Synthesis of dendritic oligothiophenes and their self-association properties by intermolecular π-π interactions

Article abstract of DOI:10.1021/ol063046r

(Chemical Equation Presented) The addition of oligothiophene into a dendritic structure causes a self-association behavior by intermolecular π-π interactions in a solution and in a solid state. Increasing the generation of the dendritic structure gives no

Full text of DOI:10.1021/ol063046r

ARTICLE
pubs.acs.org/joc
Synthesis and Characterization of Benzo[1,2-b:3,4-b0:5,6-b00]trithioph-
ene (BTT) Oligomers
Tomoya Kashiki,† Masahiro Kohara,† Itaru Osaka,† Eigo Miyazaki,† and Kazuo Takimiya*,†,‡
†Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University, Higashi-Hiroshima 739-8527, Japan
‡Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
S Supporting Information
b
ABSTRACT: Two dimers (2 and 3), dendritic tetramer (4),
hexamer (5), and decamer (6) of benzo[1,2-b:3,4-b0:5,6-b00]tri-
thiophene (BTT), a potential π-core unit with C3h symmetry,
were synthesized, characterized, and evaluated for possible use
as organic semiconductors. Single crystal X-ray analyses of the
dimers (2 and 3) revealed that they have planar molecular
structures with dihedral angles of almost 180° between two
BTT units. In accordance with the rigid and planar molecular
structure, the unsubstituted dimer (2) is poorly soluble, whereas
the octyl-substituted dimer (3) has improved solubility. Although
the solubility of the dendritic tetramer (4) is decreased, further
extended systems, i.e., the dendritic hexamer (5) and decamer (6), have solubilities better than that of 4. With increasing numbers of
BTT units in the molecule, the experimentally determined energy levels of HOMO shift upward slightly and the HOMOꢀLUMO
energy gaps become smaller, but the extent of HOMO destabilization and reduction of the HOMOꢀLUMO gap are not significant.
Taking into account the energy levels of the frontier orbitals, 3ꢀ6 could be useful as p-channel organic semiconductors rather than
n-channel. In fact, the spin-coated thin film of 3 with edge-on molecular orientation acted as an active channel of field-effect
transistors that showed hole mobilities as high as 0.14 cm2 Vꢀ1 sꢀ1, indicating that the BTT core is a useful π-conjugated system
for application to organic semiconductors, although 4ꢀ6 gave FET characteristics rather inferior to those of 3, owing to their
amorphous nature in the thin film state.
’ INTRODUCTION
thiophene moieties with C3h symmetry that enables two-dimen-
sional (2D) molecular extension and even more dendritic three-
dimensional (3D) extension with star-shaped structures, pro-
vided that multiple BTT oligomerization is possible. In fact, such
star-shaped π-conjugated oligomers have attracted recent atten-
tion as new types of organic semiconducting materials with
multiple π-conjugate units with monodisperse, well-defined,
discrete molecular structures.8
Despite its unique molecular structure and potential use as a
building block for organic semiconductors, the application of the
BTT core remains severely limited. To our knowledge, only several
application in the field of materials chemistry have been reported, e.
g., oligothiophene-substituted derivatives (1b) that have been
utilized as p-channel organic semiconductors for OPVs,9 the core
unit for cross-linked polymer with ethylenedioxythiophene (ED-
OT) units,10 and the core structure for the hexagonal columnar
mesogen (1c) with moderately high mobility.11 Simple BTT
oligomers, even the dimer of BTT, have yet to be synthesized. In
this article, we report the synthesis and characterization of BTT
dimers (2, 3), dendritic tetramer (4), hexamer (5), and decamer
Recent prevailing interest in organic electronics has prompted
synthetic chemists to innovate new π-conjugated molecules that
are applicable to electronic materials.1 Representative molecular
classes used as electronic materials include oligoacenes,2 oligo-
and polythiophenes,3 phthalocyanines,4 hexabenzocoronenes,5
and heteroarenes.6 These π-conjugated molecules and polymers,
often referred to as organic semiconductors, have been widely
utilized in various opto/electronic applications, such as organic
light-emitting diodes (OLEDs), organic field-effect transistors
(OFETs), and organic photovoltaics (OPVs). For the further
development of new molecular classes, the rational design of
molecular electronic structures is a key. In addition, the shape of
a molecule also plays a crucial role in the electronic applications,
because molecular ordering in the solid state, mainly the thin film
state, governs intermolecular orbital overlaps and hence carrier
transport properties. Given these circumstances, we have focused
on benzo[1,2-b:3,4-b0:5,6-b00]trithiophene7 (BTT 1a, Figure 1)
as a potential π-core for a new class of organic semiconductors
for the following reasons. First, its planar and rigid π-framework
can promote strong intermolecular interaction that would be
suitable for developing organic semiconducting materials. Sec-
ond, the BTT core is a rare structure having three identical
Received: March 12, 2011
Published: April 13, 2011
r
2011 American Chemical Society
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Figure 1. Structures of BTT and its oligomers.
(6) together with fabrication and characterization of their thin
films. We also examined their use as the active semiconducting
material in organic field-effect transistors (OFETs) and found
that the dimer (3) capable of affording well-ordered thin film by
solution deposition gave decent OFETs with mobility up to
monolithiation followed by oxidative coupling effected by Fe-
(acac)3 in 61% isolated yield (Scheme 1). The structure of 2 was
confirmed by mass spectrometry, combustion analysis, and
single-crystal X-ray analysis (Figure 2a). Similar to conventional
thiopheneꢀthiophene junctions in oligothiophenes,3 2 has a
planar structure with a dihedral angle of 180°. In the crystal lattice
the molecules of 2 pack tightly in the π-stacking columnar
structure with a separation of 3.54 Å (Figure 2b). Because of
its rigid and planar molecular structure as well as the tight packing
in the crystal structure, 2 is poorly soluble in a range of organic
solvents, implying difficulty of the synthesis of higher BTT
oligomers than the dimer. To circumvent this problem, we
introduced two n-octyl groups to the BTT core for solubilization
to furnish dioctyl-BTT (7), and then 7 was similarly dimerized to
tetraoctyl dimer (3), which turned out to be fairly soluble
(solubility = 1.7 g Lꢀ1 in chloroform at rt). We also confirmed
0.14 cm2 Vꢀ1 sꢀ1
.
’ RESULTS AND DISCUSSION
Synthesis. Although the first synthesis of the parent BTT (1a)
dates back to the early work of Proetzsch et al. in 1972,7 the
tediousness of the synthesis has hindered various derivatizations
of it. However, thanks to the recently established straightforward
procedure for the synthesis of 1a,10,12 it is now available in
multigram scale in our laboratory. Thus, using 1a as the starting
material, we first synthesized the dimer of BTT (2) via direct
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the molecular structureof3by means of single crystal X-ray analysis;
as in the case for the unsubstituted 2, 3 has a similar planar molecular
structure with a dihedral angle of almost 180° at the junction
between two BTT units (Figure 3a), indicating that the octyl groups
introduced do not hinder effective conjugation between the BTT
units. In addition, intermolecular π-stacking structure is preserved in
the crystal of 3, although there exists the slippage of molecules along
both the molecular short and long axes directions (Figure 3b). From
these structural aspects of 3 both at the molecular and intermolecular
level, we concluded that 7 is a useful building block for further
oligomerization with keeping good coplanarity, πꢀπ intermolecular
interaction, and sufficient solubility.
was subsequently coupled in the presence of palladium catalyst
with tribromo-BTT (9), prepared by reacting 1a with N-bromo-
succinimide in moderate yield, to give the tetramer (4) in 81%
yield after purification. For further derivatization, a trimeric
dendron unit with a bromine moiety (10) was readily prepared
via the palladium-catalyzed Stille coupling between 9 and 2-fold
8 in a moderate yield (42%). In contrast, the synthesis of
a trimeric dendron with a trimethylstannyl group (13) was
somehow troublesome. Thus, after examination of several pos-
sible synthetic routes, including a conversion of 10 to 13 via
lithiumꢀbromine exchange reaction followed by a reaction with
trimethyltin chloride, we finally found an efficient synthetic route
to 13 via the Stille coupling between tris(trimethylstannyl)BTT
(11) and dioctyl-iodo-BTT (12) (Scheme 2). With these
trimeric dendrons possessing the reacting substituents, the
hexamer (5) was easily obtained via the simple 1:1 Stille coupling
between 10 and 13 (67% isolated yield).
Using the soluble BTT monomer (7), we then synthesized the
dendritic oligomers (4ꢀ6) as depicted in Scheme 2. Monomer 7
was first converted into trimethylstannyl derivative (8), which
Scheme 1. Synthesis of BTT Dimers (2 and 3)
The dendritic decamer (6) could be synthesized via the Stille
cross-coupling reaction between 10 and 11 or 9 and 13. We
tested both combinations and found that the latter gave the
desired decamer (6) in 33% isolated yield. In sharp contrast, the
former gave a complex mixture consisting of various polymers
judged from its MALDI-TOF mass spectra. This can be ex-
plained by the concomitant reductive self-coupling reaction of 11
at the trimethylstannyl site, which competes with the desired
cross-coupling under the reaction conditions, giving a random
mixture of BTT oligomers with multiple trimethylstannyl sub-
stituents that further react to produce a mixture of various BTT
Figure 2. Molecular structure (a) and crystal structure of 2 (b).
Figure 3. Molecular structure (a) and stacking structure of 3 (b).
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Scheme 2. Synthesis of BTT Tetramer (4), Hexamer (5), and Decamer (6)
oligomers and polymers. In fact, the latter combination also gave
the hexamer (5) as a byproduct, which is supposed to be formed
via the reductive self-coupling of 13.
Molecular Properties. As mentioned above alkylated dimer
(3), tetramer (4), hexmaer (5), and decamer (6) are sufficiently
soluble for evaluation of their molecular electronic properties by
means of solution electrochemistry and optical spectroscopy.
Cyclic voltammograms of 3ꢀ6 showed oxidation processes with
oxidation onsets at þ0.72ꢀ0.92 V (vs Ag/AgCl), which corre-
sponded to the HOMO energy levels (EHOMO) of ca. 5.0ꢀ5.3 eV
below the vacuum level (Figure 4, Table 1).13
The UVꢀvis spectra of 3ꢀ6 show significant bathochromic
shifts relative to that of the octyl-substituted monomer (1d)
(Figure 5a), indicative of effective extension of π-conjugation for
3ꢀ6. In contrast, 3ꢀ6 have similar absorption maxima
(Figure 5a, Table 1), which implies that the extent of delocaliza-
tion at their frontier orbitals is more or less similar to each
other. Accordingly, the absorption edges also do not largely
shift, indicating that the LUMO energy levels (ELUMO) as well
as the energy gap between the HOMO and LUMO (Eg) are
not much influenced by the increase of the number of the BTT
units (Table 1). On the other hand, the hyperchromic effect
caused by the increased numbers of BTT units in the larger
It is interesting to note that the solubilities of 5 (5.3 g Lꢀ1 in
chloroform at rt) and 6 (6.4 g Lꢀ1) are fairly improved,
compared to that of 3 (1.7 g Lꢀ1) and 4 (0.2 g Lꢀ1). This can
be partially explained by the fact that the large oligomers have a
larger numbers of solublizing octyl side groups. However, relative
numbers the octyl groups to the BTT core are reducing with
increasing the size of oligomers: two octyl groups per BTT unit
for 3, 1.5 for 4, 1.33 for 5, and 1.2 for 6. Thus, not only the
numbers of octyl groups but also the planarity of the molecules
must play an important role for the solubility. In fact, the
molecules of 3 and 4 that can have planar molecular geometries
enables effective intermolecular πꢀstacking interaction, redu-
cing solubility. On the other hand, the larger oligomers 5 and 6
cannot assume a coplanar structure for all the BTT units because
of the steric bulk caused by the peripheral octyl groups. This
steric effect is much pronounced in 6, which well explains the
highest solubility of 6 among the present oligomers.
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oligomers is significant, and the molar extinction coefficient
of the decamer (6) at 395 nm reaches to as high as 214,000
cmꢀ1 Mꢀ1. This observation and the lack of the size-dependent
spectral shift suggest that the intramolecular electronic inter-
action between the BTT units is not so strong in the large
oligomers.
1d (1.1 eV), the shifts of 3 (0.46 eV) and 4 (0.40 eV) are smaller,
implying their rigid molecular structures with coplanarity in the
excited state. The PL spectrum of 5 centered at ca. 550 nm is very
weak and shifted bathochromically (Stokes shift 0.89 eV). This
can be interpreted by considering the large and flexible molecular
geometry of 5, which can have access to different geometrical
conformations and result in the bathochromically shifted spec-
trum. A similar red-shifted and very weak PL spectrum is also the
case for 6.
Figure 5b shows their photo luminescence (PL) spectra in
diluted solution. In contrast to the large Stokes shift observed for
It is worth pointing out that the fluorescence quantum
efficiencies of large dendritic oligomers (5 and 6) are very low
(Table 1). Similar fluorescence quenching has been reported for
a series of phenylacetylene- and oligothiophene-based dendri-
mers, and it has been interpreted by the consideration that the
larger dendritic molecules may have many modes to dissipate the
excitation energy, which enhances the nonradiative decay.14 It is
thus rational to conclude that 5 and 6 have considerable
dendrimer-like nature, whereas 4 even with a dendritic structure
is rather ordinary “small-molecule”-like.
Theoretical MO Calculation of BTT Dimer and Tetramer. In
order to understand the experimental results on the molecular
electronic properties, theoretical calculations with the DFT
method at the B3LYP/6-31 g(d) level15 were carried out for
the parent BTT (1a), dimer (2), and the unsubstituted tetramer
(Table S1 in Supporting Information). Different from the BTT
monomer possessing the doubly degenerated frontier orbitals
characteristic of the C3h symmetric molecular structure (Figure
S1 in Supporting Information), calculations of 2 indicated that
nondegenerated HOMO (ꢀ5.28 eV below the vacuum level)
and LUMO (ꢀ1.68 eV) with electron density delocalization over
Figure 4. Cyclic voltammograms (scan rate 100 mV sꢀ1) of 3ꢀ6
recorded in benzonitrile (10ꢀ3 M) solution containing tetrabutylammo-
nium hexafluorophosphate (Bu4NPF6, 10ꢀ1 M) as electrolyte with Pt
working and counter electrodes.
Table 1. Experimental Data of Molecular Electronic Properties
Eoxonset, Va
EHOMO,b eV
Eg,c eV
ELUMO,d eV
λmax, nm (ε)
λedge, nm
λmax (PL), nm
Stokes shift, eV
φn
1d
3
þ1.17
þ0.92
þ0.83
þ0.78
þ0.72
ꢀ5.5
ꢀ5.3
ꢀ5.2
ꢀ5.1
ꢀ5.0
3.9
2.9
2.7
2.6
2.5
ꢀ1.6
ꢀ2.4
ꢀ2.5
ꢀ2.5
ꢀ2.5
276 (72000)
380 (32800)
387 (95000)
393 (144000)
395 (214000)
316
433
456
475
498
370
450
450
547
545
1.1
e
0.46
0.40
0.89
0.87
0.083
4
0.055
5
e
6
e
a Versus Ag/AgCl in benzonitrile containing Bu4NPF6 (10ꢀ1 M) as supporting electrolyte. The standard Fc/Fcþ showed a redox couple at E1/2 = þ0.46
V under identical conditions. b Under the premise that the energy level of Fc/Fcþ is 4.8 eV below the vacuum level, EHOMOs were estimated from Eox
onset
.
(see ref 13). c Estimated from the absorption edge. d Calculated from the EHOMO and Eg. e Very weak PL intensity was detected with φn less than 10ꢀ7
Figure 5. UVꢀvis (a) and PL (b) spectra of 1d and 3ꢀ6. Intensity of PL spectra is normalized with concentration and ε at the excitation wavelength
(λex 300 nm for 1d, 380 nm for 3, 387 nm for 4, 393 nm for 5, and 395 nm for 6).
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levels for use as p-channel organic semiconductors. They are also
soluble enough in common organic solvents for solution-deposi-
tion of their thin films. In fact, simple spin-coating method using
the chloroform solution at room temperature gave their homo-
geneous thin films on quartz glass or Si/SiO2 substrates. De-
picted in Figure 7 are the absorption spectra and XRD patterns of
the thin films of 3ꢀ6. In absorption spectra, apparent red shifts
(∼20 nm) are observed for the thin films of 3 and 4, which is a
strong indication of intermolecular π-overlap between the planar
molecules in the thin film state as observed in the bulk single
crystal structure of 3 (vide supra). On the other hand, larger
oligomers (5 and 6) show smaller red shifts (less than 10 nm)
than those for 3 and 4, and in particular that for 6 is almost
negligible. This observation can be well-understood by the
nonplanar geometry of the large oligomers, especially 6, with
which it may be difficult to construct an intermolecularly
interactive structure suitable for effective carrier transport.
As depicted in Figure 7b, only the thin film of 3 shows clear
XRD peaks, indicating the formation of a crystalline thin film. As
clearly seen from the multiple (00l) reflections, the film has a
lamellar structure, although there exist two different molecular
phases evidenced from two sets of (00l) reflections designated by
the different colors (Figure 7b, top). Both series of XRD peaks,
however, can not be indexed with the bulk single crystal cell,
suggesting that the packing structure of 3 in the thin film is
different from that in the bulk crystal phase. The calculated
interlayer spacing (d-spacing) for the 3 thin film, 19.7 and 23.0 Å,
was much shorter than the molecular length of 3 (ca. 30 Å),
implying a large inclination of the molecular long axis from the
substrate normal or edge-on orientation with the molecular
short-axis standing on the substrate.
Figure 6. Non-degenerate HOMO and LUMO of BTT dimer (2) (a)
and doubly degenerate HOMO and LUMO of BTT tetramer (b)
calculated with the DFT method at the B3LYP/6-31 g(d) level.
In sharp contrast, the thin film of 4 with the planar molecular
geometry gives no peaks in the XRD, indicative of its amorphous
nature (Figure 7b). Although the reasons for this are not clear, we
speculate that its geometry with C3h symmetry and six octyl
groups reduce the crystallinity in the solid state. The larger
oligomers (5 and 6) gave also amorphous films as anticipated
from their nonplanar molecular structure.
In accordance with the molecular ordering in the thin film
state, OFET devices fabricated with the thin films of 3 showed
typical FET responses with moderately high field-effect mobility
(μFET, 0.14 cm2 Vꢀ1 sꢀ1) and Ion/Ioff of 105 (Figure 8a, Table 2),
which indicates that the BTT core is a useful building block
for developing electronic materials. On the other hand, μFET
values of 4-based devices were lower by 2 orders of magnitude
Figure 7. Absorption spectra (a) and XRD patterns of spin-coated thin
films of 3ꢀ6 (b).
(1.4 ꢁ 10ꢀ3 cm2 Vꢀ1
s
ꢀ1, Figure 8b, Table 2). This can be
rationalized by the amorphous nature of its thin film state. Even
though the molecule itself has a planar geometry enabling
intermolecularly interactive structure in the thin film state,
long-range ordering, i.e., crystallinity, can be a key factor to
enhance the mobility, which requires an effective and continuous
intermolecular orbital overlap in the horizontal direction on the
substrate.16 Owing to the less interactive and amorphous nature
of the thin films of 5 and 6, their FET devices showed
characteristics rather inferior to those of 3 and 4, lower field-
effect mobility (∼7 ꢁ 10ꢀ4 cm2 Vꢀ1 sꢀ1, Table 2) and smaller
Ion/Ioff ratio.
the whole molecule are characteristic (Figure 6a). In contrast, the
dendritic tetramer, i.e., the core part of 4, with C3h symmetry,
comes to have again doubly degenerated HOMO and LUMO
(Figure 6b). It should be noted that the electron density is
confined within two or three BTT parts in each orbital for the
tetramer. Owing to the localized molecular orbitals, the energy
levels of HOMO (ꢀ5.27 eV) and LUMO (ꢀ1.80 eV) are not
very different from those of the dimer, well explaining the similar
oxidation onsets in the cyclic voltammograms of 3 and 4
(Figure 4). Although the larger oligomers 5 and 6 are too large
to carry out their MO calculations and hence the detailed pictures
of their frontier orbitals are not clear, the extent of molecular
orbital delocalization is expected to be similar to that of 4.
Solution Deposited Thin Films of 3ꢀ6 and Their FET
Devices. The physicochemical data as well as the theoretical
calculations indicate that 3ꢀ6 have appropriate HOMO energy
’ CONCLUSION
We have successfully synthesized BTT oligomers up to a
dendritic decamer (2ꢀ6). Single crystal X-ray analysis of the
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Figure 8. Output and transfer curves of 3-based (a) and 4-based OFETs (b).
Table 2. Thin Film Properties of 3ꢀ6
larger oligomers gave rather lower mobility than that of 3-based
one, owing to the amorphous nature in the thin film state.
Although the FET mobilities of the higher oligomers are not
very high, the present results on BTT oligomers indicate that
the BTT core is a potential building block in developing new
π-extended materials for opto/electronic applications. To do so,
the control of morphology in the solid state is one of the key
issues, and thus further modifications, including incorporation of
other π-conjugated units and functional moieties, are now
underway.
Δλ, nm d-spacing, Å mobility, cm2 Vꢀ1 sꢀ1 Ion/Ioff Vth, V
3
4
5
6
14ꢀ20
14ꢀ22
4ꢀ9
19.7, 23.0
1.4 ꢁ 10ꢀ1
1.4 ꢁ 10ꢀ3
6 ꢁ 10ꢀ4
105
104
104
104
ꢀ15
ꢀ10
ꢀ14
ꢀ15
a
a
a
0ꢀ5
7 ꢁ 10ꢀ4
a Amorphous film.
dimers (2 and 3) demonstrated that they both have good planarity
and π-stacking crystal structures regardless of the presence/
absence of the peripheral octyl groups, which indicates that
BTT is a useful core unit that ensures coplanarity and an effective
intermolecular π-stacking structure for developing new π-con-
jugated functional materials. Although the unsubstituted dimer
(2) has poor solubility, alkylated oligomers (3ꢀ6) are soluble
enough for the physicochemical characterizations and solution-
deposition of their thin films. Evaluation of the oxidation
potentials and solution absorption spectra, aided by the theore-
tical calculations, allow us to estimate the energy levels of their
HOMO (∼5.1 eV below the vacuum level) and HOMOꢀLU-
MO gaps, which suggests that their electronic structures are not
strongly affected by the number of the BTT units in the molecule
but by the extent of orbital delocalization over the BTT units. As
a result, they are expected to be suitable as p-channel semicon-
ductors rather than n-channel. In fact, solution deposited thin
film of the dimer (3) with good molecular ordering in the thin
film state acts as the active semiconducting layer in OFETs with
μFET as high as 0.14 cm2 Vꢀ1 sꢀ1, whereas OFETs based on the
’ EXPERIMENTAL SECTION
Synthesis . All chemicals and solvents are of reagent grade unless
otherwise indicated. Toluene and tetrahydrofuran (THF) were purified
by standard distillation procedures prior to use. All reactions were
carried out under nitrogen atmosphere unless otherwise stated. Benzo-
[1,2-b:4,5-b0:5,6-b00]trithiophene (1a) was synthesized according to
reported procedures.12 Melting points were uncorrected. Nuclear
magnetic resonance spectra were, unless otherwise stated, 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 impact ionization procedure (70 eV). MALDI-TOF MS
spectra were obtained using 1,8,9-trihydroxyanthracene matrix. The
molecular ion peaks of sulfur, bromine or tin containing compounds
showed a typical isotopic pattern, and all mass peaks are reported based
on 32S, 79Br, or 120Sn, respectively.
2,20-Bi(benzo[1,2-b:3,4-b0:5,6-b00]trithiophene) (2). 1a (369
mg, 1.5 mmol) was dissolved in THF (18 mL). After the solution was
cooled to 0 °C, a hexane solution of n-butyllithium (1.66 M, 1.08 mL,
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1.8 mmol) was slowly added, and the resulting mixture was stirred at rt
for 1.5 h. Fe(acac)3 (349 mg, 0.98 mmol) was then added, and the
resulting mixture was stirred at rt for 18h to give precipitates that was
collected by filtration and washed successively with hydrochloric acid (2
M, 20 mL), water (20 mL), and ethanol (20 mL). The crude product was
purified by vacuum sublimation (340 °C/10ꢀ3 Pa) to give 2 as yellow
crystals (225 mg, 61%). Mp >300 °C; EI-MS m/z 490 (Mþ). Anal. Calcd
for C24H10S6: C, 58.74; H, 2.05%. Found: C, 58.60; H, 1.98%.
and stirring was continued for 1.5 h. After addition of saturated NH4Cl
aqueous solution (20 mL), the mixture was extracted with dichloro-
methane (10 mL ꢁ 2). The combined extract was washed with brine
(20 mL ꢁ 3), dried over MgSO4 (anhydrous), and concentrated in
vacuo. The resulting residue was subjected to flash column chromatog-
raphy on alumina eluted with hexane. The product was further purified
by GPC (JAIGEL-1H/2H, CHCl3, Rv = 148 mL) to give 8 (707 mg,
1
88%) as a white solid. Mp 41ꢀ43 °C; H NMR (400 MHz) δ 7.58
2,5-Dioctylbenzo[1,2-b:3,4-b0:5,6-b00]trithiophene (7). 1a
(800 mg, 3.25 mmol) was placed in a test tube and dissolved in THF
(80 mL). After the solution was cooled to 0 °C, a hexane solution of
n-butyllithium (1.65 M, 4.64 mL, 7.24 mmol) was slowly added and then
heated at 60 °C for 2 h. 1-Bromooctane (2.3 mL, 13 mmol) was then
added, and stirring was continued at 60 °C for 12 h. After addition of
saturated aqueous NH4Cl solution (80 mL), the mixture was extracted
with dichloromethane (10 mL ꢁ 2). The combined extract was washed
with brine (80 mL ꢁ 3), dried over MgSO4 (anhydrous), and concen-
trated in vacuo. The residue was subjected to flash column chromatog-
raphy on silica gel eluted with hexane (Rf = 0.47, φ 2.5 ꢁ 5 cm). The
product was further purified by preparative GPC (JAIGEL-1H/2H,
CHCl3, Rv = 184 mL) to give colorless crystals of 2,5-dioctylbenzo
[1,2-b:3,4-b0:5,6-b00]trithiophene (7, 597 mg, 39%) together with 2,5,
8-trioctylbenzo[1,2-b:3,4-b0:5,6-b00]trithiophene (1d, Rv = 205 mL, 411 mg,
29%). 7: mp 36ꢀ38 °C; 1H NMR (270 MHz) δ 7.53 (d, J = 5.3 Hz, 1H),
7.47 (d, J = 5.3 Hz, 1H), 7.27 (s, 1H), 7.22 (s, 1H), 2.98 (t, J = 7.6 Hz,
4H), 1.80 (quint, J = 7.6 Hz, 4H), 1.28ꢀ1.55 (m, 20H), 0.86ꢀ0.88
(m, 6H); 13C NMR (99.5 MHz) δ 145.9, 145.8, 131.6, 131.5, 131.4,
130.5, 130.2, 129.9, 124.6, 122.3, 119.1, 119.0, 32.0(ꢁ2), 31.6(ꢁ2),
30.9(ꢁ2), 29.5(ꢁ2), 29.4(ꢁ2), 29.3(ꢁ2), 22.8(ꢁ2), 12.3(ꢁ2); EI-
MS m/z = 470 (Mþ). Anal. Calcd for C28H38S3: C, 71.43; H,
8.14%. Found: C, 71.42; H, 8.34%. 2,5,8-Trioctylbenzo[1,2-b:3,4-b0:5,
6-b00]trithiophene (1d): mp 41ꢀ43 °C; 1H NMR (270 MHz, CDCl3)
δ 7.15 (s, 3H), 2.87 (t, J = 7.4 Hz, 4H), 1.72 (quint, J = 6.9 Hz, 4H),
1.24ꢀ1.28 (m, 30H), 0.87 (t, J = 6.6 Hz, 9H); 13C NMR (99.5 MHz)
δ 145.4, 131.4, 129.3, 118.9, 32.1, 31.6, 30.9, 29.6, 29.5, 29.3, 22.9, 14.3;
EI-MS m/z = 582 (Mþ). Anal. Calcd for C36H54S3: C, 74.16; H, 9.34%.
Found: C, 74.09; H, 9.45%.
2,20-Bi(5,8-dioctylbenzo[1,2-b:3,4-b0:5,6-b00]trithiophene)
(3). 7 (100 mg, 0.21 mmol) was dissolved in THF (2.5 mL). After the
solution was cooled to 0 °C, a hexane solution of n-butyllithium (1.59 M,
0.20 mL, 0.32 mmol) was slowly added, and the resulting mixture was
stirred at 60 °C for 1.5 h. Fe(acac)3 (111 mg, 0.32 mmol) was then
added, and the mixture was stirred at the same temperature for 20 h. The
mixture was then diluted with saturated ammonium chloride aqueous
solution (5 mL), and extracted with chloroform (20 mL ꢁ 2).
The combined extract was washed with brine (50 mL ꢁ 3), dried over
MgSO4 (anhydrous), and concentrated in vacuo. Column chromatog-
raphy on silica gel (φ 3 ꢁ 8 cm) eluted first with hexane and then hexane-
dichloromethane (v/v = 3:1, Rf = 0.5) gave 3 (90 mg, 90%) as a pale
yellow solid. The product was further purified by GPC followed by
recrystallization from hexane for the device preparation. Mp 158ꢀ
160 °C; 1H NMR (400 MHz) δ 7.64 (s, 2H), 7.19 (s, 2H), 7.17 (s, 1H),
2.97 (t, J = 7.0 Hz. 8H), 1.81 (quint, J = 7.0 Hz, 8H), 1.32 (m, 16H), 0.89
(t, J = 7.0 Hz, 12H); 13C NMR (99.5 MHz) δ 146.2, 146.1, 136.0, 132.0,
131.9, 131.2, 130.7, 129.9, 129.6, 119.1, 119.0, 118.9, 32.0(ꢁ2),
31.6(ꢁ2), 30.9(ꢁ2), 30.0(ꢁ2), 29.4(ꢁ2), 29.3(ꢁ2), 22.8(ꢁ2),
14.3(ꢁ2); MALDI-TOF MS m/z = 939.70 (Mþ). Anal. Calcd for
C56H74S6: C, 71.58; H, 7.94%. Found: C, 71.40; H, 7.93%.
(s, 1H), 7.27 (s, 1H), 7.21 (s, 1H), 2.95ꢀ2.99 (m, 4H), 1.77ꢀ1.83
(m, 4H), 1.55ꢀ1.28 (m, 20H), 0.86ꢀ0.96 (m, 6H), 0.46 (s, 3JSnꢀH
=
28.6 Hz, 9H); 13C NMR (99.5 MHz) δ 145.5, 145.4, 138.0, 135.3, 132.9,
131.3, 131.2, 129.9, 129.5, 129.2, 119.3, 118.8, 31.9(ꢁ2), 31.4(ꢁ2),
30.7(ꢁ2), 29.3(ꢁ2), 29.2(ꢁ2), 29.13(ꢁ2), 22.7(ꢁ2), 14.1(ꢁ2), ꢀ8.2;
EI-MS m/z = 634 (Mþ). Anal. Calcd for C31H46S3Sn: C, 58.76; H,
7.32%. Found: C, 59.03; H, 7.35%.
2,5,8-Tribromobenzo[1,2-b:3,4-b0:5,6-b00]trithiophene (9).
To a well-stirred solution of 1a (800 mg, 3.25 mmol) in dichloro-
methane (22.7 mL) and acetic acid (5.7 mL) in a 50 mL round bottom
flask under nitrogen atmosphere was slowly added N-bromosuccinimide
(1.74 g, 9.74 mmol) in small portions. The resulting mixture was stirred
at room temperature for 60 h, and then added water (10 mL) was added
to precipitate the product. The precipitate was collected by filtration,
washed with water (10 mL ꢁ 2) and ethanol (4 mL ꢁ 2), and dried in
vacuo. Recrystallization from chlorobenzene gave 9 as pale violet needles
(1.22 g, 77%). Mp 230 °C; 1H NMR (270 MHz) δ 7.50 (s, 3H); EI-MS
m/z = 480 (Mþ). Anal. Calcd for C12H3S3Br3: C, 29.84; H, 0.63%.
Found: C, 30.05; H, 0.67%.
20,50,80-Tris(5,8-dioctylbenzo[1,2-b:3,4-b0:5,6-b00]trithiophen-
2-yl)benzo[1,2-b:3,4-b0:5,6-b00]trithiophene (4).
8 (210 mg,
0.33 mmol) and 9 (44 mg, 0.091 mmol) were placed in a two-necked flask
with a reflux condenser and dissolved in DMF (7 mL). The solution was
deaerated by nitrogen stream, then Pd(PPh3)4 (36mg, 31μmol) was added,
and the resulting mixture was refluxed for 12 h. After cooling, the mixture was
diluted with water (5 mL) to precipitate the product. The precipitate was
collected by filtration, washed with water (5 mL ꢁ 2) and ethanol (5 mL ꢁ
2), and dried in vacuo to give crude 4 as a yellow solid. The solid was
subjected to column chromatography on silica gel (Rf = 0.50, hexane/CS2,
1:1, v/v, φ 5 ꢁ 10 cm) and further purified by recrystallization from CHCl3/
ethanol (1:1, v/v) to give analytically pure 4 (121 mg, 81%) as a yellow solid.
Mp 223ꢀ225 °C; 1H NMR (400 MHz) δ 7.17 (s, 3H), 7.01 (s, 3H), 6.75
(s, 3H), 6.68 (s, 3H), 2.75 (m, 12H), 1.71 (m, 12H), 1.34 (m, 60H), 0.94
(t, J = 6.3 Hz, 18H); MALDI-TOF MS m/z = 1651.81 (Mþ). Anal. Calcd
for C96H114S12: C, 69.77; H, 6.95%. Found: C, 69.50; H, 6.72%.
80-Bromo-5,500,8,800-tetraoctyl-2,20:50,200-terbenzo[1,2-b:3,4-
b0:5,6-b00]trithiophene (10). 8 (222 mg, 350 μmol) and 9 (94 mg,
195 μmol) were placed in a test tube with a reflux condenser and dissolved
in DMF (5 mL). To the deaerated solution was added Pd(PPh3)4 (16 mg,
14 μmol). The resulting mixture was heated at 80 °C for 12 h and, after
cooling, diluted with water (5 mL) to precipitate the product. The product
was collected by filtration, washed with water (5 mL ꢁ 2) and ethanol
(5 mLꢁ 2), and dried in vacuo to give crude 10 as a yellow solid. The crude
10 was subjected to flash column chromatography on alumina eluted with
dichloromethane and further purified by preparative GPC (JAIGEL-1H/
2H, CHCl3) to give 10 as a yellow solid (94 mg, 42%). Mp 111ꢀ113 °C;
1H NMR (400 MHz) δ 7.00 (s, 1H), 6.92 (s, 1H), 6.88 (s, 1H), 6.83
(s, 1H), 6.77 (s, 1H), 6.71 (s, 1H), 6.68 (s, 1H), 6.67 (s, 1H), 6.63 (s, 1H),
2.75ꢀ2.67 (m, 8H), 1.66ꢀ1.62 (m, 8H), 1.38ꢀ1.26 (m, 40H), 0.92 (t, J =
6.4 Hz, 12H); 13C NMR (126 MHz) δ 145.7(ꢁ2), 145.5(ꢁ2), 136.7(ꢁ2),
135.1, 135.0, 131.8(ꢁ2), 131.6(ꢁ2), 131.2(ꢁ4), 130.7(ꢁ2), 130.6(ꢁ2),
130.4(ꢁ2), 129.4(ꢁ2), 129.1(ꢁ2), 124.5, 118.5(ꢁ2), 118.3(ꢁ3),
118.2(ꢁ3), 113.6, 31.9 (ꢁ4), 31.2 (ꢁ2), 31.1 (ꢁ2), 30.8 (ꢁ3), 30.7,
29.5 (ꢁ4), 29.4 (ꢁ8), 22.8 (ꢁ4), 14.1(ꢁ4); MALDI-TOF MS m/z 1263
(Mþ). Anal. Calcd for C68H77BrS9: C, 64.67; H, 6.15%. Found: C, 64.72;
H, 6.04%.
(5,8-Dioctylbenzo[1,2-b:3,4-b0:5,6-b00]trithiophen-2-yl)tri-
methylstannane (8). 7 (600 mg, 1.27 mmol) was placed in a 100 mL
round-bottomed flask and dissolved in THF (40 mL). After the solution
was cooled to 0 °C, a hexane solution of n-butyllithium (1.57 M, 2.0 mL,
3.14 mmol) was slowly added, and the resulting mixture was stirred at rt
for 1.5 h. Trimethyltin chloride (586 mg, 3.14 mmol) was then added,
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2,5,8-Tris(trimethylstannyl)benzo[1,2-b:3,4-b0:5,6-b00]tri-
thiophene (11). Benzo[1,2-b:4,5-b0:5,6-b00]trithiophene (1a, 1.0 g,
4.06 mmol) was placed in a 50-mL round-bottomed flask and dissolved
in THF (50 mL). After the solution was cooled at 0 °C, a hexane solution
of n-butyllithium (1.59 M, 15.3 mL, 24.4 mmol) was slowly added and
then stirred at room temperature for 6 h. Trimethyltin chloride (2.67 g,
13.4 mmol) was then added, and the mixture was stirred at rt overnight.
After addition of water (20 mL), the mixture was extracted with
dichloromethane (50 mL ꢁ 3). The combined extracts were washed
with water (50 mL ꢁ 3), dried over MgSO4 (anhydrous), and
concentrated in vacuo. The product was purified by recrystallization
from hexane/methanol to give 11 (3.0 g, quantitative) as a white solid.
Mp 212ꢀ213 °C; 1H NMR (400 MHz) δ 7.69 (s with satellite peaks,
Evaporation of the solvent gave a crude product. Then the product
was subjected to flash column chromatography on alumina eluted with
dichloromethane and further purified by preparative GPC (JAIGEL-
1H/2H, CHCl3) to give 5 (55 mg, 67%). Mp >300 °C; 1H NMR (400
MHz, CD2Cl4, 100 °C) δ 7.2ꢀ6.2 (broad peaks, 18H), 2.7 (broad
peaks, 16H), 1.7ꢀ0.9 (broad peaks, 120H); MALDI-TOF MS m/z 2365
(Mþ). Anal. Calcd for C136H154S18: C, 69.04; H, 6.56%. Found: C,
68.96; H, 6.54%.
2,5,8-Tris{(50,80-bis(500,800-dioctylbenzo[1,2-b:3,4-b0:5,6-
b00]trithiophen-200-yl)benzo[1,2-b:3,4-b0:5,6-b00]trithiophen-
20-yl)}benzo[1,2-b:3,4-b0:5,6-b00]trithiophene (6). 9 (20 mg,
41 μmol) and 13 (200 mg, 148 μmol) were placed in a test tube with
a reflux condenser, and dissolved in toluene (2 mL). To the deaerated
solution was added Pd(PPh3)4 (5 mg, 4 μmol). The resulting mixture
was refluxed for 16 h, cooled to rt, diluted with water (1 mL), and
extracted with dichloromethane (10 mL ꢁ 2). The extract was washed
with brine (20 mL ꢁ 3) and dried over MgSO4 (anhydrous). Evapora-
tion of the solvent gave a crude product, which was subjected to flash
column chromatography on alumina eluted with dichloromethane. The
product was further purified by preparative GPC (JAIGEL-1H/2H,
CHCl3) to give mixture of 6 and 5 as a brown solid. The mixture was
again purified by preparative GPC (JAIGEL-2H/3H, CHCl3) to give 6
as a brown solid (51 mg, 33%). Mp >300 °C; MALDI-TOF MS m/z
3792 (Mþ). Anal. Calcd for C216H234S30: C, 68.41; H, 6.22%. Found: C,
68.13; H, 6.03%.
X-ray Crystallographic Analysis of 2 and 3. Single crystals suitable for
structural analysis were obtained by careful recrystallization from chloroform.
The X-ray crystal structure analysis was made on a Rigaku RAXIS-RAPID
Imaging Plate (Mo KR radiation, λ = 0.71069 Å, graphite monochromator,
T=200K, 2θmax = 55.0°). The structure was solved by the direct methods.17
Non-hydrogen atoms were refined anisotropically, and hydrogen atoms were
included in the calculations but not refined. All calculations were performed
using the crystallographic software SHELX-97.17 In the structure of 2,
orientationally disordered molecules related by the C2 axis on the molecular
long axis exist. Thus, the population of the sulfur and R-carbon atoms
suggested that ca. 32% molecules were disordered.
3
3JSnꢀH = 14 Hz, 3H), 0.476 (s with satellite peaks, JSnꢀH = 41.2 Hz,
27H); 13C NMR (99.5 MHz) δ 138.0, 135.8, 132.7, 130.4, ꢀ8.15. Anal.
Calcd for C21H30S3Sn3: C, 34.33; H, 4.12%. Found: C, 34.59; H, 3.75%.
2,5-Dioctyl-8-iodobenzo[1,2-b:3,4-b0:5,6-b00]trithiophene
(12). 7 (940 mg, 2.0 mmol) was placed in a 50 mL round-bottomed flask
and dissolved in THF (28 mL). After the solution was cooled to 0 °C, a
hexane solution of n-butyllithium (1.57 M, 1.6 mL, 2.5 mmol) was slowly
added, and the mixture was stirred at rt for 1.5 h. Then a solution of
iodine (660 mg, 2.6 mmol) in THF (28 mL) was added dropwise, and
the resulting mixture was stirred for 1.5 h. After addition of an aqueous
NaHSO3 solution (10 mL), the mixture was extracted with dichlor-
omethane (20 mL ꢁ 2). The extract was washed with an aqueous
NaHSO3 solution (20 mL ꢁ 3), dried over MgSO4 (anhydrous), and
concentrated in vacuo. The residue was purified by column chromatog-
raphy on silica gel (Rf = 0.6, hexane, φ 3.5 ꢁ 14 cm) to give 12 (920 mg,
1
78%) as a white solid. Mp 53ꢀ55 °C; H NMR (400 MHz) δ 7.70
(s, 1H), 7.19 (s, 1H), 7.16 (s, 1H), 2.96 (t, J = 8.0 Hz, 4H), 1.77 (m, 4H),
1.28ꢀ1.42 (m, 40H), 0.88 (t, J = 6.3 Hz, 6H); 13C NMR (99.5 MHz)
δ 146.3, 146.2, 135.1, 132.4, 132.0(ꢁ2), 131.7, 130.4, 128.2, 118.7(ꢁ2),
74.9, 31.9(ꢁ2), 31.4(ꢁ2), 30.7(ꢁ2), 29.3(ꢁ2), 29.2(ꢁ2), 29.1(ꢁ2),
22.7(ꢁ2), 14.1(ꢁ2); EI-MS m/z 550 (Mþ). Anal. Calcd for C28H37IS3:
C, 56.36; H, 6.25%. Found: C, 56.36; H, 6.25%.
Trimethyl(5,500,8,800-tetraoctyl-[2,20:50,200-terbenzo[1,2-b:3,4-
b0:5,6-b00]trithiophen]-80-yl)stannane (13). 12 (282 mg, 473 μmol)
and 11 (194 mg, 264 μmol) were placed in a 20 mL-round-bottomed flask,
and dissolved in DMF (9.4 mL). To the deaerated solution was added
Pd(PPh3)4 (30 mg, 12 μmol). The resulting mixture was heated at 80 °C for
12 h, cooled to rt, and then added water (5 mL) to precipitate the product.
The precipitate was collected by filtration, washed with water (5 mL ꢁ 2)
and ethanol (5 mL ꢁ 2), and dried in vacuo to give crude product as a yellow
solid. The crude product was subjected to flash column chromatography on
alumina eluted with dichloromethane, and then further purified by pre-
parative GPC (JAIGEL-1H/2H, CHCl3) togive13 asayellowsolid(265mg,
83%). 1H NMR (400 MHz) δ 7.75 (s, 1H), 7.73 (s, 1H), 7.71 (s, 1H), 7.69
(s, 1H), 7.64(s, 1H), 7.23(s, 2H), 7.20(s, 1H), 7.18(s, 1H), 3.01ꢀ2.96 (m,
8H), 1.84ꢀ1.82 (m, 8H), 1.51ꢀ1.31 (m, 40H), 0.90 (t, J = 6.4 Hz, 12H),
Crystal data for 2: C24H10S6, M = 490.70, yellow needle, 0.80 ꢁ
0.10 ꢁ 0.10 mm3, monoclinic, space group, P21/n (No. 14), a =
16.683(18), b = 8.90(4), c = 17.88(19) Å, β = 115.15(3)°, V =
1009.7(19) Å3, Z = 2, R = 0.0966, wR2 = 0.1393 for all observed
reflections (2099) and 191 variable parameters.
Crystal data for 3: C56H74S6, M = 939.56, yellow needle, 0.50 ꢁ 0.30 ꢁ
0.050 mm3, triclinic, space group, P-1 (No. 2), a = 10.255(5), b =
15.864(7), c = 17.626(8) Å, R = 66.05(1), β = 84.59(2), γ = 89.06(2) °,
V = 2608(2) Å3, Z = 2, R = 0.0622, wR2 = 0.2286 for all observed
reflections (6222) and 559 variable parameters.
Device Fabrications and Evaluations. OFETs. Si/SiO2 substrates
were treated with octyltrichlorosilane (OTS-8) by immersing the silicon
wafers to OTS-8 solution in dry toluene at room temperature under
nitrogen for 12 h.18 OFETs were fabricated in a “top-contact” configura-
tion on a heavily doped nþ-Si (100) wafer with 200-nm-thick thermally
grown SiO2 (Ci = 17.3 nF cmꢀ2). A thin film of 3 or 4 as the active layer
was spin-coated on Si/SiO2 substrates at 3000 rpm for 30 s. 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 ca. 1.5 mm, respectively.
The characteristics of the OFET devices were measured at room
temperature in air with a Keithly 4200 semiconducting parameter
analyzer. Field-effect mobility (μFET) was calculated in the saturation
regime (Vd = ꢀ60 V) of the Id using the following equation:
3
0.53 (s, JSnꢀH = 28.6 Hz, 9H); 13C NMR (126 MHz) δ 145.8(ꢁ2),
145.7(ꢁ2), 138.9(ꢁ2), 136.7, 136.3(ꢁ2), 135.6, 135.5, 133.0, 132.0, 131.9,
131.8, 131.7, 131.6, 131.2, 131.0(ꢁ2), 130.8, 130.5(ꢁ2), 130.0, 129.8,
129.7(ꢁ2), 129.5, 129.4, 118.8, 118.7(ꢁ3), 118.6(ꢁ3), 118.3, 32.0 (ꢁ4),
31.4 (ꢁ3), 31.4, 30.8 (ꢁ3), 30.7, 29.5 (ꢁ4), 29.4 (ꢁ4), 29.3 (ꢁ4), 22.7
(ꢁ4), 14.1(ꢁ4), ꢀ8.0(ꢁ4); MALDI-TOF MS m/z 1263 (Mþ). Anal.
Calcd for C71H86S9Sn: C, 63.32; H, 6.44%. Found: C, 63.27; H, 6.24%.
2,20-Bis{5,8-bis(500,800-dioctylbenzo[1,2-b:3,4-b0:5,6-b00]-
trithiophen-200-yl)}benzo[1,2-b:3,4-b0:5,6-b00]trithiophene
(5). 13 (53 mg, 40 μmol) and 10 (50 mg, 40 μmol) were placed in a test
tube and dissolved in toluene (1 mL). To the deaerated solution was
added Pd(PPh3)4 (3 mg, 2.4 μmol). The resulting mixture was refluxed
for 16 h, cooled to rt, diluted with water (1 mL), and extracted with
dichloromethane (10 mL ꢁ 2). The combined extracts were washed
with brine (20 mL ꢁ 3) and dried over MgSO4 (anhydrous).
2
Id ¼ ðWCi=2LÞμFETðVg ꢀ VthÞ
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)
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The Journal of Organic Chemistry
ARTICLE
was determined from the Id at Vg = 0 V (Ioff) and Vg = ꢀ60 V (Ion). The
μFET data reported in the present paper are values from more than 10
different devices.
M. R.; Kirkpatrick, J.; Grozema, F.; Andrienko, D.; Kremer, K.; M€ullen,
K. Nat. Mater. 2009, 8, 421–426.
(6) Several heteroarene-based p-OFETs showing μFET higher than
1.0 cm2 Vꢀ1 sꢀ1 have been reported: (a) Payne, M. M.; Parkin, S. R.;
Anthony, J. E.; Kuo, C. C.; Jackson, T. N. J. Am. Chem. Soc. 2005,
127, 4986–4987. (b) Takimiya, K.; Ebata, H.; Sakamoto, K.; Izawa, T.;
Otsubo, T.; Kunugi, Y. J. Am. Chem. Soc. 2006, 128, 12604–12605.
(c) Yamamoto, T.; Takimiya, K. J. Am. Chem. Soc. 2007, 129, 2224–2225.
(d) Ebata, H.; Izawa, T.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara,
H.; Yui, T. J. Am. Chem. Soc. 2007, 129, 15732–15733. (e) Gao, P.;
Beckmann, D.; Tsao, H. N.; Feng, X.; Enkelmann, V.; Baumgarten, M.;
Pisula, W.; M€ullen, K. Adv. Mater. 2009, 21, 213–216. (f) Kang, M. J.; Doi,
I.; Mori, H.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara, H. Adv.
Mater. 2011, 23, 1222–1225. (g) Shinamura, S.; Osaka, I.; Miyazaki, E.;
Nakao, A.; Yamagishi, M.; Takeya, J.; Takimiya, K. J. Am. Chem. Soc. 2011,
133, 5224–5035.
’ ASSOCIATED CONTENT
S
Supporting Information. Crystallographic information
b
files (CIF format) for 2 and 3, complete ref 15, FET character-
istics of 5- and 6-based OFETs, results of MO calculations, and
AFM images of thin films, NMR spectra, MALDI-TOF MS
spectra of 5 and 6. This material is available free of charge via the
Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
(7) (a) Proetzsch, R.; Bieniek, D.; Korte, F. Tetrahedron Lett. 1972,
13, 543–544. (b) Jayasuriya, N.; Kagan, J.; Owens, J. E.; Kornak, E. P.;
Perrine, D. M. J. Org. Chem. 1989, 54, 4203–4205.
Corresponding Author
*E-mail: ktakimi@hiroshima-u.ac.jp.
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’ ACKNOWLEDGMENT
This work was partially supported by a Grant-in-Aid for
Scientific Research (No. 20350088 and 23245041) from the
Ministry of Education, Culture, Sports, Science and Technology,
Japan and Founding Program for World-Leading R&D on
Science and Technology (FIRST), Japan.
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