Benzothiadiazole containing D-π-A conjugated compounds for dye-sensitized solar cells: Synthesis, properties, and photovoltaic performances

Article abstract of DOI:10.1002/asia.201000158

Two D-π-A conjugated molecules, BzTCA and BzTMCA, were developed through facile synthetic approaches for dye-sensitized solar cells. The investigation of the photophysical properties of BzTCA and BzTMCA both in dilute solutions and in thin films indicates

Full text of DOI:10.1002/asia.201000158

DOI: 10.1002/asia.201000158
Benzothiadiazole Containing D-p-A Conjugated Compounds for Dye-
Sensitized Solar Cells: Synthesis, Properties, and Photovoltaic Performances
Zheng-Ming Tang,[a] Ting Lei,[a] Ke-Jian Jiang,*[b] Yan-Lin Song,[b] and Jian Pei*[a]
Abstract: Two D-p-A conjugated mole-
cules, BzTCA and BzTMCA, were de-
veloped through facile synthetic ap-
proaches for dye-sensitized solar cells.
The investigation of the photophysical
properties of BzTCA and BzTMCA
both in dilute solutions and in thin
films indicates that their absorption ex-
hibits a wide coverage of the solar
spectrum. The absorption features for
BzTCA and BzTMCA commence at
about 710 nm in solution, and at about
800 nm in the solid state. The absorp-
tion maxima (lmax) for both BzTCA
and BzTMCA on TiO2 film are almost
the same as those in dilute solution.
Their HOMOs and LUMOs were
found to partly overlap at the center of
these dyes, which guarantees apprecia-
ble interactions between the donors
and acceptors. The investigation of the
performance of dye-sensitized solar
cells fabricated from BzTCA and
BzTMCA indicated that the power-
conversion efficiencies are 6.04% and
4.68%, respectively, which could be
comparable with the normal sensitizer
N3. BzTMCA showed lower incident
photon-to-electron conversion efficien-
cy (IPCE) and Jsc values relative to
BzTCA, which is probably because of
the weaker driving force of dye regen-
eration and electron injection process
of BzTMCA. The IPCE responsive
area reached nearly 800 nm, which pro-
vides great potential for further im-
provement of the photocurrent density
and power-conversion efficiency. Our
investigations demonstrate that both
dyes BzTCA and BzTMCA could be
promising candidates for dye-sensitized
solar cells.
Keywords: conducting materials
·
molecular devices · molecular elec-
tronics · photophysical properties ·
solar cells
Introduction
version efficiency of 20.25% with absorption onset at
940 nm.[6] Some metal-free organic dyes based on tetrahy-
Dye-sensitized solar cells (DSSCs) have attracted tremen-
dous interest because of their low-cost, light-weight, semi-
transparent characteristics, and potential applications.[1,2]
Normal sensitizers N3 and N719 have demonstrated high ef-
ficiency of up to 10–11% for DSSCs,[3–5] but ruthenium-
based dyes are relatively expensive and hard to purify. Or-
ganic dyes were expected to achieve a maximum power-con-
droquinoline,[7]
thienylenevinylene,[8]
pentaphenylene,[9]
squaraine,[10] indoline,[11] coumarin,[12] phenylenevinylene,[13]
perylene,[14] spirobifluorene,[15] boradiazaindacenes[16] units
have been developed because of their good absorption prop-
erties and facile tuning of HOMO–LUMO by structure
modification. Some of them exhibited good efficiency of up
to 7–9%.[17–19] However, to develop new organic dyes
through a facile synthetic approach to expand the utilization
area of the solar spectrum for dyes in DSSCs is still a chal-
lenge.
Recently, D (Donor)-p-A (Acceptor) molecules have
been shown to exhibit good performance in DSSCs because
of their extended absorption spectra and high molar extinc-
tion coefficients.[20] Benzothiadiazole has been widely uti-
lized in the design of bulk heterojunction solar cells.[21] It
has been shown that benzothiadiazole-containing dyes pos-
sess a broader absorption spectra and a lower HOMO–
LUMO bandgap.[22] Herein we have developed two benzo-
thiadiazole-containing D-p-A conjugated compounds,
BzTCA and BzTMCA. Their structures are presented in
Scheme 1. The introduction of alkyl chains would not only
[a] Z.-M. Tang, T. Lei, Prof. J. Pei
Beijing National Laboratory for Molecular Sciences (BNLMS)
Key Laboratory of Bioorganic Chemistry and Molecular Engineering
College of Chemistry
Peking University
Beijing 100871 (China)
Fax : (+86)10-62758145
E-mail: jianpei@pku.edu.cn
[b] Prof. K.-J. Jiang, Prof. Y.-L. Song
Beijing National Laboratory for Molecular Sciences
Key Laboratory of Organic Solids
Laboratory of New Materials
Institute of Chemistry
Chinese Academy of Sciences
Beijing 100190 (China)
Chem. Asian J. 2010, 5, 1911 – 1917
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FULL PAPERS
thienylboronate afforded compound 2 in 95% yield. A Vils-
meier reaction of compound 2 with a mixture of DMF and
POCl3 produced compound 3 in 90% yield. A Wittig–
Horner reaction between compound 3 and diethyl 4-(diphe-
nylamino) benzylphosphonate gave compound 4 in 41%
yield (with 30% compound 3 recovered). Compound 5 was
obtained by the same procedure from 3 and diethyl 4-(bis(4-
methoxyphenyl)amino)benzylphosphonate. Finally, a typical
Knoevenagel reaction between 2-cyanoacetic acid and 4 was
employed to afford BzTCA in 92% yield. Following the
same Knoevenagel reaction procedure, BzTMCA was ob-
tained through the reaction of compound 5 with 2-cyanoace-
tic acid in 95% yield. Although both compounds can be dis-
solved in common organic solvents, such as toluene, THF,
DMSO, and CH2Cl2, BzTMCA exhibited much better solu-
bility than BzTCA. The structure and purity of the new
Scheme 1. Structure of the two D-A-D-A conjugated dyes.
make the dyes more soluble and reduce aggregation in devi-
ces, but also delay the electron-hole recombination in both
liquid-electrolyte and solid-state cells.[23] All these factors
are beneficial for the improvement of device performance.
The performance of the dye-sensitized solar cells with
BzTCA and BzTMCA as the active dye shows that the
power-conversion efficiencies are comparable with the clas-
sical sensitizer N3, which indicates that both BzTCA and
BzTMCA, could be promising candidates for dye-sensitized
solar cells.
1
compounds were fully characterized by H and 13C NMR, el-
emental analysis, as well as MALDI-TOF MS. The thermal
properties of BzTCA and BzTMCA were analyzed by ther-
mal gravimetric analysis (TGA). All compounds have high
thermal stability with decomposition temperature higher
than 2808C in nitrogen atmosphere.
Results and Discussion
Photophysical and Electrochemical Properties
Synthesis
Figure 1 shows the absorption spectra of BzTCA and
BzTMCA in THF (5ꢁ10À6 m) and in thin films. In dilute so-
lution, BzTCA and BzTMCA showed similar absorption
Scheme 2 illustrates the synthetic approach to the two dyes,
BzTCA and BzTMCA. A Suzuki coupling reaction between
4,7-dibromo-2,1,3-benzothiadiazole and sodium 5-hexyl-2-
Figure 1. Absorption spectra of BzTCA and BzTMCA in THF (5ꢁ
10À6 m) and in thin films.
features because of the same backbone, which exhibited two
major bands at about 405 nm and 565 nm. As we can see,
the absorption band from 350 nm to 500 nm was largely en-
hanced because of the introduction of 2,1,3-benzothiadiazole
compared with many D-p-A dyes, which can enhance the
photocurrent. Their absorption in thin films also showed
similar features. Interestingly, both compounds exhibited an
obvious red-shift of only the longer wavelength absorption
bands. For BzTCA, the absorption band at 557 nm in solu-
tion shifted to 587 nm in film and for BzTMCA, the absorp-
tion band shifted from 574 nm to 608 nm. This phenomenon
Scheme 2. Synthetic approach to the two dyes, BzTCA and BzTMCA.
1912
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Solar Cells with Benzothiadiazole
can be explained by the strong intermolecular interaction in
the solid state, which could then affect the intramolecular
charge transfer absorption. The absorption onset of both
compounds red-shifted from about 710 nm in solution to
about 800 nm in the solid state, and their absorption fea-
tures in thin films covered nearly the whole visible range,
namely, from 300 nm to 800 nm. Such broad absorption is
greatly beneficial to the improvement of photocurrent densi-
ty and power-conversion efficiency. The photophysical prop-
erties of BzTCA and BzTMCA are summarized in Table 1.
Figure 2 exhibits the absorption spectra of BzTCA and
To ensure the charge separation and electron formation
process, the HOMO and LUMO of the dyes should match
the electrolyte redox potential and the potential of the con-
duction band edge of TiO2, respectively. The electrochemi-
cal properties of BzTCA and BzTMCA in thin films were
probed by cyclic voltammetry (CV) experiments at room
temperature. The measured HOMO and LUMO energy
levels are summarized in Table 1. As shown in Figure 3, one
single-electron reversible oxidation peak was observed at
0.92/0.71 V for BzTCA and at 0.78/0.65 V for BzTMCA.
Consecutive scans of BzTCA and BzTMCA in thin films
showed no change in their oxi-
dation process. Meanwhile, CV
experiments of BzTCA and
BzTMCA exhibited an irrever-
sible reduction pair at À1.29 V
and À1.25 V, respectively. The
Table 1. Photophysical and electrochemical properties of BzTCA and BzTMCA.
compds.
lmax
N
lmax
A
HOMO [eV][b]
LUMO [eV][b]
Bandgap [eV][b]
BzTCA
BzTMCA
393 (4.66), 557 (4.67)
400 (4.74), 574 (4.71)
390, 587
404 , 608
À5.43
À5.27
À3.57
À3.72
1.86
1.55
[a] In THF solution (5ꢁ10À6 m). [b] In thin films.
Figure 3. Cyclic voltammogram (second scan) of BzTCA and BzTMCA
in thin films cast on glassy carbon disk in nBu4NBF4/acetonitrile at
100 mVsÀ1, reference Ag/AgCl.
Figure 2. Absorption spectra of the dye-adsorbed TiO2 film.
BzTMCA adsorbed on TiO2 films, which were prepared
from the dye solutions of the same concentration. The ab-
sorption maximum (lmax) for both BzTCA and BzTMCA on
TiO2 films was almost the same as those in dilute solution.
It was observed that the longer wavelength peaks exhibit no
obvious shift for the dyes on films compared with those in
solutions, while the absorption intensity in the shorter wave-
length region were enhanced because of the combination of
TiO2 nanoparticles absorption and the absorption of dyes.
We also measured the absorption spectra of BzTCA and
BzTMCA in acetonitrile and dichloromethane. The shorter
wavelength absorption bands in these D-p-A compounds
did not show a significant shift in different solvents. Howev-
er, the longer wavelength absorption band varied in differ-
ent solvents. For BzTCA, the absorption maximum lmax was
at 392 nm and 548 nm in acetonitrile and at 392 nm and
561 nm in dichloromethane. The longer wavelength absorp-
tion band exhibited a significant red-shift in dichlorome-
thane. For BzTMCA, similarly, the absorption maxima were
397 nm, 557 nm in acetonitrile and 399 nm, 579 nm in di-
chloromethane. The solvatochromic effects further indicated
the longer wavelength absorption band as the intramolecu-
lar charge transfer absorption.
HOMO energy value in thin films was calculated relative to
Ag/AgCl, which was À5.43 eV for BzTCA and À5.27 eV for
BzTMCA with respect to vacuum level. Similarly, the
LUMO energy values in thin films were calculated to be
À3.57 eV and À3.72 eV for BzTCA and BzTMCA, respec-
tively. Consequently, their bandgaps were estimated to be
1.86 eV for BzTCA and 1.55 eV for BzTMCA, which were
in agreement with those obtained from their absorption
spectra in thin films (1.56 eV vs 1.51 eV) and those calculat-
ed by computational methods as depicted below.
Theoretical Investigation
In order to visualize the geometry, electronic structure, and
estimate the HOMO, LUMO values of the two dyes, com-
putational studies were performed with density functional
theory (DFT) using B3LYP/6-311+GACTHNUTRGNE(NUG d, p)//B3LYP/6-
31G(d) level.[24–25] All the hexyl groups were replaced with
ethyl groups for simplicity. Figure 4 shows the molecular ge-
ometries and the HOMO–LUMO orbitals of BzTCA and
BzTMCA. As expected, the generated HOMOs of these
compounds were mostly found on the triphenylamine and
thiophene conjugated part, and in contrary the LUMOs
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J. Pei et al.
FULL PAPERS
sorption compared to BzTCA.
Figure 5b shows the photocur-
rent–voltage curves of the devi-
ces fabricated from these dyes.
Devices
fabricated
from
BzTCA possessed short-circuit
photocurrent density (JSC) of
16.46 mA/cm2, an open-circuit
voltage (VOC) of 545 mV, a fill
factor (FF) of 0.67, and the
power-conversion
efficiency
(PCE, h) of 6.04%, which were
close to the parameters of the
devices fabricated from N3.
The device performance of
BzTMCA, although it had a bit
Figure 4. The HOMO (top) and LUMO (bottom) orbitals of a) BzTCA, and b) BzTMCA (using B3LYP/6-
311+GACHTUNGTRENNUNG(d, p)//B3LYP/6-31G(d) level).
broader
absorption
than
mostly exist on the cyanoacetic acid and benzothiadiazole
parts. The HOMOs and LUMOs were also found to partly
overlap at the center, which guaranteed appreciable interac-
tions between the donors and acceptors. It was predicted
that this type of donor–acceptor interaction could facilitate
intramolecular electron transfer from the donor to the ac-
ceptor moiety of the dyes, which would then be injected into
the conduction band of TiO2 on which the dyes were ad-
sorbed.[2] The calculated gas-phase HOMO and LUMO
values were very close to the measured values (see Tables 1
and 2).
Table 2. The calculated Eg, HOMO, LUMO values of the two dyes
BzTCA, BzTMCA.
Compounds
HOMO [eV][a]
LUMO [eV][a]
Bandgap [eV][a]
BzTCA
BzTMCA
À5.22
À5.03
À3.47
À3.43
1.75
1.60
[a] Molecular structures of BzTCA and BzTMCA were optimized with
B3LYP/6-31G (d) and the single point energy was calculated using
B3LYP/6-311+GACHTUNGTRENNUNG(d, p).
Figure 5. a) IPCE characteristics and b) Photocurrent-voltage curves of
DSSCs fabricated from BzTCA and BzTMCA and measured with an
aperture mask at AM 1.5G one sun light illumination.
Photovoltaic Device Performance
The photovoltaic performance of the dye-sensitized solar
cells fabricated from BzTCA, BzTMCA, and N3 on the
TiO2 films with similar thickness and electrolyte condition
were investigated. The incident photon-to-electron conver-
sion efficiency (IPCE) of the devices fabricated from
BzTCA and BzTMCA are shown in Figure 5a. The IPCE
responses of both compounds are consistent with the ab-
sorption spectra of the dyes adsorbed on TiO2 films (as
shown in Figure 2). Excitingly, BzTCA exhibited compara-
ble or even better IPCE response than the N3 dye. Al-
though the two compounds have a similar skeleton, the
IPCE of BzTMCA from 380 nm to 730 nm are much lower
than BzTCA. However, the IPCE response of BzTMCA
from 730 nm to 800 nm is higher because of its broader ab-
BzTCA, was relatively unsatisfactory, with power-conversion
efficiency of 4.68% (JSC =11.94 mA/cm2,
VOC =555 mV,
FF=0.71), which is consistent with the IPCE results. The
lower IPCE and Jsc of BzTMCA compared with those of
BzTCA is probably because of its weaker driving force of
dye regeneration and electron injection process.[26a] As we
can see from Figure 6, the HOMO of BzTMCA is À5.27 eV,
which is 0.16 eV higher than that of BzTCA. The narrowed
gap between the reduction potential of iodide/triiodide and
the HOMO of BzTMCA may lower the driving force for its
regeneration from the oxidation state by iodide/triiodide.
Similarly, the gap between the Fermi level of TiO2 and the
LUMO of BzTCA is 0.43 eV and decreases further to
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Solar Cells with Benzothiadiazole
haviors of BzTCA and BzTMCA starts at about 710 nm in
solution, and at about 800 nm in the solid state. The investi-
gation of the electrochemical properties of BzTCA and
BzTMCA also indicated appreciable interactions between
the donors and acceptors within the structure of BzTCA
and BzTMCA. The devices fabricated from BzTCA showed
power-conversion efficiency as high as 6.04%, which is close
to that of classical dye N3 under the same conditions. The
investigation of the DSSC devices indicates that BzTMCA
shows lower IPCE and Jsc values compared to BzTCA,
which probably is because of the weaker driving force of
dye regeneration and electron injection process of
BzTMCA. Moreover, the IPCE active area reached nearly
800 nm, which provides great room for further improvement
of photocurrent density and power-conversion efficiency.
This design opens up a new strategy for the preparation of
new organic metal-free dyes, especially those with low
bandgap for DSSCs. Further optimization of the device is
underway in our laboratory.
Figure 6. Schematic energy illustration for DSSCs fabricated from
BzTCA and BzTMCA (The Fermi level of TiO2 and standard potential
of the iodide/triiodide redox couple are from Ref. [2c]).
0.28 eV for BzTMCA. We speculate that this excessively
narrowed gap will also lower the driving force for electron
injection into the conduction band of TiO2.[26b] Thereupon,
the HOMO and LUMO tuning is vital in the design of dyes,
especially for those with low bandgap.
As shown in Table 3, the lower VOC value of BzTCA and
BzTMCA compared with N3 is one of the main factors that
limit their PCE property. In general, many organic dye-sen-
Experimental Section
General Methods
Chemicals were purchased from commercial sources and used as re-
ceived. 1H and 13C NMR spectra were recorded on a 300 MHz NMR in-
strument using CDCl3 as solvent unless otherwise noted. Chemical shifts
were reported in parts per million (ppm) relative to internal TMS
(0 ppm) or residual CHCl3 (7.26 ppm). UV/Vis spectra were recorded on
a PerkinElmer Lambda 35 UV/Vis Spectrophotometer. PL spectra were
Table 3. Dye-sensitized solar cell performance of BzTCA and BzTMCA.
[a]
compds.
Jsc [mAcmÀ2
]
Voc [mV][a]
FF[a]
h%[a]
carried out on
a PerkinElmer LS55 Luminescence Spectrometer.
MALDI-TOF MS spectra were recorded on a time-of-flight (TOF) mass
spectrometer using a 337 nm nitrogen laser with dithranol as matrix. Ele-
mental analyses were carried out on Elementar Vario EL (Germany) an-
alyzer. Differential scanning calorimetry analyses were performed on a
METTLER TOLEDO Instrument DSC822e calorimeter. Cyclic voltam-
metry was performed on a BASi EC epsilon workstation at the scan rate
of 100 mVsÀ1 with a Pt disc as the working electrode, Pt wire as auxiliary
electrode, Ag/AgCl as reference electrode and Bu4NPF6 (0.1m, CH3CN)
as the supporting electrolyte. Atomic force microscopy (AFM) was per-
formed with a Multimode AFM (Veeco Instruments, Santa Barbara)
equipped with a 10 mmꢁ10 mm (E) scanner and Nanoscope IIIa control-
ler using OMCL-AC160TS silicon cantilevers (Olympus, resonance fre-
quency: 300 kHz and spring constant: 42 NmÀ1) using far-off resonance
tapping-mode imaging.
BzTCA
BzTMCA
N3
16.46
11.94
18.15
545
555
630
0.67
0.71
0.68
6.04
4.68
7.80
[a] Short-circuit photocurrent density (JSC), open-circuit voltage (VOC),
fill factor (FF), and conversion efficiency (h). The ruthenium-based dye
N3 was utilized for comparison. Conditions: DSSCs were measured at
AM 1.5G one sun light intensity (100 mWcmÀ2).
sitized cells suffer from a low Voc value, which is about
100 mV lower than their conterparts fabricated from ball-
shaped N3/N719 dyes.[7,27] One possible factor that leads to a
lower Voc value for organic dyes is their hard-to-eradicate
self-aggregation in devices.[28a] Although the alkyl chains
reduce the self-aggregation to a large extent, more steric
groups seem to be necessary to further reduce self-aggrega-
tion and thus increase the Voc value.[28b]
Device Fabrication
DSSCs were fabricated according to the following procedures: a main
layer and a scattering layer of TiO2 films was prepared by doctor blading
two different TiO2 pastes on FTO glass substrate (10 WsqÀ1, Nippon
Sheet Glass). The first nano-porous layer (TiO2 particle size: 20 nm) was
transparent with a thickness of 8 mm, and the second layer (thickness:
4 mm, TiO2 particle size: 400 nm) was used to increase the absorption of
the device in the red region of the solar spectrum. The first layer of TiO2
was heated at 4508C for 30 min, and the second layer was heated at
5008C for 20 min. The resulting film was further treated with a 0.04m
aqueous TiCl4 solution and then sintered again at 5008C for 20 min.
After cooling to about 808C, the films were immersed in the dye solu-
tions (0.3 mm in dry THF for BzTCA and BzTMCA and in dry ethanol
for N3) for 8 h. In the cases of BzTCA and BzTMCA, 3a,12a-dihydroxy-
5b-cholanic acid (1 mm) was added to the solutions to prevent dye aggre-
gation on the TiO2 film. In our experiment, open cells were fabricated in
air by clamping the different dyed electrode with Pt-sputtered FTO glass
as counter electrode. The electrolyte used here was composed of 1-
Conclusions
We have developed two novel benzothiadiazole-containing
D-p-A conjugated dyes BzTCA and BzTMCA, and fabricat-
ed them into dye-sensitized solar cells. The investigation of
their photophysical properties showed that the absorption
features of BzTCA and BzTMCA both in dilute solutions
and in thin films cover the whole visible range and possesses
a wide coverage of the solar spectrum. The absorption be-
Chem. Asian J. 2010, 5, 1911 – 1917
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J. Pei et al.
FULL PAPERS
propyl-3-methylimidazolium iodide (0.6m), LiI
(0.1m), I2 (0.05m), and
BzTCA. Piperidine (34 mg, 0.40 mmol) was added to a solution of com-
pound 4 (153 mg, 0.20 mmol) and cyanoacetic acid (34 mg, 0.40 mmol) in
MeCN (20 mL) and THF (5 mL) at room temperature under nitrogen at-
mosphere. After the mixture was heated to reflux for 8 h, the mixture
was poured into an aqueous NH4Cl solution. The aqueous layers were ex-
tracted with dichloromethane. The combined organic extracts were
washed with brine and dried over Na2SO4. After removal of the solvent
under reduced pressure, the residue was purified by flash column chro-
matography (silica gel, PE/DCM/HOAc=100:50:1) to give the product
as a black solid (153 mg, 92%). 1H NMR (600 MHz, CDCl2CDCl2): d=
8.25 (s, 1H), 7.86 (s, 1H), 7.68 (s, 1H), 7.49 (s, 1H), 7.24–7.27 (m, 6H),
7.09–7.10 (m, 5H), 7.03–7.06 (m, 2H), 6.93–6.98 (m, 3H), 6.78–6.81 (d,
J=14.4 Hz, 1H), 5.17 (s, 1H), 2.78 (s, 2H), 2.49 (s, 2H), 1.71 (s, 2H),
1.57 (s, 2H), 1.27–1.47 (m, 12H), 0.88–0.97 ppm (m, 6H); 13C NMR
(150 MHz, CDCl2CDCl2): d=167.7, 157.1, 152.1, 148.7, 147.3, 144.8,
142.2, 139.9, 135.2, 131.4, 130.9, 129.5, 128.4, 127.5, 124.8, 124.0, 123.4,
123.2, 122.5, 118.0, 116.3, 94.4, 31.9, 31.8, 31.2, 30.9, 29.5, 29.3, 28.6, 22.9,
14.4 ppm; HR-ESI MS: m/z (%) calcd for C50H48N4O2S3: 832.29339;
found: 832.29583; elemental analysis: calcd (%) for C50H48N4O2S3:
C 72.08, H 5.81, N 6.72; found: C 72.21, H 5.47, N 6.53.
tert-butylpyridine (0.5m) in a mixture of acetonitrile and valeronitrile
(1:1, v/v). All the cells were prepared with an active area of 0.2 cm2 using
an aperture mask. The action spectra of monochromatic incident photo-
to-current conversion efficiency (IPCE) for solar cells were carried out
by using
a commercial setup for IPCE measurement (PV-25 DYE,
JASCO). The photocurrent–voltage (I–V) characteristics were recorded
using a computer-controlled Keithley 2400 source meter under air mass
(AM) 1.5 simulated illumination (100 mW/cm2, Oriel, 67005).
3. DMF (878 mg, 12.00 mmol) and POCl3 (1.65 g, 10.8 mmol) was added
slowly to a solution of compound 1 (936 mg, 2.00 mmol) in 1,2-dichloro-
ethane (80 mL) at 08C under nitrogen atmosphere. The mixture was
heated to reflux for 12 h. After completion of the reaction, the mixture
was poured into aqueous NaOAc solution and stirred for 0.5 h. The aque-
ous layers were extracted with dichloromethane. The combined organic
extracts were washed with brine and dried over Na2SO4. After removal
of the solvent under reduced pressure, the residue was purified by flash
column chromatography (silica gel, petroleum ether/ethyl acetate=10:1)
to give the product as a red solid (995 mg, 95%). 1H NMR (300 MHz,
CDCl3): d=10.1 (s, 2H), 8.09 (s, 2H), 7.99 (s, 2H), 3.02–3.09 (t, 4H),
1.75–1.80 (m, 4H), 1.25–1.56 (m, 12H), 0.88–0.93 ppm (t, 6H); 13C NMR
(75 MHz, CDCl3): d=182.2, 153.4, 152.3, 146.7, 138.1, 131.2, 126.8, 126.3,
31.6, 31.5, 29.0, 28.7, 22.6, 14.1 ppm. HR-ESI MS: m/z (%) calcd for
C28H32N2O2S3: 524.1625; found: 525.1698 [M+1]+; elemental analysis:
calcd (%) for C28H32N2O2S3: C 64.09, H 6.15, N 5.34; found: C 64.31,
H 6.27, N 5.23.
BzTMCA. The same procedure as described for the preparation of
BzTCA was applied to compound 5 (165 mg, 0.20 mmol) and cyanoacetic
acid (34 mg, 0.40 mmol) in dry MeCN (20 mL) and dry THF (5 mL) to
give BzTMCA as a black solid (169 mg, 95%). 1H NMR (600 MHz,
CDCl3): d=8.00 (s, H), 7.69 (s, 1H), 7.43 (s, 1H), 7.37 (s, 1H), 7.18 (s,
1H), 7.07–7.08 (m, 2H), 6.96–6.97 (m, 4H), 6.76–6.89 (m, 6H), 6.65–6.67
(m, 1H), 6.57–6.59 (d, J=14.4 Hz, 1H), 3.77 (s, 6H), 2.66 (s, 2H), 2.28 (s,
2H), 1.67 (s, 2H), 1.27–1.42 (m, 14H), 0.86–0.99 ppm (m, 6H); 13C NMR
(150 MHz, CDCl3): d=168.2, 155.9, 151.8, 151.6, 148.4, 148.2, 144.3,
141.3, 140.6, 139.9, 134.7, 130.7, 130.4, 129.2, 128.8, 128.4, 127.3, 127.1,
126.7, 123.3, 122.1, 120.1, 116.8, 115.5, 114.7, 93.9, 55.5, 31.7, 30.7, 30.6,
29.4, 29.1, 28.4, 22.7, 14.2 ppm; HR-ESI MS: m/z (%) calcd for
C52H52N4O4S3: 892.31452; found: 892.31374; elemental analysis: calcd
(%) for C52H52N4O4S3: C 69.92, H 5.87, N 6.27; found: C 69.61, H 6.07,
N 6.23.
4. A solution of tBuOK (112 mg, 1.00 mmol) in THF (10 mL) was added
dropwise to a solution of compound 3 (0.52 g, 1.00 mmol) and diethyl 4-
(diphenylamino)benzylphosphonate (395 mg, 1.00 mmol) in dry THF
(80 mL) at À58C under nitrogen atmosphere. The mixture was stirred for
0.5 h at room temperature. The mixture was then poured into an aqueous
NH4Cl solution. The aqueous layer was extracted with ethyl acetate, and
the combined organic extracts were washed with brine and dried over
Na2SO4. After removal of the solvent under reduced pressure, the residue
was purified by flash column chromatography (silica gel, PE/DCM/
EtOAc=20:10:1) to give compound 4 as a dark solid (0.31 g, 41%).
1H NMR (300 MHz, CDCl3): d=10.02 (s, 1H), 7.87 (s, 1H), 7.93 (s, 1H),
7.75–7.78 (d, J=7.8 Hz, 1H), 7.63–7.65 (d, J=7.8 Hz, 1H), 7.24–7.35 (m,
4H), 7.02–7.20 (m, 11H), 6.88–6.93 (d, J=15.9 Hz, 1H), 2.92–2.97 (t, J=
7.5 Hz, 2H), 2.64–2.69 (t, J=7.5 Hz, 2H), 1.60–1.74 (m, 4H), 1.25–1.38
(m, 12H), 0.88–0.96 ppm (m, 6H); 13C NMR (100 MHz, CDCl3): d=
181.5, 156.5, 155.9, 151.9, 151.8, 148.3, 141.4, 140.5, 140.0, 134.8, 131.0,
130.5, 129.2, 129.1, 128.6, 127.5, 127.1, 126.7, 123.6, 122.4, 120.1, 116.9,
114.7, 31.7, 31.6, 30.9, 30.7, 29.3, 29.2, 31.5, 28.4, 22.7, 22.6, 14.1 ppm;
HR-ESI MS: m/z (%) calcd for C47H47N3OS3: 766.2954; found: 766.2933;
elemental analysis: calcd (%) for C47H47N3OS3: C 73.69, H 6.18, N 5.49;
found: C 73.38, H 6.29, N 5.26.
Acknowledgements
This work was supported by the Major State Basic Research Develop-
ment Program from the Ministry of Science and Technology (Nos.
2009CB623601 and 2006CB921602) and Natural Science Foundation of
China.
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7.87–7.90 (d, J=7.8 Hz, 1H), 7.75–7.78 (d, J=7.8 Hz, 1H), 7.30–7.33 (d,
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d=181.9, 156.0, 153.3, 152.3, 152.2, 148.4, 147.5, 141.5, 140.5, 139.8, 137.1,
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Received: February 26, 2010
Revised: March 22, 2010
Published online: June 11, 2010
Chem. Asian J. 2010, 5, 1911 – 1917
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
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