Synthesis and properties of a benzo[1,2-b:4,5-b′]dithiophene core π-system that bears alkyl, alkylthio and alkoxy groups at 3,7-positions

Article abstract of DOI:10.1039/c3ra41822g

A synthetic sequence was developed to provide 3,7-didodecylbenzo[1,2-b:4,5- b′]dithiophene and its dialkylthio and dialkoxy analogues as planar and soluble building-blocks for constructing benzodithiophene-based π-systems. The benzodithiophenes were also

Full text of DOI:10.1039/c3ra41822g

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Synthesis and properties of a benzo[1,2-b:4,5-
b9]dithiophene core p-system that bears alkyl, alkylthio
and alkoxy groups at 3,7-positions3
Cite this: RSC Advances, 2013, 3,
12356
Shinya Ota,a Sojiro Minami,a Koji Hirano,a Tetsuya Satoh,a Yutaka Ie,b Shu Seki,*a
Yoshio Asob and Masahiro Miura*a
A synthetic sequence was developed to provide 3,7-didodecylbenzo[1,2-b:4,5-b9]dithiophene and its
dialkylthio and dialkoxy analogues as planar and soluble building-blocks for constructing benzodithio-
phene-based p-systems. The benzodithiophenes were also transformed to the corresponding 2,6-di(5-
phenyl-2-thienyl)-capped derivatives as the representative oligomers. Their absorption and emission
spectra as well as CV data showed that the HOMO–LUMO energy gaps of the dialkylthio and dialkoxy
derivatives are smaller than that of the dialkyl one, which is attributable to the lower ELUMO as well as
EHOMO energies of the dialkylthio analogue and the higher EHOMO energy of the dialkoxy analogue,
respectively. The intra- and intermolecular charge-carrier mobilities were then estimated by the flash-
photolysis time-resolved microwave conductivity (FP-TRMC) method and solution-processed top contact
Received 31st January 2013,
Accepted 29th April 2013
FET performance. The TRMC method showed similar high intrinsic hole mobilities (0.16–0.24 cm2 V21 s21
irrespective of the substituents, whereas the dialkyl derivative especially displayed a good field-effect
mobility of 0.023 cm2 V21 s21
)
DOI: 10.1039/c3ra41822g
www.rsc.org/advances
.
devices,1,2 the preparation of 3,7-dialkyl-substituted
benzo[1,2-b:4,5-b9]dithiophene has not been explored.3
Consequently, we recently commenced its synthesis4 by
employing the convenient double ring-closure reaction of
1,4-phenylenediacrylic acid with thionyl chloride as the key
step.5 However, the reaction was found to give rise to an
isomeric benzo[2,1-b:3,4-b9]dithiophene derivative.4b,6 We now
report an unambiguous synthesis of a 3,7-dialkyl benzo[1,2-
b:4,5-b9]dithiophene and its alkylthio and alkoxy analogues
(Fig. 1, 1a–c) involving some palladium-catalyzed key steps.
The benzodithiophenes bearing the aliphatic moieties have
been transformed to their 2,6-di(5-phenyl-2-thienyl)-capped
derivatives 2a–c as representative oligomers as well as partial
models of the corresponding polymers. Then, the photophy-
sical, electrochemical properties and hole mobility of com-
pounds 2a–c have been characterized by absorption and
emission spectrometry, cyclic voltammetry, flash-photolysis
time-resolved microwave conductivity (FP-TRMC),7 and solu-
tion-processed top contact FET performance. The properties
have also been compared with those of the cross-shaped 4,8-
dialkyl isomer 3 reported previously.4a
Introduction
Thiophene-based oligomers and polymers have recently
attracted significant attention as the organic components of
electronic devices including organic field effect transistors
(OFETs), organic light-emitting diodes (OLEDs), and organic
photovoltaics (OPVs).1 They may have good electron-donating
properties due to their relatively low electron affinities. Thus, the
synthesis of thiophene-fused aromatic compounds involving
benzothiophene and thienothiophene skeletons as well as
oligothiophenes moieties as the core frameworks for high
performance p-conjugated systems has been studied extensively.
Benzo[1,2-b:4,5-b9]dithiophene is one of the often incorpo-
rated planar cores in oligomers and polymers.1h,i For increas-
ing solution-processability, two alkyl or alkoxy chains are
usually introduced onto the 4- and 8-positions on the central
benzene ring. Though decorating the 3- and 7-positions with
aliphatic groups appears to be of principal interest as
3-alkylthiophene-based oligomers and polymers often exhibit
remarkable performances in various organic electronic
aDepartment of Applied Chemistry, Faculty of Engineering, Osaka University, Suita,
Osaka 565-0871, Japan. E-mail: seki@chem.eng.osaka-u.ac.jp;
miura@chem.eng.osaka-u.ac.jp
Results and discussion
bThe Institute of Scientific and Industrial Research, Osaka University, 8-1
Mihogaoka, Ibaraki, Osaka 567-0047, Japan
The synthesis of the 3,7-dialkylated benzodithiophene 1a was
started with commercially available 2,5-dibromoterephthalic
Electronic supplementary information (ESI) available: 1H and 13C NMR spectra
3
of compounds. See DOI: 10.1039/c3ra41822g
12356 | RSC Adv., 2013, 3, 12356–12365
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Paper
catalyst system of Pd2(dba)3/dppf/Pri2NEt8 (dba = dibenzylide-
neacetone, dppf = 1,19-bis(diphenylphosphino)ferrocene) and
the successive one-pot treatment with ButOK.5d Then, the
doubly cyclized 3,7-dihydroxy compound 6 with substantial
solubility was transformed to the ditriflate 7. The subsequent
Sonogashira coupling with 1-dodecyne9 followed by catalytic
hydrogenation in the presence of a Pd/C catalyst enabled the
introduction of two dodecyl groups onto the 3- and 7-positions
of the benzodithiophene motif. The removal of ester functions
was achieved by hydrolysis with aqueous KOH and silver-
mediated decarboxylation10 to furnish the desired 3,7-didode-
cylbenzo[1,2-b:4,5-b9]dithiophene 1a. Finally, the regioselective
dibromination with 1,2-dibromo-1,1,2,2-tetrafluoroethane
after treatment of 1a with ButLi11 and the Migita–Kosugi–
Stille coupling with tributyl(5-phenyl-2-thienyl)tin led to 2a in
a good yield. It is noted that in contrast to the reactions of the
alkylthio and alkoxy derivatives 1b and 1c (vide infra), the
bromination of 1a with N-bromosuccinimide (NBS) was not
successful due to the considerable contamination of an
unexpected tribrominated product (confirmed by MS). The
origin for the high reactivity of 1a toward NBS is, however, not
clear.
Fig. 1 Structures of benzo[1,2-b:4,5-b9]dithiophenes bearing alkyl, alkylthio and
alkoxy groups at 3,7-positions 1a–c, their 2,6-di(5-phenyl-2-thienyl)-capped
oligomers 2a–c and 4,8-dialkylated isomer 3.
acid (4) (Scheme 1). The benzo[1,2-b:4,5-b9]dithiophene core
was constructed by the esterification of 4 with butanol to give
the diester 5 followed by the palladium-catalyzed C–S coupling
with 2-ethylhexyl thioglycolate (EH = 2-ethylhexyl) using a
To avoid the hydrogenation step of 8 to 9 using an
autoclave, we also undertook to conduct the direct cross-
coupling of 7 with a dodecylmetal reagent. Before performing
the reaction of 7, we screened a number of reaction conditions
using the benzothiophene monotriflate 12 as
a model
substrate (Scheme 2). It was found that the Negishi cross-
coupling with dodecyl-ZnCl in the presence of a catalyst
system of Pd(OAc)2/RuPhos (Ruphos = dicyclohexylphosphino-
29,69-diisopropyloxybiphenyl)12 afforded the desired alkylated
compound 13 in an almost quantitative yield. The alkylation
reaction of 12 with dodecyl-9-BBN13a and dodecyl-B(OH)2
13b
under reported conditions also gave 13, while the yield was
less than 20% (GC, not shown). Application of the reaction
conditions to the dialkylation of 7 allowed the production of 9
in a good yield.
The alkylthio and alkoxy analogues, 1b/2b and 1c/2c, could
also be prepared with the ditriflate 7 and the dihydroxide 6,
respectively, as depicted in Scheme 3. The reactions of 7 and 6
with dodecanethiol and dodecyl bromide gave the correspond-
ing 3,7-dialkylthio- and 3,7-dialkoxy-benzodithiophene-2,6-
dicarboxylates 14 and 15. The target compounds were
Scheme 1 Synthetic sequence to benzodithiophenes 1a and 2a.
This journal is ß The Royal Society of Chemistry 2013
Scheme 2 Catalytic alkylation of triflates 12 and 7.
RSC Adv., 2013, 3, 12356–12365 | 12357

View Article Online
Paper
RSC Advances
Fig. 2 Absorption (top) and photoluminescence spectra (bottom) (excited at
absorption maximum) of compounds 2a–c and 3 in CHCl3 solutions.
estimated as 0.40, 0.33 and 0.43 eV for 2a, 2b and 2c,
respectively. The values of Stokes shift in solid phases show
similar trends, giving the smallest energy of 0.36 eV in 2b. It
should be noted that a considerable broken symmetry was
observed in the absorption-fluorescence spectrum of 2c solid
film as shown in Fig. 3, suggesting the presence of the
localized exciton states.
The cyclic voltammetric measurement of 2a–c in o-dichlor-
obenzene/MeCN (10 : 1, v/v) displayed two oxidation waves in
each case (Fig. 4), as 3 did.4a The first oxidation potentials of
the alkyl 2a (0.55 V) and the alkylthio 2b (0.62 V) were relatively
close, while that of the alkoxy 2c showed a lower oxidation
potential (0.42 V) (Table 1). The calculated EHOMO and ELUMO
values as listed in Table 1 may suggest that the red-shifts of 2b
and 2c in Fig. 2 are attributable to the considerably lower
Scheme 3 Synthesis of benzodithiophenes 1b, 1c, 2b and 2c.
obtained via a similar sequence to that used for the synthesis
of 1a/2a with the exception of the bromination step: NBS in
acetic acid was found to be an effective reagent for the
dibromination of 1b and 1c, while the reaction of 1c with
BrCF2CF2Br/ButLi gave an excellent yield of 19.
To define the properties of compounds 2a–c, we first
investigated their optical properties in CHCl3 solutions (Fig. 2
and Table 1). While the absorption spectrum of the alkyl
derivative 2a exhibited the major band at labs 397 nm, the
emission one showed two bands centered at lem 455 and 485
nm. These peaks were red-shifted in the alkylthio and alkoxy
compounds 2b and 2c. It should be noted that the previously
reported 4,8-didodecyl compound 3 (Fig. 1) showed a similar
absorption spectrum to those of 2b and 2c rather than to that
of 2a. Somewhat twisted structures at the ends of the isolated
molecule for 2a in the solution, while planar for 3, were
previously suggested by a DFT calculation study.4a These
results may imply that the red-shifts of 2b and 2c may arise
from the relatively effective p-conjugation in combination with
the electronic perturbation based on the insertion of S and O
atoms.1b It should be noted that a considerable red-shift of the
electronic absorption spectrum was observed in the thin solid
film of 2a (Fig. 3 versus Fig. 2), suggesting that the terminal
twisted structures of 2a are well cancelled in the solid phase,
and hence, the planar structure with effective conjugation over
the molecule is realized by inter-molecular packing interac-
tions. Interestingly, the Stokes shifts in solution were
ELUMO of 2b and higher EHOMO of 2c, respectively. Compound 3
4a
also had a relatively higher EHOMO
.
We next carried out the measurement of hole mobility by
flash-photolysis time-resolved microwave conductivity (FP-
TRMC)7 which may provide information about the inherent
charge mobility of a given p-conjugated system. The product of
inherent hole mobility and photo-induced charge separation
yield wSm of 2a obtained by the observation of microwave
conductivity transient upon 355 nm irradiation to its film on a
quartz substrate was similar to those of the alkylthio 2b and
the alkoxy 2c (Fig. 5 and Table 2). The mobility values Sm of
2a–c were then calculated by dividing with w obtained by the
photo-current integration method (Fig. 5b) to be 0.16–0.24 cm2
V21 21, which were somewhat higher than that of the 4,8-
s
dialkyl compound 3. The electronic absorption maxima of 3 at
420 and 443 nm in solution are almost consistent with those of
2b and 2c (Table 1). However the lower energy transition (443–
444 nm, 2.80 eV) in 3 is apparently diminished, suggesting the
12358 | RSC Adv., 2013, 3, 12356–12365
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Paper
Table 1 Absorption and emission wavelengths, HOMO–LUMO energy gaps and cyclic voltammogram data of compounds 2a–c and 3
Compd.
labs (nm)a
lem (nm)b
E0-0 (eV)c
E1/2 (V)d
EHOMO (eV)e
ELUMO (eV)f
ox
2a
2b
2c
3g
397
455/485
469/495
489
2.80
2.69
2.71
2.71
0.55
0.62
0.42
0.48
25.35
25.42
25.22
25.28
22.55
22.73
22.51
22.57
417/444
418/443
420/443(sh)
467/498
a
b
c
Absorption maximum in CHCl3 (5.0 6 1025 M). Emission maximum in CHCl3 (5.0 6 1026 M). Determined from the intersection of the
d
normalized absorption and emission spectra. Performed in o-dichlorobenzene/MeCN (10 : 1, v/v) in the presence of Bu4NPF6. n = 100 mV
s
ELUMO = EHOMO + E0-0
21, versus Fc/Fc+. The approximation for the Fc/Fc+ level is 24.8 eV versus vacuum: EHOMO = 24.8 2 E1/2
.
Estimated from EHOMO and E0-0
:
e
f
ox
g
.
Essentially the same values were observed in CH2Cl2 solution.4a
lower oscillator strength of the transition, and hence, the
lower density of states at HOMO and/or LUMO levels in
compound 3. This is the case giving the slightly lower degree
of positive charge delocalization and local mobility on 3.
Within the compounds 2a–2c, the slightly higher value of
mobility was observed for 2b relative to 2c and 2a. The small
Stokes shift of 2b is supportive of the delocalization of
electron–hole pairs, which may lead to the higher degree of
hole delocalization over the molecular axis of 2b. Furthermore,
the conductivity transient observed for 2b gives a characteristic
kinetic trace with an apparently long lifetime. As summarized
in Table 1, the HOMO energy level of 2b is deep-lying relatively
to those of 2a and 2c, and this is the case giving the higher
stability of holes on 2b.
allow a good performance. The transfer characteristics for the
device are shown in Fig. 6 and the parameters extracted from it
are also listed in Table 2. The mobility (m), on/off current (Ion
/
Ioff) and threshold voltage (Vth) were 0.023 cm2 V21 21, 106
s
and 239 V, respectively. The performance was thus observed
to be superior to that optimized for the 4,8-dialkylated 3.4a
This result suggests that the 3,7-dialkylated 2a is capable of
forming a relatively more arranged layer on the treated SiO2
substrate. This also may imply the importance of the
substituent position for efficient self-assembly via intermole-
cular side-chain alignment.2 However, the FET performance of
the dialkylthio compound 2b (Table 2 and Fig. 6) was lower
than that of 2a (1.1 6 1024 cm2 V21 21) and inducing FET
s
response with the dialkoxy 2c remained unsuccessful.
The top contact FET device based on 2a prepared by the
The AFM images and X-ray diffractograms of the 2a- and
2b-based thin films are shown in Fig. 7 and 8, respectively.
These observations indicate that, while both the compounds
are effectively filmed, the film with 2a is highly ordered,
whereas that with 2b is amorphous. This appears to be one of
the major factors for the difference of the FET responses. The
compound 2c did not form a suitable film on the substrate.
spin-coating technique exhibited
a typical p-type FET
response. Treatment of an SiO2 surface with b-PTS (b-phe-
nethyltrichlorosilane) and annealing at 60 uC were found to
Fig. 3 Absorption (top) and photoluminescence (bottom) (excited at 410 nm)
spectra of thin solid films of compounds 2a–c and 3 on quartz substrates in the
polycrystalline states.
Fig. 4 Cyclic voltammograms of 2a–c and 3 in o-dichlorobenzene/acetonitrile
(10 : 1, v/v) containing 0.1 M Bu4NPF6 at a scan rate of 100 mV s21
.
This journal is ß The Royal Society of Chemistry 2013
RSC Adv., 2013, 3, 12356–12365 | 12359

View Article Online
Paper
RSC Advances
Fig. 5 (a) Microwave conductivity transients of compounds 2a–c upon 355 nm
irradiation at excitation photon density of 4.5 6 1016 photons cm22. (b)
Dependence of accumulated number of photo-generated charge carriers (N)
under a variety of applied bias voltages (E).
Conclusions
We have developed an unambiguous synthetic sequence that
leads to 3,7-didodecylbenzo[1,2-b:4,5-b9]dithiophene (1a) and
its dialkylthio and dialkoxy analogues, 1b and 1c, as planar
and soluble building-blocks for constructing benzodithio-
phene-based extended p-systems. Among the 2,6-di(5-phenyl-
2-thienyl) capped derivatives 2a–2c, the dialkylated 2a espe-
cially showed good hole mobility in both FP-TRMC and FET
measurements. Although the FET performance was lower with
2b and inducing it with 2c was not successful, properly
designed p-systems involving 1b or 1c as a core moiety, e.g.
with the combination of certain acceptors,14 could be expected
to act as effective materials, as they showed similar intrinsic
charge mobilities to that of 2a in the TRMC measurement.
Thus, further applications of these cores to other p-conjugated
poly- and oligothiophene derivatives are now in progress in
our laboratories.
Fig. 6 Transfer characteristics at OFET devices of 2a (top) and 2b (bottom) (VDS
= 260 V).
a high resolution sector type double focusing mass spectro-
meter by EI or FAB ionization mode. Absorption and emission
spectra in solution were recorded on Shimadzu 2500PC and
Shimadzu RF5300PC spectrophotometers, and the spectra of
thin solid films were also recorded by JASCO V-570 and Hitachi
F-2700 spectrophotometers, respectively. CV was carried out
on a BAS CV-620 analyzer. The surface structure of the
deposited organic films was observed by atomic force
microscopy (Shimadzu SPM9600). The synthetic procedures
of materials and methods for FP-TRMC and FET measure-
ments are given below.
Dibutyl 2,5-dibromoterephthalate (5)
Experimental section
A solution of 2,4-dibromoterephthalic acid (4) (5.5 g, 17 mmol)
in BuOH (80 mL) was heated in the presence of H2SO4 (1.2 mL)
at 120 uC for 15 h. After evaporating BuOH (ca. 70 mL) and
neutralizing with aqueous NaHCO3, the product was extracted
with ethyl acetate and the solution was dried over Na2SO4.
After evaporating the solvent, the residue was purified by
column chromatography on silica gel using hexane/ethyl
General
1H and 13C NMR spectra were recorded at 400 MHz and 100
MHz, respectively, for CDCl3 solutions unless otherwise noted.
All chemical shifts are quoted in ppm relative to tetramethyl-
silane. High-resolution mass spectra (HRMS) were obtained on
Table 2 Results of measurements by FP-TRMC and top-contact FET mobilities
FP-TRMC
FETd
Compd.
wSm (cm2 V21 s21
)
wa
Sm (cm2 V21 s21
)
m (cm2 V21 s21
)
Ion/Ioff
Vth (V)
2a
2b
2c
3b
1.1 6 1024
1.5 6 1024
1.0 6 1024
3.0 6 1024
6.7 6 1024
6.1 6 1024
6.3 6 1024
6.2 6 1023c
0.17
0.24
0.16
0.048
0.023e
106
105
—
239
29
—
1.1 6 1024e
—
3.0 6 1024f
105
235
a
b
c
d
Estimated by photo-current integration method. Data taken from ref. 4a. Estimated by time-of-flight (TOF) method (ref. 4a). Channel
width (W) and length (L): W 6 L = 10 mm 6 20 mm. Spin-coated with 0.5 wt% solution in o-dichlorobenzene and annealed at 60 uC for 30
e
f
min. Treated with b-PTS. Bare.
12360 | RSC Adv., 2013, 3, 12356–12365
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Paper
167.3. HR-MS (FAB) calcd for C28H38O6S2 [M+] requires
534.2110, found 534.2131.
Di(2-ethylhexyl) 3,7-
bis(trifluoromethanesulfonyloxy)benzo[1,2-b:4,5-
b9]dithiophene 2,6-carboxylate (7)
In a 100 mL reaction flask were placed the dihydroxide 6 (1.75
g, 3.3 mmol), Tf2O (2.3 mL, 13.4 mmol), Et3N (1.35 g, 13.4
mmol), DMAP (55 mg, 0.45 mmol) and CH2Cl2 (20 mL), and
the resulting mixture was stirred at room temperature for 12 h
under nitrogen. After adding diluted aqueous HCl, the product
was extracted with diethyl ether, dried over Na2SO4, and
purified by column chromatography on silica gel using
hexane/ethyl acetate (98/2, v/v). The ditriflate 7 was obtained
Fig. 7 AFM images of the thin films of 2a (left) and 2b (right).
acetate (97.5/2.5, v/v) to give the diester 5 as a white solid (6.0
g, 14 mmol, 81%). Mp. 51.2–52.0 uC. 1H NMR (400 MHz,
CDCl3) d 0.97 (t, J = 7.3 Hz, 6H), 1.47 (sext, J = 7.3 Hz, 4H), 1.76
1
as a white solid (2.4 g, 3.0 mmol, 90%). Mp. 75.4–76.0 uC. H
NMR (400 MHz, CDCl3) d 0.92 (t, J = 6.9 Hz, 6H), 0.96 (t, J = 7.3
Hz, 6H), 1.25–1.48 (m, 16H), 1.78 (quint, J = 6.4 Hz, 2H), 4.34
(dd, J = 6.0, 14.0 Hz, 2H), 4.36 (dd, J = 6.0, 14.0 Hz, 2H), 8.31 (s,
2H). 13C NMR (100 MHz, CDCl3) d 11.1, 14.1, 23.1, 23.9, 29.0,
30.4, 38.8, 69.3, 116.9, 118.7 (q, J = 320 Hz), 126.4, 131.7, 134.6,
138.4, 159.9. HR-MS (FAB) calcd for C30H36F6O10S4 [M+]
requires 798.1095, found 798.1105.
(quint, J = 6.9 Hz, 4H), 4.35 (t, J = 6.9 Hz, 4H), 8.01 (s, 2H). 13
C
NMR (100 MHz, CDCl3) d 13.8, 19.3, 30.6, 66.4, 120.2, 135.9,
136.6, 164.5. HR-MS (FAB) calcd for C16H20Br2O4 [M+] requires
433.9728, found 433.9730.
Di(2-ethylhexyl) 3,7-bis(hydroxy)benzo[1,2-b:4,5-
b9]dithiophene 2,6-carboxylate (6)
Di(2-ethylhexyl) 3,7-bis(1-dodecynyl)benzo[1,2-b:4,5-
b9]dithiophene-2,6-dicarboxylate (8)
The diester 5 (5.51 g, 12.6 mmol), Pd2(dba)3 (576 mg, 0.63
mmol), dppf (700 mg, 1.26 mmol) and DMF (70 mL) were
placed in a 200 mL two-necked reaction flask. To the solution
The ditriflate 7 (1.4 g, 1.75 mmol), 1-dodecyne (1.05 g, 6.3
mmol), PdCl2(PPh3)2 (128 mg, 0.18 mmol), Bu4NI (258 mg, 0.7
mmol), CuI (100 mg, 0.53 mmol), Et3N (531 mg, 5.25 mmol)
and DMF (20 mL) were placed in a 100 mL reaction flask. After
being stirred for 24 h at 80 uC under nitrogen, the mixture was
poured into diluted aqueous HCl. The organic layer was
extracted with Et2O and dried over Na2SO4. Concentration in
vacuo followed by column chromatography on silica gel with
hexane/ethyl acetate (99/1, v/v) furnished compound 7 (1.22 g,
i
with stirring under nitrogen was added Pr2NEt (10.9 mL, 63
mmol) and 2-ethylhexyl thioglycolate (6.32 mL, 30.2 mmol),
and the resulting solution was heated at 100 uC for 16 h. After
cooling to room temperature, ButOK (4.1 g, 36.6 mmol) in
DMF (30 mL) was added and the mixture was stirred for a
further 3 h. Then, diluted aqueous HCl was added to
neutralize the mixture and the product was extracted with
toluene. The organic layer was passed through a column
packed with Na2SO4 and Al2O3 in this order using ethyl
acetate, and then the compound was purified by column
chromatography on silica gel using hexane/ethyl acetate (97.5/
2.5, v/v) to give the dihydroxide 6 as a yellow solid (6.05 g, 11.3
mmol, 89%). Mp. 140.8–141.6 uC. 1H NMR (400 MHz, CDCl3) d
0.92 (t, J = 7.2 Hz, 6H), 0.97 (t, J = 7.6 H, 6H), 1.34–1.48 (m,
16H), 1.74 (quint, J = 6.6 Hz, 2H), 4.28 (dd, J = 5.9 Hz, 12.7 Hz,
2H), 4.31 (dd, J = 5.9 Hz, 12.7 Hz, 2H), 8.28 (d, J = 2.8 Hz, 2H),
10.2 (bs, 2H). 13C NMR (100 MHz, CDCl3) d 11.2, 14.2, 23.1,
24.0, 29.1, 30.6, 39.0, 68.1, 104.2, 117.6, 131.8, 134.9, 158.2,
1
1.47 mmol, 84%) as a yellow oil. H NMR (400 MHz, CDCl3) d
0.85–0.98 (m, 18H), 1.27–1.59 (m, 44H), 1.72–1.80 (m, 6H), 2.63
(t, J = 6.9, 4H), 4.27–4.36 (m, 4H), 8.44 (s, 2H). 13C NMR (100
MHz, CDCl3) d 11.2, 14.20, 14.23, 20.3, 22.8, 23.1, 24.0, 28.9,
29.1, 29.28, 29.33, 29.5, 29.7, 30.6, 32.0, 39.0, 68.1, 74.0, 101.4,
118.8, 123.2, 135.5, 137.0, 140.6, 162.3 (one signal was
overlapped by another one). HR-MS (FAB) calcd for
C
52H78O4S2 [M+] requires 830.5342, found 830.5347.
Di(2-ethylhexyl) 3,7-didodecylbenzo[1,2-b:4,5-b9]dithiophene-
2,6-dicarboxylate (9)
(a) In a 50 mL autoclave reactor, 10% Pd/C (293 mg, 0.14
mmol) was placed, and the reactor was flushed with hydrogen.
After the completion of preactivation of Pd under hydrogen (1
atm, ca. 1 h), 8 (1.2 g, 1.4 mmol) and dioxane (15 mL) were
added. The resulting mixture was stirred for 96 h at room
temperature under pressurized hydrogen (1.8 MPa). The
mixture was filtered through a pad of Celite to remove Pd/C
and concentrated under reduced pressure. The hydrogenated
product 9 (1.2 g, 1.4 mmol) was obtained as a yellow oil in a
1
quantitative yield. H NMR (400 MHz, CDCl3) d 0.86–0.99 (m,
18H), 1.26–1.57 (m, 52H), 1.69–1.74 (m, 6H), 3.33 (t, J = 7.8,
4H), 4.27–4.29 (m, 4H), 8.28 (s, 2H). 13C NMR (100 MHz,
CDCl3) d 11.2, 14.2, 14.3, 22.8, 23.2, 24.1, 27.7, 29.1, 29.5, 29.7,
29.80, 29.81, 29.83, 30.2, 30.5, 30.7, 32.1, 39.1, 67.8, 117.5,
Fig. 8 X-ray diffractograms for 2a- and 2b-based thin films.
This journal is ß The Royal Society of Chemistry 2013
RSC Adv., 2013, 3, 12356–12365 | 12361

View Article Online
Paper
RSC Advances
128.9, 137.5, 139.8, 145.0, 163.4 (one signal was overlapped by
another one). HR-MS (FAB) calcd for C52H86O4S2 [M+] requires
838.5968, found 838.5958. (b) In a 20 mL two-necked flask
were placed the ditriflate 7 (100 mg, 0.125 mmol), Pd(OAc)2
(2.8 mg, 0.0125 mmol) and RuPhos (11.7 mg, 0.025 mmol) and
toluene (0.4 mL). Then, dodecyl-ZnCl(Br) in THF (0.5 M, 0.75
mL, 0.375 mmol, prepared with dodecyl-MgBr and ZnCl2) was
added and the mixture was stirred for 6 h at room temperature
under nitrogen. The reaction was quenched by adding diluted
aqueous HCl and the organic layer was extracted with ethyl
acetate, and dried over Na2SO4. Concentration followed by
purification by column chromatography with hexane/ethyl
acetate (95 : 5, v/v) and a preparative recycle GPC chromato-
graphy produced 9 (74.9 mg, 0.89 mmol, 71%) as a yellow oil,
which showed the same spectra as those obtained by the above
procedure.
extracted with diethyl ether, and dried over Na2SO4.
Concentration followed by purification by column chromato-
graphy with hexane/CH2Cl2 (1 : 1, v/v) produced the dibromide
11 (50 mg, 0.074 mmol, 78%) as a white solid. Mp. 78.3–79.0
1
uC. H NMR (400 MHz, CDCl3) d 0.88 (t, J = 6.9 Hz, 6H), 1.26–
1.43 (m, 36H), 1.65 (quint, J = 7.8 Hz, 4H), 2.86 (t, J = 7.8 Hz,
4H), 7.97 (s, 2H). 13C NMR (100 MHz, CDCl3) d 14.3, 22.8 28.1,
29.0, 29.5, 29.6, 29.70, 29.74, 29.77, 29.80, 29.82, 32.1, 112.9,
114.5, 135.7, 136.0, 137.3. HR-MS (FAB) calcd for C34H52Br2S2
[M+] requires 682.1877, found 682.1890.
3,7-Didodecyl-2,6-bis(5-phenyl-2-thienyl)benzo[1,2-b:4,5-
b9]dithiophene (2a)
Dibromobenzodithiophene 11 (50 mg, 0.074 mmol), tributyl(5-
phenyl-2-thienyl)tin15 (77 mg, 0.17 mmol), Pd(PPh3)4 (17 mg,
0.015 mmol), DMF (1 mL), and toluene (1 mL) were placed in a
20 mL two-necked reaction flask. The solution was stirred at 85
uC for 24 h under nitrogen. The mixture was quenched with
methanol and the precipitate was collected by filtration. The
solid was resolved in CHCl3 and the solution was filtered
through a silica gel pad. Evaporating the solvent followed by
column chromatography with CHCl3 gave 2a (47 mg, 0.056
mmol, 75%) as a yellow solid. Mp. 182.2–183.1 uC. 1H NMR
(400 MHz, CDCl3) d 0.87 (t, J = 6.8 Hz, 6H), 1.26–1.41 (m, 36H),
1.78 (quint, J = 7.8 Hz, 4H), 3.12 (t, J = 7.8 Hz, 4H), 7.26–7.35
(m, 6H), 7.42 (dd, J = 7.3, 7.3 Hz, 4H), 7.66 (d, J = 7.3 Hz, 4H),
8.08 (s, 2H). 13C NMR (100 MHz, CDCl3) d 14.2, 22.8, 27.8, 29.5,
29.6, 29.8, 29.9, 30.0, 30.1, 31.0, 32.1, 115.1, 123.7, 126.0,
128.0, 128.1, 129.2, 131.7, 132.7, 134.2, 136.0, 136.3, 139.2,
145.4 (one signal was overlapped by another one). HR-MS
(FAB) calcd for C54H66S4 [M+] requires 842.4047, found
842.4055. Elemental analysis calcd for C54H66S4: C, 76.90; H,
7.89; S, 15.21; found: C,76.70; H, 7.85; S, 14.87.
3,7-Didodecylbenzo[1,2-b:4,5-b9]dithiophene-2,6-dicarboxylic
acid (10)
To a mixture of 9 (1.1 g, 1.3 mmol) and KOH (365 mg, 6.5
mmol), water (4 mL) and ethanol (20 mL) were sequentially
added, and the suspension was then heated at 100 uC for 10 h.
The resulting mixture was allowed to cool to room tempera-
ture, and the ethanol was evaporated. The precipitate formed
by addition of diluted aqueous HCl to the residue was
collected and dried under high vacuum to provide dicarboxylic
acid 8 (760 mg, 1.2 mmol, 95%) as a yellow solid. Mp. . 300
uC. 1H NMR (400 MHz, DMSO-d6) d 0.85 (t, J = 6.5 Hz, 6H),
1.19–1.36 (m, 36H), 1.64 (quint, J = 7.3 Hz, 4H), 3.32 (t, J = 7.3
Hz, 4H), 8.58 (s, 2H). HR-MS (FAB) calcd for C36H54O4S2 [M+]
requires 614.3464, found 614.3479.
3,7-Didodecylbenzo[1,2-b:4,5-b9]dithiophene (1a)
The dicarboxylic acid 10 (700 mg, 1.14 mmol), AgOAc (70 mg,
0.42 mmol), K2CO3 (100 mg, 0.72 mmol) and NMP (15 mL)
were placed in a 100 mL two-necked flask, and the mixture was
then heated at 160 uC for 7 h under nitrogen. After the
completion of the reaction, the mixture was poured into
diluted aqueous HCl and extracted with diethyl ether. The
combined organic layer was dried over Na2SO4, concentrated,
and purified by silica gel column chromatography with hexane
to give the benzodithiophene 1a (383 mg, 0.73 mmol, 64%) as
Methyl 3-(trifluoromethanesulfonyloxy)benzo[b]thiophene-2-
carboxylate (12)
In a 100 mL reaction flask were placed methyl 3-hydroxyben-
zo[b]thiophene-2-carboxylate5d (2.7 g, 13 mmol), Tf2O (2.6 mL,
15.4 mmol), Et3N (2.16 mL, 15.4 mmol), DMAP (79 mg, 0.65
mmol) and CH2C12 (60 mL), and the resulting mixture was
stirred at room temperature for 4 h under nitrogen. After
adding aqueous NaHCO3, the product was extracted with
diethyl ether, dried over Na2SO4 and purified by column
chromatography on silica gel using hexane/ethyl acetate (98/2,
v/v). The triflate 12 was obtained as a white solid (4.32 g, 12.7
1
a white solid. Mp. 89.4–90.1 uC. H NMR (400 MHz, CDCl3) d
0.88 (t, J = 6.9 Hz, 6H), 1.26–1.45 (m, 36H), 1.78 (quint, J = 7.8
Hz, 4H), 2.86 (t, J = 7.8 Hz, 4H), 7.09 (s, 2H), 8.19 (s, 2H). 13C
NMR (100 MHz, CDCl3) d 14.3, 22.8, 28.9, 29.2, 29.5, 29.7,
29.80, 29.83, 31.9, 115.5, 121.4, 136.3, 137.2, 137.7 (three
signals were overlapped by others). HR-MS (FAB) calcd for
C34H54S2 [M+] requires 526.3667, found: 526.3669.
1
mmol, 98%). Mp. 72.0–73.0 uC. H NMR (400 MHz, CDCl3) d
4.00 (s, 3H), 7.53 (dt, J = 1.4, 7.8, 1H), 7.58 (ddd, J = 7.8, 7.8, 1.4
Hz, 1H), 7.845 (d, J = 7.8 Hz, 1H), 7.849 (d, J = 7.8 Hz, 1H). 13
C
NMR (100 MHz, CDCl3) d 52.9, 118.7 (q, J = 320 Hz), 122.1,
122.9, 123.6, 126.1, 128.7, 131.0, 137.5, 139.7, 160.9. HR-MS
calcd for C11H7F3O5S2 [M+] requires 339.9687, found 339.9690.
2,6-Dibromo-3,7-didodecylbenzo[1,2-b:4,5-b9]dithiophene (11)
To a 20 mL reaction flask containing 1a (50 mg, 0.095 mmol)
in THF (3 mL) was added ButLi in pentane (1.5 M, 0.17 mL,
0.26 mmol) at 278 uC under nitrogen, and the mixture was
stirred for 1 h. After warming to room temperature, stirring for
15 min, and cooling to 278 uC again, 1,2-dibromo-1,1,2,2-
tetrafluoroethane (98 mg, 0.38 mmol) was added. Then, the
mixture was stirred at room temperature for 12 h. The reaction
was quenched by adding brine and the organic layer was
Methyl 3-dodecylbenzo[b]thiophene-2-carboxylate (13)
In a 20 mL two-necked flask were placed the triflate 12 (170
mg, 0.5 mmol), Pd(OAc)2 (5.6 mg, 0.025 mmol), RuPhos (23.4
mg, 0.05 mmol), and toluene (0.7 mL) and dodecyl-ZnCl(Br) in
THF (0.5 M, 1.5 mL, 0.75 mmol) was added to the mixture,
which was then stirred for 6 h at room temperature under
nitrogen. The reaction was quenched by adding diluted
12362 | RSC Adv., 2013, 3, 12356–12365
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Paper
aqueous HCl and the organic layer was extracted with diethyl
ether, after which the organic layer was dried over Na2SO4.
Concentration followed by purification by column chromato-
graphy with hexane/ethyl acetate (97.5 : 2.5, v/v) produced 13
(176 mg, 0.49 mmol, 98%) as a colorless oil. 1H NMR (400
MHz, CDCl3) d 0.88 (t, J = 6.9 Hz, 3H), 1.38–1.15 (m, 16H), 1.45
(tt, J = 7.8 Hz, 6.4 Hz, 2H), 1.66 (quint, J = 7.8 Hz, 2H), 3.29 (t, J
= 7.8 Hz, 2H), 3.93 (s, 3H), 7.41 (dt, J = 7.8, 1.4 Hz, 1H), 7.46 (dt,
J = 1.4, 7.3 Hz, 1H), 7.83 (dd, J = 7.3, 1.4 Hz, 1H), 7.85 (dd, J =
7.3, 1.4, 1H). 13C NMR (100 MHz, CDCl3) d 14.3, 22.8, 27.6,
29.5, 29.7, 29.77, 29.79, 29.81, 29.83, 30.1, 30.5, 32.1, 52.2,
122.9, 123.9, 124.5, 126.3, 127.2, 139.7, 140.9, 146.8, 163.7. HR-
MS calcd for C22H32O2S [M+] requires 360.2123, found
360.2125.
temperature, the resulting mixture was quenched with water
and extracted with CH2Cl2. The organic layer was dried over
Na2SO4. Concentration followed by purification by column
chromatography with CHCl3 produced the dibromide 18 (1.06
g, 1.42 mmol, 80%) as a white solid. Mp. 92.0–93.5 uC. 1H NMR
(400 MHz, CDCl3) d 0.88 (t, J = 6.9 Hz, 6H), 1.22–1.57 (m, 40H),
2.84 (t, J = 7.3 Hz, 4H), 8.29 (s, 2H). 13C NMR (100 MHz, CDCl3)
d 14.3, 22.8, 28.7, 29.3, 29.5, 29.6, 29.70, 29.76, 30.1, 32.1 35.6,
116.5, 124.4, 127.3, 137.3, 137.9 (one signal was overlapped by
another one). HR-MS calcd for C34H52Br2S4 [M+] requires
746.1319, found 746.1302.
3,7-Bis(dodecylthio)-2,6-(5-phenyl-2-thienyl)benzo[1,2-b;4,5-
b9]dithiophene (2b)
Operating with 18 (100 mg, 0.13 mmol) as in the preparation
of 2a gave the dithiophene 2b (82 mg, 0.09 mmol, 68%) as a
yellow solid. Mp. 177.5–178.2 uC. 1H NMR (400 MHz, CDCl3) d
0.86 (t, J = 7.3 Hz, 6H), 1.19–1.40 (m, 36H), 1.56–1.63 (m, 4H),
2.86 (t, J = 7.3, 4H), 7.31 (d, J = 4.1 Hz, 2H), 7.33 (t, J = 7.3 Hz,
2H), 7.42 (dd, J = 7.3, 7.3 Hz, 4H), 7.58 (d, J = 4.1 Hz, 2H), 7.70
(d, J = 6.9 Hz, 4H), 8.33 (s, 2H). 13C NMR (100 MHz, CDCl3) d
14.3, 22.8, 29.0, 29.4, 29.5, 29.72, 29.74, 29.76, 29.8, 30.0, 32.1,
36.5, 116.3, 120.7, 122.9, 126.0, 128.1, 129.1, 129.3, 134.2,
135.1, 135.2, 140.9, 141.9, 146.8. HR-MS (FAB) calcd for
Di(2-ethylhexyl) 3,7-bis(dodecylthio)benzo[1,2-b; 4,5-
b9]dithiophene-2,6-dicarboxylate (14)
In a 100 mL reaction flask were placed the ditriflate 7 (2.5 g,
3.13 mmol), dodecanethiol (1.4 g, 7.2 mmol), K2CO3 (1.3 g, 9.4
mmol) and DMF (20 mL), and the resulting mixture was stirred
for 20 h at 120 uC under nitrogen. The reaction was quenched
with diluted aqueous HCl and the mixture was extracted with
diethyl ether and dried over Na2SO4. Concentration followed
by purification by column chromatography with hexane/ethyl
acetate (99 : 1, v/v) gave the dialkylthiobenzodithiophene 14
(2.7 g, 3.0 mmol, 95%) as a yellow oil. 1H NMR (400 MHz,
CDCl3) d 0.87–1.02 (m, 18H), 1.20–1.55 (m, 56H), 1.75 (quint, J
= 7.3 Hz, 2H), 3.04 (t, J = 7.3 Hz, 4H), 4.33 (m, 4H), 8.67 (s, 2H).
13C NMR (100 MHz, CDCl3) d 11.3, 14.24, 14.27, 22.80, 22.84,
23.2, 24.1, 28.9, 29.1, 29.3, 29.5, 29.6, 29.7, 29.8, 30.2, 30.7,
32.0, 36.7, 39.0, 68.3, 119.3, 133.7, 136.1, 137.0, 141.8, 161.9.
HR-MS (FAB) calcd for C52H86O4S4 [M+] requires 902.5409,
found 902.5405.
C
54H66S6 [M+] requires 906.3489, found 906.3493. Elemental
analysis calcd for C54H66S6: C, 71.47; H, 7.33; S, 21.20; found:
C, 71.46; H, 7.49; S, 21.00.
Di(2-ethylhexyl) 3,7-bis(dodecyloxy)benzo[1,2-b:4,5-
b9]dithiophene-2,6-dicarboxylate (15)
In a 100 mL reaction flask were placed dihydroxide 6 (2.16 g,
4.04 mmol), 1-bromododecane (2.69 mL, 12.1 mmol), K2CO3
(1.65 g, 12.9 mmol) and DMF (20 mL), and the resulting
mixture was stirred for 19 h at 120 uC under nitrogen. The
reaction was quenched with diluted aqueous HCl and the
mixture was extracted with a mixed solvent of hexane and ethyl
acetate and dried over Na2SO4. Concentration followed by
purification by column chromatography with hexane/ethyl
acetate (99 : 1, v/v) gave the dialkoxybenzodithiophene 15 (3.29
g, 3.78 mmol, 94%) as a yellow oil. 1H NMR (400 MHz, CDCl3)
d 0.86–1.00 (m, 18H), 1.27–1.54 (m, 52H), 1.70–1.75 (m, 2H),
1.89 (quint, J = 7.9, 4H), 4.24 (dd, J = 5.5, 11.0 Hz, 2H), 4.27 (dd,
J = 5.5, 11.0 Hz, 2H), 4.37 (t, J = 6.9 Hz, 4H), 8.23 (s, 2H). 13C
NMR (100 MHz, CDCl3) d 11.2, 14.23, 14.27, 22.8, 23.2, 24.0,
26.1, 29.1, 29.5, 29.6, 29.74, 29.76, 29.78, 29.81, 30.56, 30.61,
32.1, 39.0, 67.8, 76.2, 117.0, 117.2, 134.4, 135.2, 155.1, 161.9.
HR-MS (FAB) calcd for C52H86O6S2 [M+] requires 870.5866,
found 870.5873.
3,7-Bis(dodecylthio)benzo[1,2-b;4,5-b9]dithiophene-2,6-
dicarboxylic acid (16)
Operating with 14 (2.7 g, 3.0 mmol) as in the preparation of 10
gave the diacid 16 (1.7 g, 2.5 mmol, 83%) as a yellow solid. Mp.
1
231.0–232.0 uC. H NMR (400 MHz, (CD3)2SO) d 0.83 (t, J = 6.9
Hz, 6H), 1.10–1.39 (m, 40H), 3.05 (t, J = 6.9 Hz, 4H), 8.40 (s,
2H). HR-MS (FAB) calcd for C36H54O4S4 [M+] requires 678.2905,
found 678.2908.
3,7-Bis(dodecylthio)benzo[1,2-b;4,5-b9]dithiophene (1b)
Operating with 16 (1.7 g, 2.5 mmol) as in the preparation of 1a
gave the dithiophene 1b (1.05 g, 1.8 mmol, 71%) as a white
solid. Mp. 64.4–65.3 uC. 1H NMR (400 MHz, CDCl3) d 0.88 (t, J =
6.9 Hz, 6H), 1.24–1.41 (m, 36H), 1.63 (quint, J = 7.3 Hz, 4H),
2.90 (t, J = 7.3 Hz, 4H), 7.45 (s, 2H), 8.40 (s, 2H). 13C NMR (100
MHz, CDCl3) d 14.3, 22.8, 28.8, 29.3, 29.5, 29.65, 29.69, 29.7,
29.8, 32.1, 35.0, 116.7, 126.4, 127.9, 137.5, 137.6 (one signal
was overlapped by another one). HR-MS (FAB) calcd for
C34H54S4 [M+] requires 590.3108, found 590.3104.
3,7-Bis(dodecyloxy)benzo[1,2-b;4,5-b9]dithiophene-2,6-
dicarboxylic acid (17)
Operating with 15 (3.29 g, 3.78 mmol) as in the preparation of
10 gave the diacid 17 (2.21 g, 3.42 mmol, 90%) as a yellow
solid. Mp. 240.0–241.5 uC. 1H NMR (400 MHz, (CD3)2SO) d 0.79
(t, J = 6.9 Hz, 6H), 1.16–1.42 (m, 36H), 1.74 (quint, J = 6.9 Hz,
4H), 4.28 (t, J = 6.9 Hz, 4H), 8.40 (s, 2H). HR-MS (FAB) calcd for
2,6-Dibromo-3,7-bis(dodecylthio)benzo[1,2-b:4,5-
b9]dithiophene (18)
To a mixture of 1b (1.05 g, 1.8 mmol), AcOH (30 mL), and
CH2Cl2 (5 mL), N-bromosuccinimide (NBS, 697 mg, 3.9 mmol)
was added in one portion. After being stirred for 3 h at room
C
36H54O6S2 [M+] requires 646.3362, found 646.3342.
This journal is ß The Royal Society of Chemistry 2013
RSC Adv., 2013, 3, 12356–12365 | 12363

View Article Online
Paper
RSC Advances
diode (rise time , 1 ns) was monitored by a digital
oscilloscope from Tektronix TDS3032B. All the above experi-
ments were carried out at room temperature. The transient
photoconductivity of the samples is proportional to the
reflected microwave power (DPr/Pr) and sum of the mobilities
of charge carriers via:
3,7-Bis(dodecyloxy)benzo[1,2-b;4,5-b9]dithiophene (1c)
Operating with 17 (500 mg, 0.77 mmol) in the presence of
AgOAc (25.8 mg, 0.15 mmol) and K2CO3 (32 mg, 0.23 mmol) as
in the preparation of 1a gave the dithiophene 1c (400 mg, 0.72
mmol, 93%) as a white solid. Mp. 102.2–103.0 uC. 1H NMR (400
MHz, CDCl3) d 0.88 (t, J = 7.3 Hz, 6H), 1.27–1.53 (m, 36H), 1.87
(quint, J = 6.9 Hz, 4H), 4.13 (t, J = 6.9 Hz, 4H), 6.28 (s, 2H), 8.17
(s, 2H). 13C NMR (100 MHz, CDCl3) d 14.3, 22.8, 26.3, 29.4,
29.5, 29.6, 29.74, 29.78, 29.80, 29.83, 32.1, 70.2, 96.4, 115.0,
131.3, 134.4, 150.2. HR-MS (FAB) calcd for C34H54O2S2 [M+]
requires 558.3565, found 558.3577.
X
1 DPr
~eQN
m
A Pr
where A, e, w, N, and Sm are a sensitivity factor, elementary charge
of electron, photo-carrier generation yield (quantum efficiency),
the number of absorbed photons per unit volume, and the sum of
mobilities for negative and positive carriers, respectively.
The compounds were dissolved in o-dichlorobenzene, and
cast onto quartz substrates at 0.6–2.1 mm thick as determined
using Dektak150 surface profiler. The films were heated to 200
uC under an Ar atmosphere, and annealed at that temperature
for 30 min before the measurement. The number of photons
absorbed by the film was estimated by the direct measurement
of transmitted power of laser pulses using an Opher NOVA-
display power meter.
2,6-Dibromo-3,7-bis(dodecyloxy)benzo[1,2-b;4,5-
b9]dithiophene (19)
Operating with 1c (274 mg, 0.49 mmol) as in the preparation of
11 gave the product (327 mg, 0.46 mmol, 93%) as a yellow
solid. Mp. 69.8–70.6 uC. 1H NMR (400 MHz, CDCl3) d 0.88 (t, J =
6.9 Hz, 6H), 1.27–1.56 (m, 36H), 1.86 (quint, J = 7.3 Hz, 4H),
4.23(t, J = 6.4, 4H), 7.96 (s, 2H). 13C NMR (100 MHz, CDCl3) d
14.3, 22.9, 26.1, 29.5, 29.6, 29.75, 29.77, 29.80, 29.82, 30.4,
32.1, 74.2, 100.6, 113.9, 131.4, 134.3, 148.1. HR-MS (FAB) calcd
for C34H52Br2O2S2 [M+] requires 714.1755, found 714.1761.
The values of w in the compounds were determined by
conventional photo-current measurement in a vacuum cham-
ber (,1025 Pa) using inter-digitated Au electrodes on a sample
film-coated quartz substrate with 5 mm gap under excitation at
3,7-Bis(dodecyloxy)-2,6-(5-phenyl-2-thienyl)benzo[1,2-b;4,5-
b9]dithiophene (2c)
355 nm with the photon density of 6.0 6 1015 photons cm22
.
Operating with 19 (84 mg, 0.12 mmol) as in the preparation of
2a gave the dithiophene 2c (63 mg, 0.07 mmol, 60%) as a
Transient current was predominantly observed under a variety
of applied bias voltages (E) and monitored by a Keithley 2612
electrometer.16 The value of w was calculated based on the
number of charge carriers determined by the extrapolation of
the dependence at E = 0 where photo-induced charge carrier
1
yellow solid. Mp 202.9–203.7 uC. H NMR (400 MHz, CDCl3) d
0.89 (t, J = 6.9 Hz, 6H), 1.27–1.45 (m, 32H), 1.59–1.63 (m, 4H),
2.00 (quint, J = 6.9 Hz, 4H), 4.20 (t, J = 6.9 Hz, 4H), 7.30 (d, J =
4.6 Hz, 2H), 7.31(t, J = 7.3 Hz, 2H), 7.34 (d, J = 4.6 Hz, 2H), 7.41
(dd, J = 7.3, 7.3 Hz, 4H), 7.66 (d, J = 7.3 Hz, 4H), 7.99 (s, 2H).
13C NMR (100 MHz, CDCl3) d 14.1, 22.7, 26.2, 29.4, 29.6, 29.69,
29.72, 29.74, 30.6, 32.0, 73.8, 117.4, 125.8, 126.4, 127.8, 129.0,
132.8, 134.3, 134.5, 145.0, 145.2 (lack of 4 peaks due to low
solubility). HR-MS (FAB) calcd for C54H66O2S4 [M+] requires
879.3946, found 874.3969. Elemental analysis calcd for
C54H66O2S4: C, 74.09; H, 7.60; S, 14.65; found: C,73.66; H,
7.56; S, 14.62.
separation occurs in the TRMC measurement (E y 101
V
cm21).
The details of the set of apparatus used were described
elsewhere.7
FET measurement
The field-effect mobility of the compounds was measured
using top-contact thin-film field-effect transistor (FET) geo-
metry. The p-doped silicon substrate functions as the gate
electrode. A thermally grown 300 nm thick silicon oxide
dielectric layer on the gate substrate has a capacitance of 10.0
nF cm22. The channel width (W) and channel length (L) are 10
mm and 20 mm, respectively. The silicon oxide surface was
washed with toluene, acetone, water, and 2-propanol. The
silicon oxide surface was then activated by ozone treatment
and pretreated with b-PTS. The semiconductor layer was spin-
coated on the Si/SiO2 substrate at 1000 rpm from the 0.5 wt%
solution of compound 2 in o-dichlorobenzene. Subsequently,
it was annealed at 60 uC for 30 min. The source and drain
electrodes were constructed with gold (30 nm). The character-
istics of the OFET devices were measured at room temperature
under a pressure of 1023 Pa. The field-effect mobility (m) was
calculated in the saturated region at the VDS of 260 V using the
following equation: IDS = W/(2L)mCi(VGS 2 Vth)2, where Ci is the
capacitance of SiO2.
Measurement of absorption and emission spectra for thin
films
The films were coated onto quartz substrate after ozone
activation and subsequent treatment with b-phenethyltrichlor-
osilane (b-PTS) at 18–34 mm thick from o-dichlorobenzene
solutions (0.5 wt%) of the corresponding compounds at 65 uC.
The films were annealed at 85 uC for 5 min prior to the
measurements.
Flash-photolysis time resolved microwave conductivity (FP-
TRMC) measurement
The nanosecond laser pulses from an Nd:YAG laser (third
harmonic generation, THG (355 nm) from Spectra Physics,
INDY-HG (FWHM 5–8 ns) were used as excitation sources. The
power density of the laser was set at 9.1 6 1016 photons cm22
.
For time-resolved microwave conductivity (TRMC) measure-
ment, the microwave frequency and power were set at y9.1
GHz and 3 mW respectively. The TRMC signal picked up by a
12364 | RSC Adv., 2013, 3, 12356–12365
This journal is ß The Royal Society of Chemistry 2013

View Article Online
RSC Advances
Paper
D. T. Connor, W. A. Cetenko, M. D. Mullican, R.
J. Sorenson, P. C. Unangst, R. J. Weikert, R.
L. Adolphson, J. A. Kennedy, D. O. Thueson, C. D. Wright
and M. C. Conroy, J. Med. Chem., 1992, 35, 958.
6 Z. Hassan, S. Reimann, K. Wittler, R. Ludwig, A. Villinger
and P. Langer, Adv. Synth. Catal., 2012, 354, 731.
7 (a) S. Seki, Y. Yoshida, S. Tagawa, K. Asai, K. Ishigure,
K. Furukawa, M. Fujiki and N. Matsumoto, Philos. Mag. B,
1999, 79, 1631; (b) A. Acharya, S. Seki, Y. Koizumi, A. Saeki
and S. Tagawa, J. Phys. Chem. B, 2005, 109, 20174; (c)
A. Saeki, S. Seki and S. Tagawa, J. Appl. Phys., 2006, 100,
023703; (d) S. Sato, S. Seki, Y. Honsho, L. Wang, H. Nikawa,
G. Luo, J. Lu, M. Haranaka, T. Tsuchiya, S. Nagase and
T. Akasaka, J. Am. Chem. Soc., 2011, 133, 2766; (e) A. Saeki,
Y. Koizumi, T. Aida and S. Seki, Acc. Chem. Res., 2012, 45,
1193.
8 T. Okauchi, K. Kuramoto and M. Kitamura, Synlett,
2010(19), 2891.
9 N. L. Powell and S. D. Rychnovsky, Tetrahedron Lett., 1996,
37, 7901.
10 L. J. Goossen, C. Linder, N. Rodriguez, P. P. Lange and
A. Fromm, Chem. Commun., 2009, 7173.
11 C. T. Brown, N. Chopra, C. R. Knittel, M. Mathai,
V. Seshadri, J. Wang and B. A. Woodworth, PCT. Int.
Appl., WO 2012003485 (CAN 156 : 123531).
Acknowledgements
This work was supported, in part, by Grants-in-Aid from the
Ministry of Education, Culture, Sports, Science, and
Technology, Japan, and by the cooperative research with
Sumitomo Chemical Co., Ltd.
Notes and references
1 Recent reviews: (a) H. E. Katz, Z. Bao and S. L. Gilat, Acc.
Chem. Res., 2001, 34, 359; (b) J. Roncali, P. Blanchard and
P. Frere, J. Mater. Chem., 2005, 15, 1589; (c) K. Takimiya,
Y. Kunugi and T. Otsubo, Chem. Lett., 2007, 36, 578; (d) A.
´
R. Murphy and J. M. J. Frechet, Chem. Rev., 2007, 107, 1066;
(e) B. S. Ong, Y. Wu, Y. Li, P. Liu and H. Pan, Chem.–Eur. J.,
2008, 14, 4766; (f) S. Allard, M. Forster, B. Souharce,
H. Thiem and U. Scherf, Angew. Chem., Int. Ed., 2008, 47,
4070; (g) J. Chen and A. Y. Cao, Acc. Chem. Res., 2009, 42,
1709; (h) K. Takimiya, S. Shinamura, I. Osaka and
E. Miyazaki, Adv. Mater., 2011, 23, 4347; (i) P. Sista, M.
C. Biewer and M. C. Stefan, Macromol. Rapid Commun.,
2012, 33, 9.
2 (a) T. Yamamoto, D. Komarudin, M. Arai, B. L. Lee,
H. Suganuma, N. Asakawa, Y. Inoue, K. Kubota, S. Sasaki,
T. Fukuda and H. Matsuda, J. Am. Chem. Soc., 1998, 120,
2047; (b) B. S. Ong, Y. Wu, P. Liu and S. Gardner, J. Am.
Chem. Soc., 2004, 126, 3378; (c) Y. Wu, P. Liu, S. Gardner
and B. S. Ong, Chem. Mater., 2005, 17, 221; (d)
S. Prasanthkumar, A. Saeki, S. Seki and A. Ajyayaghosh, J.
Am. Chem. Soc., 2010, 132, 8866; (e) S. Prasanthkumar,
A. Gopal and A. Ajayaghosh, J. Am. Chem. Soc., 2010, 132,
13206.
3 During the performance of this work, a b-alkyl-substituted
dithienobenzodithiophene was reported: J. Kim, A.-R. Han,
J. H. Seo, J. H. Oh and C. Yang, Chem. Mater., 2012, 24,
3464.
4 (a) J. Kumagai, K. Hirano, T. Satoh, S. Seki and M. Miura, J.
Phys. Chem. B, 2011, 115, 8446; (b) J. Kumagai, K. Hirano,
T. Satoh, S. Seki and M. Miura, J. Phys. Chem. B, 2012, 116,
4115; (c) M. Miura, S. Ota, K. Hirano, T. Satoh and M. Ueda,
PCT Int. Appl., WO 2012105517 (CAN 157 : 262598).
5 (a) T. Higa and A. J. Krubsack, J. Org. Chem., 1975, 40, 3037;
(b) W. Ried, G. Oremek and B. Ocakcioglu, Liebigs Ann.
12 C. Han and S. L. Buchwald, J. Am. Chem. Soc., 2009, 131,
7532.
13 (a) C. Volente, S. Baglione, D. Candito, C. J. O’Brien and M.
G. Organ, Chem. Commun., 2008, 735; (b) G. A. Molander
and T. Ito, Org. Lett., 2001, 3, 393.
´
14 For some related recent examples: (a) S. Beaupre, A. Pron,
S. H. Drouin, A. Najari, L. G. Mercier, A. Robitaille and
M. Leclerc, Macromolecules, 2012, 45, 6906; (b) Y. Ie,
J. Huang, Y. Uetani, M. Karakawa and Y. Aso,
Macromolecules, 2012, 45, 4564; (c) C. Cabanetos, A.
E. Labban, J. A. Bartelt, J. D. Douglas, W. R. Mateker, J.
´
M. Frechet, M. D. McGehee and P. M. Beaujuge, J. Am.
Chem. Soc., 2013, 135, 4656; (d) B. Liu, X. Chen, Y. He, Y. Li,
X. Xu, L. Xiao, L. Li and Y. Zou, J. Mater. Chem. A, 2013, 1,
570; (e) E. Zhou, J. Cong, K. Hashimoto and K. Tajima,
Macromolecules, 2013, 46, 763.
15 A. Pelter, I. Jenkins and D. E. Jones, Tetrahedron, 1997, 53,
10357.
16 Y. Yasutani, A. Saeki, T. Fukumatsu, Y. Koizumi and
S. Seki, Chem. Lett., 2013, 42, 19.
ˇ
´
Chem., 1980, 1424; (c) M. Malesevic, G. Karminsky-Zamola,
´
M. Bajic and D. D. Boykin, Heterocycles, 1995, 41, 2691; (d)
This journal is ß The Royal Society of Chemistry 2013
RSC Adv., 2013, 3, 12356–12365 | 12365