Synthesis and photovoltaic properties of organic sensitizers containing electron-deficient and electron-rich fused thiophene for dye-sensitized solar cells

Article abstract of DOI:10.1016/j.tet.2012.04.113

Diverse fused thiophenes with electron-rich and electron-deficient blocks have been synthesized and employed as the π-conjugated spacers of organic dyes for the dye-sensitized solar cells (DSSCs). The effects of these fused thiophenes were investigated by their absorption spectra, electrochemical and photovoltaic properties. For a typical device a maximum power conversion efficiency of 6.11% was obtained under simulated AM 1.5 irradiation (100 mW cm^-2): a short-circuit current (J_SC) of 14.47 mA cm ^-2, an open-circuit voltage (V_OC) of 670 mV, and a fill factor (FF) of 0.63.

Full text of DOI:10.1016/j.tet.2012.04.113

Tetrahedron 68 (2012) 5375e5385
Contents lists available at SciVerse ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and photovoltaic properties of organic sensitizers containing electron-
deficient and electron-rich fused thiophene for dye-sensitized solar cells
*
*
Xiaobing Cheng, Mao Liang , Siyuan Sun, Yongbo Shi, Zijian Ma, Zhe Sun, Song Xue
Department of Applied Chemistry, Tianjin University of Technology, Tianjin 300384, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 4 March 2012
Received in revised form 15 April 2012
Accepted 28 April 2012
Available online 3 May 2012
Diverse fused thiophenes with electron-rich and electron-deficient blocks have been synthesized and
employed as the -conjugated spacers of organic dyes for the dye-sensitized solar cells (DSSCs). The
effects of these fused thiophenes were investigated by their absorption spectra, electrochemical and
p
photovoltaic properties. For a typical device a maximum power conversion efficiency of 6.11% was ob-
tained under simulated AM 1.5 irradiation (100 mW cmꢀ2): a short-circuit current (JSC) of 14.47 mA cmꢀ2
an open-circuit voltage (VOC) of 670 mV, and a fill factor (FF) of 0.63.
,
Keywords:
Dye-sensitized solar cell
Organic sensitizers
Ó 2012 Elsevier Ltd. All rights reserved.
Electron-deficient fused thiophene
1. Introduction
impressive performances under standard global air mass 1.5 (AM
1.5G) illumination. The majority of research on fused ring building
blocks has focused on electron-rich fused thiophene; however,
electron-deficient fused thiophene has not yet to be explored for
organic dyes. It is known that electron-deficient materials were
successfully in application of bulk heterojunction organic photo-
voltaic cells (OPVs).34e36 It can be expected that developing of new
type fused ring building blocks may lead to synthesis of interesting
photosenzitizers with tailor-made photophysical, electrochemical,
and other properties to fulfill those requirements for high perfor-
mance of DSSCs.
Herein, we report the design, syntheses, and photovoltaic
properties of a series of new triphenylamine dyes (XS35e38) in-
corporating electron-rich and electron-deficient fused thiophene
units. For obtaining high photovoltaic performance, binary
spacers of a combination of EDOT and different fused thiophenes
were introduced. In the case of XS36 and XS38, electron-rich
fused thiophene units, DTT, and 3-methylthieno[3,2-b]thiophene
(MTT) are introduced, respectively. Meanwhile, electron-deficient
fused thiophene units, dithieno[3,2-b:20,30-d]thiophene-4,4-
dioxide (DTTO) and 3-methylthieno[3,2-b]thiophene-4,4-dioxide
(MTTO) are introduced into the structure of XS35 and XS37, re-
spectively. These designed dyes allow us to better understand the
structureeproperty relationship of metal-free organic chromo-
phores. Molecular structures of these two dyes are shown in Fig. 1.
There has been considerable interest for developing cheap and
easily accessible renewable energy sources due to increasing en-
ergy demands and concerns about global warming. Compared to
traditional silicon-based solar cells, dye-sensitized solar cells
(DSSCs) are viewed as promising candidate for renewable clean
energy sources in virtue of their low manufacturing cost and im-
pressive photovoltaic performance.1 To achieve high solar power
conversion efficiency, great research efforts are focused on de-
signing and synthesizing new photosensitizers: Ru-based com-
plexes2 and organic sensitizers.3 The former holds the record of
validated efficiency of over 11%.2b Organic sensitizers with robust
availability, ease of structural tunability, and generally high molar
extinction coefficients, have emerged as a competitive alternative
to the Ru-based counterpart.4e24 So far, the metal-free organic
sensitizers have gained promising solar energy-to-electricity con-
version efficiencies (
Aside from electron donor (D) and acceptor (A) in a typical D-
system, the conjugated bridging segment ( ) is widely recognized as
h
) comparable to Ru-based complexes.25e28
-A
p
p
its significance for performance control of DSSCs. Introduction of
fused ring building blocks20,26,29e33 involved of rigid thieno[3,2-b]
thiophene (TT), dithieno[3,2-b:20,30-d]thiophene (DTT), cyclo-
pentadithiophene, dihexyl-substituted dithienosilole, and benzo
[1,2-b:4,5-b0]dithiophene in the
p-spacer is proved to be effective
strategies for enhancing the light-harvesting capacity, leading to
2. Results and discussion
The synthetic routes of four organic dyes XS35e38 are shown in
* Corresponding authors. Tel.: þ86 22 60214250; fax: þ86 22 60214252; e-mail
addresses: liangmao717@126.com (M. Liang), xuesong@ustc.edu.cn (S. Xue).
Scheme 1. DTT37 and MTT38 units were prepared according to
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2012.04.113

5376
X. Cheng et al. / Tetrahedron 68 (2012) 5375e5385
Fig. 1. Structure of dyes (XS35e38).
literature. DTTO and MTTO were obtained by using the methodol-
ogy described by Matzger et al.39 and Barbarella et al.,40 re-
spectively. XS35 was synthesized in six steps from the DTTO. The
Stille coupling of compound 2 with 4-(hexyloxy)-N-(4-(hexyloxy)
phenyl)-N-(4-(tributylstannyl)phenyl)aniline yielded compound 3.
Compound 4, synthesized from bromination with N-bromosucci-
nimide (NBS) in DMF, was cross-coupled with tributyl(2,3-
dihydrothieno[3,4-b][1,4]dioxin-5-yl)stannane to give compound
5. Aldehyde 6 was synthesized from the reaction of 5 with POCl3
and DMF through the VilsmeiereHaack reaction. Then the target
dye XS35 was obtained via Knoevenagel condensation reaction of
the aldehyde 6 with cyanoacetic acid in the presence of a catalytic
amount of piperidine. The synthetic routes for XS36e38 are similar
to that of XS35. The intermediates 10, 16, and 20 were obtained
through bromination, Suzuki coupling, and VilsmeiereHaack re-
action. Treatment of these intermediates with 4-(hexyloxy)-N-(4-
(hexyloxy)phenyl)-N-(4-(tributylstannyl)phenyl)aniline through
the Stille coupling reaction gave important intermediates of alde-
hydes 11, 17, and 21, respectively. The Knoevenagel condensation of
these aldehydes with cyanoacetic acid in the presence of piperidine
in CH3CN yielded organic sensitizers XS36e38.
and ethylenedioxyl groups compared to the XS35, XS36, and XS38
counterpart, decreasing the electronic communication between
donor and acceptor. The molar extinction coefficients of XS35e38
are 39ꢂ103, 44ꢂ103, 21ꢂ103, and 37ꢂ103 Mꢀ1 cmꢀ1, respectively.
XS37 exhibited the lowest absorptivity, reflecting the important
role of molecular conformation.
Upon adsorption onto TiO2, XS35e38 show similar hyp-
sochromic effect compared with that measured in solution (Fig. 4),
which could be ascribed to a weaker electron-withdrawing capa-
bility of the carboxylatetitanium assembly than the carboxylic
acid.41 When the four dyes are excited with visible light, they ex-
hibit strong luminescence maxima at 550e750 nm (Fig. 2b).
2.2. Electrochemical properties
The first ground-state oxidation potentials (ED/Dþ), corre-
sponding to the HOMO level of dyes, were measured by cyclic
voltammetry (CV) with 0.1 M tetrabutylammonium perchlorate in
acetonitrile solution and the results were summarized in Table 1.
The LUMO levels of sensitizer were estimated by the values of ED/Dþ
and the 0e0 band gaps. The latter is obtained by the intersection of
absorption and emission spectra. As depicted in Fig. 5, introduction
of different types of fused thiophene in the spacer can adjust the
HOMO and the LUMO levels of these dyes. Positive shifts of the
HOMO level (0.1 V) and the LUMO level (0.1 V) are observed for
XS35 versus XS36. Also, this tendency holds for XS37 versus XS38.
It is suggested that, compared to the electron-deficient thiophene,
the electron-rich fused thiophene raises the oxidation potential of
dye. The ED/Dþ values of XS35e38 within the range of 0.71e0.83 V
versus NHE are more positive than the iodine redox potential (0.4 V
vs NHE).43 Thus, these oxidized dyes can be regenerated from the
reduced species in the electrolyte to give an efficient charge sepa-
ration. The exited state reduction potentials (ED*/Dþ) of the four
dyes (ꢀ1.32 to ꢀ1.43 V vs NHE) are much more negative than the
conduction band of TiO2 at approximately ꢀ0.5 V versus NHE,
providing enough driving force for electron injection.16,44
2.1. Absorption spectra
The UVevis and emission spectra of organic dyes in chloroform
are displayed in Fig. 2. The four dyes have one intense visible ab-
sorption band centered about 500 nm corresponding to the intra-
molecular charge-transfer (ICT) band. The absorption peaks (lmax
)
for XS35, XS36, XS37, and XS38 are located at 514, 497, 492, and
494 nm, respectively. Obviously, in the case of sensitizers contain-
ing the same donor and acceptor units, the ICT band is dependent
upon the p-spacer units. The p-spacer effect on the absorption peak
is distinct in these four dyes. The bathochromic shift by 17 nm was
observed when replacing DTT unit (XS36) with DTTO unit (XS35) in
the spacer moiety. This observation arising from introduction of
deficient bridge has also been observed by other groups.25,41,42
However, such an effect is partially annihilated upon replacing
MTTO unit with MTT unit for XS37. Under the same conditions, the
XS37 sensitizer exhibits a slightly blue-shifted absorption band
relative to XS38. This observation can be interpreted from molec-
ular model studies. The structures of the dyes were analyzed using
a B3LYP/6-31G(d) hybrid function for full geometrical optimization
(Fig. 3). In the ground state, XS35, XS36, and XS38 possess a nearly
2.3. Computational analysis
To get further insight into the molecular structure and electron
distribution of these dyes, we performed TDDFT excited states
calculations at the B3LYP/6-31G(d) level in vacuo with the B3LYP/
6-31G(d) optimized ground-state geometries with Gaussian 03,45
given the negligible effect of salvation on the electronic structure.
The first and second transitions of XS35-38 with oscillator
strengths (f) above 0.5 are summarized in Table 2. There are three
co-planar conformation to achieve a maximal extent of
p-de-
localization. In the case of XS37, the torsion angle between MTTO
and EDOT (ꢀ20.3ꢁ) is lager due to the steric hindrance of sulfonyl

X. Cheng et al. / Tetrahedron 68 (2012) 5375e5385
5377
Scheme 1. Synthesis and structures of organic dyes. Reagents: (i) NBS, DMF, rt; (ii) 4-(tributylstannyl)-N,N-bis((4-hexyloxy)phenyl)aniline, Pd(PPh3)4, p-xylene, reflux; (iii) 2-
(tributylstannyl)-3,4-(ethylenedioxy)thiophene, Pd(PPh3)4, p-xylene, reflux; (iv) DMF/POCl3, 0 ꢁC/rt; (v) CNCH2COOH, CH3CN/CHCl3, piperidine, reflux; (vi) m-CPBA, CH2Cl2, 0 ꢁC/rt;
(vii) Br2, CH2Cl2, 0 ꢁC/rt.
charge-transfer excitations: HOMO/LUMO, HOMOꢀ1/LUMO,
and HOMO/LUMOþ1 (Fig. 6). The electron distribution of the
HOMOꢀ1, HOMO, and LUMO of XS35e38 are similar. HOMOꢀ1
and HOMO are populated over the triphenylamine and electron-
rich/electron-deficient fused thiophene units with considerable
contribution from the former. LUMO is delocalized through the
fused thiophene units, EDOT and cyanoacrylic acid fragments
with sizable contribution from the latter. The HOMOeLUMO ex-
citation moves the electron distribution from the diphenylvinyl
unit to the cyanoacrylic acid moiety, thus allowing an efficient
photoinduced electron transfer from the dye to the TiO2 electrode
under light irradiation. This spatially directed separation of

5378
X. Cheng et al. / Tetrahedron 68 (2012) 5375e5385
Fig. 2. Absorption (a) and normalized absorption and emission spectra (b) of dyes in chloroform (1ꢂ10ꢀ5 M).
HOMO and LUMO is an ideal condition for dye-sensitized solar
cells. In the case of LUMOþ1, electron rich or deficient linkers
have an impact on the electron distribution. For XS35 and XS37,
the electron distribution of LUMOþ1 is delocalized through the
fused thiophene units, EDOT and cyanoacrylic acid fragments
with considerable contribution from the former. It can be found
that very small electron distribution is delocalized on the tri-
phenylamine. For XS36 and XS38, the electron distribution
delocalized on the triphenylamine is large. Obviously, the spa-
tially directed separation of HOMO and LUMOþ1 of XS35/XS37
are more completely than those of XS36/XS38. In view of this,
deficient linker has a positive impact on the charge separation of
2.4. Photovoltaic performance of DSSCs
The incident monochromatic photon-to-current conversion ef-
ficiency (IPCE) measurements of DSSCs based on XS35e38 using the
redox electrolyte consisting of 0.6 M DMPImI, 0.05 M I2, 0.1 M LiI,
and 0.5 M TBP in acetonitrile are shown in Fig. 7. In agreement with
the trend in absorption spectra, the IPCE spectra of XS35, XS36, and
XS38 exhibit higher peak values and longer wavelengths than that
of XS37. It is notable that the onset of the IPCE data of XS35, XS36,
and XS38 is close to about 800 nm. The IPCE spectra of XS35 and
XS38 exceed 70% in the visible spectral region from 430 to 620 nm,
reaching their maximum of 82% and 90% around 480 nm, re-
spectively, indicating highly efficient DSSCs performances. The IPCE
D-p-A sensitizer.
Fig. 3. The optimized structures of XS35e38.

X. Cheng et al. / Tetrahedron 68 (2012) 5375e5385
5379
Table 2
Calculated details of electronic transitions with the relative oscillator strengths
larger than 0.5 of the dyes
Dye
State
Calculated
Oscillator
Transition assignmenta
energy (eV, nm)
strength (f)
XS35
1
2
1.79, 690
2.45, 505
0.79
0.97
H/L (90%)
Hꢀ1/L (58%)
H/Lþ1(30%)
H/L (90%)
Hꢀ1/L (80%)
H/Lþ1 (4%)
H/L (90%)
Hꢀ1/L (74%)
H/Lþ1(8.8%)
H/L (87%)
XS36
XS37
XS38
1
2
1.90, 649
2.54, 487
0.79
1.0
1
2
1.79, 689
2.51, 493
0.73
0.67
1
2
2.01, 616
2.67, 463
0.85
0.85
Hꢀ1/L (79%)
H/Lþ1(4.5%)
a
H means HOMO, and L means LUMO.
of XS38. By comparing the absorbance change of a dye solution
(300 M) before and after dye up-taking with a titania film, the
surface coverages ( ) of XS35, XS36, XS37, and XS38 anchored on
m
G
TiO2 film were determined to be 2.7ꢂ10ꢀ7, 2.3ꢂ10ꢀ7, 3.0ꢂ10ꢀ7, and
4.0ꢂ10ꢀ7 mol cmꢀ2, respectively. It can be found that, the surface
coverages of XS37 and XS38 are higher than that of XS35 and XS36
due to their small molecular sizes, and thus the largest IPCEs of
XS38 among the dyes can be partially ascribed to its simultaneously
better light-harvesting ability and larger surface density on TiO2.
XS37 sensitized cell generates the lowest IPCE value among the
three dyes, which may be due to its lower molar extinction co-
efficient and narrower absorption spectrum.
Fig. 4. Absorption spectra of dyes adsorbed on TiO2 film (3 mm).
Table 1
Photophysical and electrochemical data for dyes
Dye
lmaxa/nm (
3
/Mꢀ1 cmꢀ1
)
lintb (nm)
ED/Dþc/V
ED
*
d/V
/Dþ
XS35
XS36
XS37
XS38
514 (39,000)
497 (44,000)
492 (21,000)
494 (37,000)
582
581
565
574
0.81
0.71
0.82
0.83
ꢀ1.32
ꢀ1.42
ꢀ1.37
ꢀ1.43
Photovoltaic tests were conducted to evaluate the potential of
the XS35e38 dyes in DSSCs. The JeV curves of the DSSCs sensitized
by the XS35e38 dyes are shown in Fig. 8. The detailed photovoltaic
parameters are summarized in Table 3. Being consistent with the
integrals of IPCEs over the standard AM 1.5G solar emission spec-
trum, XS38 yields the highest short-circuit photocurrent density
(JSC) amongst these four photosensitizers. With an open-circuit
photovoltage (VOC) of 670 mV and a fill factor (FF) of 0.63, an
a
The absorption spectra were measured in CHCl3 solutions.
The intersect of the normalized absorption and the emission spectra.
b
c
ED/Dþ (vs NHE) was measured in acetonitrile.
d
ED
*
/Dþ
was calculated from ED
*
¼EoxꢀE0e0, E0e0¼1240/lint
/Dþ
.
XS38-based cell exhibits a power conversion efficiency (
h) of 6.11%.
XS36-based cell presents lower value than XS38-based counter-
h
part, owing to relatively low JSC and VOC. Our photovoltaic charac-
terization evidently demonstrates the superiority of MTT over DTT
in binary spacers. Compared to XS36, XS35 with the bridge alter-
ation from DTT to DTTO, not only evokes an enhancement of JSC but
concomitantly prompts a VOC improvement, leading to higher
conversion efficiency. In contrast, replacing MTT with MTTO does
not generate similar effects, and XS37 presents the lowest
h value
primarily owing to relatively low photocurrents.
2.5. Electrochemical impedance spectroscopy
The VOC values are in the sequence of XS37<XS36<XS35<XS38.
Through the introduction of electron-deficient fused thiophene
(DTTO) into the binary spacer, one notes that the XS35-based cell
gives an enhanced VOC (20 mV) in contrast to the XS36-based cell.
When the DTT unit is displaced by the MTT unit, the VOC rises re-
markably (i.e., VOC of XS38 reaches 670 mV compared to that of
XS36, 600 mV) under similar conditions, consequently leading to
an increase of power conversion efficiency. The respectable in-
crease of VOC obtained by the delicate change in molecular struc-
ture is intriguing. To scrutinize the origin of the improvement in
VOC, measurement of the electrochemical impedance spectroscopy
(EIS) is performed. The charge recombination resistance at the
TiO2/electrolyte interface (RCT) was modeled from impedance
spectroscopies as a function of applied potential bias. The charge
recombination resistance is related to the charge recombination
Fig. 5. Schematic energy levels of dyes based on absorption and electrochemical data.
performance of the DSSC with XS35 is broader and higher than
those of XS36, which can be partially attributed to the broader light
absorption. This phenomenon arises from the electron-deficient
unit was also observed by other group.42 The IPCE performance of
the DSSC based on XS38 is higher than that of XS36, despite with
the larger molar extinction coefficient and more redshifted ab-
sorption. This is likely to be due to the higher surface coverages (G)

5380
X. Cheng et al. / Tetrahedron 68 (2012) 5375e5385
Fig. 6. Computed frontier orbitals of dyes. H means HOMO, and L means LUMO.
Table 3
Photovoltaic parameters for DSSCsa
Dye
JSC/mA cmꢀ2
VOC/mV
FF
h (%)
XS35
XS36
XS37
XS38
N719
13.52
11.42
7.56
14.47
16.60
620
600
567
670
684
0.62
0.61
0.63
0.63
0.65
5.19
4.18
2.70
6.11
7.36
a
Performance of DSSCs measured in a 0.16 cm2 working area. Irradiating light:
AM 1.5G (100 mW cmꢀ2). The photovoltaic parameters are averaged values
obtained from analysis of the JeV curves of three identical working electrodes for
each device fabricated and characterized under the same experimental conditions.
rate, such that a smaller RCT means the larger charge recombination
rate. As presented in Fig. 9a, for the cobalt cells, the fitted RCT in-
creases in the order of XS37<XS36<XS35<XS38, indicating a same
order of decreased charge recombination rate. By fitting the EIS
curves, another important parameters for DSSCs, electron lifetime
Fig. 7. IPCE spectra of DSSCs.
(s
), could be extracted from the Cm and RCT using
s
¼CmRCT. The fitted
s
increases in the order of XS37<XS36<XS35<XS38, indicating
a sequence of lifetime increasing (Fig. 9b). These results are in
agreement with the observed shift in the VOC value under standard
global AM 1.5 illumination. The longer lifetime of XS38 relative to
XS36 is attributable to effective surface blocking as result of smaller
molecular structure.20,46 The results from EIS also suggest that the
two oxygen atoms of DTTO have an impact on the lifetime of dyes,
which prevent hydrophilic I3ꢀ ions approaching the TiO2 surface and
thereby lead to suppressing charge recombination/dark current
and lengthening electron lifetime.
For further support of the above viewpoint, the open-circuit
voltage decay (OCVD) measurements were carried out. This tech-
nique measures the recombination lifetime of the injected electron
with the photooxidized dye.47 Fig. 10 shows the open-circuit po-
tential decay transients of the DSSCs based on XS35e38. The
voltage of solar cells decreased in the order of
XS37>XS36>XS35>XS38. The results are consistent with mea-
surements of EIS. High capability of XS38 to quickly inject the
photogenerated electrons inside the TiO2 network before exciton
recombination induces high photovoltage, which tends to slowly
decrease due to recombination losses.48,49
Fig. 8. JeV curves of DSSCs under AM 1.5G simulated solar light (100 mW cm2).

X. Cheng et al. / Tetrahedron 68 (2012) 5375e5385
5381
3. Conclusions
In this paper, four new pushepull organic dyes incorporating
electron-rich (DTT and MTT) and electron-deficient (DTTO and
MTTO) fused thiophene as units of binary spacers have been syn-
thesized, characterized, and used as sensitizers for DSSCs. The
photovoltaic performance was shown to be quite sensitive to the
fused thiophene unit of the spacer. MTT is superior to DTT when
they are applied in binary spacer organic dyes. Compared to DTT,
the introduction of DTTO into the binary spacer is advantageous to
the light harvesting. But MTTO exhibits a slightly blue-shifted ab-
sorption relative to MTT due to the steric hindrance. The MTT-
containing dye, XS38, showed the best photovoltaic performance
with an overall conversion efficiency of 6.11% under standard global
AM 1.5 solar light condition. The results reveal that development of
new type fused thiophenes is an effective way for the development
of sensitizers.
4. Experimental
4.1. Materials and instruments
The synthetic routes for dyes are shown in Scheme 1. n-Butyl-
lithium was purchased from Alfa. N,N-Dimethylformamide was
dried over and distilled from CaH2 under an atmosphere of nitro-
gen. Phosphorus oxychloride was freshly distilled before use.
Dichloromethane and chloroform were distilled from calcium hy-
dride under nitrogen atmosphere. Titanium(IV) isopropoxide, tert-
butylpyridine, and lithium iodide were purchased from Aldrich. All
other solvents and chemicals used in this work were analytical
grade and used without further purification.
1H NMR and 13C NMR spectra were recorded on a Bruker AM-
300 or AM-400 spectrometer. Mass spectra were recorded on
a LCQ AD (Thermofinnigan, USA) mass spectrometer. The melting
point was taken on an RY-1 thermometer and temperatures were
uncorrected.
4.2. Photophysical and electrochemical measurements
Fig. 9. Interfacial charge-transfer resistance RCT (a) and electron lifetime
from impedance spectra under a series of applied potentials.
s (b) fitted
The absorption spectra of the dyes either in solution or on the
adsorbed TiO2 films were measured by HITACHI U-3310 spectro-
photometer. Adsorption of the dye on the TiO2 surface was done by
soaking the TiO2 electrode in a dry chloroform solution of the dye
(standard concentration 3ꢂ10ꢀ4 M) at room temperature for 24 h.
Fluorescence measurement was carried with a HITACHI F-4500
fluorescence spectrophotometer. FT-IR spectra were obtained with
a Bio-Rad FTS 135 FT-IR instrument.
Electrochemical measurements were performed at room tem-
perature on
a computer-controlled LK2005A electrochemical
workstation with Pt-wires as working electrode and counter elec-
trode, Ag/AgCl electrode as reference electrode at a scan rate of
100 mV sꢀ1. Tetrabutylammonium perchlorate (TBAP, 0.1 mol/L)
and MeCN were used as supporting electrolyte and solvent, re-
spectively. The measurements were calibrated using ferrocene as
standard. The redox potential of ferrocene internal reference is
taken as 0.63 V versus NHE.50
4.3. Fabrication and characterization of DSSCs
The TiO2 paste consisting of 18 wt % TiO2, 9 wt % ethyl cellulose,
and 73 wt % terpineol was firstly prepared,51 which was printed on
a conducting glass (Nippon Sheet Glass, Hyogo, Japan, fluorine-
doped SnO2 over layer, sheet resistance of 10 U/sq) using a screen
printing technique. The thickness of the TiO2 film was controlled by
selection of screen mesh size and repetition of printing. The film
was dried in air at 120 ꢁC for 30 min and calcined at 500 ꢁC for
Fig. 10. Decay transients of the open-circuit potential.

5382
X. Cheng et al. / Tetrahedron 68 (2012) 5375e5385
30 min under flowing oxygen before cooling to room temperature.
The heated electrodes were impregnated with a 0.05 M titanium
tetrachloride solution in a water-saturated desiccator at 70 ꢁC for
NMR (400 MHz, CDCl3): d 7.32e7.30 (m, 3H), 7.22e7.20 (m, 2H),
7.09 (d, J¼8.9 Hz, 4H), 6.90 (d, J¼8.8 Hz, 2H), 6.86 (d, J¼8.8 Hz, 4H),
3.96 (t, J¼6.5 Hz, 4H), 1.82e1.75 (m, 4H), 1.50e1.45 (m, 4H),
1.37e1.34 (m, 8H), 0.93 (t, J¼6.8 Hz, 6H). 13C NMR (100 MHz,
30 min and fired again to give a ca. 10
film. The TiO2 electrode was stained by immersing it into a dye
solution containing 300 M dye sensitizers (ethanol/dichloro-
mm thick mesoscopic TiO2
DMSO-d6):
d 156.2, 150.3, 149.6, 144.1, 142.0, 139.5, 136.5, 132.4,
m
132.0, 127.7, 126.9, 123.7, 120.5, 118.7, 116.0, 114.4, 68.1, 31.5, 29.2,
25.7, 22.5, 14.3. HRMS (ESI) calcd for C38H41NO4S3 (MþH)þ:
672.2270, found: 672.2279.
methane 3.5:1.5) for 24 h at room temperature. Then the
sensitized-electrode was rinsed with dry ethanol and dried by a dry
air flow. Pt catalyst was deposited on the FTO glass by coating with
a drop of H2PtCl6 solution (40 mM in ethanol) with the heat
treatment at 395 ꢁC for 15 min to give photoanode. The dye-
covered TiO2 electrode and Pt-counter electrode were assembled
into a sandwich type cell using a hot-melt Surlyn film. The elec-
trolyte consisted of 0.6 M 1,2-dimethyl-3-n-propylimidazolium io-
dide (DMPImI), 0.1 M LiI, 0.05 M I2, and 0.5 M tert-butylpyridine in
acetonitrile was introduced through a hole drilled in the back of the
counter electrode. Finally, the hole was also sealed with Surlyn film.
The photocurrentevoltage (JeV) characteristics of solar cells
were carried out using a Keithley 2400 digital source meter con-
trolled by a computer and a standard AM 1.5 solar simulator-Oriel
91160-1000 (300 W) SOLAR SIMULATOR 2ꢂ2 BEAM. The active
electrode area was 0.16 cm2. The action spectra of monochromatic
incident photon-to-current conversion efficiency (IPCE) for solar
cells were performed by using a commercial setup (QTest Station
2000 IPCE Measurement System, CROWNTECH, USA).
Electrochemical impedance spectroscopy (EIS) in the frequency
range of 100 mHz to 100 kHz was performed with a PARSTAT 2273
potentiostat/galvanostat/FRA in the dark with the alternate current
amplitude set at 10 mV. For the open-circuit voltage decay (OCVD)
measurements, the DSSC was illuminated with a green LED (OPT
Dongguan, lmax¼515 nm) as the light source. The illumination was
turned off with a computer-controlled electronic shutter. The OCVD
was recorded by an LK2005A electrochemical workstation as soon
as the shutter brought a full darkness. The measurement interval of
the voltage decay was 50e100 ms.
4.4.3. Synthesis of 2-{2-{4-[N,N-Bis(4-hexyloxyphenyl)amino]phe-
nyl}-4,40-dioxidedithieno[3,2-b:20,30-d]thiophene-6-yl}3,4-
ethylenedioxythiophene (5). Under exclusion of light, NBS (24 mg,
0.133 mmol) was added to a solution of 3 (82 mg, 0.133 mmol) in
15 mL DMF at room temperature. The mixture was stirred for 24 h
before quenching with water and the product was extracted with
DCM. The combined organic layers were washed with brine and
dried with anhydrous Na2SO4. The solvent was evaporated, and the
remaining crude product was purified by column chromatography
to give a red powder (50 mg, 50%). The crude 4 was used for the
next step without any purification.
A sample of 4 (33 mg,
0.044 mmol) and 2-(tributylstannyl)-3,4-(ethylenedioxy)thio-
phene (34 mg, 0.066 mmol) were added to a 10 mL p-xylene so-
lution of Pd(PPh3)4 (10 mol %). The mixture was refluxed under
nitrogen for 5 h. After cooling to room temperature, 25 mL water
was added to terminate the reaction and the product was extracted
with ethyl acetate. The combined organic layers were washed with
brine and dried with anhydrous Na2SO4. The solvent was evapo-
rated, and the remaining crude product was purified by column
chromatography to give a red solid of 5 (26 mg, 73%). Mp:
99e101 ꢁC. IR (KBr): 3025, 1507, 1196, 1067 cmꢀ1
.
1H NMR
(400 MHz, CDCl3):
d
7.31 (d, J¼8.5 Hz, 2H), 7.28 (s, 1H), 7.20 (s, 1H),
7.08 (d, J¼8.7 Hz, 4H), 6.89 (d, J¼8.7 Hz, 2H), 6.86 (d, J¼8.7 Hz, 4H),
6.31 (s, 1H), 4.37e4.26 (m, 4H), 3.96 (t, J¼6.5 Hz, 4H), 1.81e1.74 (m,
4H), 1.48e1.43 (m, 4H), 1.36e1.34 (m, 8H), 0.93 (t, J¼6.5 Hz, 6H). 13C
NMR (100 MHz, CDCl3):
d 156.1, 149.9, 149.7, 142.8, 141.9, 141.9,
139.7, 139.5, 138.9, 133.2, 132.6, 127.2, 126.4, 123.9, 119.4, 115.4,
114.3, 113.5, 110.7, 98.9, 68.3, 65.2, 64.5, 31.6, 29.3, 25.8, 22.6, 14.0.
HRMS (ESI) calcd for C44H45NO6S4 (MþH)þ: 812.2202, found:
812.2190.
4.4. The detailed experimental procedures and
characterization data
4.4.1. Synthesis of 2-bromo-4,40-dioxidedithieno[3,2-b:20,30-d]thio-
phene (2). A flask protected from light was charged with com-
pound 1 (251 mg, 1.101 mmol) in 15 mL DMF. NBS (177 mg,
0.991 mmol) was added stepwise over 90 min at 15 ꢁC. The mixture
was stirred for 24 h at room temperature. Water (20 mL) was added
to terminate the reaction and the product was extracted with
CH2Cl2 (DCM). The combined organic layers were washed with
brine and dried with anhydrous Na2SO4. The solvent was evapo-
rated, and the remaining crude product was purified by column
chromatography to give a yellow powder of 2 (229 mg, 75%). Mp:
4.4.4. Synthesis of 2-{2-{4-[N,N-bis(4-hexyloxyphenyl)amino]phe-
nyl}-4,40-dioxidedithieno[3,2-b:20,30-d]thiophene-6-yl}3,4-
ethylenedioxythiophene-5-carbaldehyde
(6). POCl3
(0.5 mL,
5.479 mmol) was added dropwise to dry DMF (8 mL) at 0 ꢁC. The
reaction mixture was kept at 0 ꢁC for 1 h and compound 5 (50 mg,
0.062 mmol) was added. After cooling to room temperature, the
mixture was stirred for 1 h. The pH was adjusted to 10 with 1 M
NaOH and the product was extracted with DCM. The combined
organic layers were washed with saturated NH4Cl and dried with
anhydrous Na2SO4. The solvent was evaporated, and the remaining
crude product was purified by column chromatography to give
a violet powder of 6 (0.039 g, 55%). Mp: 245e247 ꢁC. IR (KBr): 1640,
224e226 ꢁC; 1H NMR (400 MHz, CDCl3):
d
7.37 (d, 1H, J¼5.1 Hz),
7.22 (s, 1H), 7.20 (d, 1H, J¼5.1 Hz); 13C NMR (100 MHz, CDCl3):
d
142.4, 142.3, 135.9, 135.5, 130.0, 122.7, 120.4, 116.5. HRMS (ESI)
calcd for C8H3BrO2S3 (MþNa)þ: 328.8371, found: 328.8372.
1505, 1197, 1078 cmꢀ1 1H NMR (400 MHz, CDCl3):
. d 9.92 (s, 1H),
7.50 (s, 1H), 7.31 (d, J¼8.6 Hz, 2H), 7.21 (s,1H), 7.08 (d, J¼8.8 Hz, 4H),
6.89e6.84 (m, 6H), 4.46 (s, 4H), 3.95 (t, J¼6.4 Hz, 4H), 1.81e1.75 (m,
4H), 1.48e1.43 (m, 4H), 1.36e1.34 (m, 8H), 0.93 (t, J¼6.5 Hz, 6H). 13C
4.4.2. Synthesis of 2-(4-[N,N-bis(4-hexyloxyphenyl)amino]phenyl)-
4,40-dioxidedithieno[3,2-b:20,30-d]thiophene (3). A solution of 4-
(tributylstannyl)-N,N-bis((4-hexyloxy)phenyl)aniline
(210 mg,
NMR (100 MHz, CDCl3): d 179.2, 156.2, 151.3, 149.9, 148.1, 143.6,
0.286 mmol) in 10 mL p-xylene was added to a solution of 2 (55 mg,
0.179 mmol) and Pd(PPh3)4 (10 mol %) in 10 mL p-xylene. The
mixture was refluxed under nitrogen for 24 h. After cooling to room
temperature, 25 mL water was added to terminate the reaction and
the product was extracted with ethyl acetate. The combined or-
ganic layers were washed with brine and dried with anhydrous
Na2SO4. The solvent was evaporated, and the remaining crude
product was purified by column chromatography to give a tan oil of
142.0, 139.6, 138.1, 137.4, 136.0, 131.5, 127.3, 126.4, 123.5, 120.6, 119.1,
115.5, 113.4, 68.3, 65.2, 65.1, 31.6, 29.3, 25.8, 22.6, 14.0. HRMS (ESI)
calcd for C45H45NO7S4 (MþH)þ: 840.2152, found: 840.2142.
4.4.5. Synthesis of 2-(3,4-ethylenedioxythiophene)-dithieno[3,2-
b;20,30-d]thiophen (8). Compound 8 was synthesized according to
the same procedure of 5, giving a light yellow needle-like solid of 8
(192 mg, 35%). Mp: 167e169 ꢁC. 1H NMR (400 MHz, CDCl3):
d
7.39
3 (0.110 g, 75%). IR (neat): 3084, 1623, 1460, 1363, 1083 cmꢀ1 1H
.
(s, 1H), 7.31 (d, J¼5.2 Hz, 1H), 7.25 (d, J¼5.2 Hz, 1H), 6.26 (s, 1H),

X. Cheng et al. / Tetrahedron 68 (2012) 5375e5385
5383
4.34e4.22 (m, 4H). 13C NMR (100 MHz, DMSO-d6): 142.2, 141.9,
141.6, 138.7, 135.3, 130.5, 128.7, 127.8, 121.9, 116.6, 111.1, 98.6, 65.66,
64.8. HRMS (ESI) calcd for C14H8O2S4 (MþH)þ: 336.9450, found:
336.9483.
1510, 1279, 1087 cmꢀ1
.
1H NMR (400 MHz, CDCl3):
d
9.95 (s, 1H),
7.43 (d, J¼5.2 Hz,1H), 7.25 (d, J¼5.2 Hz,1H), 4.45e4.40 (m, 4H), 2.54
(s, 3H). 13C NMR (100 MHz, CDCl3):
d
179.5, 148.3,142.4,138.5,137.4,
129.1, 128.3, 127.9, 122.9, 119.9, 116.8, 65.2, 64.7, 15.5. HRMS (ESI)
calcd for C14H10O3S3 (MþH)þ: 322.9865, found: 322.9868.
4.4.6. Synthesis of 2-Bromothieno-3-methyl-1,10-dioxide[3,2-b]thio-
phene (13). A 20 mL solution of 3-chloroperbenzoic acid (75%,
0.772 g, 3.347 mmol) previously dried over magnesium sulfate was
added dropwise to a solution of 12 (0.200 g, 0.862 mmol) in 20 mL
of dichloromethane at 0 ꢁC. The mixture was stirred at room tem-
perature overnight before washing sequentially with 10% KOH, 10%
NaHCO3, and brine. The combined organic layers were dried with
anhydrous Na2SO4. The solvent was evaporated, and the remaining
crude product was purified by column chromatography to give
a gray needle-like solid of 13 (0.125 g, 55%). Mp: 183e185 ꢁC. IR
4.4.12. Synthesis of 2-{2-{4-[N,N-bis(4-hexyloxyphenyl)amino]phe-
n y l } d i t h i e n o [ 3 , 2 - b : 2 0, 3 0- d ] t h i o p h e n e - 6 - y l } 3 , 4 -
ethylenedioxythiophene-5-carbaldehyde (11). Compound 11 was
synthesized according to the same procedure of 3, giving a red solid
of 11 (174 mg, 36%). IR (KBr): 2927, 2855, 1640, 1475, 1079 cmꢀ1. 1H
NMR (400 MHz, DMSO-d6):
d 9.86 (s, 1H), 7.96 (s, 1H), 7.77 (s, 1H),
7.53 (d, J¼8.7 Hz, 2H), 7.07 (d, J¼8.7 Hz, 4H), 6.94 (d, J¼8.9 Hz, 4H),
6.80 (d, J¼8.9 Hz, 2H), 4.40 (s, 4H), 3.96 (t, J¼6.4 Hz, 4H), 1.73e1.69
(m, 4H), 1.42e1.24 (m, 12H), 0.92e0.87 (m, 6H). 13C NMR (100 MHz,
(KBr): 3098, 1348, 1301, 1131 cmꢀ1
d
.
1H NMR (400 MHz, CDCl3):
CDCl3): d 179.1, 155.8, 148.9, 148.5, 146.8, 143.4, 140.7, 140.1, 136.9,
7.51 (d, J¼5.0 Hz, 1H), 7.29 (d, J¼5.0 Hz, 1H), 2.21 (s, 3H). 13C NMR
132.1,130.9,130.0,128.8,126.9,126.3,125.8,123.6,119.9,119.1,115.2,
114.8, 68.3, 65.3, 64.8, 31.6, 29.3, 25.7, 22.6, 14.0. HRMS (ESI) calcd
for C45H45NO5S4 (MþH)þ: 808.2253, found: 808.2256.
(100 MHz, CDCl3):
d 144.0, 137.0, 133.7, 130.6, 120.9, 119.0, 14.4.
HRMS (ESI) calcd for C7H5BrO2S2 (MþH)þ: 264.8987, found:
264.8987.
4.4.13. Synthesis of 2-{2-{4-[N,N-bis(4-hexyloxyphenyl)amino]phe-
n yl } 6 - m e t h yl - 1,1 0- d i o x i d e [ 3 , 2 - b ] t h i o p h e n - 5 - y l } 3 , 4 -
ethylenedioxythiophene-5-carbaldehyde (17). Compound 17 was
synthesized according to the same procedure of 3, giving purple
4.4.7. Synthesis of 2-(3,4-ethylenedioxythiophene)-3-methyl-1,10-di-
oxide[3,2-b]thiophene (14). Compound 14 was synthesized
according to the same procedure of 8, giving yellow solid of 14 in
31% yield. Mp: 223e225 ꢁC. IR (KBr): 3117, 2917, 1488, 1429, 1148,
solid of 17 in 35% yield. IR (KBr): 2928, 2855, 1640, 1475, 1079 cmꢀ1
.
1069 cmꢀ1. 1H NMR (400 MHz, CDCl3):
d
7.42 (d, J¼5.0 Hz, 1H), 7.27
1H NMR (400 MHz, CDCl3):
d
9.96 (s, 1H), 7.34 (d, J¼8.8 Hz, 2H), 7.28
(d, J¼5.0 Hz, 1H), 6.58 (s, 1H), 4.29e4.24 (m, 4H), 2.23 (s, 3H). 13C
(s, 1H), 7.09 (d, J¼8.9 Hz, 4H), 6.90 (d, J¼8.8 Hz, 2H), 6.86 (d,
J¼8.9 Hz, 4H), 4.43e4.38 (m, 4H), 3.96 (t, J¼6.5 Hz, 4H), 2.27 (s, 3H),
1.80e1.74 (m, 4H), 1.48e1.34 (m, 12H), 0.93e0.90 (m, 6H). 13C NMR
NMR (100 MHz, CDCl3):
d 145.5, 141.8, 141.6, 137.6, 132.8, 131.0,
130.5, 120.5, 103.6, 102.0, 65.0, 64.4, 29.7, 14.8. HRMS (ESI) calcd for
C13H10O4S3 (MþH)þ: 326.9814, found: 326.9818.
(100 MHz, CDCl3): d 156.1, 150.5, 149.8, 144.0, 142.0, 139.7, 136.9,
131.9, 128.7, 127.2, 126.5, 123.7, 120.2, 119.3, 115.4, 113.5, 68.3, 31.6,
29.3, 26.9, 25.7, 22.6, 14.0. HRMS (ESI) calcd for C44H47NO7S3
(MþH)þ: 798.2587, found: 798.2599.
4.4.8. Synthesis of 2-(3,4-ethylenedioxythiophene)-3-methyl-[3,2-b]
thiophene (18). Compound 18 was synthesized according to the
same procedure of 8, giving light yellow liquid of 18 in 30% yield. IR
(KBr): 2920, 1489, 1363, 1072 cmꢀ1
.
1H NMR (400 MHz, CDCl3):
4.4.14. Synthesis of 2-{2-{4-[N,N-bis(4-hexyloxyphenyl)amino]phe-
nyl}6-methyl[3,2-b]thiophen-5-yl}3,4-ethylenedioxythiophene-5-
carbaldehyde (21). Compound 20 was synthesized according to the
same procedure of 10. The crude 20 was used for the next step
without any purification. Compound 21 was synthesized according
to the same procedure of 11, giving red oily liquid of 21 in 32% yield.
d
7.33 (d, J¼5.2 Hz,1H), 7.21 (d, J¼5.2 Hz,1H), 6.40 (s,1H), 4.28e4.22
(m, 4H), 2.23 (s, 3H). 13C NMR (100 MHz, CDCl3):
d
141.9, 141.7,
138.4, 137.1, 129.4, 127.3, 126.2, 120.0, 110.9, 99.6, 64.9, 64.5, 14.7.
HRMS (ESI) calcd for C13H10O2S3 (MþH)þ: 294.9916, found:
294.9916.
IR (KBr): 2927, 2854, 1599, 1507, 1301, 1032 cmꢀ1
.
1H NMR
4.4.9. Synthesis of 2-{dithieno[3,2-b;20,30-d]thiophen}-(3,4-
(400 MHz, CDCl3):
d
9.92 (s, 1H), 7.41 (d, J¼8.8 Hz, 2H), 7.28 (s, 1H),
ethylenedioxythiophene)-5-carbaldehyde (9). Compound
9
was
7.07 (d, J¼8.9 Hz, 4H), 6.92 (d, J¼8.8 Hz, 2H), 6.84 (d, J¼8.9 Hz, 4H),
4.41e4.38 (m, 4H), 3.94 (t, J¼6.5 Hz, 4H), 2.51 (s, 3H), 1.81e1.74 (m,
4H), 1.48e1.42 (m, 4H), 1.36e1.32 (m, 8H), 0.93 (t, J¼7.0 Hz, 6H). 13C
synthesized according to the same procedure of 6, giving a yellow
solid of 9 (324 mg, 89%). Mp: 201e203 ꢁC. IR (KBr): 3073, 1636,
1458, 1210, 1085 cmꢀ1
.
1H NMR (400 MHz, CDCl3):
d
9.92 (s, 1H),
7.64 (s, 1H), 7.42 (d, J¼5.2 Hz, 1H), 7.30 (d, J¼5.2 Hz, 1H), 4.74e4.44
(m, 4H). 13C NMR (100 MHz, CDCl3):
179.3, 148.5, 142.5, 141.8,
NMR (100 MHz, CDCl3): d 179.4, 155.8, 148.3, 147.6, 140.5, 140.2,
139.7, 137.1, 129.2, 126.9, 126.4, 123.5, 120.0, 116.3, 115.4, 113.9, 68.3,
65.2, 64.7, 31.6, 29.3, 26.7, 25.8, 22.6, 14.1. HRMS (ESI) calcd for
C44H47NO5S3 (MþH)þ: 766.2689, found: 766.2688.
d
137.1, 133.8, 131.7, 130.8, 127.0, 123.3, 120.9, 119.2, 115.0, 65.3, 64.9.
HRMS (ESI) calcd for C15H8O3S4 (MþH)þ: 364.9429, found:
364.9434.
4.4.15. Synthesis of 3-{2-{2-{4-[N,N-bis(4-hexyloxyphenyl)amino]
phenyl}-4,40-dioxidedithieno[3,2-b:20,30-d]thiophene-6-yl}3,4-
ethylenedioxythiophene-2-yl}-2-cyanoacrylic acid (XS35). To a stir-
red solution of compound 6 (100 mg, 0.119 mmol) and cyanoacetic
acid (30 mg, 0.357 mmol) in a 1:1 mixture of chloroform and acetic
4.4.10. Synthesis of 2-{3-methyl-1,10-dioxide[3,2-b]thiophene}-(3,4-
ethylenedioxythiophene)-5-carbaldehyde (15). Compound 15 was
synthesized according to the same procedure of 6, giving brown
solid of 15 in 75% yield. Mp: 254e256 ꢁC. IR (KBr): 3085, 2939,1638,
acid was added catalytic amount of piperidine (50 mL). The reaction
1445, 1302, 1085 cmꢀ1
.
1H NMR (400 MHz, CDCl3):
d
9.97 (s, 1H),
7.50 (d, J¼5.0 Hz,1H), 7.30 (d, J¼5.0 Hz,1H), 4.45e4.37 (m, 4H), 2.28
(s, 3H). 13C NMR (100 MHz, CDCl3):
145.5, 141.8, 141.6, 137.6, 132.8,
mixture was refluxed for 12 h and then the solvent was removed in
vacuo. The resulting solid was dissolved in DCM and sequentially
washed with brine and dried with anhydrous Na2SO4. The solvent
was evaporated, and the remaining crude product was purified by
column chromatography to give a purple solid of XS35 (83%). Mp:
>300 ꢁC. IR (KBr): 3400, 2930, 2861, 1600, 1510, 1320, 823 cmꢀ1. 1H
d
131.0, 130.5, 120.5, 103.6, 102.0, 65.0, 64.4, 29.7, 14.8. HRMS (ESI)
calcd for C14H10O5S3 (MþH)þ: 354.9763, found: 354.9768.
4.4.11. Synthesis of 2-{3-methyl-[3,2-b]thiophene}-(3,4-
ethylenedioxythiophene)-5-carbaldehyde (19). Compound 19 was
synthesized according to the same procedure of 6, giving yellow
solid of 19 in 80% yield. Mp: 236e238 ꢁC. IR (KBr): 3083, 2962,1626,
NMR (400 MHz, DMSO-d6): d 8.83 (s, 1H), 8.05 (s, 1H), 7.71 (s, 2H),
7.45 (s, 2H), 7.09e6.92 (m, 7H), 6.70 (s, 2H), 4.51e4.48 (m, 4H),
4.00e3.93 (m, 4H), 1.58e1.50 (m, 4H), 1.45e1.26 (m, 12H),
0.91e0.82 (m, 6H). 13C NMR (100 MHz, pyridine-d5):
d 158.5, 156.5,

5384
X. Cheng et al. / Tetrahedron 68 (2012) 5375e5385
4. Zhou, H.; Xue, P.; Zhang, Y.; Zhao, X.; Jia, J.; Zhang, X.; Liu, X.; Lu, R. Tetrahedron
2011, 67, 8477.
5. Zhang, L.; Liu, Y.; Wang, Z.; Liang, M.; Sun, Z.; Xue, S. Tetrahedron 2012, 68, 552.
6. Higashijima, S.; Miura, H.; Fujita, T.; Kubota, Y.; Funabiki, K.; Yoshida, T.; Matsui,
M. Tetrahedron 2011, 67, 6289.
7. Chang, Y. J.; Chow, T. J. Tetrahedron 2009, 65, 9626.
8. Chou, H.-H.; Hsu, C.-Y.; Hsu, Y.-C.; Lin, Y.-S.; Lin, J. T.; Tsai, C. Tetrahedron 2012,
68, 767.
9. Sahu, D.; Padhy, H.; Patra, D.; Yin, J.-F.; Hsu, Y.-C.; Lin, J.-T.; Lu, K.-L.; Wei, K.-H.;
Lin, H.-C. Tetrahedron 2011, 67, 303.
150.9,149.0,143.7,142.3,140.1,138.3,135.9,132.1,127.5,126.8,126.7,
124.3, 124.2, 123.8, 122.8, 120.0, 119.4, 117.8, 115.9, 114.2, 68.3, 65.6,
65.4, 31.5, 29.4, 25.8, 22.6, 13.9. HRMS (ESI) calcd for C48H46N2O8S4
(MþH)þ: 907.2210, found: 907.2226.
4.4.16. Synthesis of 3-{2-{2-{4-[N,N-bis(4-hexyloxyphenyl)amino]
p h e n y l } d i t h i e n o [ 3 , 2 - b : 2 0, 3 0- d ] t h i o p h e n e - 6 - y l } 3 , 4 -
ethylenedioxythiophene-2-yl}-2-cyanoacrylic acid (XS36). Com-
pound XS36 was synthesized according to the same procedure of
XS35, giving a red oily liquid of XS36 in 87% yield. Mp: >300 ꢁC. IR
10. Choi, H.; Lee, J. K.; Song, K.; Kang, S. O.; Ko, J. Tetrahedron 2007, 63, 3115.
11. Hara, K.; Sayama, K.; Ohga, Y.; Shinpo, A.; Suga, S.; Arakawa, H. Chem. Commun.
2001, 569.
(KBr): 3420, 2930, 2860, 1602, 1513, 1381, 1070 cmꢀ1
.
1H NMR
8.04 (s, 1H), 7.75 (s, 1H), 7.69 (s, 1H), 7.48 (d,
12. Wang, Z. S.; Cui, Y.; Hara, K.; Dan-Oh, Y.; Kasada, C.; Shinpo, A. Adv. Mater. 2007,
19, 1138.
(400 MHz, DMSO-d6):
d
€
13. Kuang, D.; Uchida, S.; Humphry-Baker, R.; Zakeeruddin, S. M.; Gratzel, M.
J¼8.5 Hz, 2H), 7.04 (d, J¼8.8 Hz, 4H), 6.92 (d, J¼8.8 Hz, 4H), 6.78 (d,
J¼8.5 Hz, 2H), 4.50e4.48 (m, 4H), 3.95 (t, J¼6.4 Hz, 4H), 1.72e1.68
(m, 4H), 1.43e1.40 (m, 4H), 1.32e1.31 (m, 8H), 0.90e0.87 (m, 6H).
Angew. Chem., Int. Ed. 2008, 47, 1923.
14. Thomas, K. R. J.; 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.
15. Wu, W.; Yang, J.; Hua, J.; Tang, J.; Zhang, L.; Long, Y.; Tian, H. J. Mater. Chem.
2010, 20, 1772.
13C NMR (100 MHz, pyridine-d5):
d 157.7, 151.7, 150.3, 147.6, 144.9,
16. He, J.; Wu, W.; Hua, J.; Jiang, Y.; Qu, S.; Li, J.; Long, Y.; Tian, H. J. Mater. Chem.
142.7, 142.0, 138.7, 136.3, 135.4, 130.1, 128.8, 128.2, 128.0, 125.3,
124.2, 121.6, 117.3, 116.8, 69.8, 65.7, 65.4, 33.1, 30.9, 27.3, 24.1, 15.4.
HRMS (ESI) calcd for C48H46N2O6S4 (MþH)þ: 875.2311, found:
875.2288.
2011, 21, 6054.
17. Hagberg, D. P.; Yum, J. H.; Lee, H.; De Angelis, F.; Marinado, T.; Karlsson, K. M.;
€
Humphry-Baker, R.; Sun, L. C.; Hagfeldt, A.; Gratzel, M.; Nazeeruddin, M. K. J.
Am. Chem. Soc. 2008, 130, 6259.
18. Lu, M.; Liang, M.; Han, H.; Sun, Z.; Xue, S. J. Phys. Chem. C 2011, 115, 274.
19. Liang, M.; Lu, M.; Wang, Q.; Chen, W.; Han, H.; Sun, Z.; Xue, S. J. Power Sources
2011, 196, 1657.
20. Hao, X.; Liang, M.; Cheng, X.; Pian, X.; Sun, Z.; Xue, S. Org. Lett. 2011, 13, 5424.
21. Liang, Y.; Peng, B.; Liang, J.; Tao, Z.; Chen, J. Org. Lett. 2010, 12, 1204.
22. Paek, S.; Choi, H.; Choi, H.; Lee, C.; Kang, M.; Song, K.; Nazeeruddin, M.; Ko, J. J.
Phys. Chem. C 2010, 114, 14646.
4.4.17. Synthesis of 3-{2-{2-{4-[N,N-bis(4-hexyloxyphenyl)amino]
phenyl}6-methyl-1,10-dioxide[3,2-b]thiophen-5-yl}3,4-
ethylenedioxythiophene-2-yl}-2-cyanoacrylic acid (XS37). Com-
pound XS37 was synthesized according to the same procedure of
XS35, giving a red oily liquid of XS37 in 86% yield. Mp: >300 ꢁC. IR
€
23. Choi, H.; Baik, C.; Kang, S. O.; Ko, J.; Kang, M. S.; Nazeeruddin, M. K.; Gratzel, M.
(KBr): 3421, 2931, 2865, 1611, 1512, 1243, 1071 cmꢀ1
.
1H NMR
Angew. Chem., Int. Ed. 2008, 47, 327.
24. Numata, Y.; Ashraful, I.; Shirai, Y.; Han, L. Chem. Commun. 2011, 6159.
25. Zhu, W. H.; Wu, Y. Z.; Wang, S. T.; Li, W. Q.; Li, X.; Chen, J. A.; Wang, Z.-S.; Tian,
H. Adv. Funct. Mater. 2011, 21, 756.
(400 MHz, DMSO-d6):
d
8.10 (s, 1H), 7.88 (s, 1H), 7.55(d, J¼8.6 Hz,
2H), 7.08 (d, J¼8.8 Hz, 4H), 6.94 (d, J¼8.8 Hz, 4H), 6.74 (d, J¼8.6 Hz,
2H), 4.44e4.42 (m, 4H), 3.96 (t, J¼6.4 Hz, 4H), 2.26 (s, 3H),
1.72e1.69 (m, 4H), 1.41e1.31 (m, 12H), 0.90e0.87 (m, 6H). 13C NMR
26. Zeng, W.; Cao, Y.; Bai, Y.; Wang, Y.; Shi, Y.; Zhang, M.; Wang, F.; Pan, C.; Wang, P.
Chem. Mater. 2010, 22, 1915.
27. Im, H.; Kim, S.; Park, C.; Jang, S.; Kim, C.; Kim, K.; Park, N.; Kim, C. Chem.
Commun. 2010, 1335.
(100 MHz, pyridine-d5):
d 158.1, 150.5, 142.8, 141.5, 141.2, 137.3,
28. Ito, S.; Miura, H.; Uchida, S.; Takata, M.; Sumioka, K.; Liska, P.; Comte, P.; Pechy,
136.3, 129.1, 128.4, 125.7, 125.3, 124.2, 120.9, 117.4, 116.3, 116.0, 69.7,
66.8, 66.5, 33.0, 31.2, 27.3, 24.1, 15.4. HRMS (ESI) calcd for
C47H48N2O8S3 (MþNH4) þ: 882.2911, found: 882.2898.
€
P.; Gratzel, M. Chem. Commun. 2008, 5194.
29. Chen, D.; Hsu, Y.; Hsu, H.; Chen, B.; Lee, Y.; Fu, H.; Chung, M.; Liu, S.; Chen, H.;
Chou, P. Chem. Commun. 2010, 5256.
30. Zhang, G. L.; Bala, H.; Cheng, Y. M.; Shi, D.; Lv, X. J.; Yu, Q. J.; Wang, P. Chem.
Commun. 2009, 2198.
4.4.18. Synthesis of 3-{2-{2-{4-[N,N-bis(4-hexyloxyphenyl)amino]
phenyl}6-methyl[3,2-b]thiophen-5-yl}3,4-ethylenedioxythiophene-2-
yl}-2-cyanoacrylic acid (XS38). Compound XS38 was synthesized
according to the same procedure of XS35, giving a red oily liquid of
XS38 in 91% yield. Mp: >300 ꢁC. IR (KBr): 3418, 2921, 2218, 1587,
31. Qin, H.; Wenger, S.; Xu, M.; Gao, F.; Jing, X.; Wang, P.; Zakeeruddin, S. M.;
€
Gratzel, M. J. Am. Chem. Soc. 2008, 130, 9202.
32. Kwon, T.; Armel, V.; Nattestad, A.; MacFarlane, D.; Bach, U.; Lind, S.; Gordon, K.;
Tang, W.; Jones, D.; Holmes, A. J. Org. Chem. 2011, 76, 4088.
33. Cheng, X.; Sun, S.; Liang, M.; Shi, Y.; Sun, Z.; Xue, S. Dyes Pigments 2012, 92,
1292.
34. Zhang, Z. G.; Wang, J. Z. J. Mater. Chem. 2012, 22, 4178.
35. Liu, C.; Li, Y. J.; Li, C. H.; Li, W. W.; Zhou, C. J.; Liu, H. B.; Bo, Z. S.; Li, Y. L. J. Phys.
Chem. C 2009, 113, 21970.
1374, 1075 cmꢀ1. 1H NMR (400 MHz, DMSO-d6):
d 8.09 (s, 1H), 7.65
(s, 1H), 7.51 (d, J¼8.6 Hz, 2H), 7.05 (d, J¼8.8 Hz, 4H), 6.92 (d,
J¼8.8 Hz, 4H), 6.78 (d, J¼8.6 Hz, 2H), 4.45e4.43 (m, 4H), 3.95 (t,
J¼6.4 Hz, 4H), 2.50 (s, 3H), 1.74e1.67 (m, 4H), 1.43e1.31 (m, 12H),
36. Liu, C.; Xiao, S. Q.; Shu, X. P.; Li, Y. J.; Xu, L.; Liu, T. F.; Yu, Y. W.; Zhang, L.; Liu, H.
B.; Li, Y. L. ACS Appl. Mater. Interfaces 2012, 4, 1065.
0.90e0.87 (m, 6H). 13C NMR (100 MHz, pyridine-d5):
d 157.7, 150.6,
37. Allared, F.; Hellberg, J.; Remonen, T. Tetrahedron Lett. 2002, 43, 1553.
€
38. Zhang, X.; Kohler, M.; Matzger, A. J. Macromolecules 2004, 37, 6306.
150.5, 148.5,142.1,142.0,141.3, 139.1,137.3,136.3,129.9,128.7,128.2,
128.1, 125.3, 124.2, 121.8, 117.3, 116.1, 113.2, 69.8, 67.1, 66.4, 33.0,
30.9, 27.3, 24.1, 16.7, 15.4. HRMS (ESI) calcd for C47H48N2O6S3
(MþH)þ: 833.2747, found: 833.2718.
39. Miguel, L. S.; Matzger, A. J. J. Org. Chem. 2008, 73, 7882.
40. Sotgiu, G.; Zambianchi, M.; Barbarella, G.; Aruffo, F.; Cipriani, F.; Ventola, A. J.
Org. Chem. 2003, 68, 1512.
41. Zhou, D.; Cai, N.; Long, H.; Zhang, M.; Wang, Y.; Wang, P. J. Phys. Chem. C 2011,
115, 3163.
42. 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.
Acknowledgements
€
43. Hagfeldt, A.; Gratzel, M. Chem. Rev. 1995, 95, 49.
44. Li, R. Z.; Lv, X. J.; Shi, D.; Zhou, D. F.; Cheng, Y. M.; Zhang, G. L.; Wang, P. J. Phys.
Chem. C 2009, 113, 7469.
We are grateful to the National Natural Science Foundation of
China (21003096, 21072152) and the Tianjin Natural Science
Foundation (09JCZDJC24400) for financial supports.
45. Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.;
Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.;
Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.;
Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.;
Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao,
O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken,
V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A.
J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G.
A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.;
Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Fores-
man, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov,
B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.;
Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P.
M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian
03, Revision C.01; Gaussian: Wallingford, CT, 2003.
References and notes
€
1. O’Regan, B.; Gratzel, M. Nature 1991, 353, 737.
2. (a) Gao, F.; Wang, Y.; Shi, D.; Zhang, J.; Wang, M.; Jing, X.; Humphry-Baker, R.;
€
Wang, P.; Zakeeruddin, S. M.; Gratzel, M. J. Am. Chem. Soc. 2008, 130, 10720; (b)
Nazeeruddin, M. K.; De Angelis, F.; Fantacci, S.; Selloni, A.; Viscardi, G.; Liska, P.;
€
Ito, S.; Takeru, B.; Gratzel, M. G. J. Am. Chem. Soc. 2005, 127, 16835.
3. (a) Hagfeldt, A.; Boschloo, G.; Sun, L.; Kloo, L.; Pettersson, H. Chem. Rev. 2010,
110, 6595; (b) Mishra, A.; Fischer, M. K. R.; Bauerle, P. Angew. Chem., Int. Ed.
2009, 48, 2474.

X. Cheng et al. / Tetrahedron 68 (2012) 5375e5385
5385
46. Marinado, T.; Nonomura, K.; Nissfolk, J.; Karlsson, M. K.; Hagberg, D. P.; Sun, L.;
Mori, S.; Hagfeldt, A. Langmuir 2010, 26, 2592.
47. (a) Li, J.-Y.; Chen, C.-Y.; Chen, J.-G.; Tan, C.-J.; Lee, K.-M.; Wu, S.-J.; Tung, Y.-L.;
Tsai, H.-H.; Ho, K.-C.; Wu, C.-G. J. Mater. Chem. 2010, 20, 7158; (b) Kopidakis, N.;
Benkstein, K. D.; van de Lagemaat, J.; Frank, A. J. J. Phys. Chem. B 2003, 107,
11307.
48. Kozma, E.; Concina, I.; Braga, A.; Borgese, L.; Depero, L. E.; Vomiero, A.; Sber-
veglieri, G.; Catellani, M. J. Mater. Chem. 2011, 21, 13785.
€
49. Boschloo, G.; Haggman, L.; Hagfeldt, A. J. Phys. Chem. B 2006, 110, 13144.
50. Pavlishchuk, V. V.; Addison, A. W. Inorg. Chim. Acta 2000, 298, 97.
51. Liang, M.; Wang, Z.-Y.; Zhang, L.; Han, H.-Y.; Sun, Z.; Xue, S. Renew. Energy 2011,
36, 2711.