6H-Pyrrolo[3,2-b:4,5-b′]bis[1,4]benzothiazines: Facilely synthesized semiconductors for organic field-effect transistors

Article abstract of DOI:10.1039/b809486a

6H-Pyrrolo[3,2-b:4,5-b′]bis[1,4]benzothiazine (PBBTZ, 1) and its two 6-substituted derivatives (2 and 3) were conveniently synthesized. Their optical properties were studied by UV-vis and fluorescence spectroscopy, and electrochemical properties were inve

Full text of DOI:10.1039/b809486a

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
6H-Pyrrolo[3,2-b:4,5-b0]bis[1,4]benzothiazines: facilely synthesized
semiconductors for organic field-effect transistors†
b
b
a
b
Wei Hong,a Zhongming Wei,bc Hongxia Xi,bc Wei Xu, Wenping Hu, Quanrui Wang and Daoben Zhu
*
*
*
Received 4th June 2008, Accepted 6th August 2008
First published as an Advance Article on the web 5th September 2008
DOI: 10.1039/b809486a
6H-Pyrrolo[3,2-b:4,5-b0]bis[1,4]benzothiazine (PBBTZ, 1) and its two 6-substituted derivatives (2 and
3) were conveniently synthesized. Their optical properties were studied by UV-vis and fluorescence
spectroscopy, and electrochemical properties were investigated by cyclic voltammetry (CV). Good
thermal stability was observed by thermogravimetric analysis. X-Ray analysis revealed a coplanar
structure and a column stacking in the single crystal of compound 1. OFET measurements showed that
1–3 were p-type semiconductors. The performance of these devices displayed good reproducibility at
ambient conditions. When devices containing 1 were fabricated on OTS-treated SiO2/Si substrates at
60 ꢀC, the best performance was achieved with the average hole mobility as high as 0.34 cm2 Vꢁ1 sꢁ1 and
the on/off ratio about 106–107. This performance resulted from the well-ordered molecular packing as
revealed by XRD and AFM analysis.
Introduction
Over the past decade, organic field-effect transistors (OFETs)
have attracted considerable interest, for their potential applica-
tions in low-cost integrated circuits and flexible electronics.1–6
With regards to these advantages of OFETs, the performances of
many molecules, such as mobility, on/off ratio, stability and
Scheme 1 Synthesis of 6-substituted PBBTZ (1–3).
processability, have surpassed those of amorphous hydrogenated
silicon. So far, one of the best performing p-type OFET materials
is pentacene, with mobility higher than 1.0 cm2 Vꢁ1 sꢁ1 and on/off
oligomers and their electrical properties in FET. For compound
1, the highest mobility up to 0.34 cm2 Vꢁ1 sꢁ1 and the on/off ratio
about 106–107 have been obtained. These results suggest that
PBBTZ systems, as good prototypes for organic semiconductors,
should be promising candidates for OFETs.
ratio above 106.7–9 However, pentacene has several disadvantages
such as oxidative instability in ambient conditions due to
photo-induced decomposition to endoperoxide adducts, and
extremely poor solubility in most ordinary solvents.10–13 Several
pentacene analogues were synthesized aimed at improving the
stability, and these high-performance materials were mostly
based on linear conjugated structures, such as oligoacenes,14–17
oligothiophenes5,18–20 or selenophenes,21,22 and N-heterocyclic
oligomers.23–25
PBBTZ system was first synthesized by Dimroth and Reich-
eneder in 1969.26 In that communication, a condensation method
between 2-aminothiophenol and N-phenyldichloromaleimide in
refluxing acetic acid was concisely described, and 6-phenyl-6H-
pyrrolo[3,2-b:4,5-b0]bis[1,4]benzothiazine (2) was obtained. In
1974, compound 2 was synthesized via another route by Kaul.27
Although it has been known for almost forty years, studies on
the PBBTZ system are still very limited. No more derivatives
have been reported, nor have FET properties been investigated
yet. Our choice of such structures was based on several reasons.
Firstly, we realized that PBBTZ possessed a rigid, linear,
coplanar conjugated structure similar to pentacene, yet no unit
capable of a Diels–Alder reaction occurs in these molecules.
Then, PBBTZ could possess a diverse library of derivatives with
functionalities at the central pyrrole N atom. That may be
helpful for improving the solubility, or possibly enhancing the
FET performance. Furthermore, we reckoned that it could be an
effective way to overcome the chemical instability of the high
poly(acene)s by employing sulfur and nitrogen atoms. Taking
compound 1 as an example, presumably intermolecular sulfur–
sulfur interactions, and H-bonds between thiazine nitrogens and
pyrrole hydrogens would help to form an ordered packing
structure.
Herein, we fabricated organic thin film transistors with high
performance based on facilely synthesized 6H-pyrrolo[3,2-b:4,5-
b0]bis[1,4]benzothiazine and its 6-substituted derivatives (PBBTZ
1–3, see Scheme 1). To the best of our awareness, this contri-
bution represents the first investigation of these thiazine
aDepartment of Chemistry, Fudan University, 200433 Shanghai, P. R.
China. E-mail: qrwang@fudan.edu.cn.; Fax: +86 21 65641740; Tel: +86
21 65648139
bBeijing National Laboratory for Molecular Science, CAS Key Laboratory
of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences,
Beijing, 100190, P. R. China. E-mail: zhudb@iccas.ac.cn; wxu@iccas.ac.
cn; Fax: +86 10 62569349; Tel: +86 10 62639355
cGraduate School of Chinese Academy of Sciences, Beijing, 100039, P. R.
China
† Electronic supplementary information (ESI) available: X-Ray
diffraction patterns of the thin film of 2 and 3. CCDC reference
number 690390 (1). For ESI and crystallographic data in CIF or other
electronic format see DOI: 10.1039/b809486a
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Results and discussion
Synthesis
PBBTZ 1 and its derivatives 2–3 have been synthesized by facile
one-step condensation following Dimroth’s method.26 Scheme 1
illustrates the synthesis route. In all cases, satisfactory yields
(66–83%) were obtained. The starting material 2-aminothiophenol
was readily available. More attractively, the N-functionalized
2,3-dichloromaleimides were either commercially available
or easily prepared through standard reactions between
2,3-dichloromaleic anhydride and amines.28–30 Our synthesis
route also led to easy separation of the product. Compounds 1
and 2 were almost insoluble in the reaction system, and could be
separated by simple filtration. Also, analytically pure compound
3 was obtained by column chromatography using dichloro-
methane as eluent. The target compounds were characterized by
NMR, FT-IR, mass spectrometry (MS), and elemental analysis.
The single crystal structure of 1 was determined by X-ray
diffraction. The optical band gap, ionization potential, and
thermal properties of PBBTZ derivatives were investigated by
UV-Vis spectroscopy, cyclic voltammetry (CV) and thermal
gravimetric analysis (TGA), and were compared with those
of pentacene and some analogues. Finally, the field-effect
performances and thin film morphologies of these compounds
were examined.
Physical properties
All the target compounds appear as orange solids and are soluble
in protonic solvents, such as H2SO4–H2O and CF3CO2H. 1 is
slightly soluble in THF, hot DMF and DMSO, whereas 2 and 3
are very soluble in CH2Cl2. The solids and solutions are stable in
air and resist oxidation, in contrast to solutions of pentacene
which are known to deteriorated in a few minutes.11,12
Fig. 1 Normalized UV-vis absorption spectra of 1–3 in CH2Cl2 solution
(a) and thin film (b). Thin films of 2 and 3 about 50 nm thick were
fabricated by vacuum-deposition methods on quartz substrates at
room temperature. (c) Normalized fluorescence emission spectra of 1–3
recorded in CH2Cl2 solution at room temperature.
The normalized UV-vis absorption spectra of dilute CH2Cl2
solutions and thin films of the PBBTZ samples are shown in
Fig. 1(a) and (b). The main absorption peaks in solution are
summarized in Table 1. The band at 240–260 nm can be assigned
to the electronic transition of the phenyl ring. The fact that
1 exhibits a lower lmax than 2 and 3 at the B-band could be
explained by the decrease in p-conjugation which comes from
intermolecular H-bonds. The absorption peaks at 450–490 nm,
as expected, are typical of fully linear p-conjugation compounds.
Compared with those in the solution, the absorption peaks of 1–3
in the thin film broadened and exhibited a minor red-shift of
10–30 nm, which suggested enhanced intermolecular interaction
in the film states. Optical band gaps of 1–3 could be estimated
from the absorption edges of the solution spectra31 at about
2.41 eV, 2.44 eV, and 2.45 eV, respectively. The values obtained
from the absorption edges of their thin film spectra were about
2.25 eV, larger than that of pentacene (1.77 eV), indicating higher
photostability.
The dilute non-protonic solutions of 1–3 exhibit strong yellow-
green fluorescence. The normalized emission spectra of them in
CH2Cl2 are shown in Fig. 1(c). These spectra were virtually
identical, consisting of a maximum emission at 502–504 nm and
Table 1 Physical properties of the PBBTZ derivatives 1–3
lmaxabs/nma
Energy level
Compound
Peak 1
Peak 2
Peak 3
Tdec/ꢀC
Egopt/Va
Eoxonset/V
HOMO/eV
LUMO/eV
1
2
3
240
260
258
457
454
454
488
485
485
386
324
310
2.41
2.44
2.45
1.04
0.95
0.88
ꢁ5.44
ꢁ5.35
ꢁ5.28
ꢁ3.03
ꢁ2.91
ꢁ2.83
a
Solution sample in CH2Cl2.
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310 ꢀC, respectively, while pentacene decomposed at nearly
330 ꢀC. These results demonstrated that the PBBTZ system is
thermally stable. However, substitution at the pyrrole N atom
would decrease the decomposition temperature.
X-Ray single-crystal analysis
Orange needle-shaped single crystals of 1 were obtained by slow
vacuum sublimation in a temperature-gradient furnace. X-Ray
single-crystal analysis revealed the exact packing structure of the
planar 1 molecule (Fig. 4a). 1 forms a monoclinic unit cell and
belongs to the P21/n space group with the unit cell paraꢀmeters
˚
˚
˚
a ¼ 4.7896 A, b ¼ 23.3891 A, c ¼ 11.4926 A, a ¼ 90 , b ¼
97.347ꢀ, g ¼ 90ꢀ. Fig. 4b and c show the stacking pattern of
molecule 1 in the crystal. It can be seen that the molecules were
linked to adjacent ones (symm: ꢁx + 1, ꢁy + 2, ꢁz + 1) through
intermolecular hydrogen bonds (N–H/N, C–H/N) to form
dimers. These dimers packed into columns along the a-axis
direction. Intermolecular p–p interactions could be observed in
Fig. 2 Cyclic voltammograms of 1–3 in 0.1 M (n-Bu)4NClO4 in CH2Cl2,
scan rate 50 mv sꢁ1
.
a shoulder at 533–535 nm, which indicated that 6-substituted
groups had little influence on the excited-state energies of the
PBBTZ system.
˚
the column with an inter-plane distance of about 3.401 A. These
The cyclic voltammetry (CV) measurement of 1–3 was carried
out in CH2Cl2 using an Ag/AgCl reference electrode. As shown
in Fig. 2, 1 and 2 showed two oxidation waves (reversible or half-
reversible), while 3 had only one reversible oxidation wave. The
first oxidation potentials of PBBTZ derivatives were 0.88–1.04 V,
much higher than those of pentacene (0.28 V) and tetracene
(0.52 V),32 indicating the good stability of the PBBTZ radicals.
The experiments were calibrated with the ferrocene/ferrocenium
(Fc/Fc+) redox system, the HOMO levels of 1–3 were determined
by EHOMO ¼ ꢁ[4.8 ꢁ EFOC + Eoxonset] eV z ꢁ[4.4 + Eoxonset] eV
according to the literature.31 The onset oxidation potential of
1 was 1.04 V and therefore the HOMO level of 1 was estimated to
be ꢁ5.44 eV. Comparably, the estimated HOMO level of 2 was
about ꢁ5.35 eV, and that of 3 was about ꢁ5.28 eV. The low-lying
HOMO levels accounted for the high oxidation stability of 1–3.
The HOMO levels also match well with the workfunction of
metallic gold (ꢁ5.2 eV),33 which could enhance the hole charge
injection between the electrode and semiconductor, and thus
improve the device performance. According to the HOMO level
and the HOMO–LUMO gap obtained from the absorption edge
in the UV-vis spectra, the LUMO levels of 1–3 were estimated to
be ꢁ3.03 eV, ꢁ2.91 eV and ꢁ2.83 eV.
columns were linked through S/S non-bonding interactions to
form layer structures within the a–c plane.
X-Ray diffraction
To investigate the crystallinity and preferred orientations of the
molecules 1–3, the X-ray diffraction (XRD) of the thin films
deposited on OTS/SiO2/Si (octadecyltrichlorosilane treated
SiO2/Si) substrate at various temperatures (Tsub) was performed.
A series of sharply resolved peaks assignable to multiple (00l)
reflections suggest that 1 formed a highly crystalline layer
structure in thin films (see Fig. 5). These diffraction peaks are
different from that of the simulated powder diffraction pattern
The thermal properties of 1–3 were investigated by thermog-
ravimetric analysis (TGA, see Fig. 3). The thermal decomposi-
tion temperatures of 1–3 observed were about 386 ꢀC, 324 ꢀC and
Fig. 4 X-Ray crystal structure of compound 1: (a) molecular structure
of 1 with 50% probability ellipsoids; (b) column stacking of 1 view along
the a-axis; (c) face to face stacking of 1 in the crystal.
Fig. 3 TGA plots of 1–3 with a heating rate of 10 ꢀC minꢁ1 under N2.
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Fig. 5 X-Ray diffraction patterns of the thin film of 1 deposited on
OTS/SiO2/Si substrate at various substrate temperatures (Tsub).
according to the single crystal structure of compound 1,
indicating a different stacking pattern in the thin films. The first
stronger peak at 6.02ꢀ refers to a d-spacing of 1.47 nm. This value
is close to that of the molecular length along its long axis
(1.33 nm). Considering the intermolecular van der Waals
distances, molecules of 1 must be packed almost perpendicular
on the substrate. It can be observed that the intensity of the
diffractions increased with increasing substrate temperature,
indicating an increase of the crystallinity of the thin films. Thin
films of compound 2 displayed several weak diffraction peaks,
which showed a multicrystal character of these films (see ESI†).
For compound 3, diffraction peaks could only be observed for
Fig. 6 AFM images (5 ꢂ 5 mm) of 50 nm thick films of 1–3, deposited on
OTS/SiO2/Si substrates: (a) 1, Tsub ¼ 20 ꢀC; (b) 1, Tsub ¼ 60 ꢀC; (c) 1, Tsub
¼ 100 ꢀC; (d) 2, Tsub ¼ 20 ꢀC; (e) 2, Tsub ¼ 60 ꢀC; (f) 2, Tsub ¼ 100 ꢀC; (g)
3, Tsub ¼ 20 ꢀC; (h) 3, Tsub ¼ 60 ꢀC; (i) 3, Tsub ¼ 100 ꢀC.
FET characteristics
Thin-film transistors of PBBTZ 1–3 were fabricated on OTS/
SiO2/Si substrates in a top-contact configuration using Au as
source and drain electrodes. The results at different temperatures
are listed in Table 2. All these compounds performed as
p-channel semiconductors. The mobility of devices was deter-
ꢀ
the films deposited at 60 C as a serials of (00l) reflections. The
first strong peak at 3.94ꢀ showed a d-spacing of 2.24 nm
(see ESI†). This value is larger than the molecular size of
compound 3. So, the molecular stacking of 3 in the thin film
could not be derived from its diffraction data.
mined in the saturation regime using the equation IDS
¼
mCi(VG ꢁ VT)2 W/2L, where IDS is the drain–source current, m is
the field-effect mobility, Ci is the capacitance of the gate dielectric
per unit area (7.5 nF cmꢁ2), W is the channel width, L is the
channel length, and VT is the threshold voltage.
Film morphology
It is generally recognized that the performances of FET devices
strongly depend upon their thin-film morphology. 50 nm thick
films of 1–3 deposited on OTS-treated SiO2/Si substrates at
various substrate temperatures were investigated by atomic force
microscopy (AFM) (see Fig. 6). All the films were fabricated by
the vacuum-deposition method. When the substrate temperature
was at room temperature (20 ꢀC), the film of 1 was smooth with
some small grains with an average diameter of about 100 nm.
When the substrate temperature was 60 ꢀC, larger and inter-
connected crystal grains with an length exceeding 1 mm were
observed and the film became very ordered. When the substrate
temperature increased to 100 ꢀC, the grains became much larger
and varied in shape for the film. However, film discontinuity and
large gaps increased as well. For the films of 2 and 3, the trend of
film morphology was similar and corresponded to their FET
characteristics, too. High quality of the film may be beneficial for
the elimination of the disordering effect and hence provide high
mobility. As the substrate temperature was increased to 100 ꢀC,
the film of 3 became cracked and lamellar crystalline grains were
observed, which led to contact problems and the vanishing of the
field effect.
It can be seen from Table 2 that FET performances largely
depend on the substrate temperature. The mobility was rather
low at room temperature (20 ꢀC). Higher deposition tempera-
tures greatly enhanced the mobility and on/off ratio, especially
for compound 1. The best performances of all devices were
Table 2 OFET characteristics of compounds 1–3 deposited on OTS/
SiO2/Si at different substrate temperatures. The mobilities were the
average values of 7 typical devices
Mobility/
cm2 Vꢁ1 sꢁ1
Ion/Ioff
ratio
Threshold
voltage/V
Compound
Tsub/ꢀC
1
20
60
100
20
60
100
20
8.48 ꢂ 10ꢁ4
0.34
103–104
ꢁ11.9 ꢃ 2.5
ꢁ28.0 ꢃ 5.7
ꢁ26.0 ꢃ 3.2
ꢁ39.8 ꢃ 5.0
ꢁ16.8 ꢃ 4.8
ꢁ27.7 ꢃ 5.3
ꢁ16.2 ꢃ 3.6
ꢁ13.6 ꢃ 5.1
106–107
0.068
106–107
2
3
8.65 ꢂ 10ꢁ5
1.77 ꢂ 10ꢁ4
8.17 ꢂ 10ꢁ5
6.88 ꢂ 10ꢁ4
3.01 ꢂ 10ꢁ3
No field effect
1–5 ꢂ 104
104–105
1–2 ꢂ 104
104–105
60
100
1–5 ꢂ 105
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106–107, as shown in Fig. 8. All the results indicate that
6-H PBBTZ 1 is a high-performance stable p-type organic
semiconductor.
Experimental
Instrumentation
1H-NMR (400 MHz) and 13C-NMR (100 MHz) spectra were
obtained on a Bruker DMX-400 NMR spectrometer at room
temperature. EI mass spectra were collected on a GCI-MS
micromass UK spectometer. IR spectra were recorded on
a Tensor 27 FT-IR spectrometer. UV-vis spectra were recorded
on a Hitachi U-3010 spectrophotometer. Thermal gravimetric
analysis of these molecules was condꢀucted on a TA Instruments
DTG60 TGA. A heating rate of 10 C minꢁ1 under flowing N2
was used with runs being conducted from room temperature to
high temperature. Cyclic voltammetric measurements were
recorded on a CHI660C voltammetric analyzer (CH Instru-
ments, USA). They were carried out in a conventional three-
electrode cell using Pt button working electrodes of 2 mm
diameter, a platinum wire counter electrode, and a Ag/AgCl
reference electrode at room temperature. Conditions: 0.1 M
(n-Bu)4ClO4 in dichloromethane. X-Ray diffraction measure-
ments of thin films were performed in reflection mode at 40 kV
and 200 mA with Cu Ka radiation using a 2 kW Rigaku X-ray
diffractometer. Atomic force microscopy (AFM) images of the
organic thin films were obtained on a Nanoscope IIIa AFM
(Digital Instruments) operating in tapping mode.
Fig. 7 The typical output (a) and transfer (b) (VD ¼ 100 V) character-
istics of FET devices of 1 on OTS-treated SiO2/Si substrate (Tsub
60 ꢀC).
¼
reached at 60 ꢀC. For the FET device based on 1, an average
mobility of 0.34 cm2 Vꢁ1 sꢁ1 and an on/off ratio up to 106–107 were
achieved, which were higher than those of the devices based on 2
and 3. Compared with compound 1, the substituents of phenyl
and alkyl groups might retard the efficient p–p interactions,
resulting in decreased charge transport properties. Fig. 7 shows
the typical output and transfer characteristics of the device based
on 1 at 60 ꢀC. However, when the substrate temperature was
further enhanced to 100 ꢀC, the mobility of the devices of 1 and 2
decreased again. Compared with the mobility of most pentacene
analogues at high temperature,1 the value obtained from 1 was
still promising. No field effect was found at 100 ꢀC for the device
of 3, possibly because of the discontinuity of the thin film.
During a period of 8 weeks storage in a desiccator, the mobility
of the device of 1 deposited at 60 ꢀC changed very slightly,
with the corresponding on/off ratio maintained on the order of
The single crystals of 1 were obtained by vacuum sublimation.
X-Ray crystallographic data were collected with a Bruker Smart
CCD diffractometer, using graphite-monochromated Mo Ka
˚
radiation (l ¼ 0.71073 A). The data were collected at 113 K and
the structure was resolved by the direct method and refined by
full-matrix least-squares on F2. The computation was performed
with the SHELXL-97 program.34 All non-hydrogen atoms were
refined anisotropically.
Material synthesis and characterization
Chemicals were purchased from Alfa Aesar, Fluka and used as
received. Solvents and other common reagents were obtained
from the Beijing Chemical Plant and purified as usual.
N-substituted 2,3-dichloromaleimides were synthesized conve-
niently from 2,3-dichloromaleic anhydride according to the
literature.28–30
6H-Pyrrolo[3,2-b:4,5-b0]bis[1,4]benzothiazine (1) was produced
as follows. A mixture of 2-aminothiophenol (1.002 g, 8 mmol)
and 2,3-dichloromaleimide (0.664 g, 4 mmol) was dissolved in
24 mL of acetic acid. The reaction mixture was refluxed under
nitrogen atmosphere for 6 h. The dark precipitate from the reac-
tion mixture was collected. The crude product was washed several
times with methanol, acetone and THF. 1 was obtained as an
orange powder in a yield of 83% (1.02 g). An analytical sample was
prepared by vacuum sublimation as fresh orange needles. Anal.
calcd for: C16H9N3S2: C 62.52, H 2.95, N 13.67, S 20.86; found:
1
C 62.43, H 2.97, N 13.55, S 20.97%. MS (EI+) 307. H-NMR
(CF3CO2D): d (ppm) 7.90–7.92 (m, 2H, Ar–H), 7.86–7.88 (m, 2H,
Ar–H), 7.77–7.82 (m, 4H, Ar–H), 1.50 (s, 1H, N–H). IR (KBr disc,
cmꢁ1): 3446, 2947, 2772, 1632, 1572, 1360, 1122, 753.
Fig. 8 Mobility and on/off ratio for a FET device based on 1 tested over
a period of eight weeks.
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Compound 2 was prepared as described above for compound
1, from 2-aminothiophenol (1.252 g, 10 mmol) and N-phenyl-
2,3-dichloromaleimide (1.210 g, 5 mmol). Yield: 1.42 g, 74%.
An analytical sample was prepared by vacuum sublimation as
fresh orange powder. Anal. calcd for: C22H13N3S2: C 68.90, H
3.42, N 10.96; found: C 68.97, H 3.49, N 10.92%. MS (EI+) 383.
1H-NMR (CF3CO2D): d (ppm) 7.88–7.92 (m, 1H), 7.81–7.85
(m, 2H), 7.69–7.73 (m, 4H), 7.54–7.62 (m, 6H). IR (KBr disc,
cmꢁ1): 3442, 3050, 1610, 1500, 1457, 1435, 1408, 1130, 949,
752, 687.
including optical, electrochemical, electrical and thermal
properties were studied in detail and good thermal stability was
observed. The crystal structure of 1 was investigated by X-ray
single-crystal diffraction analysis and a sandwich-herringbone
arrangement in the single crystal was found. FET devices based
on 1–3 were successfully fabricated and they all performed as
p-type semiconductors. The best performance was recorded
when the devices based on 1 was fabricated on OTS-treated
SiO2/Si substrates at 60 ꢀC, with the average hole mobility up to
0.34 cm2 Vꢁ1 sꢁ1 and the on/off ratio about 106–107. The devices
showed good stability in terms of mobility and on/off ratio for
several weeks. The well-ordered molecular packing mode may
account for this good performance.
Compound 3 was prepared as described above for compound
1, from 2-aminothiophenol (1.252 g, 10 mmol) and N-octyl-2,3-
dichloromaleimide (1.391 g, 5 mmol). The residue was purified
by column chromatography on silica gel (CH2Cl2) to afford
1.38 g (66% yield) of 3 as fine orange needles. Anal. calcd for:
C24H25N3S2: C 68.70, H 6.01, N 10.01; found: C 68.28, H 5.91, N
9.98%. MS (EI+) 419. HRMS (EI+): calcd for: C24H25N3S2
419.1490, found 419.1492. 1H-NMR (CDCl3): d (ppm) 7.48–7.50
(m, 2H, Ar–H), 7.22–7.25 (m, 4H, Ar–H), 7.08–7.12 (m, 2H, Ar–H),
4.13–4.16 (t, J ¼ 7.2 Hz, 2H, N–CH2), 1.80–1.84 (m, 2H, CH2),
1.35–1.39 (m, 4H, 2CH2), 1.28–1.30 (m, 6H, 3CH2), 0.85–0.89
(t, J ¼ 6.6 Hz, 3H, CH3). 13C-NMR (CDCl3): d (ppm) 150.53,
140.88, 130.25, 127.48, 126.03, 125.42, 118.41, 109.62, 40.28,
32.05, 29.37, 29.35, 28.69, 26.87, 22.82, 14.25. IR (KBr disc, cmꢁ1):
3447, 2918, 2850, 1609, 1568, 1459, 1369, 1093, 756.
N-Octyl-2,3-dichloromaleimide was prepared from 2,3-
dichloromaleic anhydride and n-octylamine according to the
same method for preparing the known compound N-octyl-
maleimide30 and purified by flash chromatography on silica gel
(EtOAc and petroleum ether, 1 : 5). Mp 44–46 ꢀC, MS (EI+) 241,
1H-NMR (CDCl3): d (ppm) 3.57–3.60 (t, J ¼ 7.1 Hz, 2H,
N–CH2), 1.59–1.61 (m, 2H, CH2), 1.26–1.28 (m, 10H, 5CH2),
0.86–0.89 (t, J ¼ 6.5 Hz, 3H, CH3). IR (KBr disc, cmꢁ1): 3495,
2975, 2916, 1730, 1626, 1465, 1375, 1195, 1062, 1005, 937, 880,
732, 633.
Acknowledgements
We thank the National Natural Science Foundation of China
(Grants 20572113, 20632020, 20721061), State Key Basic
Research Program (2006CB806201) and Chinese Academy of
Sciences for financial support.
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ꢁ1
ꢁ1
˚
˚
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Conclusions
In conclusion, we have demonstrated a facile synthesis of three
6-subsituted PBBTZ compounds 1–3. Their physical properties
This journal is ª The Royal Society of Chemistry 2008
J. Mater. Chem., 2008, 18, 4814–4820 | 4819

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This journal is ª The Royal Society of Chemistry 2008