Tuning the spectroscopic, electrochemical, and photovoltaic properties of triaryl amine based sensitizers through ring-fused thiophene bridges

Article abstract of DOI:10.1002/asia.201100748

The ring-fused thiophene derivatives benzo[c]thiophene and its precursor bicyclo[2.2.2]octadiene (BCOD) have been introduced as π-conjugated spacers for organic push-pull sensitizers with dihexyloxy-substituted triphenylamine as donor and cyanoacrylic acid as acceptor (OL1-OL6). The effects of the fused ring on the spectroscopic and electrochemical properties of these sensitizers and their photovoltaic performance in dye-sensitized solar cells have been evaluated. Introduction of a binary benzo[c]thiophene and ethylenedioxy thiophene as π bridge caused a significant red shift of the characteristic intramolecular charge-transfer band to 642 nm. It is found that the sensitizer OL3, which contains one benzo[c]thiophene unit as π linker, gives the highest overall conversion efficiency of 5.03% among all these dyes. Copyright

Full text of DOI:10.1002/asia.201100748

DOI: 10.1002/asia.201100748
Tuning the Spectroscopic, Electrochemical, and Photovoltaic Properties of
Triaryl Amine Based Sensitizers through Ring-Fused Thiophene Bridges
Quan Liu,[a] Quan-You Feng,[c] Hiroko Yamada,*[b] Zhong-Sheng Wang,*[c]
Noboru Ono,[b] Xiao-Zeng You,[a] and Zhen Shen*[a]
Abstract: The ring-fused thiophene de-
rivatives benzo[c]thiophene and its pre-
cursor bicycloACHTUNGTRENNUNG[2.2.2]octadiene (BCOD)
have been introduced as p-conjugated
spacers for organic push–pull sensitiz-
ers with dihexyloxy-substituted triphe-
nylamine as donor and cyanoacrylic
acid as acceptor (OL1–OL6). The ef-
fects of the fused ring on the spectro-
scopic and electrochemical properties
of these sensitizers and their photovol-
taic performance in dye-sensitized
solar cells have been evaluated. Intro-
duction of a binary benzo[c]thiophene
and ethylenedioxy thiophene as
p bridge caused a significant red shift
of the characteristic intramolecular
charge-transfer band to 642 nm. It is
found that the sensitizer OL3, which
contains one benzo[c]thiophene unit as
p linker, gives the highest overall con-
version efficiency of 5.03% among all
these dyes.
Keywords: charge transfer · donor–
acceptor systems
· dye-sensitized
solar cells · dyes/pigments · thio-
phenes
Introduction
forth.[2] Recently, significant achievements have been made
based on various organic dyes as sensitizers for DSSCs.[3]
Donor–p–acceptor or donor–acceptor–p–acceptor[4] struc-
tures are commonly adopted for the design of these dyes,
since intramolecular charge separation is easily achieved.
Triaryl amines have good electron-donating and -transport-
ing capabilities and are usually used as the donor;[5] long
alkyl chains have been introduced to improve device perfor-
mance.[6] Oligothiophene and its derivatives, such as 3,4-eth-
ylenedioxythiophene (EDOT), thienothiophene (TT), di-
thienothiophene (DTT), 2,2’-bithiophene (BT), and thiazole
have been employed as p bridges,[7] affording a conjugated
pathway for charge transfer and extending the absorption
spectra of dyes. Most of the thiophene-bridged sensitizers
have exhibited superior photoelectronic properties, and
some of them showed high thermostability and produced an
overall light-to-power conversion of over 10%[8] which ap-
proaches the performance of ruthenium-based sensitizers.
Although polyisothianaphthene (PITN) has been synthe-
sized and investigated for decades,[9] to our knowledge, its
monomer isothianaphthene, namely benzo[c]thiophene and
its derivatives have not been applied in DSSCs. Recently
Swager and co-workers reported a series of push–pull com-
pounds utilizing benzo[c]thiophene and benzo[c]furan to
furnish near-infrared fluorophores.[10] Previously, Onoꢁs
group has reported a facile synthesis of isothianaphthene
As a kind of renewable, green, and clean energy source, the
solar cell has been explored as one of the candidates to
meet the needs of increasing demands for decades. Since
Grꢀtzelꢁs group first reported a notable power conversion
efficiency of about 7% based on a ruthenium complex,[1]
dye-sensitized solar cells (DSSCs) have attracted great at-
tention in recent years. In light of the limited availability of
ruthenium and its toxicity, metal-free organic dyes are con-
sidered to be promising candidates due to their high molar
extinction coefficients, structural diversity, easy design and
synthesis, low cost, environmental friendliness, and so
[a] Q. Liu, Prof. X.-Z. You, Prof. Z. Shen
State Key Laboratory of Coordination Chemistry
Nanjing University
210093, Nanjing, Jiangsu (P.R. China)
Fax : (+86)25-83314502
E-mail: zshen@nju.edu.cn
[b] Prof. H. Yamada,+ Prof. N. Ono
Graduate School of Science and Engineering
Ehime University
2-5 Bunkyo-cho, Matsuyama 790-0853 (Japan)
[c] Q.-Y. Feng, Prof. Z.-S. Wang
Lab of Advanced Materials, Department of Chemistry
Fudan University
2205 Songhu Road, Shanghai, 200438 (P.R. China)
E-mail: zs.wang@fudan.edu.cn
[+] Present address:
oligomers using bicycloACTHUNRGTNE[NUG 2.2.2]octadiene (BCOD) thiophene
as a synthon.[11] The p-electron delocalization in the oligoi-
sothianaphthenes were significantly enhanced. The UV/Vis
absorption spectra of oligoisothianaphthene derivatives ex-
hibited considerable bathochromic shift compared to the
cases of other oligothiophene analogues, and cyclic voltam-
metry measurement showed narrowed HOMO–LUMO
Graduate School of Material Science Nara Institute of Science and
Technology and CREST, JST 8916-5, Takayama-cho, Ikoma, Nara
630-0192 (Japan)
E-mail: hyamada@ms.naist.jp
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201100748.
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gaps. Herein, we incorporate isothianaphthene as a bridge
and EDOT as a binary bridge into the sensitizer containing
dihexyloxy-substituted triphenylamine as the donor and cya-
noacrylic acid as the acceptor (Scheme 1). Their absorption
and emission spectra, electrochemical and photovoltaic
properties have been measured to investigate the effect of
fused-ring on the thiophene bridged push–pull dyes.
Spectroscopic Properties
To examine the effect of the fused ring on thiophene moiety
on the spectroscopic properties of these dyes, their absorp-
tion spectra were measured in dichloromethane. All the
dyes showed characteristic intramolecular charge-transfer
bands in the visible region, peaking in the range from 485 to
642 nm (Figure 1).[12] The transformation of BCOD-thio-
Figure 1. Normalized electronic absorption spectra of six dyes in CH2Cl2.
phene into benzo[c]thiophene extended the p conjugation
and led to a bathochromic shift in the absorption spectra.[11]
Dyes OL3, OL4, and OL6 bearing one or two benzo[c]thio-
phene unit, or one benzo[c]thiophene and a binary EDOT
spacer, exhibited peaks that are red-shifted by 88, 105, and
114 nm compared to the corresponding BCOD-fused precur-
sors OL1, OL2, and OL5, respectively. As the number of
thiophene units increased, the bathochromic shift become
larger. Among the six dyes, OL6 exhibited the highest ab-
sorption coefficient and the longest-wavelength charge-
transfer absorption band, which may favor light harvesting
and hence photocurrent generation in DSSCs.
Scheme 1. Ring-fused thiophene-bridged triaryl amine based push–pull
sensitizers.
Results and Discussions
Synthesis of the Ring-Fused Thiophene-Bridged Triaryl
Amine Based Push–Pull Dyes
Electrochemical Properties
The syntheses of these dyes are shown in Scheme 2. For
dyes OL1 and OL2, BCOD-thiophene was attached to the
triaryl amine donor through Suzuki coupling reaction, then
the corresponding aldehydes were obtained by Vilsmeier re-
action, and these condensed with 2-cyanoacetic acid to give
the final product. The intermediate aldehydes of BCOD-thi-
ophenes, 6 and 7, were converted into the aldehydes of ben-
zo[c]thiophene (8 and 9) by retro-Diels–Alder reaction
under heat and vacuum. Aldehydes 8 and 9 condense with
2-cyanoacetic acid to afford OL3 and OL4, respectively.
Dyes OL5 and OL6 are prepared using a similar method as
mentioned above, but with a binary EDOT linker combined
with BCOD-thiophene or benzo[c]thiophene, respectively.
The oxidation potentials of the dyes adsorbed on TiO2 nano-
crystalline film on FTO (fluorine-doped tin oxide, 15 ohm
per square, transmittance of 90%, Nippon Sheet Glass,
Japan) were measured using cyclic voltammetry (see
À
Table 1). The results revealed that the HOMO level of I3 /IÀ
electrolyte (À4.85 eV vs. vacuum)[2c] is higher than that of
all the dyes and that this system is able to regenerate the
dyes from electron donation on DSSCs. The LUMO levels
of these dyes were higher than the conduction band edge of
the TiO2 electrode (À4.00 eV vs. vacuum).[13] However, to
induce a sufficient electron injection, an energy gap of ap-
proximately 0.2 eV between the LUMO of the dye and the
conduction band edge of TiO2 must be a necessary driving
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Triaryl Amine Based Sensitizers
Scheme 2. Synthetic route to the ring-fused thiophene-bridged triaryl amine based push–pull dyes. NBS=N-bromosuccinimide.
Table 1. Electrooptical and electrochemical properties of the dyes.
duction of benzo[c]thiophene significantly stabilized the
LUMO energy level rather than destabilizing the HOMO
(DLUMO values were 0.340, 0.652, and 0.448 eV from OL1
to OL3, OL2 to OL4, and OL5 to OL6, respectively;
DHOMO values were À0.008, À0.004, and 0.071 eV from
OL1 to OL3, OL2 to OL4, and OL5 to OL6, respectively).
The introduction of a binary electron-rich EDOT unit in
OL5 and OL6 further lifted the HOMO and lowered the
LUMO energy levels and narrowed the energy gap.[11] These
results are in accordance with the trend observed in their
electronic absorption spectra.
Dye
lmax [nm] (loge)[a]
EHOMO [eV][b]
E0À0 [eV][c]
ELUMO [eV][d]
OL1
OL2
OL3
OL4
OL5
OL6
485 (4.42)
485 (4.38)
573 (4.47)
590 (4.21)
528 (4.47)
642 (4.53)
À5.526
À5.435
À5.518
À5.431
À5.279
À5.350
2.262
2.246
1.914
1.590
1.987
1.610
À3.264
À3.189
À3.604
À3.841
À3.292
À3.740
[a] The absorption spectra were measured in CH2Cl2. [b] Energy levels
for the highest occupied molecular orbitals (HOMOs) were measured
from dye-loaded films. [c] The gap was derived from the onset wave-
length at which the absorbance is 10% of the maximum from the UV/Vis
absorption spectra of the dye-loaded film. [d] The energy levels of the
lowest unoccupied molecular orbitals (LUMOs) were estimated from the
equation ELUMO =EHOMO+E0À0.
Molecular Orbital Calculations
MO calculations were performed for these sensitizers using
the Gaussian03 program package[15] at the B3LYP/6-31G(d)
level of theory (Figure 2). It can be seen that when the p
bridges change from BCOD-thiophene to benzo[c]thio-
force.[14] Therefore except for OL4, the other five dyes allow
effective electron injection into the TiO2 electrode. Compar-
ing the HOMO and LUMO levels of these dyes, the intro-
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phene, the HOMOs of the sensitizers are delocalized over
the whole molecule. This transformation also leads to an ob-
vious stabilization of the LUMOs, while there is little effect
on the HOMOs and finally a smaller energy gap between
the two. In the push–pull dyes, the contribution of charge
separated quinoid resonance structure can be further stabi-
lized by introducing fused benzene ring on the thiophene
bridge[10] (Scheme 3). As the LUMO is mainly located on
the thiophene bridge and the acceptor part, the extension of
the p conjugation by fusion with benzene ring on the thio-
phene bridge thus stabilized the LUMO significantly com-
pared to its contribution to the HOMO. These results are in
accordance with the trend observed in their electrochemical
properties.
Scheme 3. Aromatic and quinoid resonance structures of the sensitizers.
Photovoltaic Performance
The dye-sensitized solar cells fabricated with these dyes and
the reference dyes such as C213[12] and N719 were tested,
and their photovoltaic performances are listed in Table 2. It
should be noted that the solar-cell performance for the new
and reference dyes were compared under the same but not
optimal conditions, and the efficiencies for C213 and N719
listed in Table 2 were much lower than the reported highest
values, as they were not optimized in this work. Figure 3
shows that compared with C213, which consists of the same
donor and acceptor units linked with a simple thiophene,
OL1 bearing one BCOD-fused thiophene linker exhibited
higher short-circuit photocurrent density (Jsc) but lower
open-circuit photovoltage (Voc). Overall, the loss in Voc can-
celed the enhanced Jsc and led to a relatively lower power
conversion efficiency (h) for OL1. Introducing two BCOD-
fused thiophene units as linker in OL2 also increased both
the Jsc and Voc values, and the h value for the cell using OL2
was slightly higher than for that with C213. Sensitizer OL5
possess one BCOD-fused thiophene unit and a binary
EDOT showed slightly higher Jsc and Voc values and better
energy conversion efficiency than OL2. However, the Jsc
value and the overall power conversion efficiency for OL4,
which contains two benzo[c]thiophene units, were almost
Table 2. Photovoltaic performance of dyes OL1–OL6 and C213.[a]
Dye
Voc [mV]
Jsc [mAcmÀ2
]
FF
h [%]
OL1
OL2
OL3
OL4
OL5
OL6
C213
N719[b]
534
680
640
405
674
514
680
720
9.21
8.11
11.23
0.67
8.47
4.05
7.87
14.80
0.72
0.74
0.70
0.58
0.73
0.70
0.69
0.76
3.54
4.08
5.03
0.16
4.16
1.45
3.69
8.00
[a] Experiments were carried out with 0.2304 cm2 working area of the
cell under the illumination intensity of 100 mWcmÀ2 at 1.5 AM sunlight
condition. FF=fill factor. [b] The efficiency was obtained with 12 mm
transparent TiO2. The efficiency was raised to 9.77% (Jsc =
17.24 mAcmÀ2, Voc =765 mV, FF=0.741) with 4 mm scattering layer on
the transparent layer.
Figure 2. Calculated MOs of OL1–OL6.
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Triaryl Amine Based Sensitizers
Figure 4. The incident photon-to-current conversion efficiency spectra for
DSSCs based on OL1-OL6 and C213.
Figure 3. Current–voltage curves of DSSCs based on OL1–OL6 and C213
under irradiation of 100 mWcmÀ2 at 1.5AM sunlight condition.
negligible. The small short-circuit photocurrent for OL4
might be mainly due to the fact that its LUMO does not
match well with the conduction band of TiO2, which pre-
vents sufficient electron injection into the TiO2 electrode. To
confirm this point, a higher concentration of LiI in the elec-
trolyte, which is able to down-shift the conduction band
edge for TiO2, was used for OL4. The value of Jsc increased
remarkably, due to the enlarged driving force for electron
injection, but remained much lower than for the other dyes.
Similar results were found in the case of OL6. Among the
six dyes, OL3 with one benzo[c]thiophene linker produced
Conclusions
In summary, we have introduced benzo[c]thiophene and its
precursor as p bridges into a series of organic push–pull
dyes for application in DSSCs for the first time. Fusion with
a benzene ring on the thiophene bridge significantly stabi-
lized the LUMO level of the sensitizer and narrowed the
energy gap, which prominently bathochromically shifted the
absorption spectra. Dye-sensitized solar cells fabricated with
one benzo[c]thiophene bridged sensitizer produced the high-
est h value of 5.03%, which is higher than that of C213 mea-
sured under the same conditions, mainly due to the larger
short-circuit photocurrent density resulted from extending
the p conjugation. Further efforts to fine tune the frontier
MOs thus improving the photovoltaic performance in other
D–p–A dyes are currently underway.
the highest
h
(5.03%), with Jsc =11.23 mAcmÀ2, Voc =
640 mV, and FF=0.70. Dyes OL2, OL3, and OL5 generated
similar Voc values as the reference dye C213, but the other
dyes generated much lower Voc values. It seems that the
higher the LUMO, the higher the Voc, except for OL1. The
low Voc values for some of these dyes may be ascribed to the
lower LUMO, recombination losses, non-optimal dye pack-
ing, or other factors, which will be investigated in detail in
the future.
Experimental Section
Materials and Reagents
The incident-photon-to-current conversion efficiency
(IPCE) spectra (Figure 4) of these dyes showed that OL1
and OL2 bearing one or two BCOD ring-fused thiophene
units have very similar spectral responses and maintain over
50% conversion efficiency in the region of 400–500 nm. The
reference dye C213 possesses about 70% efficiency in the
range of 400–550 nm and cutoff at 700 nm. Compared with
C213 dye, OL5 and OL3 exhibited the response of 60%
from 500 to 750 and 800 nm, respectively. Unlike other ana-
logues, the spectral intensities of OL4 and OL6 were very
low. In particular, the IPCE value of dye OL4 is lower than
10% in the whole visible region. Although the highest IPCE
value of OL6 is just 20% at about 550 nm, it was notable
that the response of OL6 extended to about 850 nm, which
is the farthest among all these dyes.
All reagents were obtained from commercial suppliers and used without
further purification unless otherwise indicated. Dry solvents were pre-
pared using standard techniques. LiI, I2, acetonitrile, and 4-tert-butylpyri-
dine (TBP) were obtained from Acros. 1,2-dimethyl-3-n-propylimidazoli-
um iodide (DMPImI) was obtained from Tomiyama Pure Chemical In-
dustries Ltd., Japan. N719 was obtained from Solaronix SA. F-doped
SnO2 conductive glass (FTO, resistance 15 W per square, transmittance
80%) was purchased from Nippon Sheet Glass Co., Japan and ultrasoni-
cally rinsed in acetone and in water before use. 4-bromo-N,N-bis(4-
ACHTUNGTRENNUNG(hexy-
loxy)phenyl)aniline,[7d]
2-{4-[N,N-bis(4-hexyloxyphenyl)amino]phenyl}-
3,4-(ethylenedioxy)thiophene,[3a] 2-(4,7-dihydro-4,7-ethanobenzo[c]thio-
phen-1-yl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane,[11] and 4,7-dihydro-4,7-
ethanobenzo[c]thiophene and its dimer[11] were prepared according to the
literature. NMR spectra were recorded on a JEOL JNM-AL 400 spec-
trometer or Bruker DRX500 spectrometer and referenced to the residual
proton signals of the solvent. Mass spectra were measured on a Bruker
Daltonics Autoflex IITM MALDI TOF spectrometer or a Voyager DEPro
(Applied Biosystems) spectrometer. Elemental analyses were recorded
on a Vario MICRO analyzer.
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Fabrication and Evaluation of DSSCs
nique and then protected with argon. Tetrakis(triphenylphosphine)palla-
dium (90 mg) was added in one portion. The reaction mixture was heated
at reflux for two days. CHCl3 and water were added, and the aqueous
layer was extracted with CHCl3. The combined organic layers were
washed with water and brine and dried with Na2SO4. The product was
purified by silica gel column chromatography using CH2Cl2/hexane (v/v=
1:1) as eluent to obtain the product as an orange oily solid (339 mg) after
removal of volatiles under reduced pressure, yield 56%.1H NMR
(400 MHz, CDCl3): d=7.25 (d, J=8.5 Hz, 2H), 7.12–6.99 (m, 4H), 6.95–
6.89 (m, 2H), 6.85–6.79 (m, 4H), 6.63 (s, 1H), 6.56–6.42 (m, 2H), 4.11 (d,
J=6.0 Hz, 1H), 3.92 (dd, J=9.0, 4.0 Hz, 4H), 3.82 (d, J=5.5 Hz, 1H),
1.77 (dd, J=9.2, 5.7 Hz, 4H), 1.60 (m, 4H), 1.52–1.40 (m, 4H), 1.34 (dt,
J=10.5, 5.1 Hz, 8H), 0.98–0.88 ppm (m, 6H). MS calcd: m/z 605.33 ([M+
]), TOF-MS found 605.63 ([M+]).
TiO2 films (12 mm thick) were coated on FTO glass using a screen-print-
ing method with a paste consisting of TiO2 nanoparticles (ca. 20 nm di-
ameter) prepared according to a published method.[16] TiO2 films were
colored by soaking them overnight in the dye solution (0.3 mm). The dye-
loaded TiO2 film as the working electrode and the Pt-coated conductive
glass as the counter electrode were separated by a hot-melt Surlyn film
(30 mm thick) and sealed together by hot-pressing. The redox electrolyte
(0.1m LiI, 0.05m I2, 0.6m 1,2-dimethyl-3-n-propylimidazolium iodide, and
0.3m TBP using anhydrous acetonitrile as a solvent) was injected into the
interspace between the photoanode and counter electrode through a pre-
drilled hole. Finally, the hole was sealed with a Surlyn film covered with
a thin glass slide under heat. The DSSCs were evaluated by recording I–
V curves with a Keithley 2400 Source Meter under illumination of simu-
lated AM1.5G solar light coming from a solar simulator (Oriel-91193
equipped with a 1000 W Xe lamp and an AM1.5 filter). The light intensi-
ty was calibrated using a reference Si solar cell (Oriel-91150) and adjust-
ed with appropriate neutral density filters. IPCE spectra were measured
with an Oriel-74125 system (Oriel Instruments, USA), where intensity of
monochromatic light was measured with a Si detector (Oriel-71640).
4-(Hexyloxy)-N-(4-(hexyloxy)phenyl)-N-(4-(5,5’,8,8’,10,10’,11,11’-octahy-
dro-[1,1’-bi(4,7-ethanobenzo[c]thiophen)]-3’-yl)phenyl)aniline (5): The
procedure was similar to that described in synthesis of 4. Orange-brown
solid, yield 64%.1H NMR (400 MHz, CDCl3): d=7.27 (d, J=8.7 Hz,
2H), 7.10–7.05 (m, 4H), 6.93 (d, J=8.6 Hz, 2H), 6.86–6.80 (m, 4H), 6.70
(s, 1H), 6.58–6.48 (m, 4H), 4.14 (s, 2H), 4.09 (s, 1H), 3.93 (t, J=6.5 Hz,
4H), 3.85 (s, 1H), 1.82–1.72 (m, 4H), 1.60 (d, J=4.9 Hz, 8H), 1.52–1.41
(m, 4H), 1.34 (td, J=7.0, 3.4 Hz, 8H), 0.97–0.87 ppm (m, 6H). MS calcd:
m/z 765.37 ([M+]), TOF-MS found: 765.62 ([M+]).
Synthesis
(4-
ACHTUNGTRENNUNG(Bis(4-ACHTUNGTRENNUNG
3-(4-(Bis(4-ACTHNUTRGNE(UNG hexyloxy)phenyl)amino)phenyl)-4,7-dihydro-4,7-ethanoben-
N,N-bis(4-ACHTUNGTRENNUNG
zo[c]thiophene-1-carbaldehyde (6): Compound 4 (339 mg, 0.56 mmol)
was dissolved in anhydrous THF (20 mL), protected with argon, and
cooled to À788C. nBuLi(1.6m in hexane, 0.40 mL, 0.64 mmol) was added
through a syringe. When addition was finished, the solution was main-
tained at this temperature and stirred for 30 min. Freshly distilled DMF
(0.10 mL, excess) was added dropwise. The mixture was slowly warmed
to ambient temperature and stirred overnight. HCl (0.5n, 30 mL) was
added to stop the reaction. The aqueous layer was extracted with CHCl3.
The combined organic layers were washed with water and brine and
dried with Na2SO4. The product was purified by silica gel column chro-
matography using CH2Cl2/hexane (v/v=1:1) as eluent to give the product
as orange solid (147 mg) after removal of volatiles under reduced pres-
sure, yield 41%. 1H NMR (400 MHz, CDCl3): d=9.96 (s, 1H), 7.33–7.27
(m, 2H), 7.15–7.06 (m, 4H), 6.92 (d, J=8.7 Hz, 2H), 6.89–6.80 (m, 4H),
6.61–6.45 (m, 2H), 4.46 (d, J=5.4 Hz, 1H), 4.20 (s, 1H), 3.94 (t, J=
6.5 Hz, 4H), 1.84–1.73 (m, 4H), 1.64 (m, 4H), 1.52–1.41 (m, 4H), 1.35
(td, J=6.8, 3.4 Hz, 8H), 0.91 ppm (t, J=6.9 Hz, 6H). MS calcd: m/z
633.33 ([M+]), TOF-MS found 633.55 ([M+]).
in 20 mL anhydrous THF and protected with argon. The solution was
cooled to À788C. nBuLi (1.6m in hexane, 1.67 mL, 2.68 mmol) was
added slowly, and then the reaction mixture was stirred for 1 h. BACTHNUTRGNE(NUG OMe)3
(0.32 mL, 2.68 mmol) was added through a syringe. After addition was
completed, the reaction mixture was gradually warmed to room tempera-
ture and stirred overnight. Water was added to quench the reaction, 6n
HCl was used to acidify until the pH of the mixture is less than 7, and
then stirred for 15 min. The mixture was extracted with CH2Cl2 (3ꢃ
50 mL). The combined organic layers were washed with water and brine
and dried with Na2SO4. The product was purified by silica gel column
chromatography using CH2Cl2/EtOAc (v/v=5:1) as eluent. A pale green
solid (441 mg) was obtained after removal of volatiles under reduced
pressure, yield 50%. 1H NMR (400 MHz, CDCl3): d=7.93 (d, J=8.5 Hz,
2H), 7.09 (d, J=8.9 Hz, 4H), 6.92 (d, J=8.6 Hz, 2H), 6.84 (d, J=8.9 Hz,
4H), 3.94 (t, J=6.5 Hz, 4H), 1.84–1.72 (m, 4H), 1.51–1.41 (m, 4H), 1.34
(dd, J=8.8, 5.3 Hz, 8H), 0.91 ppm (t, J=6.9 Hz, 6H). MS calcd: m/z
489.31 ([M+]), TOF-MS found 445.63 ([M+-B(OH)2]).
1-Iodo-4,7-dihydro-4,7-ethanobenzo[c]thiophene (2): 4,7-dihydro-4,7-
ethanobenzo[c]thiophene (205 mg, 1.25 mmol) was dissolved in anhy-
drous THF (20 mL) and protected with argon. The solution was cooled
to À788C, and nBuLi (1.6m in hexane, 0.80 mL, 1.25 mmol) was added
dropwise. After addition was completed, the reaction mixture was gradu-
ally returned to room temperature and stirred for 1 h. Then it was cooled
to À788C again, and a solution of iodine in anhydrous THF (369 mg,
1.4375 mmol, 20 mL) was added through a syringe. The reaction mixture
was warmed to room temperature slowly and stirred for 1 h. Saturated
Na2SO3 solution was used to quench the reaction, and the product was
with CH2Cl2 (3ꢃ50 mL). The combined organic layers were washed with
water and brine and dried with Na2SO4. The product was purified by
silica gel column chromatography using hexane as eluent and was ob-
tained as a white solid (286 mg) after removal of volatiles under reduced
pressure, yield 79%. 1H NMR (400 MHz, CDCl3): d=6.83 (s, 1H), 6.53–
6.41 (m, 2H), 3.88 (d, J=4.7 Hz, 1H), 3.73 (d, J=4.8 Hz, 1H), 1.63–
1.44 ppm (m, 4H).
3’-(4-(Bis(4-ACTHNUTRGNE(UNG hexyloxy)phenyl)amino)phenyl)-5,5’,8,8’,10,10’,11,11’-octahy-
dro-[1,1’-bi(4,7-ethanobenzo[c]thiophene)]-3-carbaldehyde (7): The pro-
cedure was similar to that described in the synthesis of 6. Orange solid,
yield 92%.1H NMR (400 MHz, CDCl3): d=9.98 (s, 1H), 7.27 (d, J=
8.6 Hz, 2H), 7.08 (t, J=6.1 Hz, 4H), 6.94 (d, J=8.6 Hz, 2H), 6.83 (t, J=
6.1 Hz, 4H), 6.66–6.46 (m, 4H), 4.46 (d, J=5.8 Hz, 1H), 4.33 (t, J=
7.0 Hz, 1H), 4.26 (d, J=9.8 Hz, 1H), 4.14 (s, 1H), 3.93 (t, J=6.5 Hz,
4H), 1.85–1.73 (m, 4H), 1.72–1.60 (m, 8H), 1.45 (dd, J=14.7, 7.1 Hz,
4H), 1.41–1.28 (m, 8H), 0.91 ppm (t, J=7.0 Hz, 6H). MS calcd: m/z
793.36 ([M+]), TOF-MS found: 793.31 ([M+]).
OL1: Compound
6 (127 mg, 0.20 mmol), 2-cyanoacetic acid (55 mg,
0.60 mmol), and piperidine (120 mg, 1.40 mmol) were dissolved in CHCl3
(20 mL). The reaction mixture was heated to reflux overnight. The mix-
ture was cooled to room temperature, CHCl3 and water were added, and
the aqueous layer was extracted with CHCl3. The combined organic layer
was washed with 1n HCl, water, and brine and dried with Na2SO4. The
product was purified by silica gel column chromatography using CHCl3/
CH3OH (v/v=9:1) as eluent to give product as dark red solid (68 mg)
after removal of volatiles under reduced pressure, yield 48%. 1H NMR
(400 MHz, CDCl3): d=8.46 (s, 1H), 7.34 (d, J=8.5 Hz, 2H), 7.08 (d, J=
8.8 Hz, 4H), 6.91 (d, J=8.6 Hz, 2H), 6.85 (d, J=8.8 Hz, 4H), 6.54 (m,
2H), 4.26 (s, 2H), 3.94 (t, J=6.5 Hz, 4H), 1.86–1.72 (m, 4H), 1.61 (s,
4H), 1.46 (dd, J=14.3, 7.0 Hz, 4H), 1.41–1.28 (m, 8H), 0.91 ppm (t, J=
6.9 Hz, 6H). MS calcd: m/z 701.3368 ([M+]), HRMS found: 701.3394
([M+]). Elemental anal. calcd for C44H48N2O4S: C 75.40, H 6.90, N 4.00;
found: C 75.31, H 6.81, N 3.99.
3-Iodo-5,5’,8,8’,10,10’,11,11’-octahydro-1,1’-bi(4,7-ethano-benzo[c]thio-
phene (3): The procedure was similar to that described in synthesis of 2.
The product was obtained as a white or light yellow solid, yield 91%.
1H NMR (400 MHz, CDCl3): d=6.72 (s, 1H), 6.57–6.44 (m, 4H), 4.09 (s,
1H), 4.05 (d, J=6.2 Hz, 1H), 3.85 (d, J=5.7 Hz, 1H), 3.74 (d, J=6.0 Hz,
1H), 1.59 ppm (d, J=2.7 Hz, 8H).
4-(4,7-Dihydro-4,7-ethanobenzo[c]thiophen-1-yl)-N,N-bis(4-
phenyl) aniline (4): Compounds 1 (286 mg, 1 mmol) and 2 (492 mg,
1 mmol) were dissolved in THF (10 mL), 2n K2CO3 solution(1 mL) was
added, and the mixture was degassed using the freeze–pump–thaw tech-
ACHTUNGTRENUN(NG hexyloxy)-
AHCTUNGTRENNUNG
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Triaryl Amine Based Sensitizers
OL2: The procedure was similar to that described in the synthesis of
OL1. Dark red solid, yield 76%. H NMR (400 MHz, CDCl3): d=8.46 (s,
(12): Compound 10 (667 mg, 1 mmol) and 2-(4,7-dihydro-4,7-ethanoben-
zo[c]thiophen-1-yl)-4,4,5,5-tetra-methyl-1,3,2-dioxaborolane (424 mg,
1
1H), 7.28 (d, J=8.7 Hz, 2H), 7.09 (dd, J=9.5, 2.7 Hz, 4H), 6.94 (d, J=
8.7 Hz, 2H), 6.89–6.79 (m, 4H), 6.67–6.45 (m, 4H), 4.46–4.36 (m, 1H),
4.29 (dd, J=17.4, 5.7 Hz, 2H), 4.16 (d, J=3.9 Hz, 1H), 3.94 (t, J=6.5 Hz,
4H), 1.85–1.74 (m, 4H), 1.63 (d, J=23.2 Hz, 8H), 1.46 (dd, J=14.7,
7.1 Hz, 4H), 1.40–1.29 (m, 8H), 0.91 ppm (t, J=7.0 Hz, 6H). MS calcd:
m/z 861.3715 ([M+]), HRMS found: 861.3748 ([M+]). Elemental anal.
calcd for C54H56N2O4S2: C 75.31, H 6.55, N 3.25; found: C 75.24, H 6.68,
N 3.26.
1.47 mmol) were dissolved in THF (20 mL). K2CO3 solution (2n, 10 mL)
was added, and the mixture was degassed using the freeze–pump–thaw
technique and then protected with argon. Tetrakis(triphenylphosphine)-
palladium (120 mg) was added in one portion. The reaction mixture was
heated at reflux for two days. CHCl3 and water were added, the phases
were separated, and the aqueous layer was extracted with CHCl3. The
combined organic layers were washed with water and brine and dried
with Na2SO4. Silica gel column chromatography using CHCl3/petroleum
ether (v/v=1:4) as eluent gave the crude product (400 mg), with polarity-
closed debrominated starting material as byproduct. The crude product
(400 mg) was dissolved in anhydrous THF (30 mL), protected with argon,
and cooled to À788C. nBuLi (1.6m in hexane, 0.40 mL, 0.64 mmol) was
added through a syringe. While addition was finished, the solution was
maintained at this temperature and stirred for 30 min. Freshly distilled
DMF(0.30 mL, excess) was added dropwise. The mixture was slowly
warmed to ambient temperature and was stirred overnight. HCl (0.5n,
60 mL) was added to stop the reaction. The aqueous layer was extracted
with CHCl3. The combined organic layers were washed with water and
brine and dried with Na2SO4. Silica gel column chromatography using
CHCl3/petroleum ether (v/v=1:1) as eluent gave the product as an
orange solid (300 mg) after removal of volatiles under reduced pressure,
yield 39%. 1H NMR (500 MHz, CDCl3): d=10.07 (s, 1H), 7.61 (d, J=
8.8 Hz, 2H), 7.08 (t, J=8.9 Hz, 4H), 6.95 (t, J=7.9 Hz, 4H), 6.89 (d, J=
8.8 Hz, 2H), 6.64 (t, J=6.9 Hz, 1H), 6.57 (t, J=6.6 Hz, 1H), 4.62 (d, J=
6.3 Hz, 1H), 4.54 (d, J=6.0 Hz, 1H), 4.47 (m, 4H), 4.01 (t, J=5.8 Hz,
4H), 1.84–1.73 (m, 4H), 1.67 (dd, J=25.5, 11.2 Hz, 2H), 1.50 (m, 4H),
1.43–1.32 (m, 8H), 0.93 ppm (d, J=6.1 Hz, 6H). MS calcd: m/z 773.32
([M+]), MALDI-TOF found: 773.34 ([M+]).
3-(4-(Bis(4-ACHTUNGTRENNUNG(hexyloxy)phenyl)amino)phenyl)benzo[c]thiophene-1-carbal-
dehyde (8): In a glass tube oven, 6 (62 mg) was heated under vacuum at
2708C for 30 min. Then it was cooled to room temperature. A dark red
solid (58 mg) was obtained in quantitative yield. 1H NMR (400 MHz,
CDCl3): d=10.25 (s, 1H), 8.30 (d, J=8.4 Hz, 1H), 7.91 (d, J=8.7 Hz,
1H), 7.50 (d, J=8.6 Hz, 2H), 7.40 (dd, J=8.7, 6.6 Hz, 1H), 7.25–7.19 (m,
1H), 7.13 (d, J=8.8 Hz, 4H), 6.99 (d, J=8.6 Hz, 2H), 6.87 (d, J=8.8 Hz,
4H), 3.95 (t, J=6.5 Hz, 4H), 1.86–1.70 (m, 4H), 1.47 (dt, J=14.5, 7.1 Hz,
4H), 1.35 (td, J=6.7, 3.3 Hz, 8H), 0.91 ppm (t, J=6.8 Hz, 6H). MS
calcd: m/z 605.30 ([M+]), TOF-MS found: 605.61 ([M+]).
3’-(4-(Bis(4-ACHTUNGTRENNUNG(hexyloxy)phenyl)amino)phenyl)-[1,1’-bibenzo[c]thio-phene]-
3-carbaldehyde (9): The procedure was similar to that described in the
synthesis of 8. Purple solid. Quantitative yield. 1H NMR (400 MHz,
CDCl3): d=10.26 (s, 1H), 8.28 (d, J=8.5 Hz, 1H), 8.08 (dd, J=8.8,
0.8 Hz, 1H), 8.03–7.96 (m, 1H), 7.86 (d, J=8.8 Hz, 1H), 7.45 (d, J=
8.6 Hz, 2H), 7.43–7.35 (m, 1H), 7.21 (dt, J=22.9, 4.9 Hz, 2H), 7.15–7.07
(m, 5H), 7.00 (d, J=8.6 Hz, 2H), 6.85 (d, J=8.7 Hz, 4H), 3.93 (t, J=
6.5 Hz, 4H), 1.77 (dd, J=14.7, 6.7 Hz, 4H), 1.54–1.41 (m, 4H), 1.40–1.30
(m, 9H), 0.91 ppm (q, J=6.6 Hz, 7H). MS calcd: m/z 737.30 ([M+]),
TOF-MS found: 737.47 ([M+]).
OL5: The procedure was similar to that described in the synthesis of
OL1. Dark purple-red solid, yield 78%. 1H NMR (500 MHz,
[D6]acetone): d=8.44 (s, 1H), 7.62 (d, J=8.6, 2H), 7.08 (d, J=8.7, 4H),
6.93 (d, J=8.7, 4H), 6.88 (d, J=8.6, 2H), 6.63 (t, J=6.8, 1H), 6.57 (t, J=
6.7, 1H), 4.58 (d, J=5.7, 1H), 4.49 (d, J=4.7, 2H), 4.45 (d, J=4.4, 2H),
4.41 (d, J=4.9, 1H), 3.99 (t, J=6.4, 4H), 1.82–1.73 (m, 4H), 1.73–1.54
(m, 4H), 1.48 (m, 4H), 1.42–1.32 (m, 8H), 0.91 ppm (t, J=6.6, 6H).MS
calcd: m/z 840.33 ([M+]), MALDI-TOF found: 812.58 ([M+-C2H4]). Ele-
mental anal. calcd for C50H52N2O6S2: C 71.40, H 6.23, N 3.33; found: C
71.45, H 6.24, N 3.30
OL3: The procedure was similar to that described in the synthesis of
OL1, purple solid (26 mg), yield 48%. H NMR (400 MHz, [D6]acetone):
1
d=8.68 (s, 1H), 7.90 (d, J=6.7 Hz, 1H), 7.80 (d, J=6.8 Hz, 1H), 7.44 (d,
J=6.3 Hz, 2H), 7.31 (s, 1H), 7.17 (s, 1H), 7.01 (d, J=8.4 Hz, 4H), 6.81
(d, J=8.6 Hz, 6H), 3.85 (t, J=6.4 Hz, 4H), 1.72–1.54 (m, 4H), 1.33 (dd,
J=14.6, 7.1 Hz, 5H), 1.27–1.18 (m, 8H), 0.84–0.65 ppm (m, 6H). MS
calcd: m/z 673.3055 ([M+]), HRMS found: 673.3100 ([M+]). Elemental
Anal. calcd for C42H44N2O4S: C 74.97, H 6.59, N 4.16; found: C 75.01, H
6.51, N 4.10
OL4: The procedure was similar to that described in the synthesis of
OL1, dark blue solid, yield 45%. 1H NMR (400 MHz, CDCl3): d=8.83
(d, J=11.3 Hz, 1H), 8.19 (dt, J=17.4, 9.5 Hz, 2H), 7.92 (dt, J=16.3,
8.9 Hz, 2H), 7.52–7.42 (m, 2H), 7.31 (s, 2H), 7.19 (d, J=8.0 Hz, 1H),
7.12 (d, J=6.7 Hz, 4H), 7.00 (dd, J=7.9, 2.4 Hz, 2H), 6.87 (d, J=8.3 Hz,
4H), 6.78 (s, 1H), 3.95 (t, J=6.5 Hz, 4H), 1.78 (dd, J=14.7, 6.7 Hz, 4H),
1.53–1.43 (m, 4H), 1.35 (dt, J=10.6, 3.5 Hz, 8H), 0.92 ppm (t, J=7.0 Hz,
6H). MS calcd: m/z 805.3089 ([M+]), HRMS found: 805.3128 ([M+]). El-
emental anal. calcd for C50H48N2O4S2: C 74.60, H 6.01, N 3.48; found: C
74.42, H 6.14, N 3.40
3-(7-(4-(Bis(4-
ACHUTGTNREN(NUG hexyloxy)phenyl)amino)phenyl)-2,3-dihydrothienoACHTUNGTRENNUNG[3,4-b]-
AHCTUNGTRENNUNG
was similar to that described in the synthesis of 8, purple solid, quantita-
tive yield. 1H NMR (500 MHz, [D6]acetone): d=10.37 (s, 1H), 8.41 (d,
J=8.6 Hz, 1H), 8.36 (d, J=8.9 Hz, 1H), 7.69 (d, J=8.8 Hz, 2H), 7.54–
7.45 (m, 1H), 7.42–7.32 (m, 1H), 7.10 (d, J=8.9 Hz, 4H), 6.95 (d, J=
8.9 Hz, 4H), 6.90 (d, J=8.8 Hz, 2H), 4.65 (dd, J=5.0, 2.8 Hz, 2H), 4.54
(dd, J=4.9, 2.8 Hz, 2H), 4.00 (t, J=6.5 Hz, 4H), 1.84–1.72 (m, 4H),
1.55–1.45 (m, 4H), 1.42–1.32 (m, 8H), 0.92 ppm (t, J=6.8 Hz, 6H). MS
calcd: m/z 745.29 ([M+]), MALDI-TOF found: 745.47 ([M+]).
4-(7-Bromo-2,3-dihydrothienoCAHTUNGTREN[NNGU 3,4-b]ACHTUNREGTG[NNUN 1,4]dioxin-5-yl)-N,N-bis(4-ACHTNUGTNER(NUGN hexylox-
OL6: The procedure was similar as that described in the synthesis of
y)phenyl)aniline (10): 2-{4-[N,N-bis(4-hexyloxyphenyl)amino]phenyl}-3,4-
(ethylenedioxy)thiophene(602 mg, 1.03 mmol) was dissolved in anhy-
drous THF (20 mL), protected under argon, and cooled to 08C. NBS,
215 mg, 1.21 mmol) was added in one portion. The reaction mixture was
stirred for 3 h. Saturated sodium hyposulfite solution was added to stop
the reaction. CHCl3 and water were added, the phases were separated,
and the aqueous layer was extracted with CHCl3. The combined organic
layer was washed with brine and dried with Na2SO4. The product was pu-
rified by silica gel column chromatography using EtOAc/hexane (v/v=
1:8) as eluent to give the product as dark green oil (667 mg) after remov-
al of volatiles under reduced pressure, yield 98%. 1H NMR (500 MHz,
[D6]acetone): d=7.45 (d, J=8.8 Hz, 2H), 7.08–7.01 (m, 4H), 6.94–6.89
(m, 4H), 6.84 (d, J=8.8 Hz, 2H), 4.34 (s, 4H), 3.98 (t, J=6.5 Hz, 4H),
1.84–1.71 (m, 7H), 1.48 (m, 5H), 1.41–1.31 (m, 8H), 0.91 ppm (t, J=
6.9 Hz, 6H). MS calcd: m/z 663.20 ([M+]), MALDI-TOF found: 663.38
([M+]).
1
OL1, dark blue solid, yield 38%. H NMR (500 MHz, [D6]DMSO) d 8.78
(s, 1H), 8.32 (d, J=8.7 Hz, 1H), 8.13 (d, J=8.7 Hz, 1H), 7.65 (d, J=
8.8 Hz, 2H), 7.56–7.50 (m, 1H), 7.50–7.41 (m, 1H), 7.05 (d, J=8.9 Hz,
4H), 6.93 (d, J=8.9 Hz, 4H), 6.80 (d, J=8.8 Hz, 2H), 4.60 (d, J=2.4 Hz,
2H), 4.47 (d, J=1.9 Hz, 2H), 3.95 (t, J=6.4 Hz, 4H), 1.76–1.66 (m, 4H),
1.47–1.37 (m, 4H), 1.31 (dd, J=7.0, 3.3 Hz, 8H), 0.89 ppm (t, J=6.9 Hz,
6H). MS calcd: m/z 812.30 ([M+]), MALDI-TOF found: 812.44 ([M+]).
Elemental anal. calcd for C48H48N2O6S2: C 70.91, H 5.95, N 3.45; found:
C 70.82, H 6.05, N 3.26
Acknowledgements
This work was supported by the National Natural Science Foundation of
China (Nos. 20971066, 21021062, 20971025 and 90922004), National Basic
Research Program of China (Nos. 2011CB808704, 2007CB925103,
3-(7-(4-(Bis(4-
ACHTUNGTRENNUNG(hexyloxy)phenyl)amino)phenyl)-2,3-dihydrothienoHCATUNGTRENN[UGN 3,4-b]-
ACHTUNGTRENNUNG
Chem. Asian J. 2012, 00, 0 – 0
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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H. Yamada, Z.-S. Wang, Z. Shen et al.
FULL PAPERS
2011CB933302), the Program for New Century Excellent Talents in Uni-
versity (No. NCET-08–0272), the Fundamental Research Funds for the
Central Universities (No. 1093020505), Shanghai Pujiang Project
(09J1401300), Shanghai non-governmental international cooperation pro-
gram (10530705300), Grant-in-Aids for Scientific Research from the Min-
istry of Education, Culture, Sports, Science and Technology, Japan (No.
22350083 to H.Y.), JST, CREST (to H.Y.).
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ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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ÝÝ These are not the final page numbers!

FULL PAPERS
Sensitive souls: A series of sensitizers
for dye-sensitized solar cells features
ring-fused thiophene bridges between
donor and acceptor moieties. The
absorption spectra of the push–pull
sensitizers all exhibit intense intramo-
lecular charge transfer bands in the
visible region (see picture), and solar
cells based on the dyes show good inci-
dent photon to current conversion effi-
ciencies.
Dyes
Q. Liu, Q.-Y. Feng, H. Yamada,*
Z.-S. Wang,* N. Ono, X.-Z. You,
Z. Shen*
&&& — &&&
Tuning the Spectroscopic, Electro-
chemical, and Photovoltaic Properties
of Triaryl Amine Based Sensitizers
through Ring-Fused Thiophene
Bridges
Chem. Asian J. 2012, 00, 0 – 0
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
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