Consecutive thiophene-annulation approach to π-extended thienoacene-based organic semiconductors with [1]benzothieno[3,2-b][1] benzothiophene (BTBT) substructure

Article abstract of DOI:10.1021/ja406257u

We describe a new synthetic route to the [1]benzothieno[3,2-b][1] benzothiophene (BTBT) substructure featuring two consecutive thiophene-annulation reactions from o-ethynyl-thioanisole substrates and arylsulfenyl chloride reagents that can be easily derived from arylthiols. The method is particularly suitable for the synthesis of unsymmetrical derivatives, e.g., [1]benzothieno[3,2-b]naphtho[2,3-b]thiophene, [1]benzothieno[3,2-b] anthra[2,3-b]thiophene, and naphtho[3,2-b]thieno[3,2-b]anthra[2,3-b]thiophene, a selenium-containing derivative, [1]benzothieno[3,2-b][1]benzoselenophene. It also allows us to access largely π-extended derivatives with two BTBT substructures, e.g., bis[1]benzothieno[2,3-d:2′,3′-d′]benzo[1, 2-b:4,5-b′]dithiophene and bis[1]benzothieno[2,3-d:2′,3′- d′]naphtho[2,3-b:6,7-b′]dithiophene (BBTNDT). It should be emphasized that these new BTBT derivatives are otherwise difficult to be synthesized. In addition, since various substrates and reagents, o-ethynyl-thioanisoles and arylthiols, respectively, can be combined, the method can be regarded as a versatile tool for the development of thienoacene-based organic semiconductors in this class. Among the newly synthesized materials, highly π-extended BBTNDT afforded very high mobility (>5 cm² V^-1 s^-1) in its vapor-deposited organic field-effect transistors (OFETs), which is among the highest for unsubstituted acene- or thienoacenes-based organic semiconductors. In fact, the structural analyses of BBTNDT both in the single crystal and thin-film state indicated that an interactive two-dimensional molecular array is realized in the solid state, which rationalize the higher carrier mobility in the BBTNDT-based OFETs.

Full text of DOI:10.1021/ja406257u

Article
pubs.acs.org/JACS
Consecutive Thiophene-Annulation Approach to π‑Extended
Thienoacene-Based Organic Semiconductors with
[1]Benzothieno[3,2‑b][1]benzothiophene (BTBT) Substructure
Takamichi Mori,†,§ Takeshi Nishimura,† Tatsuya Yamamoto,†,¶ Iori Doi,† Eigo Miyazaki,† Itaru Osaka,§,†
and Kazuo Takimiya*,§,†
§Emergent Molecular Function Research Group, RIKEN Center for Emergent Matter Science (CEMS), Wako, Saitama 351-0198,
Japan
†Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
S
* Supporting Information
ABSTRACT: We describe a new synthetic route to the
[1]benzothieno[3,2-b][1]benzothiophene (BTBT) substruc-
ture featuring two consecutive thiophene-annulation reactions
from o-ethynyl-thioanisole substrates and arylsulfenyl chloride
reagents that can be easily derived from arylthiols. The method
is particularly suitable for the synthesis of unsymmetrical
derivatives, e.g., [1]benzothieno[3,2-b]naphtho[2,3-b]-
thiophene, [1]benzothieno[3,2-b]anthra[2,3-b]thiophene, and
naphtho[3,2-b]thieno[3,2-b]anthra[2,3-b]thiophene, a sele-
nium-containing derivative, [1]benzothieno[3,2-b][1]-
benzoselenophene. It also allows us to access largely π-
extended derivatives with two BTBT substructures, e.g., bis[1]benzothieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene and
bis[1]benzothieno[2,3-d:2′,3′-d′]naphtho[2,3-b:6,7-b′]dithiophene (BBTNDT). It should be emphasized that these new BTBT
derivatives are otherwise difficult to be synthesized. In addition, since various substrates and reagents, o-ethynyl-thioanisoles and
arylthiols, respectively, can be combined, the method can be regarded as a versatile tool for the development of thienoacene-
based organic semiconductors in this class. Among the newly synthesized materials, highly π-extended BBTNDT afforded very
high mobility (>5 cm2 V−1 s−1) in its vapor-deposited organic field-effect transistors (OFETs), which is among the highest for
unsubstituted acene- or thienoacenes-based organic semiconductors. In fact, the structural analyses of BBTNDT both in the
single crystal and thin-film state indicated that an interactive two-dimensional molecular array is realized in the solid state, which
rationalize the higher carrier mobility in the BBTNDT-based OFETs.
(DAcTTs) represented by [1]benzothieno[3,2-b][1]-
benzothiophene (BTBT)10 and dinaphtho[2,3-b:2′,3′-f ]thieno-
[3,2-b]thiophene (DNTT) derivatives11 are one of the most
promising organic semiconductors owing to their excellent
stability and high mobility (>1.0 cm2 V−1 s−1) in various
transistor architectures (Figure 1).12,13 Such superior properties
can be rationalized by their low-lying HOMO energy levels
(stability)14 and interactive solid-state structure enabling
intermolecular large orbital overlap (high mobility). For
INTRODUCTION
■
Highly extended polyacenes, such as pentacene1 and
naphthacene,2 have been prototypical organic semiconductors
applicable to the high-performance organic field-effect tran-
sistors (OFETs). In fact, they have driven the field of organic
electronics in the past decade.3 Although the carrier mobility of
such polyacenes-based OFETs is generally enhanced by
increasing the number of fused aromatic rings, too large
polyacenes,4 e.g., hexacene5,6 and heptacene,7 are not chemi-
cally stable,7 unless bulky groups that kinetically protect them
from possible reactions are substituted, which makes their
devices less stable under ambient conditions, preventing the
practical use of the larger polyacenes-based OFETs.6 In order
to avoid such instability of simple hydrocarbon-based large
acenes, heteroaromatics, thiophene among others, are incorpo-
rated into the acene structures, affording thienoacens,8 which in
many cases realizes good stability and enables high carrier
mobility simultaneously.
Figure 1. Molecular structures of diacene-fused thieno[3,2-b]-
thiophenes.
Among a vast numbers of the thienoacene-based organic
Received: June 21, 2013
semiconductors,9 diacene-fused thieno[3,2-b]thiophenes
© XXXX American Chemical Society
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Scheme 1. Conventional Synthesis of BTBT and Its Related
Compounds
Scheme 2. New BTBT Synthesis via the Consecutive
Thiophene-Annulation Reactions
realizing these, the thieno[3,2-b]thiophene substructure in-
corporated into the acene framework plays important roles,8
and thus, to develop related DAcTTs is a promising approach
to create new superior materials for OFETs.
consisting of two consecutive thiophene-annulation (thienan-
nulation) reactions (Scheme 2). The initial one is the Larock
reaction from readily available o-ethynylthioanisoles with an
electrophile:18 When the reaction is carried out with phenyl-
sulfenyl chloride as the electrophile, the product, 3-
phenylthiobenzo[b]thiophene, contains all the carbon and
sulfur atoms needed for constructing the BTBT framework.
The intermediate is then supposed to be further cyclized into
the BTBT framework via an intramolecular aryl−aryl
coupling.19
According to the strategy, we first examined the synthesis of
parent BTBT from o-[2-(trimethylsilyl)ethynyl]thioanisole
(1).18 The first cyclization with phenylsulfenyl chloride
(PhSCl) proceeded smoothly to afford corresponding 2,3-
disubstituted benzo[b]thiophenes (2a) in an excellent yield.18
Since PhSCl is not commercially available, we also carried out
the reaction with in situ generated PhSCl from benzenethiol
and N-chlorosuccinimide (NCS).20 Although the isolated yield
was slightly reduced, 2a was obtained in an acceptable yield
(70%). Then the α-TMS group in 2a can be converted into the
iodine (2b) by an action of iodine monochloride (ICl)21 or
bromide group (2c) by deprotection of the TMS group
followed by a reaction with N-bromosuccinimide. The final
palladium catalyzed intramolecular aryl−aryl coupling to build
the second benzo[b]thiophene moiety also proceeded
smoothly to afford BTBT in 73% (from 2b) or 81% yield
(from 2c). Note that the final step is a relatively rare example of
intramolecular aryl−aryl coupling to construct a thiophene ring
(Scheme 2).19
With the successful synthesis of BTBT, we confirmed that
the new synthetic strategy is useful. At the same time, we also
recognized that the method inherently includes “synthetic
flexibility”, as various substrates and reagents can be chosen and
combined. We thus applied the method to the synthesis of: (i)
[1]benzothieno[3,2-b][1]benzoselenophene (BTBS) by using
commercial phenyl selenenyl chloride; (ii) unsymmetrical
BTBT derivatives with five-, six-, or seven-fused aromatic ring
systems by employing naphthalene- and/or anthracene-based
substrate and reagent; and (iii) largely extended derivatives
with two thieno[3,2-b]thiophene moieties by using substrates
with two-fold cyclization sites.
The synthesis of DAcTTs are generally attained by the
iodine-promoted cyclization of o-bis(methylthio)stilbene pre-
cursors (Scheme 1) to form the BTBT substructure,15 the merit
of which is in fact manifold: a straightforward synthesis with
good reproducibility, applicability to selenium analogues,11a,16
and amenability to two-fold reactions affording largely π-
extended thienoacenes, such as bis[1]benzothieno[2,3-d:2′,3′-
d′]benzo[1,2-b:4,5-b′]dithiophene (BBTBDT) and bis-
(naphtho[2,3-b]thieno)[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]-
dithiophene (BNTBDT).17 On the other hand, a drawback of
the method associated with relatively poor accessibility of the o-
bis(methylthio)stilbene precursors limits the material diversity.
The low synthetic yields in the two-fold reactions17 also
prevent the practical access to the largely extended derivatives
with plural thienothiophene moieties. In addition, although
unsymmetrical BTBT derivatives have recently been revealed as
promising organic semiconductors showing very high mobility
and good thermal stability,11c,d the conventional method based
on the iodine-promoted cyclization illustrated in Scheme 1 may
not be amenable to the synthesis of unsymmeterical derivatives.
It is thus very important to devise new synthetic approaches to
the BTBT substructure, the most basic structure of DAcTTs,
for further material developments in this class.
With these motivations, we first describe a new synthetic
approach to parent BTBT and then its application to the
synthesis of various BTBT-based compounds including unsym-
metrical, selenium-containing, or largely π-extended ones with
two-fold thieno[3,2-b]thiophene moieties (Figure 2). In
addition to the synthetic works, we have characterized new
BTBT-based materials and found that among the newly
developed materials, bis[1]benzothieno[2,3-d:2′,3′-d′]naphtho-
[2,3-b:6,7-b′]dithiophene (BBTNDT) with eight aromatic rings
is a superior organic semiconductor that affords excellent thin-
film transistors showing very high field-effect mobility (>5 cm2
V−1 s−1).
RESULTS AND DISCUSSIONS
■
Synthesis. Synthesis of Parent BTBT As a Model
Synthesis. For the development of a new method for the
synthesis of the BTBT framework, we designed a strategy
Synthesis of BTBS. For the synthesis of BTBS, in which one
of two thiophene rings in BTBT is substituted by selenophene,
the reagent in the first step was changed from PhSCl to
phenylselenenyl chloride (Scheme 3). The first cyclization
afforded corresponding 2,3-disubstituted benzo[b]thiophenes
(3a) in a very high yield.18 Conversion of 3a to the
corresponding idodide (3b) by an action of ICl,21 however,
gave 2,3-diiodebenzo[b]thiophene as a byproduct, which
reduces the yield of desired 3b to 54% yield. Instead, a
reaction of iodine with in situ generated α-lithium intermediate
after the desilylation with tetrabutylammonium fluoride gave
Figure 2. New BTBT derivatives targeted in the present work.
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Scheme 3. Synthesis of BTBS
Scheme 5. BTNT Synthesis via a “Reverse” Combination of
the Substrate and Reagent
smoothly to give the precursors (8b and 8c) for the second
thienannulation reaction. The precursors, however, have two
possible reaction sites, i.e., 1- or 3- position on the naphthalene,
likely producing an isomeric mixture. We first examined the
reaction from 8b, but to our surprise, the reaction proceeded
very slowly, and during prolonged reaction time, the iodine
atom was cleaved off to afford 8a as the major product. On the
contrary, with the bromide (8c) as the precursor, the
annulation reaction proceeded smoothly, and almost a
quantitative amount of the cyclized product was obtained. Its
1H NMR spectrum (Figure 3a) clearly shows that the product
consists of two isomers including BTNT, which can be readily
assignable by the comparison with the spectrum of the
authentic BTNT sample obtained from the route demonstrated
in Scheme 4. The diagnostic peaks for the linear-shaped BTNT
are two singlets assignable to the 6- and 11-positions (Figure
3a, top), whereas that for the angular isomer is a doublet at the
lowest magnetic field region (∼ 8.5 ppm) assignable to the 1-
hydrogen at the bay position (Figure 3a bottom, see also Table
S1 for calculated and observed chemical shifts of BTNT and
the isomer). From the integrals of these diagnostic hydrogen
peaks, the product ratio of the linear BTNT to the angular
isomer is ca. 9:1, which is quite fortunate because the linear-
the desired 3b in 90% isolated yield. The corresponding
bromide (3c) can be also synthesized by the same sequence.
The selenophene ring annulation via the palladium catalyzed
intramolecular coupling was found to be less effective
compared to the thiophene ring formation. In the case of the
iodide precursor (3b), BTBS can be obtained in a moderate
yield (44%), whereas the selenophene-annulation reaction from
the bromide precursor (3c) proceeded very slowly, and virtually
only a trace amount of BTBS was detected from the reaction
mixture.
Synthesis of Unsymmetrical BTBT Derivatives. To develop
new π-extended derivatives with unsymmeterical structures,
[1]benzothieno[3,2-b]naphtho[2,3-b]thiophene (BTNT)22
and -anthra[2,3-b]thiophene (BTAT), we employed 2-methyl-
thio-3-(trimethylsilyl)ethynyl-naphthalene (4) and -anthracene
(6), respectively, as the substrates combined with the PhSCl
reagent (Scheme 4). Different from the above BTBT synthesis
in Scheme 2, the direct iodination of 5a and 7a using ICl did
not afford the desired 2-iodo intermediates (5b and 7b), owing
to the preferential chlorination on the naphthalene or
anthracene part as the major reaction.23 Alternatively, two-
step iodination and bromination consisting of the initial
desilylation followed by lithiation and electrophilic halogen-
ation was carried out to obtain 5b, 7b (iodides) and 5c, 7c
(bromides), and the second cyclization gave the corresponding
thienoacenes (BTNT and BTAT) in good yields regardless of
the halogen functionality.
Scheme 4. Synthesis of Unsymmetrical Thienoacenes
From these results, it is obvious that the present approach is
quite suitable for the synthesis of unsymmetrical BTBT
derivatives. On the other hand, compared to versatility of the
substrate, i.e., o-[(trimethylsilyl)ethynyl]thioanisole derivatives,
the reagent, arylsulfenyl chloride, is rather limited, especially for
one with π-extended structure. Thus, to extend the utility of the
present method, we examined 2-naphthylsulfenylchloride in
situ generated from 2-naphthalenethiol and NCS, where o-[2-
(trimethylsilyl)ethynyl]thioanisole (1) was employed as the
substrate (Scheme 5).
Figure 3. (a) 1H NMR spectra of the products (bottom) and authentic
BTNT (top), and (b) proposed palladacycle intermediates for both
isomers.
As shown in Scheme 5, the initial benzo[b]thiophene
formation gives 8a, and the following halogenation proceeded
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shaped isomer, BTNT, is more desirable as an organic
semiconductor.24 Since the angular-shaped isomer has higher
solubility in common organic solvents than that of the linear
isomer, the former can be easily removed from the mixture by
washing with ethanol, and the isomerically pure BTNT was
isolated in 80% yield.
The preferential formation of the linear isomer can be
interpreted by the steric issue in the intramolecular coupling
reaction, where six-membered palladacycles are supposed to
have intermediacy (Figure 3b). One of the intermediates having
the palladacycle with the naphthalene 1-position seems to be a
less favorable structure owing to the steric hindrance between
the ligands on the palladium atom and the 8-hydgogen on the
naphthalene ring (Figure 3b, left). On the other hand, such
steric problem does not occur in the linear intermediate (Figure
3b, right), and therefore the naphthalene 3-position preferen-
tially undergoes the oxidative addition to afford linear BTNT as
the major product.
(11a) in 79% yield. After bromination of the thiophene α-
positions to give 11b, the palladium-catalyzed double
thienannulation reaction afforded BBTBDT. It should be
noted that even for the two-fold reaction in each step the
yield is high, and the total yield of BBTBDT is better than the
former synthesis.17
With the successful application to the synthesis of BBTBDT,
we further exploited the versatility of the method to synthesize
BBTNDT, a BTBT-fused dimer (Scheme 7), which is
otherwise very difficult to be synthesized. Starting from 2,6-
bis(methylthio)-3,7-bis[(trimethylsilyl)ethynyl]naphthalene
(12),25 the first thienannulation reaction afforded naphtho[2,3-
b:6,7-b′]dithiophene derivative (13a) with phenylthio sub-
stituents at the appropriate 3- and 8-positions (64%). Although
the second thienannulation gave the desired BBTNDT, the
reaction was affected by the halogen substituents. When the
dibromide (13c) was used, the isolated yield of BBTNDT is
rather lower (47%) than that from the corresponding iodide
(13b, 81%). We speculate that the limited reactivity of the
bromide (13c) and poor solubility of a monocyclized
intermediate could be related: Even after the monocyclization
the intermediate has a six-ring-fused structure, which should
not be quite soluble, and thus, before the second reaction, the
monocyclized intermediate may precipitate out ending up in
producing monocyclized byproducts. On the contrary, rather
smooth cyclization reaction at the both reaction sites can take
place for the iodide (13b) case with better reactivity, resulting
in higher yield than the bromide case.
With this successful use of in situ generated 2-naphthylsul-
fenyl chloride, we also examined another π-extended unsym-
metrical BTBT derivative, i.e., NTAT (Scheme 6), by using 6 as
the substrate. As expected, NTAT can be obtained, though the
isolated yield was moderate owing to difficulty in the separation
from the isomer having rather little solubility difference.
Scheme 6. Synthesis of NTAT
Compared to the previous synthesis of the extended BTBT
derivatives with two thieno[3,2-b]thioiphene moieties via
double iodine-promoted cyclization,17 the present synthesis of
BBTBDT and BBTNDT has many advantages: better yields
and good reproducibility at the final step and, more
importantly, better accessibility to the substrates and reagent,
particularly, for the synthesis of BBTNDT, where virtually
inaccessible multi and selective functionalized naphthalene
intermediates, i.e., 3,7-bis(methylthio)naphthalene-2,6-dialde-
hyde is required for the preparation of potential precursor for
BBTNDT in the double iodine-promoted cyclization (Figure
4).
Synthesis of Larger BTBT Derivatives with Two Thieno[3,2-
b]thiophene Moieties. Further utility of the present method
was examined by applying the synthesis of larger BTBT
derivatives with two thieno[3,2-b]thiophene moieties. As the
first trial, we chose BBTBDT17 as the target (Scheme 7), and
thus 1,4-bis(methylthio)-2,5-bis[2-(trimethylsilyl)ethynyl]-
benzene (10)21 was reacted with two-fold PhSCl to afford
the corresponding benzo[1,2-b:4,5-b′]dithiophene derivative
Figure 4. Potential precursor for BBTNDT via the double iodine-
promoted cyclization.
Scheme 7. Synthesis of BBTBDT and BBTNDT
Characterization of New BTBT Derivatives. Electronic
Structures. Electronic structures of the BTBT derivatives newly
synthesized were evaluated by cyclic voltammetry (CV),
photoemission yield spectroscopy in air (PESA, Figure S1)
and UV−vis absorption spectra (Figure 5). Figure 5a shows the
absorption spectra of BTBT, BTBS, and [1]benzoslenopheno-
[3,2-b][1]benzoselenophene (BSBS) in chloroform, clearly
indicating the gradual bathochromic shift caused by substituting
the sulfur atom by selenium atom. On the other hand, the
HOMO energy level estimated from their oxidation onsets in
CV indicates that the first substation of the sulfur by selenium
atom is effective to raise the HOMO, and the effect from the
second substitution is rather marginal.
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Table 1. Electronic Properties of BTBT Derivatives
a
a
ab
,
compd
EHOMO, eV
λmax, nm
λedge, nm
Eg, eV
e
c
BTBT
−5.8
−5.6
−5.6
−5.4
−5.4
−5.1
−5.1
−5.1
332
338
344
340
350
357
3.6
3.5
3.5
c
BTBS
f
c
BSBS
d
BTNT
376 (403)
403 (447)
448 (488)
461 (510)
487 (565)
385 (415)
434 (494)
404 (431)
431 (475)
474 (514)
487 (539)
509 (602)
406 (435)
453 (515)
3.1 (2.9)
2.9 (2.6)
2.6 (2.4)
2.5 (2.3)
2.4 (2.1)
3.1 (2.8)
2.7 (2.4)
g
d
DNTT
BTAT
NTAT
d
d
h
d
DATT
i
d
BBTBDT
−5.2
−5.1
d
BBTNDT
a
From absorption spectra in solution and evaporated thin film on a
b
c
quarts substrate (in parentheses). Calculated from λedge. Determined
from the onset potential in cyclic valtammogram (CV, Figure S1)
d
Determined by photoemission yield spectroscopy in air (PESA,
e
f
g
h
i
Figure S1). Ref 29. Ref 16 Ref 11a. Ref 26. Ref 17.
orbitals and elevated EHOMO are characteristic for BTAT
(Figure S2). Consideration of the anthra[2,3-b]thiophene-
dominant frontier orbitals also well explain similar HOMO
energy levels (EHOMOs, −5.1 eV for both) and Egs (2.6 and 2.5
eV in solution and 2.4 and 2.3 eV in the thin film, respectively)
of BTAT and NTAT. A similar interpretation is also possible
for almost the same EHOMOs of BTNT and DNTT; the EHOMO
of BTNT should be governed by the naphtho[2,3-b]thiophene
substructure.
Depicted in Figure 5d,e is the absorption spectra of
BBTBDT and BBTNDT with two thieno[3,2-b]thiophene
moieties and seven- or eight-fused aromatic rings, respectively.
It is interesting to note that their absorption bands are rather
blue-shifted, in other words, larger Egs, compared to the
monothieno[3,2-b]thiophene counterparts with the same
number of aromatic rings, i.e., NTAT and DATT. This can
be understood by the effect of thieno[3,2-b]thiophene inserted
into oligoacene framework, which effectively adds the phene-
like electronic structure in the resulting system.14a On the other
hand, the EHOMOs of BBTBDT and BBTNDT are almost the
same with NTAT and DATT, respectively (Table 1). The DFT
calculations imply that the electronic structures of their
HOMOs are mainly contributed by the central part, dithieno-
[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]dithiophene27 and naphtho-
[2,3-b:6,7-b′]dithiophene,28 respectively (Figure S2); in other
words, the EHOMO could be scaled to some extent by these
acenedithiophene substructures. In addition, their strongly
interactive structures in the solid state may also play an
important role in the present evaluation of HOMO by PESA
using evaporated thin films. In particular, a π-stacking structure
with a close face-to-face interaction (3.58 Å) in BBTBDT as
previously mentioned could significantly affect its EHOMO in the
thin-film state.17 In summary, although the extent of π-
extension and the incorporation manner of the thieno[3,2-
b]thiophene moiety alters the EHOMOs and Egs, all the present
BTBT derivatives keep a relatively low-lying EHOMO sufficient
for stable operation of their p-channel OFETs under ambient
conditions.14
Figure 5. Absorption spectra of new BTBT derivatives with related
compounds: BTBT, BTBS, and BSBS in chloroform solution (a); a
series of compounds with one thieno[3,2-b]thiophene moiety in
chlorobenzene solution (100 °C) (b) and in the evaporated thin film
(c); and BBTBDT and BDTNDT with two thieno[3,2-b]thiophene
moieties in chlorobenzene solution (100 °C) (d) and in the
evaporated thin film (e).
Being different from highly soluble BTBT-BSBS series, the
other derivatives were evaluated by using chlorobenzene
solution at 100 °C or evaporated thin films. Figure 5b,c
shows the absorption spectra of a series of extended BTBT
derivatives with one thieno[3,2-b]thiophene moiety. With
increasing the number of aromatic rings, the absorption
bands shift bathochromically, which can be reasonably
understood by the fact that the HOMO−LUMO energy gap
(Eg) reduces with extension of the conjugation system (Table
1).11a,17,26 However, comparing the absorption spectra of
DNTT and BTAT, which are structural isomers to each other
with six-fused aromatic rings, the latter with the unsymmetrical
structure definitely has red-shifted absorption bands, e.g.,
smaller Eg. This can be explained by different contribution of
local substructures in both compounds to their frontier orbitals.
In DNTT, the two naphtho[2,3-b]thiophene substructures
contribute equally to its frontier orbitals, whereas the
anthra[2,3-b]thiophene substructure may dominate the elec-
tronic structures of the BTAT’s HOMO and LUMO, resulting
in smaller of Eg by ca. 0.2 eV. This qualitative explanation is
supported by the theoretical calculations using the DFT
methods, where the anthra[2,3-b]thiophene-dominant frontier
Molecular and Crystal Structures of BTAT and BBTNDT.
Molecular and packing structures in the solid state are one of
the most important materials factors for organic electronics
application. In the present work, the structural analyses are
thought to be very important, since the molecular structures of
the BTBT derivatives discussed here are rather “unconven-
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Figure 6. Crystal structure of BTAT: (a) molecular structure, (b)
packing structure projected along the crystallographic a-axis, and (c)
herringbone packing structure in the crystallographic ab-cell.
Calculated intermolecular transfer integrals of HOMOs (tHOMOs) are
ta1 = 62, ta2 = 53, tp1 = 32, tp2 = 35, tp3 = 73, and tp4 = 89 meV,
respectively.
Figure 7. Crystal structure of BBTNDT: (a) molecular structure, (b)
packing structure projected along the crystallographic a-axis
representing a molecular lamella structure, and (c) herringbone
packing structure in the crystallographic bc-cell and calculated transfer
integrals. Calculated intermolecular transfer integrals of HOMOs
(tHOMOs) are tc = 75, tp = 32, and tq = 41 meV, respectively.
tional”; we should elucidate how the unsymmetrical structure
affects the packing, or how two thieno[3,2-b]thiophene
moieties in the largely extended molecule, e.g., BBTNDT,
can contribute to intermolecular interaction in the solid state.
With these motivations, we carefully prepared single crystals of
BTAT and BBTNDT suitable for X-ray analyses by the physical
vapor transport method.30 Depicted in Figures 6 and 7 are
molecular and packing structures of these molecules.
The BTAT crystal was found to have a triclinic P1 space
group with two crystallographically independent molecules in
the unit cell. Both the BTAT molecules having almost planar
structures are virtually identical. Unsymmetrical molecules
often form dimers with the inversion center to diminish
asymmetric nature, but in the present case, as expected from
the P1 space group, such dimeric structure is not formed, and
all the molecules in the crystal structure can be thus expressed
by the translation symmetry operation of the molecules in the
asymmetric unit, indicating that all the molecules point the
same direction (Figure 6b). The packing structure of BTAT can
be described as a layer-by-layer structure with the herringbone
motif, which is quite typical for BTBT and DNTT-based
molecules so far reported (Figure 6b,c).8 Owing to its
unsymmetrical unit cell, the thieno[3,2-b]thiophene moieties
are nicely aligned in the crystallographic ab plane direction,
which results in effective intermolecular interactions via the
sulfur atoms with nonbonded distances shorter than or close to
the sum of van der Waals radius of sulfur atom (3.6 Å). As a
result, calculated orbital overlaps of HOMO (transfer integrals,
Being different from the structure of BTAT, BBTNDT
crystallizes into a monoclinic P21/n space group (Figure 7a). Its
packing structure is, however, similar to that of BTAT,
representing the typical layer-by-layer structure with herring-
bone parking motif (Figure 7b). It should be emphasized that
BBTBDT crystallizes into the π-stacking structure,17 which is
strikingly different from the present BBTNDT, despite their
structural similarity, i.e., the linearly π-extended thienoacene
structure with two thieno[3,2-b]thiophene moieties. This
marked difference in molecular arrangements in the solid
state could be explained by the presence/absence of the CH−π,
hydrogen bond-like intermolecular interaction, which facilitates
the face-to-edge bimolecular interaction, resulting in herring-
bone structures.32 The increased number of peri-hydrogen
atoms at the central part of BBTNDT compared to BBTBDT
may play a crucial role for the face-to-edge bimolecular
interaction. The electronic structure in the herringbone cell of
BBTNDT estimated by the calculation of tHOMOs (Figure 7c) is
mostly two-dimensional with well-balanced large orbital
overlaps in each direction, implying again its potential as
high-performance organic semiconductor (vide infra).31
Thin-Film FET Devices of New BTBT Derivatives.
Device Characteristics for Monothieno[3,2-b]thiophene
Series. To evaluate the utility of the new BTBT derivatives
for organic semiconductors, we fabricated FET devices using
their vapor deposited thin films with a bottom gate, top-contact
configuration on Si/SiO2 substrates. Depicted in Figure 8 are
the output- and transfer- characteristics of the FETs evaluated
under ambient conditions, and their field-effect mobilities
(μFET) extracted from the saturation regime are summarized in
Table 2.
tHOMO) in the two-dimensional BTAT layer are similar to what
was observed for other π-extended BTBT derivatives, such as
DNTT and DATT (Figure 6c), implying the BTAT can be
another candidate for high-performance organic semiconductor
for OFET application.31
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Table 2. FET Characteristics
b
compd
BTNT
SAM
Tsub, °C μFET , cm2 V−1 s−1 Ion/Ioff Vth, V
c
OTS
rt
rt
0.15 (0.14)
0.25 (0.23)
0.30 (0.28)
0.55 (0.42)
0.36 (0.27)
0.11 (0.08)
0.12 (0.11)
0.29 (0.19)
0.33 (0.25)
0.41 (0.37)
0.38 (0.28)
0.07 (0.05)
0.14 (0.10)
0.21 (0.16)
0.19 (0.17)
0.48 (0.39)
2.2 (1.8)
105
105
105
105
105
104
105
105
106
105
105
105
105
105
104
105
106
107
105
105
107
107
−11
−6.0
−7.3
−1.0
−5.6
−3.7
+3.6
−1.5
−7.8
−3.1
−4.2
+0.50
−7.6
−3.1
−2.0
+1.0
−4.0
−3.0
−3.8
−8.0
−6.0
−6.0
c
c
ODTS
c
BTAT
OTS
rt
60
100
rt
ODTS
60
100
rt
c
NTAT
OTS
60
100
rt
c
ODTS
60
100
rt
c
BBTNDT
OTS
60
100
150
rt
5.1 (3.4)
c
ODTS
0.15 (0.11)
0.40 (0.38)
5.6 (4.7)
60
100
150
4.4 (3.3)
a
b
Substrate temperature during deposition of the thin film. Typical
and averaged values (in parentheses) obtained from>10 devices with L
c
= 50 μm and W = 1500 μm. OTS: octyltrichlorosilane, ODTS:
octadecyltrichlorosilane.
calculated for the herringbone cell of BTAT (Figure 6c), which
are almost comparable to those for DNTT and DATT, the
results on the present OFETs showing lower mobility by 1
order of magnitude are rather puzzling.
To understand these unexpected results, we first examined
the crystallinity and molecular orientation in the evaporated
thin films by XRD measurements. As clearly seen in the out-of-
plan XRDs (Figure 9a−c), all these molecules tend to stand
perpendicular to the substrate surfaces, which is a common
feature for the BTBT-based organic semiconductors. Also in
the in-plan XRDs, three characteristic peaks for the herringbone
ab-cell are observed, indicating that the molecular orientation
and crystallinity of the thin films are not significantly different
from what was observed for other BTBT-based organic
semiconductors.10,11 On the other hand, one possible
explanation of low mobility for the unsymmetrical derivatives
could be the localized HOMO on one side of the molecule; in
the case of BTAT, its HOMO is localized on the anthra[2,3-
b]thiophene moiety, which affords nonuniform HOMO
distribution in the solid state as depicted in the schematic
picture for HOMO distribution of the crystallographic ac-cell
(Figure 10), where the dense parts (anthra[2,3-b]thiophene
moiety) and dilute parts (benzo[b]thiophene moiety) of
HOMO alternately exist along the c-axis direction. In the
actual thin films consisting of many crystalline domains/grains,
it is natural to consider that, although the crystallites orient
along the c-axis (as evidenced by the XRDs), the direction of
the domains/grains should not be always the same, in other
words, the crystallites could orient either along the 001 or 001
directions randomly. In such circumstance, the electronic
coupling between the crystallites with the reverse orientation
should be poor. From these experimental results and also the
theoretical considerations, the BTBT derivatives with unsym-
Figure 8. Transfer and output characteristics of top contact, bottom
gate OFET devices fabricated on the OTS-treated substrate by using
vapor deposited thin films. (a) BTNT (Tsub = rt), (b) BTAT (Tsub
=
60 °C), (c) NTAT (Tsub = 60 °C), and (d) BBTNDT (Tsub = 150 °C).
Owing to the relatively low molecular weight, the BTNT thin
film can be deposited only on the substrate kept at rt (Tsub
=
rt). On the other hand, thin films of other compounds can be
deposited on the substrates at higher Tsubs. Field-effect
mobilities extracted from the saturation regime for the
BTNT, BTAT, and NTAT-based transistors, however, were
in the range of 0.1−0.5 cm2 V−1 s−1 (Table 2). Compared to
the reported mobility for the DNTT-11a and DATT-based
semiconductors, up to 3.0 cm2 V−1 s−1,26 the mobilities
obtained from unsymmetrical derivatives appear to be quite
low. In particular, considering the relatively large tHOMOs
̅
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Figure 10. Schematic picture of HOMO distribution in the ac-cell of
BTAT: HOMO coefficients are superimposed on the packing
structure of BTAT.
exceed 5 cm2 V−1 s−1, which is comparable to the highest
mobility so far reported for small-molecule-based OFETs with
multigrain thin films as the active semiconducting channel. It
should be noted that the HOMO energy level of BBTNDT
(5.1 eV below the vacuum level, Table 1) can realize a relatively
small injection barrier from the gold source electrode to the
semiconducting layer (Figure 8d, output). Furthermore,
BBTNDT with the largely π-extended structure ensures
thermal stability in thin-film state on the substrate, and in
fact the OFET devices resisted thermal treatments up to 200
°C for 15 min (Figure S3).33 These excellent semiconducting
behaviors can be rationalized by its packing structure in the thin
film state; all the peaks observed in both the out-of-plane and
in-plane XRDs (Figure 9d) are well indexed by the single
crystal cell, indicating that a highly intermolecularly interactive
structure with the edge-on molecular orientation and
herringbone arrangement (Figure 7b,c) is also realized in the
thin-film state, as observed in many related high-performance
thinenoacene-based organic semiconductors.
Discussion on Largely π-Extended Thienoacens As High-
Performance Organic Semiconductors. Recent intensive
efforts in the material development have produce many high-
performance organic semiconductors showing mobility higher
than 5 cm2 V−1 s−1, but most of them have substituents such as
long alkyl10b,d,11c,d or (trialkylsilyl)ethynyl group4b,34 that
promotes self-assembling of the π-conjugated cores, facilitating
the efficient intermolecular interaction in the active semi-
conducting layer. In this relation, it has been recently pointed
out that the substituents (e.g., long alkyl groups) may also act
as “screen” from possible charge trapping effect caused by the
coupling between the charge carriers in the channel and the
electrical polarization in the gate dielectric.35 Both of these two
effects from the substituents can facilitate effective charge
transport. In fact, FET mobilities reported for thin film
transistors based on “naked” thienoacenes without the
substituents are relatively limited: e.g., ∼0.30 cm2 V−1 s−1 for
ADT,36 ∼0.15 cm2 V−1 s−1 for DBTBT,37 ∼0.57 cm2 V−1 s−1
for PT,38 ∼0.94 cm2 V−1 s−1 for BNTBDT (Figure 11),17 ∼0.14
cm2 V−1 s−1 for BBTBDT (Scheme 7),17 ∼3.0 cm2 V−1 s−1 for
Figure 9. Out-of-plane (left) and in-plan XRD patterns (right) of
evaporated thin film on the Si/SiO2 substrate: (a) BTNT (Tsub = rt),
(b) BTAT (Tsub = 60 °C), (c) NTAT (Tsub = 60 °C), and (d)
BBTNDT (Tsub = 100 °C).
metrical core structures seem to be less favorable for the
development of high-performance organic semiconductors.
Device Characteristics for BBTNDT. In sharp contrast, the
BBTNDT-based devices showed quite high mobilities (Table 2,
Figure 8d). As summarized in Table 2, although the mobility
largely depended on Tsubs, the devices showed excellent FET
characteristics with the mobility higher than 2 cm2 V−1 s−1 at
higher Tsubs than 100 °C. In particular, the best mobilities
H
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DNTT11a and DATT26 (Figure 1). From the viewpoint of the
structure−property relationship, BBTNDT can be regarded as a
very promising and interesting new thienoacene core structure
for further investigations both for device applications and
theoretical investigation.
impact ionization procedure (70 eV). The molecular ion peaks of the
chlorine, bromine, sulfur, or selenium containing compounds showed
a typical isotopic pattern, and all the mass peaks are reported based on
35Cl, 79Br, 32S, 80Se, respectively.
3-Phenylthio-2-(trimethylsilyl)benzo[b]thiophene (2a). A
solution of phenylsulfenyl chloride (0.7 mL, 7.5 mmol) in dichloro-
methane (50 mL) was added to a solution of 1 (1.1 g, 5 mmol) in
dichloromethane (70 mL) at 0 °C. The reaction mixture was stirred at
rt for 4 h. The mixture was diluted with dichloromethane (10 mL) and
washed with water (50 mL × 3) and brine (50 mL). The organic layer
was dried (MgSO4) and concentrated in vacuo. The residue was
purified by column chromatography on silica gel (ethyl acetate−
hexane, 1:10 v/v, Rf
= 0.8) to give 3-(phenylthio)-2-
trimethylsilylbenzo[b]thiophene (2a, 1.4 g, 93%) as a white solid.
Mp. 82−84 °C; 1H NMR (400 MHz) δ 0.41 (s, 9H), 6.97 (td, J = 1.4,
7.2 Hz, 2H), 7.05 (tt, J = 1.4, 7.2 Hz, 1H), 7.15 (dt, J = 1.1, 7.2 Hz,
2H), 7.30 (dt, J = 1.1, 7.0 Hz, 1H), 7.35 (dt, J = 1.3, 7.2 Hz, 1H), 7.73
(d, J = 7.4 Hz, 1H), 7.89 (d, J = 7.4 Hz, 1H); 13C NMR (100 MHz) δ
0.1, 122.7, 123.4, 125.0, 125.1, 125.3, 126.3, 129.2, 129.5, 138.4, 142.0,
143.0, 149.7; EI-MS (70 eV) m/z = 314 (M+); Anal. calcd for
C17H18S2Si: C, 64.91; H, 5.77%. Found: C, 64.86; H, 5.57%.
Figure 11. Molecular structures of π-extended thienoacenes.
CONCLUSION
■
2-Iodo-3-(phenylthio)benzo[b]thiophene (2b). A solution of
ICl in dichloromethane (1 M, 0.6 mL, 0.6 mmol) was added to a
solution of 2a (157 mg, 0.5 mmol) in dichloromethane (5 mL) at −40
°C. The mixture was stirred for 3 h at the same temperature and then
poured into a saturated aqueous solution of Na2S2O5 (3 mL). The
resulting mixture was extracted with dichloromethane (10 mL × 3),
and the combined extracts were washed with brine (15 mL × 3), dried
(MgSO4), and concentrated in vacuo. The residue was purified by
column chromatography on silica gel (chloroform, Rf = 0.9) to give 2-
iodo-3-(phenylthio)benzo[b]thiophene as a white solid (2b, 167 mg,
In summary, we have established new synthetic route to the
BTBT substructure featuring two consecutive thienannulation
reactions from o-ethynyl-thioanisole substrates and arylsulfenyl
chloride reagents. The method is suitable to the synthesis of
unsymmetrical derivatives, a selenium-containing derivative and
also largely π-extended derivatives with two BTBT sub-
structures. It should be emphasized that these new derivatives
are otherwise difficult to be synthesized, and thus the present
method is quite useful for the development of materials in this
class. In fact, the merits of the present method for the synthesis
of the BTBT-based materials are summarized as follows: (1)
the various substrates and reagents are readily accessible and
can be combined, which can lead to a wide range of materials;
(2) each reaction in the method proceeds in a good yield; and
(3) the present method is suitable to the synthesis of
unsymmetrical derivatives and two-BTBT incorporated de-
rivatives. In fact, BBTNDT, a newly developed π-extended
thienoacene by using this method, behaves as an excellent p-
channel organic semiconductor showing mobility as high as 5
cm2 V−1 s−1 in thin-film transistor settings, which indicates that
such π-extended heteroacenes with an appropriate molecular
design are potential materials for high-performance organic
semiconductors. We believe that the present method can
accelerate the design and synthesis of new π-extended
heteroacenes to develop superior organic semiconductors,
and the new high-performance organic semiconductor,
BBTNDT, will be utilized into sophisticated applications in
future.
1
90%). Mp. 97−98 °C; H NMR (400 MHz) δ 7.08−7.14 (m, 3H),
7.20 (t, J = 7.8 Hz, 2H), 7.28−7.35 (m, 2H), 7.79 (dd, J = 2.3, 6.9 Hz,
2H); 13C NMR (100 MHz) δ 95.7, 122.1, 124.0, 125.4, 125.5, 126.1,
127.4, 129.3, 131.6, 136.0, 139.0, 143.9; EI-MS (70 eV) m/z = 368
(M+); Anal. calcd for C14H9IS2: C, 45.66; H, 2.46%. Found: C, 46.04;
H, 2.08%.
2-Bromo-3-phenylthiobenzo[b]thiophene (2c). To a solution
of 2a (150 mg, 0.5 mmol) in THF (5 mL) and water (0.1 mL) was
added a solution of tetrabutylammonium fluoride (1 M, 1 mL, 1.0
mmol). The mixture was stirred for 4 h at rt, then poured into water
(10 mL), and extracted with ethyl acetate (10 mL × 3). The combined
extracts were washed with brine (20 mL × 3), dried (MgSO4), and
concentrated in vacuo. The residue was purified by column
chromatography on silica gel (chloroform, Rf = 0.9) to give 3-
phenylthiobenzo[b]thiophene (115 mg, quantitative) as colorless oil.
1H NMR (400 MHz) δ 7.10−7.23 (m, 5H), 7.36 (dt, J = 1.6, 7.1 Hz,
1H), 7.40 (dt, J = 1.6, 7.1 Hz, 1H), 7.72 (s, 1H), 7.80 (dd, J = 2.1, 6.6
Hz, 1H), 7.90 (dd, J = 2.4, 7.6 Hz, 1H), 13C NMR (100 MHz) δ 123.3,
123.4, 124.3, 125.1, 125.3, 126.2, 127.8, 129.3, 132.5, 136.9, 139.2,
140.3; EI-MS (70 eV) m/z = 242 (M+); HRMS (APCI) m/z calcd for
C14H11S2 [M + H]+: 243.02967. Found: 243.02963.
To a solution of 3-phenylthiobenzo[b]thiophene (115 mg, 0.48
mmol) in chloroform (3 mL) was added N-bromosuccinimide (89 mg,
0.5 mmol), and the resulting mixture was stirred at rt for 12 h. The
mixture was poured into water (10 mL) and was extracted with
chloroform (5 mL × 3). The combined extracts were washed with
brine (10 mL), dried (MgSO4), and concentrated in vacuo. The
residue was purified by column chromatography on silica gel
(chloroform, Rf = 0.9) to give 2-bromo-3-phenylthiobenzo[b]-
EXPERIMENTAL SECTION
■
General. All chemicals and solvents are of reagent grade unless
otherwise indicated. Tetrahydrofuran (THF), triethylamine, N,N-
dimethylformamide, (DMF), and dichloromethane were purified with
standard distillation procedures prior to use. 2-Iodothioanisole was
purchased from Tokyo Chemical Industry Co., Ltd. 2-[2-
(Trimethylsilyl)ethynyl]thioanisole (1),18 3-(methylthio)naphthalen-
2-yl-trifluoromethanesulfonate,11 3-(methylthio)anthracen-2-yl-tri-
fluoromethanesulfonate,26 2,6-dimethoxy-3,7-bis(methylthio)-
naphthalene,39 1,4-bis(methylthio)-2,5-bis[2-(trimethylsilyl)ethynyl]-
benzene,21 and phenylsulfenyl chloride40 were prepared according to
reported procedures. All reactions were carried out under nitrogen
atmosphere unless otherwise mentioned. Melting points were
uncorrected. NMR spectra were obtained in deuterated chloroform
with TMS as internal reference; chemical shifts (δ) are reported in
parts per million. EI-MS spectra were obtained using an electron
1
thiophene (2c, 129 mg, 85%) as a white solid. Mp. 86−87 °C; H
NMR (400 MHz) δ 7.11−7.22 (m, 5H), 7.33 (dt, J = 1.6, 7.1 Hz, 1H),
7.37 (dt, J = 1.6, 7.1 Hz, 1H), 7.74−7.79 (m, 2H); 13C NMR (100
MHz) δ 122.3, 123.9, 125.5, 125.72, 125.73, 125.76, 126.3, 127.6,
129.4, 135.8, 139.3, 139.9; EI-MS (70 eV) m/z = 320 (M+); HRMS
(APCI) m/z calcd for C14H9BrS [M]+: 319.93236. Found: 319.93259.
[1]Benzothieno[3,2-b][1]benzothiophene (BTBT). To a dea-
erated solution of 2b (150 mg, 0.4 mmol), sodium acetate (67 mg, 0.8
mmol), in N,N-dimethylacetamide (8 mL) was added PdCl2(PPh3)2
(14 mg, 0.02 mmol). The mixture was stirred for 12 h at 140 °C and
I
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then quenched by adding hydrochloric acid (1 M, 20 mL). The
resulting mixture was extracted with ethyl acetate-hexane (1:1 v/v, 50
mL), and the extract was washed with brine (50 mL × 3), dried
(MgSO4), and concentrated in vacuo. The residue was purified by
column chromatography on silica gel (hexane, Rf = 0.3) to give BTBT
as a white solid (72 mg, 73%). Mp. 213−215 °C (ref 41 216−218 °C);
1H NMR (400 MHz,) δ 7.41 (dt, J = 1.4, 7.6 Hz, 2H), 7.47 (dt, J = 1.4,
7.6 Hz, 2H), 7.90 (dd, J = 1.4, 7.6 Hz, 2H), 7.93 (dd, J = 1.4, 7.6 Hz,
2H); 13C NMR (100 MHz) δ 122.0, 124.4, 125.3, 125.4, 133.6, 133.9,
142.8; EI-MS (70 eV) m/z =240 (M+). BTBT was also obtained from
2c in the same manner as described above. 81% isolated yield.
3-Phenylseleno-2-(trimethylsilyl)benzo[b]thiophene (3a).
The title compound was obtained in the same manner as described
in ref 18a (quantitative yield). Yellow oil. 1H NMR (400 MHz) δ 0.43
(s, 9H), 7.05−7.14 (m, 5H), 7.25−7.3 (m, 2H), 7.82 (dd, J = 1.4, 7.1
Hz, 1H), 7.90 (dd, J = 1.4, 7.1 Hz, 1H); 13C NMR (100 MHz) δ 0.33,
122.4, 124.5, 125.0, 125.1, 125.6, 126.0, 128.8, 129.4, 133.7, 142.9,
143.3, 149.4; EI-MS (70 eV) m/z = 362 (M+).
0.5 mmol), and the mixture was stirred for 10 h at 90 °C. The mixture
was poured into water (150 mL) and was extracted with ethyl acetate-
hexane (1:1 v/v, 100 mL × 3). The combined extracts were washed
with brine (50 mL × 3), dried (MgSO4), and concentrated in vacuo.
The residue was purified by column chromatography on silica gel
(hexane, Rf = 0.2) to give 2-methylthio-3-[(2-trimethylsilyl)ethynyl)]-
naphthalene (4.1 g, quantitative) as yellow oil. 1H NMR (400 MHz) δ
0.31 (s, 9H), 2.58 (s, 3H), 7.39 (dt, J = 1.3, 6.9 Hz, 1H), 7.45 (s, 1H),
7.46 (dt, J = 1.3, 6.9 Hz, 1H), 7.72 (m, 2H), 7.96 (s, 1H); 13C NMR
(100 MHz) δ 0.3, 15.5, 101.1, 102.5, 120.0, 121.9, 125.7, 126.9, 127.2,
127.8, 130.6, 133.0, 133.7, 138.6; EI-MS (70 eV) m/z = 270 (M+);
Anal. calcd. for C16H18SSi: C, 71.05; H, 6.71%. Found: C, 70.83; H,
6.99%.
3-Phenylthio-2-(trimethylsilyl)naphtho[2,3-b]thiophene
(5a). A similar procedure to the synthesis of 2a gave title compound
from 4 and phenylsulfenyl chloride (quantitative). White solid; Mp.
170−172 °C ;1H NMR (400 MHz) δ 0.44 (s, 9H), 7.00−7.07 (m,
3H), 7.15 (t, J = 7.6 Hz, 2H), 7.41 (dt, J = 1.2, 7.3 Hz, 1H), 7.47 (dt, J
= 1.2, 7.3 Hz, 1H), 7.78 (d, J = 8.2 Hz, 1H), 7.91 (d, J = 8.2 Hz, 1H),
8.25 (s, 1H), 8.38 (s, 1H); 13C NMR (100 MHz) δ 0.0, 120.9, 121.8,
125.4, 126.1, 126.3, 127.5, 125.6, 129.0, 129.1, 129.2, 131.3, 131.5,
138.3, 140.6, 140.8, 152.9; EI-MS (70 eV) m/z = 364 (M+); Anal.
calcd for C21H20S2Si: C, 69.18; H, 5.53%. Found: C, 69.56; H, 5.29%.
2-Iodo-3-(phenylthio)naphtho[2,3-b]thiophene (5b). To a
solution of 5a (1.0 g, 2.7 mmol) in THF (100 mL) and water (1
mL) was added a solution of tetrabutylammonium fluoride (1 M, 4.1
mL, 4.1 mmol) at rt. The mixture was stirred for 4 h at the same
temperature and then poured into water (100 mL), and the resulting
precipitate was collected by filtration and washed with ethanol and
hexane. The crude product was purified by column chromatography
on silica gel (chloroform, Rf = 0.9) to give 3-(phenylthio)naphtho[2,3-
2-Iodo-3-(phenylseleno)benzo[b]thiophene (3b). The title
compound was obtained in the same manner for the synthesis of 2b
1
(54% isolated yield). White solid; Mp. 86−87 °C; H NMR (400
MHz) δ 7.15−7.25 (m, 5H), 7.29 (dt, J = 1.9, 5.0 Hz, 1H), 7.31(dt, J =
1.9, 5.0 Hz, 1H), 7.77−7.79 (m, 1H), 7.82−7.85 (m, 1H); 13C NMR
(100 MHz) δ 96.0, 121.9, 125.4, 125.6, 125.7, 127.0, 129.7, 130.3,
131.7, 132.7, 140.6, 144.5; EI-MS (70 eV) m/z = 416 (M+); HRMS
(APCI) m/z Calcd for C14H9ISSe [M]+: 415.86294. Found:
415.86227.
3b was also synthesized via desilylation and following lithiation/
electrophilic iodination: treatment of 3a with a solution of
tetrabutylammonium fluoride gave 3-(phenylseleno)benzo[b]-
thiophene as colorless oil (quantitative): 1H NMR (400 MHz) δ
7.14−7.18 (m, 3H), 7.27−7.29 (m, 2H), 7.36 (t, J = 6.0 Hz, 1H), 7.38
(t, J = 6.0 Hz, 1H), 7.72 (s, 1H), 7.82−7.86 (m, 1H), 7.88−7.91 (m,
1H); 13C NMR (100 MHz) δ 119.6, 123.0, 124.4, 125.15, 125.20,
126.8, 129.6, 130.5, 132.0, 132.8, 140.3, 140.4; EI-MS (70 eV) m/z =
290 (M+); HRMS (EI) m/z calcd for C14H10SSe [M]+: 289.9667.
Found: 289.9663.
To a solution of 3-(phenylseleno)benzo[b]thiophene (211 mg, 0.73
mmol) in THF (5 mL) was added n-butyllithium (1.63 M in hexane,
0.53 mL, 0.87 mmol) at 0 °C. The mixture was warmed to rt and then
stirred for 1 h. Iodine (221 mg, 0.87 mmol) was added to the mixture
at 0 °C, and the resulting mixture was stirred for 10 h at rt, and then
poured into hydrochloric acid (1 M, 10 mL). The resulting mixture
was extracted with dichloromethane (10 mL × 3), and the combined
extracts were washed with brine (15 mL × 3), dried (MgSO4), and
concentrated in vacuo. The residue was purified by column
chromatography on silica gel (chloroform, Rf = 0.9) to give 3b as a
white solid (274 mg, 90%).
1
b]thiophene as a white solid (quantitative). Mp. 136−138 °C; H
NMR (400 MHz) δ 7.11−7.21 (m, 5H), 7.45 (dt, J = 1.4, 7.9 Hz, 1H),
7.50 (dt, J = 1.4, 7.9 Hz, 1H), 7.78 (s, 1H), 7.93 (d, J = 7.9 Hz, 2H),
8.31 (s, 1H), 8.39 (s, 1H); 13C NMR (100 MHz) δ 121.7, 121.9,
123.9, 125.5, 126.1, 127.5, 128.0, 128.9, 129.3, 131.2, 131.4, 134.3,
134.4, 136.7, 137.9, 138.3; EI-MS (70 eV) m/z = 292 (M+); Anal.
calcd for C18H12S2: C, 73.93; H, 4.14%. Found: C, 73.83; H, 3.90%.
To a solution of 3-(phenylthio)naphtho[2,3-b]thiophene (146 mg,
0.5 mmol) in THF (5 mL) was added n-butyllithium (1.63 M in
hexane, 0.46 mL, 0.75 mmol) at 0 °C. The mixture was warmed to rt
and then stirred for 1 h, and iodine (190 mg, 0.75 mmol) was added to
the mixture at 0 °C. The resulting mixture was stirred for 6 h at rt,
poured into an aqueous solution of Na2S2O5 (saturated, 5 mL), and
extracted with dichloromethane (50 mL × 3). The combined extracts
were washed with brine (50 mL × 3), dried (MgSO4), and
concentrated in vacuo. The residue was purified by column
chromatography on silica gel (chloroform, Rf = 0.9) to give 5b (138
1
mg, 66%) as a pale yellow solid. Mp. 194−196 °C; H NMR (400
2-Bromo-3-(phenylseleno)benzo[b]thiophene (3c). A similar
MHz) δ 7.10−7.22 (m, 5H), 7.46 (dt, J = 1.4, 7.5 Hz, 1H), 7.51 (dt, J
= 1.4, 7.5 Hz, 1H), 7.90 (t, J = 7.5 Hz, 2H), 8.28 (s, 1H), 8.30 (s, 1H);
13C NMR (100 MHz) δ 99.0, 120.4, 122.6, 126.0, 126.5, 126.6, 127.4,
127.5, 129.0, 129.5, 131.2, 131.4, 131.4, 135.9, 137.4, 141.3; EI-MS (70
eV) m/z = 418 (M+); HRMS (APCI) m/z calcd for C18H11IS2 [M]+:
417.93414, Found: 417.93405.
procedure using 1,2-dibromo-1,1,2,2-tetrachloroethane instead of
1
iodine gave 3c in quantitative yield. White solid; Mp. 60−63 °C; H
NMR (400 MHz) δ 7.15−7.19 (m, 3H), 7.25−7.28 (m, 2H), 7.31−
7.37 (m, 2H), 7.72−7.84 (m, 2H); 13C NMR (100 MHz) δ 122.0,
123.1, 125.13, 125.15, 125.6, 125.7, 127.0, 129.6, 130.5, 131.2, 140.5,
140.7; EI-MS (70 eV) m/z = 368 (M+); HRMS (EI) m/z calcd for
C14H9BrSSe [M]+: 367.8768, Found: 367.8768.
2-Bromo-3-(phenylthio)naphtho[2,3-b]thiophene (5c). A
similar procedure using 1,2-dibromo-1,1,2,2-tetrachloroethane instead
of iodine gave 5c in 93% yield. Pale-yellow solid; Mp. 181−183 °C; 1H
NMR (400 MHz) δ 7.10−7.23 (m, 5H), 7.46 (dt, J = 1.3, 6.8 Hz, 1H),
7.51 (dt, J = 1.3, 7.9 Hz, 1H), 7.91(t, J = 7.9 Hz, 2H), 8.26 (s, 1H),
8.28 (s, 1H); 13C NMR (100 MHz) δ 120.7, 122.4, 125.3, 126.0,
126.3, 126.5, 127.51, 127.53, 127.9, 128.9, 129.5, 131.5, 131.7, 135.7,
137.6, 137.8; EI-MS (70 eV) m/z = 370 (M+); HRMS (APCI) m/z
calcd for C18H11BrS2 [M]+: 369.94801. Found: 369.94739.
[1]Benzothieno[3,2-b]naphtho[2,3-b]thiophene (BTNT). The
title compound was obtained in the same manner as for the synthesis
of BTBT: 91% isolated yield from 5b and 90% yield from 5c. Yellow
solids; Mp. 289−291 °C; 1H NMR (400 MHz) δ 7.43 (dt, J = 1.3, 7.2
Hz, 1H), 7.48 (dt, J = 1.3, 7.2 Hz, 1H), 7.52 (t, J = 6.5 Hz, 1H), 7.53
(t, J = 6.5 Hz, 1H), 7.89−7.96 (m, 3H), 8.02 (dd, J = 3.5, 6.5 Hz, 1H),
[1]Benzothieno[3,2-b][1]benzoselenophene (BTBS). The title
compound was obtained in the same manner as for the synthesis of
BTBT. BTBS was purified by column chromatography on silica gel
(hexane-chloroform, 5:1 v/v, Rf = 0.6) as a white solid (44%). Mp.
1
208−209 °C; H NMR (400 MHz) δ 7.33 (dt, J = 1.3, 7.6 Hz, 1H),
7.38−7.48 (m, 3H), 7.82 (dd, J = 1.3, 7.6 Hz, 1H), 7.87−7.97 (m,
3H); 13C NMR (100 MHz) δ 122.7, 123.6, 124.3, 125.3, 125.4, 125.7,
125.8, 127.5, 132.2, 135.7, 136.1, 136.2, 141.7, 142.6; EI-MS (70 eV)
m/z = 288 (M+); HRMS (APCI) m/z calcd for C14H8SSe [M]+:
287.95064, Found: 287.95059.
2-Methylthio-3-[2-(trimethylsilyl)ethynyl]naphthalene (4).
To a deaerated solution of 3-(methylthio)naphthalen-2-yl-trifluor-
omethanesulfonate (5 g, 15.5 mmol), tributyl(trimethylsilylethynyl)tin
(6.6 g, 17.1 mmol) in DMF (150 mL) was added Pd(PPh3)4 (537 mg,
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8.36 (s, 1H), 8.39 (s, 1H); 13C NMR (100 MHz) δ 120.1, 122.3,
122.8, 124.4, 125.4, 125.7, 126.0, 126.1, 127.7, 127.8, 128.6, 131.7,
131.8, 132.8, 133.7, 134.9, 141.1, 143.2; EI-MS (70 eV) m/z = 290
(M+); HRMS (APCI) m/z calcd for C18H11S2 [M + H]+: 291.02967,
Found: 291.02997.
2-Methylthio-3-[2-(trimethylsilyl)ethynyl]anthracene (6).
The title compound was obtained as a yellow solid from 3-
(methylthio)anthracen-2-yl-trifluoromethanesulfonate in the same
manner as for the synthesis of 4. 84% isolated yield. Mp. 161−164
°C; 1H NMR (400 MHz) δ 0.33 (s, 9H), 2.62 (s, 3H), 7.41−7.48 (m,
2H), 7.56 (s, 1H), 7.94 (d, J = 7.9 Hz, 1H), 7.96 (d, J = 7.9 Hz, 1H),
8.14 (s, 1H), 8.25 (s, 1H), 8.29 (s, 1H); 13C NMR (100 MHz) δ 0.3,
15.6, 101.4, 102.6, 119.9, 121.1, 124.7, 125.7, 126.4, 126.6, 128.3,
128.7, 129.2, 131.6, 131.7, 133.0, 133.6, 137.6; EI-MS (70 eV) m/z =
320 (M+); HRMS (APCI) m/z calcd for C20H20SSi [M]+: 320.10495.
Found: 320.10550.
3-Phenylthio-2-(trimethylsilyl)anthra[2,3-b]thiophene (7a).
The title compound was synthesized from 6 and phenylsulfenyl
chloride. Yellow solid (86%). Mp. 193−196 °C ; 1H NMR (400 MHz)
δ 0.46 (s, 9H), 7.05−7.18 (m, 5H), 7.38 (dt, J = 1.6, 6.6 Hz, 1H), 7.42
(dt, J = 1.6, 6.6 Hz, 1H), 7.94 (dd, J = 1.6, 7.9 Hz, 1H), 7.98 (dd, J =
1.6, 7.9 Hz, 1H), 8.44 (s, 1H), 8.52 (s, 2H), 8.55 (s, 1H); 13C NMR
(100 MHz) δ 0.0, 120.7, 121.9, 125.3, 125.4, 125.5, 125.6, 126.3,
127.6, 128.4, 128.5, 129.0, 129.3, 129.8, 120.0, 131.5, 132.0, 138.2,
140.0, 140.7, 153.8; EI-MS (70 eV) m/z = 414 (M+). HRMS (APCI)
m/z calcd for C25H22S2Si [M]+: 414.09267. Found: 414.09299.
2-Iodo-3-(phenylthio)anthra[2,3-b]thiophene (7b). 3-
(Phenylthio)anthra[2,3-b]thiophene was synthesized from 7a in the
same as for the synthesis of 3-(phenylthio)naphtho[2,3-b]thiophene
(quantitative). Yellow solid; Mp. 240−242 °C; 1H NMR (400 MHz) δ
7.15−7.29 (m, 5H), 7.42 (dt, J = 2.2, 6.8 Hz, 1H), 7.44 (dt, J = 2.2, 6.8
Hz, 1H), 7.76 (s, 1H), 7.98 (d, J = 9.1 Hz, 1H), 8.01 (d, J = 9.1 Hz,
1H), 8.49 (s, 1H), 8.53 (s, 1H), 8.56 (s, 2H); 13C NMR (100 MHz) δ
120.4, 121.7, 122.3, 125.5, 125.6, 125.8, 126.6, 127.5, 128.4 128.5,
128.6, 129.5, 129.8, 129.9, 130.2, 131.8, 132.2, 134.5, 136.6, 138.1; EI-
MS (70 eV) m/z = 342 (M+); HRMS (APCI) m/z calcd for C22H14S2
[M]+: 342.05314. Found: 342.05371.
Anal. calcd for C22H12S2: C, 77.61; H, 3.55%. Found: C, 77.50; H,
3.16%.
3-(2-Naphthylthio)benzo[b]thiophene (8a). To a solution of 2-
naphthalenethiol (147 mg, 0.92 mmol) in dichloromethane (5 mL)
was added N-chlorosuccinimide (123 mg, 0.92 mmol) at 0 °C. After
the mixture was stirred for 20 min at rt, the resulting dichloromethane
solution of 2-naphthylsulfenyl chloride was added to a solution of 1
(135 mg, 0.61 mmol) in dichloromethane (5 mL) at 0 °C. After
stirring at rt for 2 h, a solution of tetrabutylammonium fluoride (1 M,
1.2 mL, 1.2 mmol) was added to the mixture, and the resulting mixture
was stirred for 3 h, and the poured into saturated aqueous K2CO3
solution (50 mL). The mixture was extracted with dichloromethane
(10 mL × 3), and the combined extracts were washed with brine (15
mL × 3), dried (MgSO4), and concentrated in vacuo. The residue was
purified by column chromatography on silica gel (chloroform-hexane,
1:2 v/v, Rf = 0.6) to give 3-(2-naphthylthio)benzo[b]thiophene as a
1
white solid (115 mg, 87%). Mp. 61−62 °C; H NMR (400 MHz) δ
7.28 (dd, J = 1.9, 8.7 Hz, 1H), 7.34 (dt, J = 1.1, 7.0 Hz, 1H), 7.37−7.44
(m, 3H), 7.60−7.64 (m, 2H), 7.68 (d, J = 8.5 Hz, 1H), 7.73 (dd, J =
2.4, 7.0 Hz, 1H), 7.76 (s, 1H), 7.81 (d, J = 7.9 Hz, 1H), 7.91 (d, J = 7.9
Hz, 1H); 13C NMR (100 MHz) δ 123.3, 123.4, 124.3, 125.2, 125.4,
126.0, 126.2, 126.9, 127.5, 128.1, 129.0, 129.3, 132.1, 132.4, 134.0,
134.3, 139.2, 140.4; EI-MS (70 eV) m/z = 292 (M+); HRMS (APCI)
m/z calcd for C18H13S2 [M + H]+: 293.04532. Found: 293.04523.
2-Iodo-3-(2-naphthylthio)benzo[b]thiophene (8b). The title
compound was obtained in the same manner as for the synthesis of 5b
1
(67%). White solid; Mp. 155−158 °C; H NMR (400 MHz) δ 7.18
(dd, J = 2.1, 8.9 Hz, 1H), 7.25−7.33 (m, 2H), 7.38 (dt, J = 1.4, 6.8 Hz,
1H), 7.41 (dt, J = 1.4, 6.8 Hz, 1H), 7.52 (s, 1H), 7.62 (d, J = 7.4 Hz,
1H), 7.66 (d, J = 8.9 Hz, 1H), 7.73 (d, J = 7.4 Hz, 1H), 7.80 (td, J =
2.1, 7.6 Hz, 2H); 13C NMR (100 MHz) δ 95.6, 122.2, 124.1, 125.5,
125.62, 125.64, 125.65, 126.0, 126.9, 127.4, 128.1, 129.1, 131.5, 132.0,
133.5, 134.0, 139.1, 144.0; EI-MS (70 eV) m/z = 418 (M+); HRMS
(ESI) m/z calcd for C18H11IS2 [M + H]+: 418.9425. Found: 418.9420.
2-Bromo-3-(2-naphthylthio)benzo[b]thiophene (8c). The title
compound was obtained in the same manner as for the synthesis of 2c
1
(67%). White solid; Mp. 121−123 °C; H NMR (400 MHz) δ 7.22
To a solution of 3-(phenylthio)anthra[2,3-b]thiophene (200 mg,
0.58 mmol) in THF (40 mL) was added n-butyllithium (1.63 M in
hexane, 0.7 mL, 1.17 mmol) at 0 °C. The mixture was warmed to rt
and stirred for 1 h. Iodine (297 mg, 1.17 mmol) was added to the
mixture at 0 °C, and the resulting mixture was stirred for 6 h at rt and
then poured into an aqueous solution of Na2S2O5 (saturated, 10 mL).
The resulting precipitate was collected by filtration and washed with
ethanol and hexane. The crude product was purified by recrystalliza-
tion from chlorofrom to give 2-iodo-3-(phenylthio)anthra[2,3-b]-
(dd, J = 1.9, 8.7 Hz, 1H), 7.31 (dt, J = 1.1, 7.6 Hz, 1H), 7.36−7.44 (m,
3H), 7.56 (d, J = 1.9 Hz, 1H), 7.63 (dd, J = 1.9, 7.4 Hz, 1H), 7.68 (d, J
= 8.7 Hz, 1H), 7.74 (dd, J = 1.9, 7.4 Hz, 1H), 7.77−7.81 (m, 2H); 13C
NMR (100 MHz) δ 122.3, 123.8, 125.5, 125.70, 127.72, 125.75,
125.79, 125.9, 126.0, 126.9, 127.4, 128.0, 129.1, 132.0, 133.2, 134.0,
139.4, 139.9; EI-MS (70 eV) m/z = 370 (M+); HRMS (APCI) m/z
calcd for C18H11BrS2 [M]+: 369.94801. Found: 369.94739.
[1]Benzothieno[3,2-b]naphtho[2,3-b]thiophene (BTNT). The
palladium catalyzed cyclization reaction on 8b proceeded very slowly,
and only a trace amount of BTNT was detected by MS spectra. On the
other hand, the reaction of 8c gave an isomeric mixture of cyclized
compounds (see main text) in quantitative yield. The ratio of the
BTNT and its isomer, [1]benzothieno[2,3-a]naphtho[2,1-b]-
thiophene, was ca. 9:1 judged from the ratio of the diagnostic protons
(see Figure 3a). The latter isomer with better solubility can be
removed by washing with ethanol, and isomerically pure BTNT can be
isolated in 80% yield. To confirm the structures of BTNT and
[1]benzothieno[2,3-a]naphtho[2,1-b]thiophene, their chemical shifts
1
thiophene as a yellow solid (204 mg, 75%). Mp. 266−268 °C; H
NMR (400 MHz) δ 7.12−7.22 (m, 5H), 7.42 (dt, J = 1.6, 6.4 Hz, 1H),
7.46 (dt, J = 1.6, 6.4 Hz, 1H), 7.99 (t, J = 9.0 Hz, 2H), 8.44 (s, 1H),
8.49 (s, 1H), 8.50 (s, 1H), 8.55 (s, 1H); EI-MS (70 eV) m/z = 468
(M+); HRMS (APCI) m/z calcd for C22H13IS2 [M]+: 467.94979.
Found: 467.95032.
2-Bromo-3-(phenylthio)anthra[2,3-b]thiophene (7c). The title
compound was obtained as the same manner described above by using
1,2-dibromo-1,1,2,2-tetrachloroethane as the electrophile (65%).
1
1
Yellow solid; Mp. 245−246 °C; H NMR (400 MHz) δ 7.13−7.23
on H NMR spectra were simulated by using Gaussian 03 program.
(m, 5H), 7.43 (dt, J = 1.6, 6.6 Hz, 1H), 7.46 (dt, J = 1.6, 6.6 Hz, 1H),
7.99 (t, J = 8.6 Hz, 2H), 8.42 (s, 1H), 8.47 (s, 1H), 8.50 (s, 1H), 8.55
(s, 1H); EI-MS (70 eV) m/z = 420 (M+); HRMS (APCI) m/z calcd
for C22H14BrS2 [M + H]+: 420.97148. Found: 420.97165.
The calculated and observed chemical shifts are listed in Table S1,
which clearly states that the present characterization of each
1
compound by H NMR spectra is decent.
3-(2-Naphthylthio)anthra[2,3-b]thiophene (9a). As described
in the synthesis of 8a, a reaction of 6 (962 mg, 3 mmol) with in situ
generated 2-naphthylsulfenyl chloride (4.5 mmol) gave 9a (925 mg,
[1]Benzothieno[3,2-b]anthra[2,3-b]thiophene (BTAT). The
palladium catalyzed cyclization reaction on 7b and 7c gave the
desired BTAT in quantitative and 93% isolated yield. Yellow solid. For
the device fabrication, BTAT was further purified by vacuum
sublimation (source temperature, 220 °C under 10−3 Pa). Mp. >300
1
79%) as a yellow solid. Mp. 227−229 °C; H NMR (400 MHz) δ
7.25−7.45 (m, 5H), 7.64 (dd, J = 2.5, 6.8 Hz, 1H), 7.69−7.76 (m,
3H), 7.81 (s, 1H), 7.92 (dd, J = 1.5, 7.5 Hz, 1H), 7.90 (dd, J = 1.5, 7.5
Hz, 1H), 8.50 (s, 1H), 8.51 (d, J = 1.6 Hz, 1H), 8.52 (s, 1H), 8.56 (s,
1H); 13C NMR (100 MHz) δ 121.7, 122.25, 122.27, 124.5, 125.5,
125.6, 125.8, 126.2, 126.6, 126.9, 127.0, 127.5, 127.6, 128.1, 128.5,
128.5, 128.6, 129.2, 130.0, 130.2, 131.8, 132.2, 134.0, 134.2, 134.5,
1
°C; H NMR (400 MHz) δ 7.46 (m, 4H), 4.88 (d, J = 7.7 Hz, 1H),
7.95 (d, J = 7.7 Hz, 1H), 8.03 (d, J = 7.9 Hz, 2H), 8.52 (s, 2H), 8.54
(s, 1H), 8.63 (s, 1H); EI-MS (70 eV) m/z = 340 (M+); HRMS
(APCI) m/z Calcd for C22H12S2 [M]+: 340.03749, Found 340.03787;
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138.1; EI-MS (70 eV) m/z = 392 (M+); HRMS (APCI) m/z calcd for
C26H17S2 [M + H]+: 393.07662. Found: 393.07578.
anhydride (1.5 mL, 9 mmol) at 0 °C. After the mixture was stirred for
5 h, water (10 mL) and hydrochloric acid (1 M, 10 mL) were added.
The resulting mixture was extracted with chloroform, and the residue
was purified by column chromatography on silica gel eluted with
chloroform (Rf = 0.9) to give 3,7-bis(methylthio)-2,6-bis-
(trifluoromethanesulfonyloxy)naphthalene as a white solid (1.14 g,
74%). Mp. 171−174 °C; 1H NMR (500 MHz) δ 2.61 (s, 6H) 7.60 (s,
2H), 7.69 (s, 2H); 13C NMR (125 MHz) δ 15.8, 118.5, 119.1 (q, J =
319.7 Hz), 126.3, 130.7, 133.1, 146.7; EI-MS (70 eV) m/z 516 (M+);
HRMS (APCI) m/z calcd for C14H10F6O6S4 [M]+: 515.92589. Found:
515.92560.
The title compound was obtained from 3,7-bis(methylthio)-2,6-
bis(trifluoromethanesulfonyloxy)naphthalene in the same manner as
the synthesis of 4 (84%). Yellow solid from chloroform-ethanol;
Mp.179−180 °C; 1H NMR (400 MHz) δ 0.30 (s, 18H) 2.55 (s, 6H),
7.33 (s, 2H), 7.83 (s, 2H); 13C NMR (100 MHz) δ 0.2, 15.4, 102.1,
102.3, 121.2, 121.4, 130.6, 131.5, 138.3; EI-MS (70 eV) m/z = 412
(M+); Anal. calcd for C22H28S2Si2: C, 64.02; H, 6.84%. Found: C,
64.31; H, 6.77%.
3,8-Bis(phenylthio)naphtho[2,3-b:6,7-b′]dithiophene (13a).
The title compound was synthesized from 12 and phenylsulfenyl
chloride, and purified by recrystallization from chloroform as a yellow
solid (64%). Mp. 251−253 °C; 1H NMR (400 MHz) δ 7.12−7.24 (m,
10H), 7.78 (s, 2H), 8.37(s, 2H), 8.47 (s, 2H); 13C NMR (100 MHz) δ
121.2, 122.4, 124.5, 126.5, 128.4, 129.4, 129.5, 134.6, 136.6, 138.0,
138.3; EI-MS (70 eV) m/z = 456 (M+); Anal. calcd for C26H16S4: C,
68.38; H, 3.53%. Found: C, 68.30; H, 3.32%.
2,7-Diiodo-3,8-bis(phenylthio)naphtho[2,3-b:6,7-b′]-
dithiophene (13b). To a solution of 3,7-(phenylthio)naphtho[2,3-
b:6,7-b′]dithiophene (758 mg, 1.7 mmol) in THF (100 mL) was
added n-butyllithium (1.63 M in hexane, 3.1 mL, 5 mmol) at 0 °C.
The mixture was warmed to rt and then stirred for 1 h. Iodine (1.27 g,
5 mmol) was added to the mixture at 0 °C, and the resulting mixture
was stirred for 6 h at rt and then poured into an aqueous solution of
Na2S2O5 (saturated, 100 mL). The resulting precipitate was collected
by filtration and washed with ethanol and hexane. The crude product
was purified by recrystallization from toluene to give 13b as a yellow
solid (738 mg, 63%). Mp. 290−291 °C; 1H NMR (400 MHz) δ 7.11−
7.25 (m, 10H), 8.33 (s, 2H), 8.34 (s, 2H); EI-MS (70 eV) m/z = 708
(M+); HRMS (APCI) m/z calcd for C26H15I2S4 [M + H]+: 708.81405.
Found: 708.81384.
2-Bromo-3-(2-naphthylthio)anthra[2,3-b]thiophene (9b). To
a solution of 9a (500 mg, 1.5 mmol) in THF (50 mL) was added n-
butyllithium (1.63 M in hexane, 1.2 mL, 2.0 mmol) at 0 °C. The
mixture was warmed to rt and then stirred for 1 h. 1,2-Dibromo-
1,1,2,2-tetrachloroethane (645 mg, 2.0 mmol) was then added to the
mixture at 0 °C, and the resulting mixture was stirred for 10 h at rt,
and poured into a mixture of hydrochloric acid (1 M, 10 mL) and
ethanol (50 mL), and a precipitate solid was collected by filtration and
washed with ethanol and hexane. The crude product was purified by
recrystallization from chlorofrom to give 9b as a yellow solid (502 mg,
70%). Mp. 245−246 °C; 1H NMR (400 MHz) δ 7.31 (dd, J = 1.9, 8.6
Hz, 1H), 7.37−7.46 (m, 4H), 7.64−7.68 (m, 2H), 7,69 (d, J = 8.7,
1H), 7.74 (dd, J = 1.7, 7.1, 1H), 7.95 (d, J = 7.9 Hz, 1H), 8.00 (d, 7.9
Hz, 1H), 8.44 (s, 1H), 8.50 (s, 2H), 8.52 (s, 1H); EI-MS (70 eV) m/z
= 470 (M+); HRMS (APCI) m/z calcd for C26H16BrS2 [M + H]+:
470.98713 Found: 470.98724.
Naphtho[3,2-b]thieno[3,2-b]anthra[2,3-b]thiophene (NTAT).
The palladium catalyzed cyclization reaction on 9b gave a dark-red
solid, which was extracted thoroughly with chloroform by using the
Soxhlet apparatus. From the insoluble portion (residual solid), NTAT
was obtained in 46% yield as a red solid. Although the extract
contained NTAT, no attempt was made for isolating NTAT. For the
device fabrication, NTAT was further purified by vacuum sublimation
(source temperature, 300 °C under 10−3 Pa). HRMS (APCI) m/z
calcd for C26H14S2 [M]+: 390.05314, Found 390.05215; Anal. calcd for
C26H14S2: C, 79.96; H, 3.61%. Found: C, 80.03; H, 3.26%.
3,7-Bis(phenylthio)benzo[1,2-b:4,5-b′]dithiophene (11a). As
described for the synthesis of 2a, treatment of 1,4-bis(methylthio)-2,5-
bis[2-(trimethylsilyl)ethynyl]benzene with phenylsulfenyl chloride
gave corresponding bis(trimethylsilyl) derivative of 11a, which was
then desilylated by an action of tetrabutylammonium fluoride to give
the title compound as a white solid. The crude product was purified by
column chromatography on silica gel eluted with chloroform to give
11a as a white solid (79%). Mp. 251−253 °C; 1H NMR (400 MHz) δ
7.12−7.24 (m, 10H), 7.78 (s, 2H), 8.31 (s, 2H); 13C NMR (100
MHz) δ 117.5, 123.1, 126.3, 127.7, 129.5, 134.4, 136.7, 137.6, 138.2;
EI-MS (70 eV) m/z = 406 (M+); HRMS (APCI) m/z calcd for
C22H15S4 [M + H]+: 407.00511. Found: 407.00482.
2,6-Dibromo-3,7-bis(phenylthio)benzo[1,2-b:4,5-b′]-
dithiophene (11b). The title compound was synthesized from 11a
with the same procedure for the synthesis of 2c, and the product
purified by column chromatography on silica gel (hexane-chloroform,
2,7-Dibromo-3,8-bis(phenylthio)naphtho[2,3-b:6,7-b′]-
dithiophene (13c). A similar procedure for the synthesis of 13b
using 1,2-dibromo-1,1,2,2-tetrachloroethane gave 13c as a yellow solid
1
1
(81%). Mp. 289−291 °C; H NMR (400 MHz) δ 7.13−7.23 (m,
5:1 v/v, Rf = 0.5) (83% yield). White solid; Mp. 247−249 °C; H
10H), 8.316 (s, 2H), 8.323 (s, 2H); EI-MS (70 eV) m/z = 612 (M+);
HRMS (APCI) m/z calcd for C26H15Br2S4 [M + H]+: 612.84179.
Found: 612.84229.
NMR (400 MHz) δ 7.11−7.26 (m, 10H), 8.18 (s, 2H); 13C NMR
(100 MHz) δ 116.9, 124.8, 126.5, 127.2, 127.5, 129.6, 135.4, 137.5,
137.8; EI-MS (70 eV) m/z = 562 (M+); HRMS (APCI) m/z calcd for
C22H13Br2S4 [M + H]+:562.82613. Found: 562.82581.
Bis[1]benzothieno[2,3-d:2′,3′-d′]naphtho[2,3-b:6,7-b′]-
dithiophene (BBTNDT). The title compound was obtained in the
same manner for the synthesis of BBTBDT. The crude product was
washed thoroughly with acetone (12 h) and chloroform (12 h) by
using the Soxhlet apparatus to give BBTNDT (310 mg, 81%) as an
orange solid. For the device fabrication, BBTNDT was further purified
by vacuum sublimation (source temperature, 360 °C under 10−3 Pa).
HRMS (APCI) m/z calcd for C26H12S4 [M]+: 451.98163. Found
451.98148; Anal. calcd for C26H12S4: C, 68.99; H, 2.67%. Found: C,
68.66; H, 2.34%.
Device Fabrication and Characterization. OFETs were fabricated
in a “top-contact” configuration on a heavily doped n+-Si (100) wafer
with a 200 nm thermally grown SiO2 (Ci = 17.3 nF cm−2). The
substrate surfaces were treated with OTS, or ODTS as reported
previously.10a A thin film of the organic semiconductors as the active
layer was vacuum deposited on the Si/SiO2 substrates maintained at
various temperatures (Tsub) at a rate of 1 Å s−1 under a pressure of
∼10−3 Pa. On top of the organic thin film, gold films (80 nm) as drain
and source electrodes were deposited through a shadow mask. For a
typical device, the drain-source channel length (L) and width (W) are
50 μm and 1.5 mm, respectively. Characteristics of the OFET devices
were measured at rt under ambient conditions with a Keithley 4200
Bis[1]benzothieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b′]-
dithiophene (BBTBDT). The palladium catalyzed cyclization reaction
on 11b gave BBTNDT; the crude product was washed thoroughly
with acetone (12 h) and chloroform (12 h) by using the Soxhlet
apparatus to give BBTBDT (310 mg, 61%) as a yellow solid. EI-MS
(70 eV) m/z = 402 (M+).
2,6-Bis(methylthio)-3,7-bis[2-(trimethylsilyl)ethynyl]-
naphthalene (12). To a solution of 2,6-dimethoxy-3,7-bis-
(methylthio)naphthalene (841 mg, 3 mmol) in dichloromethane (30
mL) was added boron tribromide (BBr3, 12 mL, 12 mmol, 1 M in
dichloromethane). The solution was stirred for 20 h at rt, and the
resulting precipitate was collected by filtration and washed with water
to give 2,6-dihydroxy-3,7- bis(methylthio)naphthalene as a white solid
(760 mg, quantitative). Mp. 224−225 °C; 1H NMR (400 MHz) δ 2.43
(s, 6H), 6.40 (s, 2H), 7.20 (s, 2H), 7.82 (s, 2H); 13C NMR (100 MHz,
DMSO) δ 14.5, 108.1, 121.5, 127.9, 128.6, 151.1; EI-MS (70 eV) m/z
= 252 (M+); HRMS (APCI) m/z calcd for C12H12O2S2 [M]+:
252.02732. Found: 252.02768.
To a suspension of 2,6-dihydroxy-3,7-bis(methylthio)naphthalene
(757 mg, 3 mmol) and triethylamine (3.2 mL, 23 mmol) in
dichloromethane (30 mL) was slowly added trifluoromethanesulfonic
L
dx.doi.org/10.1021/ja406257u | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Article
semiconducting parameter analyzer. Field-effect mobility (μFET) was
calculated in the saturation (Vd = −60 V) of the Id using the following
equation,
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Id = Ciμ (W/2L)(V − V )2
g
th
FET
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where Ci is the capacitance of the SiO2 insulator, and Vg and Vth are
the gate and threshold voltages, respectively. Current on/off ratio (Ion/
Ioff) was determined from the Id at Vg = 0 V (Ioff) and Vg = −60 V
(Ion). The μFET data reported are typical values from more than 10
different devices.
ASSOCIATED CONTENT
* Supporting Information
■
S
NMR spectra, calculated and observed 1H NMR chemical shifts
of BTNT and [1]benzothieno[2,3-a]naphtho[2,1-b]thiophene,
CIF for BTAT and BBTNDT, CVs, PESA, and DFT
calculations. This material is available free of charge via the
Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
takimiya@riken.jp
■
Present Address
¶Nippon Kayaku Co., Ltd. 31−12 Shimo, Kita-Ku, 115−8588,
Japan
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was financially supported by Grants-in-Aid for
Scientific Research (no. 23245041) from MEXT, Japan and by
Japan Advanced Printed Electronics Technology Research
Association (JAPERA), Japan. HRMSs were carried out at the
Natural Science Center for Basic Research and Development
(N-BARD), Hiroshima University and at the Materials
Characterization Support Unit in RIKEN Advanced Technol-
ogy Support Division. We also thank Rigaku Corp. for the
single crystal X-ray analysis, and Dr. Shoji Shinamura (Nippon
Kayaku Co. Ltd.) for valuable discussions.
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