Macrocyclic triphenylamine based organic dyes for efficient dye-sensitized solar cells

Article abstract of DOI:10.1016/j.tet.2012.08.027

A novel class of organic D-π-A dyes employing macrocyclic triphenylamine dimer as electron donor was designed and synthesized for dye-sensitized solar cells. The prepared compounds showed high chemical and elelctrochemical stabilities as well as good long-wave absorption. Photovoltaic devices based on these dyes showed high open circuit voltage (higher than that of N3) and achieved a solar energy to electricity conversion efficiency of 6.31%. All the performances indicate the dyes containing macrocyclic triphenylamine dimer is a good candidate for dyes sensitized solar cells.

Full text of DOI:10.1016/j.tet.2012.08.027

Tetrahedron 68 (2012) 9113e9118
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Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Macrocyclic triphenylamine based organic dyes for efficient dye-sensitized solar
cells
,
Yun Zhao a, Kejian Jiang b, Wei Xu a, Daoben Zhu a
*
a Beijing National Laboratory for Molecular Sciences, Organic Solids Laboratory, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China
b Beijing National Laboratory for Molecular Sciences, Laboratory of New Materials, Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 June 2012
Received in revised form 4 August 2012
Accepted 10 August 2012
Available online 16 August 2012
A novel class of organic D-p-A dyes employing macrocyclic triphenylamine dimer as electron donor was
designed and synthesized for dye-sensitized solar cells. The prepared compounds showed high chemical
and elelctrochemical stabilities as well as good long-wave absorption. Photovoltaic devices based on
these dyes showed high open circuit voltage (higher than that of N3) and achieved a solar energy to
electricity conversion efficiency of 6.31%. All the performances indicate the dyes containing macrocyclic
triphenylamine dimer is a good candidate for dyes sensitized solar cells.
Keywords:
Ó 2012 Elsevier Ltd. All rights reserved.
Dye sensitized solar cells
Macrocyclic triphenylamine
Electron retardation
Organic dyes
Auxiliary electron donor
1. Introduction
triphenylamines are conjugated with each other, so the better
intramolecular charge transfer, as well as strengthened electron
Dye-sensitized solar cells (DSSCs) have attracted intense in-
terests for their high performance in converting solar energy to
electricity at low cost. So far the best solar energy conversion effi-
ciency of DSSCs based on Ru complexes exceed 10%.1,2 Recently,
there are increasing interests in metal-free organic dyes due to
their advantageous features, such as high molar extinction co-
efficients, easily modified molecular structure, and relatively low
cost.3 The metal-free organic dyes commonly consist of donor,
linker, and acceptor groups. Their various properties could be finely
tuned by alternating independently or matching the different
groups. Triphenylamine, fluorene, thiophene, indoline, mer-
ocyanine, coumarin, etc. have been employed as donor units in the
development of metal-free sensitizers and exhibit promising device
characteristics.3e6
donating ability can be expected.8 Thus, compared to the single
bridge connected triphenylamine dimers, the macrocycle would
have more advantages in stabilizing the initially formed radical
cation by
s-p
through-bond and through-space interactions,9
extending the absorption region, and preventing the direct
charge recombination between TiO2 and I3ꢀ by the bulky aryl group
covering TiO2 surfaces.10e12 The triphenylamine is chosen as donor
unit due to its good electron donating ability, thermal, and chemical
stabilities.13
2. Results and discussion
2.1. Molecular design
It has been found the incorporation of an auxiliary electron
donor can bring about superior performance over the simple D-p-A
As shown in Fig. 1, we prepared the organic dyes MC-T-CA and
MC-HT-CA, which contained thiophene linker with macrocyclic
triphenylamine dimer as an electron donor and cyanoacrylic acid as
an acceptor moiety. The synthetic procedure included well known
reactions and gave a moderate yield. For MC-T-CA, the macrocycle
moiety was coupled with 2-formylthiophene via Suzuki reaction,
followed by conversion of the aldehyde group to cyanoacetic acid
through Knoevenagel reaction in the presence of piperidine. The
synthesis of MC-HT-CA was similar. However, during the Suzuki
coupling reaction, the bulk center part of compound 6 made the
reaction very difficult to be accomplished, and in the
configuration, in terms of bathochromically extended absorption
spectra, enhanced molar extinction coefficients and more stabilized
photoexcited states.7,4 Here, we would like to present two novel
macrocycle derived organic dyes, each contained two triphenyl-
amine units linked by vinylene bridges. In the macrocycle, the
* Corresponding author. Tel.: þ86 10 6254 4083; fax: þ86 10 6256 9349; e-mail
addresses: zhaoyun@iccas.ac.cn (Y. Zhao), zhudb@iccas.ac.cn (D. Zhu).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.08.027

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Y. Zhao et al. / Tetrahedron 68 (2012) 9113e9118
Fig. 1. Molecular structure of the organic dyes.
transmetalation procedure one of bromine atom was eliminated.
Finally, we only got one-substituted product.14
2.2. General procedures
The synthetic procedure of compound 1 and 2 was shown in
Scheme 1. All manipulations of air/moisture-sensitive materials
were handled under nitrogen atmosphere using Schlenk tech-
niques. Dioxane was distilled over sodium/benzophenone. Pyridine
was distilled over NaOH. All reagents were used as received unless
otherwise noted. 1H NMR and 13C NMR spectra were obtained on
Bruker Advance 400 or 600 spectrometers. EIMS measurements
were performed on UK GCT-Micromass or SHIMADZU G-MS-
QP2010 spectrometers. High-resolution mass spectrometry mea-
surements (HRMS) were performed on UK GCT-Micromass spec-
trometers. Elemental analyses were carried out on a Carlo Erba
1106 elemental analyzer.
Fig. 2. Absorption spectra of MC and organic dyes in dichloromethane.
Scheme 1. Synthetic route to prepare the dyes 1 and 2. Reagents and conditions: (i) DMF, POCl3, 90 ꢁC, 4 h, 84%; (ii) Pd(dppf)Cl2, KOAc, bis(pinacolato)diboron, dioxane, 80 ꢁC, 6 h;
(iii) Pd(OAc)2, Ligand, CsF, dioxane, 110 ꢁC, 20 h, 23%; (iv) CNCH2COOH, piperidine, CHCl3, 70 ꢁC, 6 h, 94%.
2.3. Electrochemical and photophysical data
state.4 Compared to the dye, which contained a triphenylamine
monomer, the absorption center of MC-T-CA is red shifted from
463 nm to 492 nm.16 However, the absorption maximum is blue-
shifted by 42 nm when the hexyl chain is introduced. This result
can be presumably ascribed to the reduced conjugation degree
caused by the large steric hindrance effect of hexyl group. Pre-
viously, J. Nishida and his co-workers had observed the similar
phenomena,17 and in their report, they ascribed the blue-shifted
absorption band to the twisted molecular structure resulted from
the introduction of large alkyl chain. The absorption spectra of the
two dyes adsorbed onto the surface of TiO2 were shown in Fig. 4.
Compared to that in solutions, the absorption spectra of MC-T-CA
and MC-HT-CA have blue-shifted by 23 and 38 nm. That may came
from dyeeTiO2 interactions or deprotonation of the dyes at the
surface of the TiO2 film.4
Fig. 2 shows the absorption spectra of the triphenylamine
macrocycle (MC) and the two dyes in CH2Cl2, and the cyclic vol-
tammogram measurements are shown in Fig. 3. All the related
photophysical data are summarized in Table 1. The LUMO levels of
the two dyes were ꢀ3.02 and ꢀ3.00 eV, respectively, sufficiently
higher in energy than the conduction band edge of TiO2 (ꢀ4.0 eV).15
Hence, an effective electron injection from the excited dye to the
TiO2 is ensured. The HOMO levels were ꢀ5.19 and ꢀ5.25 eV, re-
spectively, sufficiently lower than the iodide/triiodide redox couple
(ꢀ4.83 eV vs vacuum). And it will be sufficient for the regeneration
of the oxidized dye. Both the dyes exhibit two absorption peaks.
The short-wavelength band appearing in 340 nm is assigned to the
pep* electron transition and the long-wavelength band appearing
in the range of 450e500 nm is assigned to the charge-transfer
transition between the triphenylamine dimer and cyanoacrylic
segments, which produce the efficient charge-separation excited
To verify our result, molecular geometry optimization were
carried out at the density functional theory (DFT) level using
Gaussian 03 program package.18 And we found that dihedral angel

Y. Zhao et al. / Tetrahedron 68 (2012) 9113e9118
9115
Fig. 3. Cyclic voltammogram measurements of MC-T-CA and MC-HT-CA.
AM 1.5 irradiation (100 mW cmꢀ2) with 0.9 cm2 active surface area
defined by a metal mask. The incident photon-to-current efficient
curves are shown in Fig. 6. It can be seen that the photocurrent
response of MC-T-CA sensitized DSC is better due to the IPCE ex-
ceeding 70% in the range of 420e480 nm, and the maximum IPCE
(85%) was obtained at 450 nm. When light absorption and re-
flection by the conducting glass are taken into account, this may
correspond to almost the unity quantum yield. MC-HT-CA also
shows a good photocurrent response with the maximum IPCE value
of 76% at 425 nm. Both the IPCE spectra of the two dyes are con-
sistent with their absorption spectra. The decrease of the IPCE
above 600 nm toward the long-wavelength region is ascribed to the
decrease of light harvesting for both dyes.
Table 1
Optical and electrochemical properties of the new dyes
Entry
lmaxa/nm( /Mꢀ1 cmꢀ1 Eox1b/V HOMOc/eV E0e0d/eV LUMOe/eV
3 )
MC-T-CA
340(22,500)
492(16,000)
0.79
ꢀ5.19
ꢀ5.25
2.17
ꢀ3.02
ꢀ3.00
MC-HT-CA 340(20,000)
0.85
2.25
450(8000)
a
Absorption spectra were measured in Dichloromethane.
b
c
The potentials were got from cyclic voltammogram measurements (vs Ag/AgCl).
The HOMO levels were calibrated by the potentials vs Ag/AgCl.
E0e0 values were estimated from the edge of absorption spectra.
Calculated from the bandgap and HOMO value.
d
e
Measurement were performed under AM 1.5 irradiation on the
DSC devices with 0.25 cm2 active surface area defined by a metal
mask. Jsc, short circuit current; Voc, open circuit voltage; FF, fill
factor; h, conversion efficiency.
Fig. 7. shows the IeV curves of DSSCs based on the as-
synthesized dyes. Consistent with the result of IPCE and absorp-
tion spectra, MC-T-CA also shows better photovoltaic properties. Its
overall conversion efficiency reaches 6.31%, which was obtained
with JSC¼12.47 mA cmꢀ2, Voc¼720 mV, and ff¼0.69. The Voc and ff
values derived from both newly synthesized dyes are even higher
than those of device based on N3 measured at the same conditions.
This benefits from the molecular structures of the two dyes, and the
introduction of the macrocyclic triphenylamine is thought to be the
main reason for the excellent performances. And it has been proved
that high Voc were closely related with retardation of charge re-
combination,19 either from injected electrons with the oxidized dye
or with the oxidized electrolyte.17 More thorough research will be
carried out in our next work. The macrocyclic triphenylamine acts
not only as a secondary electron-donating group, which would
retard the rate of charge recombination by increasing the distance
between the dye cation center and the TiO2 surface,12 but it may be
very favorable for the stabilization of the initially formed radical
cation since it exhibits good intramolecular electron charge
transfer.
As shown in Fig. 7, the dye MC-T-CA also shows higher short
circuit current. The obviously higher photocurrent of MC-T-CA may
be the result of its favorable absorption spectrum.20 Thus, it can be
inferred that a good absorption spectra is crucial for the photo-
voltaic performance since the Voc and ff are almost equally high for
the DSSCs based on our synthesized dyes. Interestingly, although
the absorption spectra blue-shifted when a hexyl group is in-
troduced to the thiophene unit, the Voc of the DSSCs based on the
dye keeps at a quite high level. Based on it, we could tune the ab-
sorption spectra by properly modifying the linker unit without
lowering the Voc value. The further research is still in progress.
Fig. 4. Absorption spectra of the organic dyes adsorbed on TiO2 surface.
between thiophene ring and the mean plane of the macrocycle
became quite larger in the MC-HT-CA compared to that of MC-T-CA,
the dihedral angle between thiophene and macrocycle is 49.11ꢁ for
MC-T-CA, but it increases to 71.45ꢁ for MC-HT-CA, which meant
a more twisted conformation. So a larger energy would be required
to stimulate the intramolecular charge transfer. That is well account
for the weak and blue-shifted maximum absorption band in
MC-HT-CA. Moreover, as depicted in the optimized molecular
conformation (Fig. 5), the HOMOs were localized on the triphe-
nylamine macrocycle in both the two dyes, while the LUMOs were
distributed over the cyanoacrylic acid and the adjacent benzene.
This confirms the charge transfer type (HOMOeLUMO) reflected in
the absorption spectra, which is consistent with the aforemen-
tioned experimental results.
The photovoltaic properties of the newly synthesized dyes are
summarized in Table 2. All measurements were performed under

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Y. Zhao et al. / Tetrahedron 68 (2012) 9113e9118
Fig. 5. The molecular conformation of the two dyes. HOMO (a), LUMO (b) of MC-T-CA, and HOMO (c), LUMO (d) of MC-HT-CA, respectively.
Table 2
Photovoltaic parameters of DSCs based on the new dyes
Dyes
Jsc/mA/cm2
Voc/mV
FF
h/%
MC-T-CA
MC-HT-CA
N3
12.47
9.81
18.33
736
720
656
0.69
0.68
0.62
6.31
4.79
7.49
Fig. 7. Photocurrent densityephotovoltage curves of MC-T-CA and MC-HT-CA.
The solution was stirred for 1 h. Then 2-bromothiophene (3)
(1.94 ml, 20 mmol) dissolved in 1,2-dechloroethane (30 ml) was
injected. The reaction was kept at 90 ꢁC for 4 h under N2. After
cooling to room temperature, the reaction mixture was poured to
200 ml ice water, neutralized with saturated NaOH solution, and
then extracted with dichloromethane twice. The combined organic
layer was washed with H2O and brine, dried over Na2SO4, and
evaporated under reduced pressure. The crude product was puri-
fied by column chromatography (petroleum/EtOAc¼5/1) to obtain
compound 4 (3196 mg, 84.1%) as yellow liquid. MS(EI): m/z¼190
Fig. 6. IPCE spectra for the DSSCs based on MC-T-CA, MC-HT-CA and N3 [ruthenium(II)
cis-(2,20-bipyridyl-4,40-dicarboxylate)2(NCS)2].
3. Conclusion
In summary, we have developed a novel type of highly efficient
organic sensitizer using macrocyclic triphenylamine dimer as
electron donor moiety, yielding maximum 85% IPCE and 6.31%
power conversion efficiency. Introduction of a macrocyclic triphe-
nylamine group as the electron-donor unit brought about improved
photovoltaic performance, with Voc and ff even better than those of
N3. This result demonstrates that the macrocyclic triphenylamine
dimer is a good candidate as donor unit for dye molecular design
for DSSCs.
(Mþ). 1H NMR (CDCl3, 400 M Hz)
7.19 (d,1H).
d/ppm: 9.78 (s, 1H), 7.52 (d, 1H),
4.1.2. 2-(4,4,5,5-Tetramethy-1,3,2-dioxaborolan-2-yl)-thiophene-5-
carbaldehyde22 (5). A solution of 4 (1.68 g, 8.8 mmol), bis(pinaco-
lato)diboron (3.4 g, 13.2 mmol), PdCl2(dppf) (756 mg, 0.88 mmol),
and KOAc (2.587 g, 26.4 mmol) in degassed 1,4-dioxane (60 ml) was
stirred at 80 ꢁC for 6 h under N2. The reaction was quenched by
adding water, and extracted by dichloromethane. The organic
phase was dried over Na2SO4, and concentrated under reduced
pressure. The crude product was purified by silica gel chromatog-
raphy (petroleum/dichloromethane¼1/3) to give compound 5
(1.86 g, 88.9%) as yellow solid. Mp: 73 ꢁC. MS(EI): m/z¼238 (Mþ). 1H
4. Experimental section
4.1. Compound synthesis
4.1.1. 2-Bromo-5-formylthiophene21 (4). To the cold solvent dry
DMF (20 ml) at 0 ꢁC, POCl3 (18 ml) was added dropwise.

Y. Zhao et al. / Tetrahedron 68 (2012) 9113e9118
9117
NMR (CDCl3, 400 M Hz)
1H), 1.34 (s, 12H).
d
/ppm: 9.92（s, 1H）, 7.73 (d, H), 7.43 (d,
chromatography (petroleum/dichloromethane¼1/3) to give com-
pound 10 (2.78 g, 86.3%) as yellow liquid. MS (EI): m/z¼322. 1H NMR
(400 MHz, CDCl3) d: 9.90 (s, 1H), 7.63 (s, 1H), 2.87 (t, 2H), 1.59e1.56
4.1.3. N,N0-Diphenyl-4-bromoaniline dimer8(6). It was prepared
according to literature procedure with a little modification. Mp:
(m, 2H), 1.34 (s, 12H), 1.31e1.29 (m, 6H), 0.87 (t, 3H).
>300 ꢁC 1H NMR (400 MHz, THF-d4)
d
7.18 (d, 4H); 6.88 (d, 8H);
6.78e6.82 (m, 12H); 6.48 (s, 4H). 13C NMR (100 M HZ, THF-d4)
(ppm) 147.96, 133.31, 132.15, 130.66, 130.38, 125.03, 123.29;
HRMS(ESI): calcd for C40H28Br2N2 696.0599, found: 696.0606 (Mþ).
4.1.8. Compound (11).23
A solution of compound 6 (350 mg,
0.5 mmol), compound 10 (970 mg, 3 mmol), Pd(OAc)2 (20 mg,
0.1 mmol), Ligand (80 mg, 0.2 mmol), and CsF (220 mg, 1.5 mmol) in
degassed 1,4-dioxane (50 ml) was stirred at 110 ꢁC for 20 h under N2.
The reaction was quenched by adding water, and extracted by
dichloromethane. The organic phase was dried over Na2SO4, and
concentrated under reduced pressure. The crude product was puri-
fied by silica gel chromatography (petroleum/dichloromethane¼1/
1) to give compound 11 (79 mg, 21.5%) as orange solid. Mp>300 ꢁC
d
4.1.4. Compound (7).23
A solution of compound 6 (350 mg,
0.5 mmol), compound 5 (760 mg, 3 mmol), Pd(OAc)2 (20 mg,
0.1 mmol), Ligand (80 mg, 0.2 mmol), and CsF (220 mg,1.5 mmol) in
degassed 1,4-dioxane (50 ml) was stirred at 110 ꢁC for 20 h under
N2. The reaction was quenched by adding water, and extracted by
dichloromethane. The organic phase was dried over Na2SO4, and
concentrated under reduced pressure. The crude product was pu-
1H NMR (400 MHz, CDCl3)
d 9.83 (s, 1H); 7.63 (d, 1H); 7.29 (d, 2H);
7.20 (t, 2H); 7.09e7.02 (m, 8H); 7.0e6.95 (m, 8H); 6.92e6.88 (m, 5H);
6.60 (s, 4H), 2.70 (t, 2H),1.65e1.59 (m, 2H),1.35e1.28 (m, 6H), 0.89 (t,
rified
dichloromethane¼1/1) to give compound 7 (76 mg, 23.5%) as or-
ange solid. Mp>300 ꢁC 1H NMR (400 MHz, CDCl3)
9.85 (s, 1H);
by
silica
gel
chromatography
(petroleum/
3H). 13C NMR (100 MHz, CDCl3)
d 180.33, 146.91, 146.31, 146.14,
145.86, 145.37, 139.82, 138.08, 137.12, 132.12, 130.55, 129.07, 128.52,
128.35, 127.54, 124.97, 123.81, 123.34, 121.69, 120.32, 119.30, 30.30,
29.30, 27.72, 27.22, 21.19, 12.14. HRMS(ESI): calcd for C51H44N2OS
732.3174, found 732.3178.
d
7.70 (d, 1H); 7.48 (d, 2H); 7.28 (d, 1H); 7.20 (t,2H); 7.07e7.02 (m,
8H); 6.96 (d, 8H); 6.93e6.89 (m, 5H); 6.60 (s, 4H). 13C NMR
(100 MHz, CDCl3) d/ppm: 182.70, 154.84, 148.23, 148.07, 147.22,
146.76, 141.35, 137.85, 133.70, 132.40, 131.96, 131.03, 130.99, 130.76,
130.62, 130.46, 130.10, 129.17, 127.38, 126.07, 125.77, 125.42, 124.97,
122.83, 121.84, 120.98. HRMS(ESI): calcd for C45H32N2OS 648.2235,
found: 648.2239 (Mþ).
4.1.9. Compound (2).21 Compound 11 (70 mg, 0.1 mmol), cyano-
acetic acid (50 mg, 0.5 mmol), and piperidine (100 ml) were added to
CHCl3 (30 ml). The solution was stirred at 80 ꢁC for 6 h. The reaction
was quenched by adding water, and extracted by dichloromethane.
The organic phase was dried over Na2SO4, and concentrated under
reduced pressure. The crude product was purified by silica gel
chromatography (first acetone/dichloromethane¼1/1, then acetic
acid) to give compound 1 (72 mg, 93.2%) as red solid. Mp>300 ꢁC. 1H
4.1.5. Compound (1).21 Compound 7 (70 mg, 0.1 mmol), cyanoacetic
acid (50 mg, 0.5 mmol), and piperidine (100 ml) were added to CHCl3
(30 ml). The solution was stirred at 80 ꢁC for 6 h. The reaction was
quenched by adding water, and extracted by dichloromethane. The
organic phase was dried over Na2SO4, and concentrated under re-
duced pressure. The crude product was purified by silica gel chro-
matography (first acetone/dichloromethane¼1/1, then acetic acid) to
give compound 1 (72 mg, 93.2%) as red solid. Mp>300 ꢁC. 1H NMR
NMR (400 MHz, CDCl3) d ppm: 8.27 (s, 1H), 7.71 (s, 1H), 7.65 (d, 2H),
7.21 (t, 2H), 7.07e7.02 (m, 8H), 7.00e6.96 (m, 8H), 6.91e6.87(m, 5H),
6.59 (s, 4H), 2.38 (t, 2H),1.66e1.60 (m, 2H),1.30e1.26 (m, 6H), 0.90 (t,
3H). 13C NMR (100 MHz, CDCl3),
d ppm: 148.39, 147.48, 146.90,
132.59, 130.78, 130.65, 130.34, 130.25, 130.14, 130.12, 130.06, 129.35,
125.52, 125.16, 121.99, 120.82, 32.26, 31.57, 29.69, 29.66, 23.02, 14.44.
HRMS(ESI): calcd for C54H45N3O2S 799.3232, found: 799.3236 (Mþ).
(400 MHz, CDCl3)
(d, 1H), 7.21 (t, 2H), 7.06e7.02 (m, 8H), 6.97 (d, 8H), 6.92e6.89 (m,
5H), 6.60(s, 4H). 13C NMR (100 MHz, CDCl3)
/ppm: 148.21, 147.16,
d/ppm: 8.27 (s, 1H), 7.72 (d, 1H), 7.53 (d, 2H), 7.31
d
146.73, 133.53, 132.40, 130.65, 130.62, 130.13, 129.17, 128.37, 127.28,
125.44, 125.36, 125.00, 121.80, 120.80. HRMS(ESI): calcd for
C48H33N3O2S 715.2293, found: 715.2300 (Mþ).
4.2. Computational methodology
To get further insight into the molecular structure and electron
distribution of MC-T-CA and MC-HT-CA, molecular calculations were
carried out with the Gaussian 03 program package. Equilibrium
ground state geometry and electronic properties of basic unit of the
dyes were optimized by means of the density functional theory
(DFT) method at the B3LYP level of theory (Beckes-style three-
parameter density functional theory using the LeeeYangePar cor-
relation functional) with the 6-31G(d,p) basic set.
4.1.6. 2-Bromo-3-hexyl-5-formylthiophene (9). To the cold solvent
dry DMF (25 ml) at 0 ꢁC, POCl3 (22.5 ml) was added dropwise. The
solution was stirred for 1 h. Then 2-bromothiophene (8) (3.31 g,
13.4 mmol) dissolved in 1,2-dechloroethane (30 ml) was injected.
The reaction was kept at 90 ꢁC for 4 h under N2. After cooling to
room temperature, the reaction mixture was poured to 200 ml ice
water, neutralized with saturated NaOH solution, and then
extracted with dichloromethane twice. The combined organic layer
was washed with H2O and brine, dried over Na2SO4, and evapo-
rated under reduced pressure. The crude was purified by column
chromatography (petroleum/EtOAc¼5/1) to obtain compound 9
(3.217 g, 87.3%) as yellow liquid. MS(EI): m/z¼274 (Mþ). 1H NMR
4.3. Electrochemical properties
Cyclic voltammetric measurements were recorded on
a CHI660C voltammetric analyzer (CH Instruments, USA). They
were carried out in a conventional three-electrode cell using Pt
button working electrodes in 0.1 M dry dichloromethane solution
of (n-Bu)4NPF6, a platinum wire counter electrode, and an Ag/AgCl
reference electrode at room temperature.
(400 MHz, CDCl3) d: 9.75 (s, 1H), 7.16 (s, 1H), 2.60 (t, 2H), 1.62e1.57
(m, 2H), 1.36 (m, 6H), 0.88 (t, 3H).
4.1.7. 2-(4,4,5,5-Tetramethy-1,3,2-dioxaborolan-2-yl)-3-
hexylthiophene-5-carbaldehyde22 (10). A solution of
9
(2.72 g,
4.4. DSSC device fabrication
10 mmol), bis(pinacolato)diboron (5.08 g, 20 mmol), PdCl2(dppf)
(860 mg, 1 mmol), and KOAc (3.94 g, 30 mmol) in degassed 1,4-
dioxane (80 ml) was stirred at 80 ꢁC for 6 h under N2. The reaction
was quenched by adding water, and extracted by dichloromethane.
The organic phase was dried over Na2SO4, and concentrated under
reduced pressure. The crude product was purified by silica gel
For fabrication of the devices,24 two layers of TiO2, the main
layer, and the scattering layer, were prepared by screen-printing
TiO2 pastes on FTO glass substrate (10
The main layer (thickness, 14 m; TiO2 particle size, 18 nm) and
scattering layer (thickness, 8 m; TiO2 particle size, 400 nm) were
U/sq, Nippon Sheet Glass).
m
m

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Y. Zhao et al. / Tetrahedron 68 (2012) 9113e9118
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Acknowledgements
The authors are grateful to financial support from the National
Natural Science Foundation of China (20952001, 21021091), the
State Key Basic Research Program (2011CB808401), and the Chinese
Academy of Sciences.
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