High-performance phototransistors based on organic microribbons prepared by a solution self-assembly process

Article abstract of DOI:10.1002/adfm.200901662

Oligoarenes as an alternative group of promising semiconductors in organic optoelectronics have attracted much attention. However, high-performance and low-cost opto-electrical devices based on linear asymmetric oligoarenes with nano/microstructures are still rarely studied because of difficulties both in synthesis and high-quality nano/microstructure growth. Here, a novel linear asymmetric oligoarene 6-methyI-anthra[2,3-fc]benzo[dJthiophene (MeABT) is synthesized and its high-quality microribbons are grown by a solution process. The solution of Me-ABT exhibits a moderate fluorescence quantum yield of 0.34, while the microribbons show a glaucous light emission. Phototransistors based on an individual Me-ABT microribbon prepared by a solution-phase self-assembly process showed a high mobility of 1.66 cm² V^-1 s ^-1 a large photoresponsivity of 12000 A W^-1, and a photocurrent/darkcurrent ratio of 6000 even under low light power conditions (30 p. W cm^-2). The measured photoresponsivity of the devices is much higher than that of inorganic single-crystal silicon thin film transistors. These studies should boost the development of the organic semiconductors with high-quality microstructures for potential application in organic optoelectronics.

Full text of DOI:10.1002/adfm.200901662

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High-Performance Phototransistors Based on Organic
Microribbons Prepared by a Solution Self-Assembly
Process
By Yunlong Guo, Chunyan Du, Gui Yu,* Chong-an Di, Shidong Jiang,
Hongxia Xi, Jian Zheng, Shouke Yan, Cailan Yu, Wenping Hu, and Yunqi Liu*
microstructures. However, in previous
works, most of the progress and attention
has focussed on high-performance device
fabrication based on PVTdue to the higher
quality nano/microstructure growth. Only
recently have various devices based on
nano/microstructures grown from solution
been developed greatly.[1c,5–8] Among these
devices, organic nano/microstructure
phototransistors (ON/MPTs) as one of the
functional devices that integrate the switch-
ing ability of a transistor with light detec-
tion, have attracted many researchers’
attention.[2] However, synthetic materials
with comprehensively excellent properties
and high-quality nano/microstructures
for ON/MPTs obtained by a solution
process are still limited. Furthermore, the
mechanism of high-performance ON/
MPTs is not well understood, and it is
important to guide the material synthesis
and device fabrication.
Oligoarenes as an alternative group of promising semiconductors in organic
optoelectronics have attracted much attention. However, high-performance
and low-cost opto-electrical devices based on linear asymmetric oligoarenes
with nano/microstructures are still rarely studied because of difficulties both
in synthesis and high-quality nano/microstructure growth. Here, a novel
linear asymmetric oligoarene 6-methyl-anthra[2,3-b]benzo[d]thiophene (Me-
ABT) is synthesized and its high-quality microribbons are grown by a solution
process. The solution of Me-ABT exhibits a moderate fluorescence quantum
yield of 0.34, while the microribbons show a glaucous light emission.
Phototransistors based on an individual Me-ABT microribbon prepared by a
solution-phase self-assembly process showed a high mobility of 1.66 cm2 Vꢀ1
s
ꢀ1, a large photoresponsivity of 12 000 A Wꢀ1, and a photocurrent/dark-
current ratio of 6000 even under low light power conditions (30 mW cmꢀ2).
The measured photoresponsivity of the devices is much higher than that of
inorganic single-crystal silicon thin film transistors. These studies should
boost the development of the organic semiconductors with high-quality
microstructures for potential application in organic optoelectronics.
The synthesis of organic semiconduct-
ing materials is a key driving force for the development of organic
electronics. In previous reports, the symmetric oligoarenes have
been an important part of synthetic organic semiconductors. Only
recently, asymmetric oligoarenes as an alternative group of
promising materials have attracted considerable attention because
of their unique molecular structures and excellent electronic
properties.[9] However, there are few reports on the intrinsic opto-
electrical behavior of the asymmetric oligoarenes because of the
complicated synthesis and the difficulty in crystal growth.
Correspondingly, the exploration of the optical and electrical
properties of asymmetric oligoarenes based on high-quality nano/
microstructures prepared by a low-cost process could be an
alternative way to further discern the intrinsic properties of these
materials. Therefore, the search for new asymmetric organic
semiconductors and growth of high-quality microstructures with
novel opto-electrical properties by a low-cost solution process are
highly desiredfor thedevelopment of theorganic semiconductors.
In this study, we present a linear asymmetric oligoarene,
6-methyl-anthra[2,3-b]benzo[d]thiophene (Me-ABT) with excellent
opto-electrical properties. Moreover, we fabricated organic photo-
transistors (OPTs) based on an individual Me-ABT microribbon
utilizing the solution assembly process. The organic microribbon
1. Introduction
Organic nano/microstructure semiconductors have undergone
great development in the past decade because of their merits in
studying intrinsic properties, their high-performance and promis-
ing applications in low-cost microelectronics, such as active matrix
displays, phototransistors, memory arrays, organic lasers, solar
cells, and gas sensors.[1–4] From the point of nano/microstructure
growth, physical vapor transport techniques (PVTs) and solution
process are the two major ways to obtain quality nano/
[*] Prof. Y. Liu, Prof. G. Yu, Y. Guo, C. Du, Dr. C.-a. Di, Dr. S. Jiang, H. Xi,
J. Zheng, Prof. S. Yan, C. Yu, Prof. W. Hu
Beijing National Laboratory for Molecular Sciences
Institute of Chemistry
Chinese Academy of Sciences
Beijing 100190 (P. R. China)
E-mail: yugui@iccas.ac.cn; liuyq@iccas.ac.cn
Y. Guo, C. Du, H. Xi, J. Zheng
Graduate School of Chinese Academy of sciences
Beijing 100049 (P. R. China)
DOI: 10.1002/adfm.200901662
Adv. Funct. Mater. 2010, 20, 1019–1024
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phototransistor (OMPT) exhibits a high light sensitivity with a
responsivity (R) of 12 000 A Wꢀ1, a photocurrent/dark-current
ratio (P) of 6000, and a hole mobility of 1.66 cm2 Vꢀ1 ꢀ1. For
s
comparison, thin film OPTs were also fabricated by vacuum
deposition and show a moderate light sensitivity with a
responsivity (R) of 447 A Wꢀ1, a photocurrent/dark-current ratio
(P) of 4000, and a hole mobility of 0.18 cm2 Vꢀ1 sꢀ1. Furthermore,
the mechanism was also analyzed on OPTs with different
condensed states of Me-ABT (i.e., thin film and microribbon) to
explore the origin of the high device performance.
2. Results and Discussion
The compound Me-ABT was synthesized according to Scheme 1
and purified by repeated sublimation after recrystallization.
Notably, considering the structure of 4-methyl-phthalic anhydride,
the reactions of the Friedel–Crafts acylation may induce two
possible isomers (1a and 1b), as illustrated by Scheme 1. Since the
elemental analysis and mass spectrometry of the product exclude
the presence of significant amounts of chemical impurities, the
1
multipeaks and complicated adjacent H interactions in the H
NMR,NOESYandCOSYNMRspectrahaveprovedthepresenceof
the isomer (see Fig. S1ꢀS3). According to the mechanism of
Friedel–Crafts acylation, we assigned compound 1a to be the main
product. In practice, however, this separation of the different
isomer fractions was often found to be difficult because of the
rather small differences of sublimation temperature. So the
compound here is investigated as a mixture of Me-ABTa and Me-
ABTb, and to ease the complication of the article, we only refer to
thesampleasMe-ABTanddrawitasthestructureofMe-ABTa. The
sample used was purified by using a three-zone furnace
sublimation three times. The physical properties of Me-ABTwere
characterized by thermogravimetric analysis (TGA), UV-vis
absorption spectroscopy, and cyclic voltammetry (CV). No
decomposition was observed for Me-ABT until about 300 8C,
which suggests a good thermal stability of the compound (Fig. 1A).
Although the Me-ABT has a molecular structure similar to that of
pentacene, it is quite soluble in common non-polar organic
solvents, for example, toluene and chloroform. On the other hand,
the Me-ABT molecule becomes insoluble in more-polar solvents
such as alcohol and methanol.
Figure 1. a) TGA plots of Me-ABT with a heating rate of 10 8C minꢀ1 under
N2. b) The absorption and PL spectra of the Me-ABT in dichloromethane.
c) Cyclic voltammogram of the compound Me-ABT.
TheabsorptionspectrumofMe-ABTindichloromethaneshows
a maximum peak at 437 nm (Fig. 1B). The optical bandgap of Me-
ABT is 2.76 eV determined by extrapolating the
long-wavelengthabsorptionedge.Theoxidation
potential of Me-ABT was studied by CV
measurements (Fig. 1C). The Me-ABT exhibits
reversible oxidation waves with a half-oxidation
potential of 1.02–1.07 eVand an onset oxidation
potential of 0.94 eV. The energy levels of the
highest occupied molecular orbitals were
estimated from the onset oxidation potential
to be around ꢀ5.34 eV, which matches well with
the work function of gold metal (ꢀ5.2 eV).[8d]
This datum is lower than that observed for
pentacene and most oligothiophenes, which
indicates better environmental stability. The
fluorescence quantum yield of Me-ABT in
dichloromethane was measured to be 0.34 by
using 9,10-diphenylanthracene as a standard.
Scheme 1. The synthesis of Me-ABT.
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Figure 3. a) SEM image of the Me-ABT microstructure assemblies. b) The
XRD data of the large area Me-ABT microribbons on the silicon substrate
and the evaporated thin films on OTS-treated SiO2 substrate. c) TEM image
of a Me-ABT microribbon, and d) its corresponding selected area electron
diffraction pattern.
representative Me-ABT microribbon, and Figure 3D shows the
selected area electron diffraction (SAED) pattern obtained from
the same microribbon, which demonstrated the high quality of the
ribbons. The optical image of the microribbons with glaucous
emissionwasshowninFig. S5A. Thefluorescencespectrumofthe
Me-ABTmicroribbons on the quartz substrate are shown in Figure
S5B with a maximum peak at 494 nm.
Figure 2. Microstructure self-assembly process of the Me-ABT molecules
through the solvent exchange method in the solution phase. a) Heating at
60 8C to dissolve Me-ABT in chloroform and obtain its saturated solution.
b) Injection of ethanol into the solution. c) Precipitation of the Me-ABT
microribbons from chloroform/ethanol solution. d) A photograph of the
solution with the Me-ABT microstuctures.
Top-contact OMPTs were fabricated using an individual Me-
ABTmicroribbon precipitated from chloroform/alcohol solution.
A heavily doped n-type Si substrate and a 500 nm SiO2 layer with a
capacitance per unit area of 7.5 nF cmꢀ2 were used as a gate
electrode and gate dielectric layer, respectively. The microribbon
was dropped on the n-octadecyltrimethoxysilane (OTS)-treated
SiO2/Si substrate. Gold shadow masks were used to deposit the
gold source/drain electrodes. A typical schematic diagram of the
device is shown in Figure 4A. An optical image of the microribbon
device is shown in Figure 4B. The microribbon with a width of
2 mm and a thickness of 80 nm was characterized by atomic force
microscopy (AFM) (see inset of Fig. 4B). The electrical
characteristics of transistors based on individual Me-ABT
microribbons are shown in Figure 4C and D. The mobility of
the OMPTs in the saturation region was extracted from the
following equation:
TheMe-ABTmicrostructureswerepreparedfromthepowderas
the starting material by a solvent-exchange method in the solution
phase (Fig. 2). A saturated solution of the Me-ABT in chloroform
(about 1 mL) was injected into a closed chamber at 60 8C. The
heating was stopped and 2 mL of ethanol was added into the
chamber to lead to the self-assembly of the Me-ABT molecules.
The assembled catkin-like product was suspended at the surface
of the chloroform/ethanol (see Fig. 2D). The Me-ABT easily self-
assembles into microribbons with a width of 1–8 mm and a length
of hundreds of micrometers (see Fig. 3A). The X-ray diffraction
(XRD) measurement was performed on the Me-ABT evaporated
and microribbon thin films (see Fig. 3B). The microribbon thin
films show serial high-ordered diffraction peaks at 2u values of
5.6208,11.3398,17.2618,22.9028,and28.8018,whichindicatesthat
microribbons in a large area have a high crystallinity. However, the
evaporated thin films show a less ordered structure with two
diffraction peaks at 2u of 5.6208 and 11.8108. In fact, the twist
microribbons were found in scanning electron microscopy (SEM)
images of the Me-ABTproduct and still can be bent by a machine
probe, which demonstrates their excellent flexibility. It is clear to
see that an individual ribbon with a length of about 1000 mm was
bent like a ‘C’ shape, which may demonstrate a potential
application in flexible electronics (see Fig. S4). Although both
Me-ABTaandMe-ABTbexistinthepowderproduct, surprisingly, a
high-quality microribbon can still be obtained. Figure 3C shows
the transmission electron microscopy (TEM) image of a
W
2
IDS
¼
mCiðVGS ꢀ VthÞ
(1)
2L
where IDS is the source–drain current, m is the field-effect
mobility, Ci is the capacitance per unit area of the gate dielectric
layer, VGS is the gate voltage, Vth is the threshold voltage, and L
and W are the channel length and width, respectively. The Vth of
the device was determined by extrapolating the (jIDS,satj)1/2 vs VGS
plot to IDS ¼ 0. The transistors exhibit a p-channel behavior with a
highest m of 1.66 cm2 Vꢀ1 sꢀ1 estimated from the saturation
current, a Vth of ꢀ10 V, and a high on/off ratio of 106, which is one
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value of 12 000 A Wꢀ1 and with a P value of
6000 at the cross point of the two curves with
VDS ¼ ꢀ80 V and VGS ¼ ꢀ18 V (see Fig. 6A and
B). The measured photosensitivity of the
devices is much higher than that of inorganic
single-crystal silicon thin film transistors
(300 A Wꢀ1).[12] To the best of our knowledge,
the result obtained here is one of the highest
value of photosensitivity for OPTs. On the other
hand, we also fabricated OPTs based on the Me-
ABT thin film. Compared with the microribbon
devices, the Me-ABT thin film transistors
exhibit a lower mobility of 0.18 cm2 Vꢀ1 sꢀ1
at a deposit substrate temperature of 40 8C
(output and transfer curves, see Fig. S6A and
B), a lower light sensitivity R of 477 A Wꢀ1, and
a smaller P of 4000 at the cross point of the
two curves with VDS ¼ ꢀ100 V and VGS ¼ 12 V
(see Fig. S6C and D). The mobility and
R values obtained are lower than those of
our previous reported thin film phototransis-
tors based on anthra[2,3-b]benzo[d]thiophene
(ABT) with a mobility of 0.40 cm2 Vꢀ1 sꢀ1 and
Figure 4. Field-effect characteristics of OFETs based on an individual Me-ABT microribbon.
a) Schematic diagram of the microribbon phototransistor. b) The microscope image of the OFET
based on the individual Me-ABT microribbon. Inset is the corresponding AFM image. c) Output
and d) transfer characteristics.
R of 1000 A Wꢀ1 [2h]
but the R and P values
,
are still higher than those of OPTs based on
of the best results for a microribbon transistor formed by a
solution process. In previous reports, the performance of devices
was always affected by the thickness of the microribbons.[2a,3a]
Therefore, devices based on Me-ABTmicroribbons with different
thickness were fabricated and the mobilities ranged from 0.34 to
1.66 cm2 Vꢀ1 sꢀ1, with an average value of 0.85 cm2 Vꢀ1 sꢀ1 (see
Fig. 5A), which demonstrated that our microribbon is thin
enough (most thicknesses lower than 100 nm) to fabricate high
performance transistors. The on/off current cycle test was
performed on one representative device and a good stability was
shown over 1000 test cycles (see Fig. 5B).
For inorganic and organic phototransistors, the mobility, light
responsivity (R), and photocurrent/dark-current ratio (P) are three
key parameters. The R is defined by the following equation:[11]
Iph
Il ꢀ Idark
R ¼
¼
(2)
Pill
Pill
where Iph is the photocurrent, Pill the incident illumination power
on the channel of the device, Il the drain current under
illumination, and Idark the drain current in the dark. The
responsivity reveals to what extend the optical power is converted
into an electrical current. The other merit is the photocurrent/
dark-current ratio (P):
Iph
signal
noise
Il ꢀ Idark
P ¼
¼
¼
(3)
Id
Idark
where all terms have been previous defined. Here, the I–V
characteristics of the transfer curve based on the OMPT shows a
large change, even under 30 mW cmꢀ2 low-power condition. The
transistor exhibits a high mobility of 1.66 cm2 Vꢀ1 sꢀ1 at the
saturation area. The OMPT shows high light sensitivity with a R
Figure 5. a) Field-effect mobility of the Me-ABT microribbon transistors
plotted as a function of the ribbon thickness. b) The on/off current cycle
testing of one representative device.
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will impart a higher Il with the same light conditions and almost
the same Idark. According to Equation (2), you will then obtain a
higher R value. For the Me-ABT OPTs with the same light
absorbanceandelectrodesforcollection(withsame S–Dmaterial),
the condensed states with efficient exiton dissociation, exiton
separation, and fast travelling of free charges, will achieve a higher
R value. That is to say, the performance of OMPTs is higher than
that of the thin-film phototransistors based on Me-ABT, which is
consistent with the previous report of F16CuPc.[2a,2i]
3. Conclusions
A novel organic semiconductor, Me-ABT, which easily self-
assembles to form high-quality microribbons, is synthesized.
The OMPTs were fabricated based on individual microribbons
prepared by a solution-phase self-assembly process. The OMPTs
showed a large mobility, high R, and P values. Furthermore,
the mechanism of the OPTs fabrication was analyzed for different
Me-ABT condensed states. All these studies should boost the
development of the asymmetric organic semiconductors with
microstructures for potential application in the high-performance
and low-energy exhaust organic optoelectronics.
Figure 6. a) The transfer characteristics of OMPTs based on an individual
Me-ABT microribbon in the dark and under white light irradiation with a low
power of 30 mW cmꢀ2. b) Responsivity (R) and photocurrent/dark-current
ratio (P) versus VGS behavior for the OMPT.
4. Experimental
Instrumentation: Elemental analyses were obtained with a Carlo Erba
model 1160 elemental analyzer. Mass spectra were obtained on a
Micromass GCT-MS spectrometer. The 1H NMR spectra were measured
on a Bruker DMX-300 NMR spectrometer using tetramethylsilane as an
internal standard. The photoluminescence (PL) and absorption spectra
were measured on an F-4500 fluorescence spectrophotometer and a
U-3010 UV-vis spectrophotometer, respectively. Cyclic voltammetric
measurements were carried out on a computer-controlled CHI660C
instrument at room temperature with CH2Cl2 as solvent, 0.1 M Bu4NPF4 as
a supporting electrode, and Ag/AgCl electrode as a referring electrode. TGA
was performed on a TA SDT 2960 thermogravimeter under a dry nitrogen
gas flow at a heating rate of 10 8C minꢀ1. The XRD of thin films was
obtained in the reflection mode at 40 kV and 200 mA with Cu Ka radiation
using a 2 kW Rigaku X-ray diffractometer. Fluorescence microscopy was
performed on an Olympus IX 71. An SEM image was measured on a
Hitachi S-4300 field emission scanning electron microscope. The
fluorescence decay was measured by the Edinburgh Analytical
Instruments-FLS920. TEM images were obtained on a Hitachi H-800
transmission electron microscope. AFM images were determined with a
Nanoscope IIIa AFM (Digital Instruments) in tapping mode.
Device Preparation and Characterization: The thin film transistors were
fabricated with a top contact configuration. The substrate, gate electrode,
insulator and its modified layer are all the same as for OMPT using OTS-
treated SiO2/Si substrate with a heavily N-doped Si gate electrode. The Me-
ABT thin films were thermally evaporated under a vacuum pressure of
2 ꢂ 10ꢀ4 Pa. Shadow masks with a length of 50 mm and a width of 3 mm
were used to deposit the gold source–drain (S–D) electrodes. The electrical
characteristics of the devices were measured with a Keithley 4200 SCS
semiconductor parameter analyzer under ambient conditions at room
temperature.
pentacene or tetracene.[10] Although the exact mechanism for the
highly sensitive phenomenon of our devices is not precisely
understood, we propose a possible mechanism and analyze it
based on the following two aspects. First, the intrinsic property of
the Me-ABT is the main factor, i.e., the moderate quantum yield
of 0.34, that determines the exciton-yield quality and numbers
under the same conditions (i.e., with same light power and
wavelength).[2f] Second, the life-time of excitons demonstrate
excitons with enough time to be separated into free charges by the
vertical VGS and the parallel VDS, which is an important factor to
improve the performance of OPTs.[10] The fluorescence decay of
the Me-ABT microribbons was measured by an Edinburgh
Analytical Instruments-FLS920 and the life-time of excitons was
between 0.7 and 5 ns (see Fig. S7), which is higher than that of
pentacene (ꢁ1 ps) and tetracene (ꢁ0.2 ns).[10]
The high-quality microstructure has less disorder and grain
boundariesthanthethinfilms.Correspondingly,theOMPTscould
showhigher carriermobilityandhigherlightsensitivity than those
of the thin films.[2a,2i] For this phenomenon, we performed an
analysis based on Me-ABT. Different condensed states of Me-ABT
such as a thin-film and a microribbon own different degrees of
ordered molecular packing. The XRD data shows more ordered
molecular packing in microribbons than thin film ones, which
may demonstrate the higher mobility of the microribbons.[2]
Meanwhile, high ordered molecular packing has also provided a
higher velocity conducting-channel for the separated charges.
Furthermore, the exciton dissociation in a disordered thin film is
inefficient because of recombination at the disordered area and
dissipation.[2a] Therefore, for OPTs with the same organic
semiconductor material, the higher ordered condensed states
Synthetic Procedures of the Compounds: Here we only list the 1H NMR of
the main products.
1) 2-(3-Methyl-2-carboxybenzoyl)dibenzothiophene (1): A suspension
of 4-methyl-phthalic anhydride (1.7 g, 10.5 mmol) in 20 mL of dichloro-
methane was added to a solution of aluminum chloride (4 g) in
dichloromethane (100 mL). After the addition was complete, the reaction
mixture was stirred for 30 min, and then dibenzothiophene (2 g, 11 mmol)
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was added dropwise into the reaction mixture under cooling with ice. The
reaction mixture was stirred for 4 h at room temperature, and then was
poured into a solution of water (100 mL) and concentrated hydrochloric
acid (40 mL). The organic layers were separated and dried. The solvents
were removed under a reduced pressure. The product was purified by
recrystallization from ethanol to provide an orange solid (2.9 g, 80%). 1H
NMR (400 MHz, CDCl3, d): 2.34 (s, 3H), 7.50–7.52 (m, 2H), 7.67–7.71
(m, 2H), 7.87 (s, 1H), 7.98–8.02 (m, 2H), 8.08 (s, 1H), 8.27 (s, 1H), 8.55
(s, 1H), 11.55 (s, 1H). EIMS (m/z): 346 (Mþ) (Calcd. for C21H14O3S:
346.1).
2) 6-Methyl-9,10-dione-anthra[2,3-b]benzo[d]thiophene (2): To 20 mL of
dry 1,2-dichlorobenzene was added compound 1 (2 g, 5.8 mmol) and PCl5
(1.8 g, 8.6 mmol), and AlCl3 (1.15 g, 8.6 mmol). After the reaction mixture
was heated at 140 8C for 12 h, the solution was cooled to room
temperature. The solvents were removed under a reduced pressure. The
crude product was purified by column chromatography on silica gel using
toluene as eluent to give a yellow green solid (1.3 g, 68.6%). 1H NMR
(400 MHz, CDCl3, d): 2.34 (s, 3H), 7.50–7.52 (m, 3H), 7.59 (s, 1H), 7.76
(s, 1H), 7.98 (m, 1H), 8.35–8.40 (m, 3H). EIMS: (m/z): 328 (Mþ) (Calcd.
for C21H12O2S: 328.1).
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tetrahydrofuran (100 mL) was added compound 2 (1 g, 3 mmol under a
nitrogen atmosphere). The mixture was maintained for 1 h at 0 8C and then
was stirred at 100 8C for another 12 h. After HCl (6 M, 50 mL) was slowly
added under cooling with ice, the reaction mixture was stirred at room
temperature for 30 min. The residue was filtered, washed with water,
ethanol, and hexane, and further recrystallized from tetrahydrofuran,
to afford 0.447 g (49.2%) of Me-ABT as a yellow solid. 1H NMR
(400 MHz, CDCl3, d): 2.5–2.6 (s, 3H), 7.30–7.33 (d, 1H), 7.45–7.52
(m, 2H), 7.78–7.79 (m, 2H), 7.93–7.95 (m, 1H), 8.27–8.28 (m, 1H), 8.40
(s, 1H), 8.45 (s, 1H), 8.54 (s, 1H), 8.76 (s, 1H). EIMS: (m/z): 298 (Mþ)
(Calcd. for C21H14S: 298.1). Anal. calcd for C21H14S: C 84.53, H 4.73; found:
C 84.62, H 4.99.
¨
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Acknowledgements
Financial support from the National Natural Science Foundation of China
(20825208, 60736004, 20721061, 60911130231), the National Major State
Basic Research Development Program (2006CB806203, 2006CB932103,
2009CB623603), and the Chinese Academy of Sciences is kindly
acknowledged. Supporting Information is available online from Wiley
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Received: September 4, 2009
Revised: December 8, 2009
Published online: March 1, 2010
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