5012.
2-[N,N-Bis(p-methoxyphenyl)amino]-4,9-dihydro-4,4,9,9-(p-
hexoxyphenyl)-s-indaceno[1,2-b:5,6-b′]dithiophene (5c). A
mixture of 4 (1.05 g, 1.01 mmol), bis(4-methoxyphenyl)amine (0.30
g, 1.31 mmol), palladium(II) acetate (0.011 g, 0.048 mmol), sodium
tert-butoxide (0.77 g, 7.99 mmol), and tri-tert-butylphosphine (0.05 M
in toluene, 0.20 mL, 0.010 mmol) in toluene (30 mL) was stirred
under reflux for 12 h. After that, the mixture was cooled to room
temperature and extracted with dichloromethane and water. The
combined organic extracts were dried over anhydrous magnesium
sulfate, filtered, and evaporated. The resulting crude product was
purified by column chromatography on silica gel (washed with 1%
triethylamine) with dichloromethane and hexane (v/v, 1/4) as the
eluent to afford 5c as a yellow-brown solid (0.97 g, 80%): mp 81 °C
(DSC); 1H NMR (CDCl3, 400 MHz) δ 7.36 (s, 1H), 7.26 (d, J = 5.2
Hz, 1H), 7.19 (s, 1H), 7.13−706 (m, 12H), 6.83−6.72 (m, 12H), 6.43
(s, 1H), 3.95−3.89 (m, 8H), 3.80 (s, 6H), 1.80−1.47 (m, 8H), 1.46−
1.43 (m, 8H), 1.37−1.32 (m, 16), 0.95−0.91 (m, 12H); 13C NMR
(CD2Cl2, 100 MHz) δ 157.9, 156.0, 155.8, 155.6, 154.0, 153.7, 152.2,
141.4, 141.3, 136.9, 136.8, 136.0, 133.9, 131.9, 129.1, 129.0, 127.1,
124.6, 122.9, 117.0, 116.1, 114.6, 114.2, 113.0, 68.1, 68.0, 63.0, 62.1,
55.7, 31.9, 29.6, 29.5, 26.1, 22.9, 14.4; IR (KBr) ν 3034, 2948, 2929,
2-Bromo-4,9-dihydro-4,4,9,9-(p-hexoxyphenyl)-s-indaceno-
[1,2-b:5,6-b′]dithiophene (4). To a solution of 3 (2 g, 2.05 mmol)
dissolved in dichloromethane (15 mL) was added dropwise a solution
of NBS (0.47 g, 2.67 mmol) dissolved in dichloromethane (80 mL).
The mixture was stirred at room temperature for 2 h and extracted
with dichloromethane and water. The combined organic extracts were
dried over anhydrous magnesium sulfate and filtered, and the solvent
was evaporated. The resultant compound was purified by column
chromatography on silica gel with dichloromethane and hexane as the
1
eluent (v/v, 1/5) to afford 4 as a yellow oil (1.1 g, 51%): H NMR
(CD2Cl2, 400 MHz) δ 7.40 (s, 1H), 7.36 (s, 1H), 7.28 (d, J = 4.8 Hz,
1H), 7.13−7.10 (m, 8H), 7.00 (s, 1H), 6.97 (d, J = 4.8 Hz, 1H), 6.77−
6.74 (m, 8H), 3.89 (q, J = 4.1 Hz, 8H), 1.75−1.70 (m, 8H), 1.43−1.31
(m, 24H), 0.88 (t, J = 6.6 Hz, 12H); 13C NMR (CD2Cl2, 100 MHz) δ
158.4, 158.3, 156.6, 155.1, 154.1, 152.9, 141.4, 140.9, 136.5, 136.0,
135.4, 134.6, 129.0, 128.9, 128.3, 126.1, 123.0, 117.4, 114.5, 114.4,
113.8, 68.3, 63.1, 62.3, 32.0, 29.6, 26.1, 23.0, 14.3; IR (KBr) ν 3043,
2933, 2858, 1606, 1507, 1467, 1246, 1175, 822 cm−1; HRMS (m/z,
FAB+) calcd for C64H73Br79O4S2 1048.4134, found 1048.4132; HRMS
(m/z, FAB+) calcd for C64H73Br81O4S2 1050.4113, found 1050.4119.
2-(N,N-Diphenylamino)-4,9-dihydro-4,4,9,9-(p-hexoxyphen-
yl)-s-indaceno[1,2-b:5,6-b′]dithiophene (5a). A mixture of 4 (1.2
g, 1.14 mmol), diphenylamine (0.252 g, 1.48 mmol), palladium(II)
acetate (13 mg, 0.057 mmol), sodium tert-butoxide (0.73 g, 7.6 mmol),
and tri-tert-butylphosphine (0.05 M in toluene, 0.24 mL, 0.012 mmol)
in toluene (15 mL) was stirred under reflux for 10 h. The mixture was
cooled to room temperature and extracted with dichloromethane and
water. The combined organic extracts were dried over anhydrous
magnesium sulfate and filtered, and the solvent was evaporated. The
resulting crude product was purified by column chromatography on
silica gel (washed with 1% triethylamine) with dichloromethane and
hexane (v/v, 1/4) as the eluent to afford 5b as a yellow solid (1.12 g,
2857, 1607, 1580, 1507, 1460, 1291, 1244, 1177, 1034, 826, 655 cm−1
;
HRMS (m/z, FAB+) calcd for C78H87NO6S2 1197.5975, found
1197.5963.
2-(N,N-Diphenylamino)-4,9-dihydro-4,4,9,9-(p-hexoxyphen-
yl)-7-formyl-s-indaceno[1,2-b:5,6-b′]dithiophene (6a). To a
solution of 5a (0.33 g, 0.29 mmol) in dry DMF (6 mL) was added
phosphorus oxychloride (0.05 mL, 0.62 mmol) dropwise at 0 °C, and
the mixture was stirred at 0 °C for 1 h. The mixture was warmed to
room temperature and heated at 80 °C for 4 h. The mixture was
cooled to room temperature, and an aqueous sodium acetate solution
was added to quench the reaction. The mixture was then extracted
with diethyl acetate and water. The organic solution was washed with a
saturated brine solution, dried over anhydrous magnesium sulfate,
filtered, and evaporated. The resulting crude solid was purified by
gradient column chromatography on silica gel (washed with 1%
triethylamine) with dichloromethane and hexane as the eluent (v/v,
from 1/3 to 1/1) to afford 6a as an orange solid: mp 69 °C (DSC); 1H
NMR (CD2Cl2, 400 MHz) δ 9.77 (s, 1H), 7.62 (s, 1H), 7.53 (s, 1H),
7.29−7.24 (m, 5H), 7.15−7.10 (m, 12H), 7.06−7.03 (m, 2H), 6.78−
6.75 (m, 8H), 6.40 (s, 1H), 3.91 (q, J = 6.4 Hz, 8H), 1.75−1.69 (m,
8H), 1.42−1.31 (m, 24H), 0.88 (m, 12H); 13C NMR (CD2Cl2, 100
MHz) δ 182.7, 158.5, 158.3, 156.2, 155.8, 155.4, 155.4, 153.2, 151.2,
147.6, 145.5, 138.6, 136.1, 135.7, 133.2, 132.5, 132.0, 129.4, 129.0,
128.9, 123.7, 123.1, 118.7, 116.5, 116.1, 114.5, 114.4, 68.3, 63.2, 62.5,
32.0, 30.1, 29.6, 26.1, 23.0, 14.3; IR (KBr) ν 3065, 3035, 2948, 2929,
2857, 2768, 1661, 1606, 1507, 1467, 1426, 1246, 1177, 1138, 1028,
826, 753, 695, 657, 526 cm−1; TOF MS (m/z, ESI+) 1166; HRMS
(m/z, FAB+) calcd for C77H83NO5S2 1165.5713, found 1165.5692.
2-[N,N-Bis(p-tolyl)amino]-4,9-dihydro-4,4,9,9-(p-hexoxy-
phenyl)-7-formyl-s-indaceno[1,2-b:5,6-b′]dithiophene (6b).
To a solution of 5b (0.37 g, 0.22 mmol) in dry DMF (10 mL) was
added phosphorus oxychloride (0.043 mL, 0.46 mmol) dropwise at 0
°C, and the mixture was stirred at 0 °C for 1 h. The mixture was
warmed to room temperature and heated to 70 °C for 4 h. The
mixture was cooled to room temperature; an aqueous sodium acetate
solution was added to quench the reaction, and a solid appeared and
precipitated after the addition. The solid was collected, washed with
water, dissolved in dichloromethane, and washed with water. The
combined extracts were collected, dried over anhydrous magnesium
1
86%): mp 66 °C (DSC); H NMR (CD2Cl2, 400 MHz) δ 7.39 (s,
1H), 7.27−7.22 (m, 6H), 7.13−7.08 (m, 12H), 7.03−6.97 (m, 2H),
6.96 (d, J = 4.8 Hz, 1H), 6.74 (t, J = 9.6 Hz, 8H), 6.65 (s, 1H), 3.88 (q,
J = 6.8 Hz, 8H), 1.74−1.67 (m, 8H), 1.404 (m, 8H), 1.32−1.30 (m,
16H), 0.89−0.86 (m, 12H); 13C NMR (CD2Cl2, 100 MHz) δ 158.2,
156.2, 154.1, 154.0, 153.8, 152.7, 147.8, 141.1, 136.7, 136.6, 135.8,
134.6, 134.5, 129.3, 129.1, 129.0, 127.8, 123.4, 123.0, 122.8, 117.3,
117.2, 116.6, 114.4, 68.3, 63.2, 62.2, 32.0, 29.7, 26.1, 23.1, 14.3; IR
(KBr) ν 3034, 2951, 2927, 1856, 1607, 1506, 1493, 1425, 1245, 1177,
823, 751, 695, 655 cm−1; TOF MS (m/z, ESI+) 1138; HRMS (m/z,
FAB+) calcd for C76H83NO4S2 1137.5764, found 1137.5793.
2-[N,N-Bis(p-tolyl)amino]-4,9-dihydro-4,4,9,9-(p-hexoxy-
phenyl)-s-indaceno[1,2-b:5,6-b′]dithiophene (5b). A mixture of
4 (1.05 g, 1.01 mmol), di-p-tolylamine (0.26 g, 1.31 mmol),
palladium(II) acetate (0.011 g, 0.048 mmol), sodium tert-butoxide
(0.77 g, 7.99 mmol), and tri-tert-butylphosphine (0.05 M in toluene,
0.20 mL, 0.010 mmol) in toluene (15 mL) was stirred under reflux for
12 h. The mixture was cooled to room temperature and extracted with
dichloromethane and water. The combined organic extracts were dried
over anhydrous magnesium sulfate, filtered, and evaporated. The
resulting crude product was purified by column chromatography on
silica gel (washed with 1% triethylamine) with dichloromethane and
hexane (v/v, 1/4) as the eluent to afford 5b as a yellow-brown solid
(0.96 g, 82%): mp 76−78 °C; 1H NMR (CD2Cl2, 400 MHz) δ 7.41 (s,
8982
dx.doi.org/10.1021/jo201730a|J. Org. Chem. 2011, 76, 8977−8985

The Journal of Organic Chemistry
Article
sulfate, filtered, and evaporated. The resulting crude solid was purified
by gradient column chromatography on silica gel (washed with 1%
triethylamine) with dichloromethane and hexane as the eluent (v/v,
from 1/3 to 1/1) to afford 6b as an orange solid (0.15 g, 42%): mp
80−82 °C; 1H NMR (CDCl3, 400 MHz) δ 9.78 (s, 1H), 7.69 (s, 1H),
7.46 (s, 1H), 7.18 (s, 1H), 7.02−7.15 (m, 16H), 6.72−6.82 (m, 8H),
6.54 (s, 1H), 3.91 (q, J = 6.9 Hz, 8H), 2.31 (s, 6H), 1.69−1.82 (m,
8H), 1.25−1.51 (m, 24H), 0.86−0.95 (m, 12H); 13C NMR (CD2Cl2,
100 MHz) δ 182.5, 158.4, 158.2, 157.0, 153.0, 145.2, 145.1, 136.1,
135.6, 133.5, 131.5, 129.8, 128.9, 128.7, 123.2, 118.4, 116.0, 114.3,
114.2, 113.6, 68.1, 62.9, 62.1, 31.9, 31.6, 30.1, 29.7, 29.3, 29.2, 29.1,
25.7, 25.6, 22.7, 22.6, 20.5, 13.9, 13.8; IR (KBr) ν 3040, 2952, 2927,
2856, 1662, 1507, 1247, 1177, 826 cm−1; MS (m/z, FAB+) 1015 (22),
1111 (13), 1194 (91); HRMS (m/z, FAB+) calcd for C79H87NO5S2
1193.6026, found 1193.6018.
dichloromethane, and then washed with water. The organic extracts
were collected, dried over anhydrous magnesium sulfate, filtered, and
evaporated. The resulting crude solid was purified by column
chromatography on silica gel with dichloromethane and THF as the
eluent (v/v, from 1/0 to 0/1) to afford DTInDT as a black solid (84
mg, 82%): mp 134−136 °C; 1H NMR (CD2Cl2, 400 MHz) δ 8.33 (s,
1H), 7.64 (s, 1H), 7.59 (s, 1H), 7.25 (s, 1H), 7.01−7.18 (m, 16H),
6.71−6.86 (m, 8H), 6.54 (1H), 3.93 (q, J = 7.1 Hz, 8H), 2.33 (s, 6H),
1.65−1.82 (m, 8H), 1.18−1.52 (m, 24H), 0.82−0.96 (m, 12H); 13C
NMR (CDCl3, 100 MHz) δ 158.3, 158.1, 145.1, 136.0, 135.5, 133.4,
131.4, 129.9, 128.9, 128.8, 123.3, 114.4, 114.3, 67.9, 62.8, 62.1, 31.6,
30.3, 29.2, 25.7, 22.6, 20.8, 14.0; IR (KBr) ν 3412, 2952, 2925, 2853,
2214, 1646, 1506, 1454, 1359, 1246, 1177, 1011 cm−1; MS (m/z,
FAB+) 1082 (4), 1178 (4), 1261 (24); HRMS (m/z, FAB+) calcd for
C82H88N2O6S2 1260.6084, found 1260.6083.
2-[N,N-Bis(p-methoxyphenyl)amino]-4,9-dihydro-4,4,9,9-(p-
hexoxyphenyl)-s-indaceno[1,2-b:5,6-b′]dithiophen-7-yl-2-cya-
noacrylic Acid (DMPInDT). A mixture of 6c (0.1 g, 0.081 mmol),
cyanoacetic acid (0.02 g, 0.39 mmol), and ammonium acetate (0.02 g,
0.26 mmol) in glacial acetic acid (5 mL) was stirred at 80 °C for 10 h.
After the mixture had been cooled to room temperature, deionized
water was added to quench the reaction, and a black solid precipitated.
The solid was filtered out, washed with water, dissolved in
dichloromethane, and washed with water. The organic extracts were
collected, dried over anhydrous magnesium sulfate, filtered, and
evaporated. The resulting crude solid was purified by column
chromatography on silica gel with dichloromethane and THF as the
eluent (v/v, from 1/0 to 0/1) to afford DMPInDT as a black solid (80
2-[N,N-Bis(p-methoxyphenyl)amino]-4,9-dihydro-4,4,9,9-(p-
hexoxyphenyl)-7-formyl-s-indaceno[1,2-b:5,6-b′]-ithiophene
(6c). To a solution of 5c (0.35 g, 0.29 mmol) in dry DMF (10 mL)
was added phosphorus oxychloride (0.043 mL, 0.46 mmol) dropwise
at −78 °C. The mixture was warmed to room temperature and heated
at 50 °C. After 3 h, the mixture was cooled to room temperature, and
10% hydrochloric acid was added to quench the reaction. The mixture
was extracted with ethyl ether and water; the combined organic
extracts were collected, washed with a saturated brine solution, dried
over anhydrous magnesium sulfate, and filtered, and the solvent was
evaporated. The resulting crude solid was purified by gradient column
chromatography on silica gel (basified with 1% triethylamine) with
dichloromethane and hexane as the eluent (v/v, from 1/3 to 1/1) to
1
1
mg, 76%): mp 136−138 °C; H NMR (CDCl3, 400 MHz) δ 8.26 (s,
afford 6c as an orange solid (0.16 g, 46%): mp 89 °C (DSC); H
1H), 7.56 (s, 1H), 7.45 (s, 1H), 7.05−7.20 (m, 12H), 6.98 (s, 1H),
6.71−6.86 (m, 12H), 6.40 (s, 1H), 3.90 (t, J = 7.1 Hz, 8H), 3.79 (s,
6H), 1.68−1.82 (m, 8H), 1.21−1.52 (m, 24H), 0.81−0.98 (m, 12H);
13C NMR (CDCl3, 100 MHz) δ 158.2, 158.1, 156.3, 140.9, 136.1,
NMR (CD2Cl2, 400 MHz) δ 9.77 (s, 1H), 7.49 (s, 1H), 7.14−7.09 (m,
12H), 6.85−6.82 (m, 4H), 6.82−6.75 (m, 8H), 6.38 (s, 1H), 3.91 (q, J
= 6.53 Hz, 8H), 3.78 (s, 6H), 1.79−1.71 (m, 8H), 1.47−1.40 (m, 8H),
1.40−1.28 (m, 16H), 0.93−0.87 (m, 12H); 13C NMR (CD2Cl2, 100
MHz) δ 182.5, 158.6, 158.4, 156.4, 156.0, 155.9, 155.4, 152.8, 151.3,
145.2, 140.9, 138.9, 136.2, 135.8, 131.9, 131.7, 129.7, 129.0, 128.9,
125.4, 118.4, 115.8, 114.7, 114.5, 114.4, 110.4, 68.3, 63.1, 62.4, 31.9,
29.6, 29.6, 26.07, 26.05, 23.0, 14.2; IR (KBr) ν 3031, 2929, 2857, 1659,
1603, 1505, 1430, 1243, 1177, 1033, 827 cm−1; TOF MS (m/z, ESI+)
1126. Anal. Calcd: C, 77.35; H, 7.15; S, 5.23. Found: C, 77.61; H,
7.17; S, 5.21.
135.5, 128.9, 128.8, 125.5, 125.2, 114.6, 114.4, 114.3, 67.9, 62.7, 62.0,
55.5, 31.6, 31.5, 30.3, 29.7, 29.3, 29.2, 25.7, 22.6, 22.5, 21.2, 14.0; IR
(KBr) ν 3392, 2958, 2924, 2853, 2217, 1606, 1528, 1350, 1259, 1024,
801, 732 cm−1; HRMS (m/z, FAB+) calcd for C82H89N2O8S2 (M +
H+) 1293.6060, found 1293.6097.
Measurement of Absorption Spectra of Dye-Loaded Nano-
porous TiO2 Films. A 7 μm thick transparent porous TiO2
nanoparticle layer (adopting 20 nm anatase TiO2 nanoparticles) was
coated on a glass plate by the doctor-blade method. After being
sintered at 500 °C for 30 min, the TiO2 film was immersed into 0.5
mM dye solutions in acetonitrile and tert-butanol (1/1 volume ratio)
at room temperature for 24 h. The UV−vis absorption spectrum of the
dye-loaded TiO2 film was then recorded on a spectrophotometer.
Fabrication of Dye-Sensitized Solar Cells. To prepare the
DSSC working electrodes, the FTO glass plates were first cleaned in a
detergent solution using an ultrasonic bath for 15 min and then rinsed
with water and ethanol. A layer of 20 nm anatase TiO2 nanoparticles
for the transparent nanocrystalline layer was first coated on the FTO
glass plates by the doctor-blade method. After the film was dried at
120 °C, another layer of 400 nm anatase TiO2 nanoparticles was then
deposited as the light-scattering layer of the DSSC. The resulting
working electrode was composed of a 12 μm thick transparent TiO2
nanoparticle layer (particle size of 20 nm) and a 4 μm thick TiO2
scattering layer (particle size of 400 nm). The nanoporous TiO2
electrodes were then sequentially heated at 150 °C for 10 min, 300 °C
for 10 min, 400 °C for 10 min, and finally 500 °C for 30 min. After the
solutions had cooled, the nanoporous TiO2 electrodes were immersed
in the 0.5 mM dye solutions in acetonitrile and tert-butanol (1/1
volume ratio) at room temperature for 24 h. Counter electrodes of the
DSSC were prepared by depositing 40 nm thick Pt films on the FTO
glass plates by e-beam evaporation. The dye-adsorbed TiO2 working
electrode and a counter electrode were then assembled into a sealed
DSSC cell with a sealant spacer between the two electrode plates. A
drop of electrolyte solution [0.6 M 1-butyl-3-methylimidazolium
iodide (BMII), 0.05 M LiI, 0.03 M I2, 0.5 M 4-tert-butylpyridine, and
0.1 M guanidinium thiocyanate in a mixture of acetonitrile and
valeronitrile (85/15, v/v)] was injected into the cell through a drilled
2-(N,N-diphenylamino)-4,9-dihydro-4,4,9,9-(p-hexoxyphen-
yl)-s-indaceno[1,2-b:5,6-b′]-dithiophen-7-yl-2-cyanoacrylic
acid (DPInDT). A mixture of 6a (0.14 g, 0.12 mmol), cyanoacetic
acid (0.03 g, 0.59 mmol), and ammonium acetate (0.02 g, 0.26 mmol)
in glacial acetic acid (5 mL) was stirred at 80 °C for 4 h. After the
mixture had been cooled to room temperature, deionized water was
added to quench the reaction, and a black solid precipitated. The solid
was filtered out, washed with water, dissolved in dichloromethane, and
washed with water. The organic extracts were collected, dried over
anhydrous magnesium sulfate, filtered, and evaporated to afford
1
DPInDT as a black solid (0.14 g, 96%): mp 135−137 °C; H NMR
(CD2Cl2, 400 MHz) δ 8.30 (s, 1H), 7.61 (s, 1H), 7.58 (s, 1H), 7.29−
7.25 (m, 5H), 7.17−7.05 (m, 14H), 6.79−6.75 (m, 8H), 6.64 (s, 1H),
3.91 (q, J = 7.06 Hz, 8H), 1.77−1.70 (m, 8H), 1.44−1.27 (m, 24H),
0.92−0.89 (m, 12H); 13C NMR (CD2Cl2, 100 MHz) δ 158.5, 158.3,
156.6, 156.4, 155.9, 154.6, 153.5, 153.3, 148.3, 148.3, 147.5, 139.4,
138.1, 136.0, 135.8, 135.4, 134.3, 132.8, 132.1, 129.4, 128.9, 128.8,
123.8, 123.6, 119.0, 116.5, 116.4, 115.5, 114.5, 114.4, 94.2, 68.3, 63.2,
62.4, 32.0, 30.1, 29.6, 29.5, 26.1, 23.0, 14.2; IR (KBr) ν 3444, 2926,
2855, 2211, 1692, 1606, 1579, 1507, 1493, 1419, 1177, 1153, 1030,
824, 696 cm−1; HRMS (m/z, FAB+) calcd for C80H84N2O6S2
1232.5771, found 1232.5740.
2-[N,N-Bis(p-tolyl)amino]-4,9-dihydro-4,4,9,9-(p-hexoxy-
phenyl)-s-indaceno[1,2-b:5,6-b′]dithiophen-7-yl-2-cyanoa-
crylic Acid (DTInDT). A mixture of 6b (0.1 g, 0.081 mmol),
cyanoacetic acid (0.02 g, 0.39 mmol), and ammonium acetate (0.02 g,
0.26 mmol) in glacial acetic acid (5 mL) was stirred at 80 °C for 10 h.
After the mixture had been cooled to room temperature, deionized
water was added to quench the reaction, and a black solid precipitated.
The solid was filtered out, washed with water, dissolved in
8983
dx.doi.org/10.1021/jo201730a|J. Org. Chem. 2011, 76, 8977−8985

The Journal of Organic Chemistry
Article
hole. Finally, the hole was sealed using the sealant and a cover glass.
An antireflection coating film was adhered to the DSSC. A mask with
an aperture area of 0.125 cm2 was covered on a testing cell during
photocurrent−voltage and incident photon-to-current conversion
efficiency measurements.
1193. (i) Yang, H.-Y.; Yen, Y.-S.; Hsu, Y.-C.; Chou, H.-H.; Lin, J.-T.
Org. Lett. 2010, 12, 16.
(4) Chen, Z.; Li, F.; Huang, C. Curr. Org. Chem. 2007, 11, 1241.
(5) (a) Hara, K.; Kurashige, M.; Ito, S.; Shinpo, A.; Suga, S.; Sayama,
K.; Arakawa, H. Chem. Commun. 2003, 252. (b) Kitamura, T.; Ikeda,
M.; Shigaki, K.; Inoue, T.; Anderson, N. A.; Ai, X.; Lian, T.; Yanagida,
S. Chem. Mater. 2004, 16, 1806.
(6) (a) Hara, K.; Sayama, K.; Ohga, Y.; Shinpo, A.; Suga, S.; Arakawa,
H. Chem. Commun. 2001, 569. (b) Hara, K.; Kurashige, M.; Dan-oh,
Y.; Kasada, C.; Shinpo, A.; Suga, S.; Sayama, K.; Arakawa, H. New J.
Chem. 2003, 27, 783. (c) Hara, K.; Sato, T.; Katoh, R.; Furube, A.;
Ohga, Y.; Shinpo, A.; Suga, S.; Sayama, K.; Sugihara, H.; Arakawa, H. J.
Phys. Chem. B 2003, 107, 597. (d) Wang, Z. S.; Cui, Y.; Hara, K.; Dan-
oh, Y.; Kasada, C.; Shinpo, A. Adv. Mater. 2007, 19, 1138.
(7) (a) Kim, S.; Lee, J. K.; Kang, S. O.; Ko, J.; Yum, J.-H.; Fantacci,
Photocurrent−Voltage Measurement. The photocurrent−
voltage characteristics of the DSSCs were measured under illumination
with AM 1.5G solar light from a 300 W xenon lamp solar simulator.
The incident light intensity was calibrated as 100 mW/cm2.
Photocurrent−voltage curves were obtained by applying an external
bias voltage to the cell and measuring the generated photocurrent.
Incident Monochromatic Photon-to-Current Conversion
Efficiency Measurement. The incident monochromatic photon-
to-current conversion efficiency (IPCE) spectra were recorded by
using a 75 W xenon lamp as the light source coupled to a
monochromator. The IPCE data were taken by illuminating
monochromatic light on the solar cells (with a wavelength sampling
interval of 10 nm from 300 to 750 nm) and measuring the short-circuit
current of the solar cells. The IPCE measurement was performed with
a lock-in amplifier, a low-speed chopper, and a bias light source under
full computer control.
Electrochemical Impedance Spectroscopy Measurement.
The electrochemical impedance of the cells was measured by using an
impedance analyzer with a frequency range of 20 Hz to 1 MHz. In this
study, during the impedance measurement, the cell was under constant
AM 1.5G 100 mW/cm2 illumination. The impedance of the cell
(throughout the frequency range of 20 Hz to 1 MHz) was then
measured by applying a bias at the open-circuit voltage (VOC) of the
cell and by using an ac amplitude of 10 mV.
S.; De Angelis, F.; Di Censo, D.; Nazeeruddin, M. K.; Gratzel, M. J.
̈
Am. Chem. Soc. 2006, 128, 16701. (b) Koumura, N.; Wang, Z.-S.;
Mori, S.; Miyashita, M.; Suzuki, E.; Hara, K. J. Am. Chem. Soc. 2006,
128, 14256. (c) Choi, H.; Baik, C.; Kang, S. O.; Ko, J.; Kang, M.-S.;
Nazeeruddin, M. K.; Gratzel, M. Angew. Chem., Int. Ed. 2008, 47, 327.
̈
(d) Wang, Z.-S.; Koumura, N.; Cui, Y.; Takahashi, M.; Sekiguchi, H.;
Mori, A.; Kubo, T.; Furube, A.; Hara, K. Chem. Mater. 2008, 20, 3993.
(e) Juntin Thomas, K. R.; Hsu, Y.-C.; Lin, J. T.; Lee, K.-M.; Ho, K.-C.;
Lai, C.-H.; Cheng, Y.-M.; Chou, P.-T. Chem. Mater. 2008, 20, 1830.
(f) Kim, S.; Kim, D.; Choi, H.; Kang, M.-S.; Song, K.; Kang, S. O.; Ko,
J. Chem. Commun. 2008, 4951. (g) Yum, J. H.; Hagberg, D. P.; Moon,
S. J.; Karlson, K. M.; Marinado, T.; Sun, L.; Hagfeldt, A.; Nazeeruddin,
M. K.; Gratzel, M. Angew. Chem., Int. Ed. 2009, 48, 1576. (h) Wang,
̈
Z.-S.; Koumura, N.; Cui, Y.; Miyashita, M.; Mori, S.; Hara, K. Chem.
Mater. 2009, 21, 2810. (i) Yang, H. Y.; Yen, Y. S.; Hsu, Y. C.; Chou, H.
H.; Lin, J. T. Org. Lett. 2010, 12, 16. (j) Liang, Y.; Peng, B.; Liang, J.;
Tao, Z.; Chen, J. Org. Lett. 2010, 12, 1204.
ASSOCIATED CONTENT
■
S
* Supporting Information
1H and 13C NMR spectra for all new compounds and
theoretical calculation with DFT. This material is available
free of charge via the Internet at http://pubs.acs.org.
(8) Justin Thomas, K. R.; Lin, J. T.; Hsu, Y.-C.; Ho, K.-C. Chem.
Commun. 2005, 4098.
(9) (a) Cho, N.; Choi, H.; Kim, D.; Song, K.; Kang, S. O.; Ko, J.
Tetrahedron 2009, 65, 6236. (b) Heredia, D.; Natera, J.; Gervaldo, M.;
Otero, L.; Fungo, F.; Lin, C.-Y.; Wong, K.-T. Org. Lett. 2010, 12, 12.
(10) (a) Tian, H.; Yang, X.; Chen, R.; Hagfeldt, A.; Sun, L. Energy
Environ. Sci. 2009, 2, 674. (b) Tian, H.; Yang, X.; Cong, J.; Chen, R.;
Liu, J.; Hao, Y.; Hagfeldt, A.; Sun, L. Chem. Commun. 2009, 6288.
(11) Lin, J.-T.; Chen, P.-C.; Yen, Y.-S.; Hsu, Y.-C.; Chou, H.-H.; Yeh,
P. M.-C. Org. Lett. 2009, 11, 97.
(12) Li, R.; Lv, R.; Shi, D.; Zhou, D.; Cheng, Y.; Zhang, G.; Wang, P.
J. Phys. Chem. C 2009, 113, 7469.
(13) (a) Yen, Y.-S.; Hsu, Y.-C.; Lin, J.-T.; Chang, C.-W.; Hsu, C.-P.;
Yin, D.-J. J. Phys. Chem. C 2008, 112, 12557. (b) Li, Q.; Zhong, C.;
Huang, J.; Huang, Q.; Shi, J.; Jin, X.; Peng, T.; Qin, J.; Li, Z. Chem.
Eur. J. 2009, 15, 9664.
AUTHOR INFORMATION
Corresponding Author
*E-mail: kenwong@ntu.edu.tw; chungwu@cc.ee.ntu.edu.tw.
■
ACKNOWLEDGMENTS
■
We are grateful for the financial support from the National
Science Council of Taiwan (NSC 98-2119-M-002-007-MY3
and NSC 99-2221-E-002-118-MY3).
REFERENCES
(1) O’Reagen, B.; Gratzel, M. Nature 1991, 353, 737.
(2) (a) Nazeerudin, M. K.; Kay, A.; Rodicio, L.; Humphry-Baker, R.;
■
(14) Choi, H.; Choi, H.; Paek, S.; Song, K.; Kang, M.-S.; Ko, J. Bull.
Korean Chem. Soc. 2010, 31, 125.
̈
(15) Lin, L.-Y.; Tsai, C.-H.; Wong, K.-T.; Huang, T.-W.; Wu, C.-C.;
Chou, S.-H.; Lin, F.; Chen, S.-H.; Tsai, A.-I. J. Mater. Chem. 2011, 21,
5950.
(16) Li, Y.-T.; Chen, C.-L.; Hsu, Y.-Y.; Hsu, H.-C.; Chi, Y.; Chen, B.-
S.; Liu, W.-H.; Lai, C.-H.; Lai, T.-Y.; Chou, P.-T. Tetrahedron 2010, 66,
4223.
Muller, E.; Liska, P.; Vlachopoulos, N.; Gratzel, M. J. Am. Chem. Soc.
̈
̈
́
1993, 115, 6382. (b) Nazeeruddin, M. K.; Pechy, P.; Renouard, T.;
Zakeeruddin, S. M.; Humphry-Baker, R.; Comte, P.; Liska, P.; Cevey,
L.; Costa, E.; Shklover, V.; Spiccia, L.; Deacon, G. B.; Bignozzi, C. A.;
Gratzel, M. J. Am. Chem. Soc. 2001, 123, 1613. (c) Gratzel, M. J.
̈
̈
Photochem. Photobiol., A 2004, 168, 235.
(17) (a) Chen, C.-H.; Hsu, Y.-C.; Chou, H.-H.; Thomas, K. R. J.;
Lin, J.-T.; Hsu, C.-P. Chem.Eur. J. 2010, 16, 3184. (b) Chen, B.-S.;
Chen, Y.-J.; Chou, P.-T. J. Mater. Chem. 2011, 21, 4090.
(18) (a) Scherf, U. J. Mater. Chem. 1999, 9, 1853. (b) Setayesh, S.;
(3) (a) Mishra, A.; Fischer, M. K. R.; Bauerle, P. Angew. Chem., Int.
Ed. 2009, 48, 2474. (b) Ooyama, Y.; Harima, Y. Eur. J. Org. Chem.
2009, 2903. (c) Hwang, S.; Lee, J. H.; Park, C.; Lee, H.; Kim, C.; Park,
C.; Lee, M.-H.; Lee, H.; Park, J.; Kim, K.; Park, N.-G.; Kim, G. Chem.
Commun. 2007, 4887. (d) Ito, S.; Miura, H.; Uchida, S.; Takata, M.;
Marsitzky, D.; Mullen, K. Macromolecules 2000, 33, 2016. (c) Jacob, J.;
̈
Zhang, J.; Grimsdale, A. C.; Mullen, K.; Gaal, M.; List, E. J. W.
̈
Sumioka, K.; Liska, P.; Comte, P.; Pechyb, P.; Gratzel, M. Chem.
́
̈
Macromolecules 2003, 36, 8240. (d) Qin, H.; Wenger, S.; Xu, M.; Gao,
Commun. 2008, 5194. (e) Kim, J.-J.; Choi, H.; Lee, J.-W.; Kang, M.-S.;
Song, K.; Kang, S. O.; Ko, J. J. Mater. Chem. 2008, 18, 5223. (f) Ning,
Z.; Zhang, Q.; Pei, H.; Luan, J.; Lu, C.; Cui, Y.; Tian, H. J. Phys. Chem.
C 2009, 113, 10307. (g) Zeng, W.; Cao, Y.; Bai, Y.; Wang, Y.; Shi, Y.;
Zhang, M.; Wang, F.; Pan, C.; Wang, P. Chem. Mater. 2010, 22, 1915.
(h) Choi, H.; Raabe, I.; Kim, D.; Teocoli, F.; Kim, C.; Song, K.; Yum,
F.; Jing, X.; Wang, P.; Nazeeruddin, M. K.; Gratzel, M. J. Am. Chem.
̈
Soc. 2008, 130, 9202. (e) Ko, S.; Choi, H.; Kang, M.-S.; Hwang, H.; Ji,
H.; Kim, J.; Ko, J.; Kang, Y. J. Mater. Chem. 2010, 20, 2391. (f) Lin, L.-
Y.; Tsai, C.-H.; Wong, K.-T.; Huang, T.-W.; Hsieh, L.; Liu, S.-H.; Lin,
H.-W.; Wu, C.-C.; Chou, S.-H.; Chen, S.-H.; Tsai, A.-I. J. Org. Chem.
2010, 75, 4778.
J.-H.; Ko, J.; Nazeeruddin, M. K.; Gratzel, M. Chem.Eur. J. 2010, 16,
̈
8984
dx.doi.org/10.1021/jo201730a|J. Org. Chem. 2011, 76, 8977−8985

The Journal of Organic Chemistry
Article
(19) (a) Wong, K. T.; Chao, T.-C.; Chi, L.-C.; Chu, Y.-Y.; Balaiah,
A.; Chiu, S.-F.; Liu, Y.-H.; Wang, Y. Org. Lett. 2006, 8, 5033. (b) Pina,
J.; Seixas de Melo, J.; Burrow, H. D.; Bunnagel, T. W.; Dolfen, D.;
̈
Kunla, C. J.; Scherf, U. J. Phys. Chem. B 2009, 113, 15928.
(20) (a) Chan, S.-H.; Chen, C.-P.; Chao, T.-C.; Ting, C.; Lin, C.-S.;
Ko, B.-T. Macromolecules 2008, 41, 5519. (b) Chen, C.-P.; Chan, S.-
H.; Chao, T.-C.; Ting, C.; Ko, B.-T. J. Am. Chem. Soc. 2008, 130,
12828. (c) Yu, C.-Y.; Chen, C.-P.; Chan, S.-H.; Hwang, G.-W.; Ting,
C. Chem. Mater. 2009, 21, 3262. (d) Chan, S.-H.; Hsiao, Y.-S.; Hung,
L.-I.; Hwang, G.-W.; Chen, H.-L.; Ting, C.; Chen, C.-P. Macro-
molecules 2010, 43, 3399. (e) Chen, Y.-C.; Yu, C.-Y.; Fan, Y.-L.; Hung,
L.-I.; Chen, C.-P.; Ting, C. Chem. Commun. 2010, 46, 6503. (f) Chen,
Y.-C.; Yu, C.-Y.; Chen, C.-P.; Chan, S.-H.; Ting, C. J. Sol. Energy Eng.
2010, 132, 021103. (g) Tsai, J.-H.; Chueh, C.-C.; Chen, W.-C.; Yu, C.-
Y.; Hwang, G.-W.; Ting, C.; Chen, E.-C.; Meng, H.-F. J. Polym. Sci.,
Part A: Polym. Chem. 2010, 48, 2351. (h) Zhang, Y.; Zou, J.; Yip, H.-
L.; Chen, K.-S.; Zeigler, D. F.; Sun, Y.; Jen, A. K.-Y. Chem. Mater.
2011, 23, 2289.
(21) Wang, Z.-S.; Cui, Y.; Dan-oh, Y.; Kasada, C.; Shinpo, A.; Hara,
K. J. Phys. Chem. C 2007, 111, 7224.
(22) Hao, Y.; Yang, X.; Cong, J.; Tian, H.; Hagfeldt, A.; Sun, L.
Chem. Commun. 2009, 4031.
(23) Klein, C.; Nazeeruddin, M. K.; Censo, D. D.; Liska, P.; Gratzel,
̈
M. Inorg. Chem. 2004, 43, 4216.
8985
dx.doi.org/10.1021/jo201730a|J. Org. Chem. 2011, 76, 8977−8985