Quinoidal oligothiophenes with (acyl)cyanomethylene termini: Synthesis, characterization, properties, and solution processed n-channel organic field-effect transistors

Article abstract of DOI:10.1021/cm102109p

A new class of oligothienoquinoidal derivatives with newly employed (acyl)cyanomethylene termini are reported. For the synthesis of (acyl)cyanomethylene-substituted thienoquinoidals, similar methods successfully employed for the synthesis of related dicyanomethylene-or ((alkyloxy)carbonyl) cyanomethylene-substituted thienoquinoidals were not applicable, and thus a new synthetic route was developed. The introduced (acyl)cyanomethylene terminal groups act both as a solublizing group to facilitate solution processability and an electron-withdrawing group to keep the LUMO energy levels sufficiently low for n-channel organic semiconductors. The LUMO energy levels estimated from their reduction potential are ～4.2 eV below the vacuum level, which just falls in between those for the corresponding dicyanomethylene-and ((alkyloxy)carbonyl)cyanomethylene-substituted thienoquinoidals. This qualitatively agrees with the electron-withdrawing nature of the terminal groups; the order of the electron withdrawing nature is cyano-> acyl-> (alkyloxy)carbonyl-groups. Spin-coating chloroform solutions of (acyl)cyanomethylene-substituted thienoquinoidals gave homogeneous thin films on the Si/SiO₂ substrates, and the thin films based on the terthienoquinoidal derivatives became highly crystalline upon thermal annealing. The annealed film acted as the active semiconducting channel in the FET devices under ambient conditions, and the electron mobilities extracted from the saturation regime were ～0.06 cm² V^-1 s^-1. These n-channel FET characteristics are nearly the same or slightly better than those of the FETs based on the related ((alkyloxy)carbonyl)cyanomethylene- terminated terthienoquinoidal, indicating that the (acyl)cyanomethylene moiety is a useful terminal group on the thienoquinoidals for the development of soluble n-channel organic semiconductors.

Full text of DOI:10.1021/cm102109p

Chem. Mater. 2011, 23, 795–804 795
DOI:10.1021/cm102109p
Quinoidal Oligothiophenes with (Acyl)cyanomethylene Termini:
Synthesis, Characterization, Properties, and Solution Processed
n-Channel Organic Field-Effect Transistors†
Yuki Suzuki,‡ Masafumi Shimawaki,‡ Eigo Miyazaki,‡ Itaru Osaka,‡ and Kazuo Takimiya*,‡,§
§
‡Department of Applied Chemistry, Graduate School of Engineering and Institute for Advanced Materials
Research, Hiroshima University, Higashi-Hiroshima 739-8530, Japan
Received July 28, 2010. Revised Manuscript Received September 2, 2010
A new class of oligothienoquinoidal derivatives with newly employed (acyl)cyanomethylene termini are
reported. For the synthesis of (acyl)cyanomethylene-substituted thienoquinoidals, similar methods
successfully employed for the synthesis of related dicyanomethylene- or ((alkyloxy)carbonyl)cyano-
methylene-substituted thienoquinoidals were not applicable, and thus a new synthetic route
was developed. The introduced (acyl)cyanomethylene terminal groups act both as a solublizing group to
facilitate solution processability and an electron-withdrawing group to keep the LUMO energy levels
sufficiently low for n-channel organic semiconductors. The LUMO energy levels estimated from their
reduction potential are ∼4.2 eV below the vacuum level, which just falls in between those for the
corresponding dicyanomethylene- and ((alkyloxy)carbonyl)cyanomethylene-substituted thienoquin-
oidals. This qualitatively agrees with the electron-withdrawing nature of the terminal groups; the order of
the electron withdrawing nature is cyano- > acyl- > (alkyloxy)carbonyl- groups. Spin-coating chloro-
form solutions of (acyl)cyanomethylene-substituted thienoquinoidals gave homogeneous thin films on the
Si/SiO2 substrates, and the thin films based on the terthienoquinoidal derivatives became highly crystalline
upon thermal annealing. The annealed film acted as the active semiconducting channel in the FET devices
under ambient conditions, and the electron mobilities extracted from the saturation regime were ∼0.06 cm2
V-1 s-1. These n-channel FET characteristics are nearly the same or slightly better than those of the FETs
based on the related ((alkyloxy)carbonyl)cyanomethylene-terminated terthienoquinoidal, indicating that
the (acyl)cyanomethylene moiety is a useful terminal group on the thienoquinoidals for the development of
soluble n-channel organic semiconductors.
Introduction
1980s as a promising electron accepting molecules for con-
ducting CT salts.5
7,7,8,8-Tetracyanoquinodimethane (TCNQ, Figure 1),
the archetypical electron-accepting molecule, has played
important roles in the field of conducting charge-transfer
(CT) complexes since the discovery of the first metallic
organic material, terathiafulvalene-TCNQ CT salt, reported
by Cowan et al. in 1970s.1 Since then, a variety of TCNQ
derivatives2 as well as its related quinoidal compounds3 have
been developed. Dicyanomethylene-terminated quinoidal-
thiophenes or thiophene TCNQs are among such com-
pounds4 and were intensively studied by Ogura et al. in the
Recent rising interests in the field of organic electronics
has renewed the interests in the TCNQ-type compounds
as n-channel organic semiconductors.6 In fact, the parent
TCNQ7 and its π-extended analogue, 9,9,10,10-tetra-
cyanonaphtho-2,6-quinodimethane (TNAP) (Figure 1),8
were examined as an active material in the field-effect
transistors (FETs) showing relatively good field-effect
electron mobility. Several dicyanomethylene-terminated
thienoquinoidals have also been examined as active
n-channel materials in OFET devices.9 However, the parent
bithienoquinoidal- (1a) or terthienoquinoidal (1b)-based
FETs showed poor device characteristics with low mobility
† Accepted as part of the “Special Issue on π-Functional Materials”.
*Corresponding author. E-mail: ktakimi@hiroshima-u.ac.jp.
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2010 American Chemical Society
Published on Web 09/22/2010
pubs.acs.org/cm

796 Chem. Mater., Vol. 23, No. 3, 2011
Suzuki et al.
Figure 2. Thienoqunioidal derivatives with soluble terminal groups.
Figure 1. Structures of representative dicyanomethylene-substituted
benzoquinoidal and thienoquinoidal compounds.
(∼1ꢀ10-4 cm2 V-1 s-1) because of their poor molecular
ordering in the thin film state.9c,10 In sharp contrast, the
derivatives of 1b with substituents on the thienoquinoidal
core (2) act as superior n-channel organic semiconductors
showing mobility up to 0.2 cm2 V-1 s-1 9a,b
Furthermore, a
.
Figure 3. Calculated HOMO and LUMO of terthienoquinoidal deriva-
tives with different terminal groups (1b, 4b, and 5b).
proper modification with a solubilizing group affords a
solution processable derivative (3) with retaining high
mobility.9d,e These fruitful results on 2 and 3 imply that
the molecular modification on the thienoquinoidal core
would be a key not only for solubilizing the materials but
also enabling molecular ordering in the thin-film state.
However, the core substitution often requires elaborated
synthesis,9d which makes the material less practical, even
though the given material provides superior semiconductor
characteristics.
good air stability due to their low-lying LUMO energy level
(<4.0 eV below the vacuum level).11 In these new thieno-
quinoidals, the ((alkyloxy)carbonyl)cyanomethylenetermini
serves both as a solubilizing and an electron-withdrawing
group: in other words, this chemical structure satisfies
simultaneously the criteria requested for developing soluble,
air-stable n-channel organic semiconductors.
Theses results impelled us to explore related thieno-
quinoidals terminated with (acyl)cyanomethylene groups
(Figure 2, 5) as new potential n-channel organic semi-
conductors. In fact, theoretical calculations predict that
the (acyl)cyanomethylene-substituted thienoquinoidals
have slightly lower LUMO energy levels than those of
((alkyloxy)carbonyl)cyanomethylene-substituted ones,
reflecting the enhanced electron-withdrawing nature of
the acyl group compared to that of alkyloxycarbonyl group
(Figure 3).12 We report herein the synthetic approaches to
new soluble oligothienoquinoidals terminated with (acyl)-
cyanomethylene groups (5) that provides a new class of
soluble n-channel organic semiconductors for solution-
On the other hand, we have pursued another approach for
developing superior new n-channel organic semiconductors
based on the quinoidal thiophene structure rather than the
molecular modification on the quinoidal core. Actually, we
have recently found that a newly employed terminal group
containing solublizing long alkyl group, namely the ((alkyl-
oxy)carbonyl)cyanomethylene terminus instead of the con-
ventional dicyanomethylene terminus is quite effective to
develop a series of new thienoquinoidals. Thus developed
((alkyloxy)carbonyl)cyanomethylene-substituted thienoquin-
oidals (Figure 2, 4) can act as soluble n-channel organic
semiconductors that afford solution-processed OTFTs with
processed OFETs with mobility up to 0.06 cm2 V-1 s-1
.
electron mobility up to 0.015 cm2 V-1 s-1 10
The devices
.
based on 4 can operate under ambient conditions, indicating
Results and Discussions
Synthesis. The synthesis of the target thienoqunioidals
(5) was thought to be deceptively simple by employing the
(9) (a) Pappenfus, T. M.; Chesterfield, R. J.; Frisbie, C. D.; Mann,
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Matsumoto, M.; Muto, T.; Nakao, A.; Aoyama, T. Adv. Mater. 2010,
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B3LYP/6-31g(d) level using Gaussian 03 program package. Frisch,
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Article
Chem. Mater., Vol. 23, No. 3, 2011 797
Scheme 1. Attempted Synthesis of 3a
Scheme 2. Synthetic Strategy for (Acyl)Cyanomethylene-
Substituted Thienoquinoidals
Scheme 3. Synthesis of Bithienoquinoidal Compounds (5a)
successful synthetic methods for the related ((alkyloxy)-
carbonyl)cyanomethylene-substituted thienoqunioidals
(4). However, initial attempts to synthesize 5a (R =
CH3) as a model compound were failed: the first at-
tempted route (route A in Scheme 1) consisting of the
direct substitution reaction of acetylcyanomethanoide
anion13 with 5,50-dibromo-2,20-bithiophene (6) gave an
ill-characterized complex mixture. This is due to poor
reactivity of (acetyl)cyanomethanoide anion in situ gen-
erated from cyanoacetone and sodium hydride compared
with the ((alkyloxy)carbonyl)cyanomethanoide anion,
because the (acetyl)cyanomethanoide anion is stabilized
by the enolate form (Scheme 1).
As the next attempt, we tried to introduce acetyl groups
on the benzyl carbon atoms of the 5,50-bis(cyanomethyl)-
2,20-bithiophene10 (7, Scheme 1, route B). However, the
isolated product was an overreacted one, 5,50-bis-
(diacetylcyanomethyl)-2,20-bithiophene (8).
These results sharply contrast to the easy accessibility of 4
and related ((alkyloxy)carbonyl)cyanomethylene-substi-
tuted thienoquinoidals.10 We then examined several differ-
ent synthetic trials for 5 and finally found a reproducible
synthetic method for the target oligothienoquinoidals. Key
features in the newly developed synthesis are to construct the
R-thienylketone moiety (A) and subsequent introduction of
a cyano group to give the (acyl)cyanomethyl-substituted
thiophene (B), which is supposed to be oxidized to the target
thienoquinoidal (Scheme 2).
corresponding acetals (11). Functionalization of the vacant
5-position of 11 was easily done as the ordinary thiophene
derivatives, and dimerization of 11 via AgNO3/KF-mediated
coupling gave 12.15 After deprotection of the acetal moieties
(13), treatment of 13 with LDA and 2-chlorobenzylthio-
cyanate16 followed by oxidation with N-iodosuccinimide
finally gave desired 5a compounds (R = C2H5, n-C6H13).
In the case of the synthesis of the dodecyl derivative (5a, R =
n-C12H15), only a complex mixture was obtained, and the
desired 5a could not be isolated.
Although the desired 5a compounds were obtained,
their isolated yields were very low even after careful
optimizations of the reaction conditions and the sub-
sequent workup processes. One of the reasons for such
low yields is the formation of byproducts: from the
reaction mixture, a crystalline byproduct (14) was iso-
lated and characterized by means of single-crystal
X-ray analysis (Figure 4). As depicted in Figure 4, 14
may form via a reaction of the carbanion intermediate
(A0) with 2-chlorobenzylthiocyanate at the benzyl car-
bon atom (blue arrows) instead of the desired nitrile
carbon atom (red arrows).
Actual synthesis of 5a is shown in Scheme 3. Thienyl
ketones (10) were first synthesized via a ring-opening reac-
tion of epoxides with 2-thienyl lithium to form the alcohol
intermediates (9) followed by oxidation.14 In the oxidation
reaction, careful control of the oxidant was crucial, otherwise
an overreacted thienyl dione (100, Scheme 3) was easily
formed. Because monoketo thiophenes (10) were labile and
decomposed rapidly, 10 were isolated and purified as the
(15) (a) Masui, K.; Ikegami, H.; Mori, A. J. Am. Chem. Soc. 2004, 126,
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K.; Mori, A. Org. Lett. 2005, 7, 5083–5085. (c) Takahashi, M.;
Masui, K.; Sekiguchi, H.; Kobayashi, N.; Mori, A.; Funahashi,
M.; Tamaoki, N. J. Am. Chem. Soc. 2006, 128, 10930–10933.
(16) (a) Bryce, M. R.; Hasan, M.; J., A. G. J. Chem. Soc., Chem.
Commun. 1989, 529–530. (b) Bryce, M. R.; Grainger, A. M.; Hasan,
M.; Ashwell, G. J.; Bates, P. A.; Hursthouse, M. B. J. Chem. Soc.,
Perkin Trans. 1 1992, 611–614.
(13) Blount, J. F.; Coffen, D. L.; Katonak, D. A. J. Org. Chem. 1978, 43,
3821–3824.
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M.; Shirai, K. Bull. Chem. Soc. Jpn. 1986, 59, 3097–3101.

798 Chem. Mater., Vol. 23, No. 3, 2011
Suzuki et al.
Scheme 5. Synthesis of Terthienoquinoidal Compounds (5b)
Figure 4. Structure of 14 and the plausible reaction path to 14.
The terthienoquinoidal derivatives (5b) were also synthe-
sized in a similar manner to that of 5a. Bromination at the
5-position of the protected thienyl ketone (11) with NBS
smoothly gave 15, which was then utilized to the Stille
coupling with 2,5-bis(trimethylstannyl)thiophene19 to give
terthiophene intermediate (16). After deprotection of the
acetal moieties, introduction of the cyano groups on the ben-
zylic carbon atoms followed by oxidation gave 5b in good
yields (Scheme 5). All these new thienoquinoidal compounds
were well-characterized by means of spectroscopic and
combustion elemental analysis (see Experimental Section).
Physicochemical Evaluation. Cyclic voltammetry of 5a
and 5b showed similar redox behaviors to those of
corresponding 1 and 4 (Figure 5, Table 1). As expected from
the extent of electron-withdrawing nature of the cyano, ester,
and acyl groups20 and the DFT calculation results described
above (Figure 3), the empirical reduction potentials of 5 are
in between those of 1 and 4 (Figure 5). The LUMO energy
levels of 5a and 5b estimated from the onset of the redox
wave are around 4.2-4.3 eV below the vacuum level, which
meets the criteria for air-stable n-channel OFET materials.11
Similar to the voltamograms of 1b and 4b, the terthienoquin-
oidal derivatives 5b also show oxidation peaks, indicating
that the HOMO energy levels of 5b are relatively high
compared to those of 5a as in the cases for 1b and 4b.
Judging from the HOMO energy levels of 5b (5.5 eV below
the vacuum level), the hole injection from the gold electrode
to the 5b thin film might take place,9b,e,f,h which brings about
the p-channel transistor behavior. However, we could not
observe any p-channel response in the 5b-FET devices (vide
infra), although the actual reasons for the lack of ambipolar
behavior are not clear.
Scheme 4. Improved Synthesis of 5a (R = C2H5, n-C6H13) with
1-Cyano-1H-1,2,3-bezotriazole
It is also interesting to note that the molecular structure
of 14 at the (acyl)cyanomethane terminus has the Z-
isomer form as observed for the molecular structure of
((alkyloxy)carbonyl)cyanomethylene-substituted thieno-
quinoidals as previously reported.10 This is probably due
to the intramolecular interaction between the sulfur atom
in the thiophene ring and the carbonyl oxygen atom (2.65
17
˚
A) shorter than the sum of van der Waals radii. In
addition, a similar short intramolecular nonbonded con-
˚
tact exists in the other terminus (2.59 A) between the
sulfur atom in the thiophene ring and the carbonyl oxygen
atom. These structural features, in combination with a
similar intramolecular nonbonded contact in the ((alkyloxy)-
carbonyl)cyanomethylene-substituted thienoquinoidals,10
indicate that this type of intramolecular attractive inter-
action is common for theses classes of thienoquinoidal
compounds with carbonyl groups at the exomethylene
moiety and may define the terminal structure as the
Z-form.
The formation of 14 and other structurally related by-
products should be avoided to improve the yield of 5 in the
cyanation reaction, and thus we tried to use another cycano
source, 1-cyano-1H-1,2,3-bezotriazole, instead of 2-chloro-
benzylthiocyanate (Scheme 4).18 In this case, the isolated
yields of 5a were improved to 37% (R = C2H5) and 32%
(n-C6H13), respectively, although the decyl derivative (5a,
n-C12H25) could not be synthesized, perhaps because of the
poor solubility of the precursor, 13 (n-C12H25).
Absorption spectra of 5a and 5b depicted in Figure 6
show a slight bathochromic shift compared to the corre-
sponding 1 and 4. This is provably due to more effective
conjugation of the carbonyl group with the thienoquin-
oidal core than those of the cyano or ester group in 1 and 4.
(19) Pham Chiem, V.; Macomber, R. S.; Mark, H. B.; Zimmer, H.
J. Org. Chem. 1984, 49, 5250–5253.
(20) Advanced Organic Chemistry, Reactions, Mechanisms, and Struc-
ture, 4th ed.; March, J., Ed.; John Wiley and Sons: New York, 1992;
p 278.
(17) Bondi, A. J. Phys. Chem. 1964, 68, 441–451.
(18) Hughes, T. V.; Hammond, S. D.; Cava, M. P. J. Org. Chem. 1998,
63, 401–402.

Article
Chem. Mater., Vol. 23, No. 3, 2011 799
Figure 5. Cyclic volatmmogram of 5 (R=n-C6H13) in comparison with 1 and 4 (R=n-C6H13): (a) bithienoquinoidals, 1a, 4a, and 5a; (b) terthienoquin-
oidals, 1b, 4b, and 5b.
Table 1. Comparison of Bithienoquinoidal (1a, 4a, and 5a) and Terthienoquinoidal Compounds (1b, 4b, and 5b) with Different Terminal Groups
E1/2red (V )a
Eonset red (V)a
LUMO (eV)b
E1/2ox/V
λ
max (log ε) (nm)
λ
onset (nm)
Eg (eV)c
HOMO (eV) b,d
5ae
4ae
1a
-0.23 (1e), -0.35 (1e)
-0.34 (1e), -0.48 (1e)
-0.10 (1e), -0.32 (1e)
-0.22 (2e)
-0.16
-0.26
-0.03
-0.16
-0.23
-0.04
-4.24
-4.14
-4.37
-4.24
-4.17
-4.36
575 (4.87)
556 (4.92)
550 (4.86)
668 (5.06)
649 (5.04)
643 (5.02)
647
610
612
797
785
811
1.9
2.0
2.0
1.5
1.5
1.5
-6.1 d
-6.1 d
-6.4 d
-5.5 b
-5.5 b
-5.7 b
5be
4be
1b
þ1.10
þ1.10
þ1.35
-0.32 (2e)
-0.12 (2e)
a V vs Ag/AgCl. All the potentials were calibrated with the Fc/Fcþ (E1/2 = þ0.43 V measured under identicalconditions). b Estimated with a following
equation: E (eV) = -4.4 - Eonset. c Calculated from λonset d Estimated from the LUMO energy level and Eg. e Compounds with R = n-C6H13 were used.
.
However, overall similarity of the absorption spectra for
1, 4, and 5 again confirms that the electronic perturbation
from the acyl groups are not significant, and 5a and 5b
would be potential n-channel organic semiconductors as
1 and 4.
with that in the solution. This spectroscopic behavior in
the thin film state and the aforementioned thin film XRD
indicates that the molecular ordering nature of 5a is quite
different from those of analogous 4a and 5b.21
Thin Film FET Devices. OFET devices using the spin-
coated thin films of 5a (R = n-C6H13) and 5b (R = n-C6H13,
n-C12H25) as the active semiconducting channel were eval-
uated with a top-contact, bottom gate device configuration
on the Si/SiO2 substrate modified with octadecyltrichloro-
silane. As expected from the poor molecular ordering in the
thin film state, 5a-based OFETs did not show decent
n-channel FET responses. On the other hand, 5b-based ones
showed typical n-channel FET behaviors under ambient
conditions: without thermal annealing of the thin films, the
Thin Film Deposition. Spin-coating chloroform solu-
tions of 5a (R = n-C6H13) and 5b (R = n-C6H13, n-
C12H25) gave homogeneous thin films on Si/SiO2 and
quartz glass substrates. As-spun films were amorphous-
like in all three cases, whereas annealing (∼120 °C) clearly
improved the molecular ordering in the thin film state of
5b (R = n-C6H13, n-C12H25), as evident from the X-ray
diffraction (XRD) patterns (Figure 7b). In case of the 5a
(R = n-C6H13) thin film, no noticeable change in XRD
pattern on annealing was observed (Figure 7a), which
reflects its poor crystallinity, or in other words inherent
amorphous nature of 5a in the thin film state. This
contrasts to 4a, the bithienoquinoidal counterpart with
the ((alkyloxy)carbonyl)cyanomethylene termini, that gives
well-ordered crystalline thin films by spin-coating and
subsequent annealing.
Improved molecular ordering in the thin film of 5b
(R = n-C6H13, n-C12H25) on annealing was concomitant
with hypsochromic shifts in the UV-vis spectra of thin
films as shown in Figure 8b, which is reminiscent of
similar hypsochromic shifts for 4a and 4b.10 In sharp
contrast, the 5a (R = n-C6H13) thin film does not show
such hypsochromic shifts (Figure 8a); rather, bathochro-
mic shift was observed in the thin film state compared
mobilities were on the order of 1 ꢀ 10-5 cm2 V-1 s-1
,
whereas the mobilities for the devices with annealed thin
films extracted from the saturated regime are 0.007 cm2
V-1 s-1 for 5b (R = n-C6H13) and 0.06 cm2 V-1 s-1 for 5b
(R = n-C12H25), respectively (Figure 9).
These mobilities are nearly the same as or slightly higher
than those reported for ((alkyloxy)carbonyl)cyanomethyl-
ene-substituted terthienoquinoidals (4b, μ ≈ 0.015 cm2 V-1
s-1), indicating that the (acyl)cyanomethylene moiety is a
(21) As in the cases for the thin films of 4a and 4b, the large hypsochro-
mic shift for thin films of 5b would be ascribed to the H-type
molecular aggregation in the thin film state (see ref 10). In contrast,
the bathochromic shift observed for the thin film of 5a should be
related to J-type aggregation. These totally different behaviors in
the thin film state of 5a and 5b are in contrast to those for 4a and 4b,
although the cause for such differences can not be well explained.

800 Chem. Mater., Vol. 23, No. 3, 2011
Suzuki et al.
Figure 6. Absorption spectra of (a) 1a, 4a, and 5a; (b) 1b, 4b, and 5b. 1, green lines; 4 (R = n-C6H13), red lines’ and 5 (R = n-C6H13), blue lines.
Figure 7. XRD patterns of spin-coated thin films: (a) 5a (R = n-C6H13), (b) 5b (R = n-C12H25).
Figure 8. Absorption spectra of spin-coated thin films upon annealing: (a) 5a (R = n-C6H13), (b) 5b (R = n-C12H25).
useful terminal group on the thienoquinoidals for the devel-
opment of soluble n-channel organic semiconductors. One
notable characteristic is that the derivatives with longer
n-C12H25 groups gave higher mobility by ca. 1 order of
magnitude than that with the shorter n-C6H13 groups. Such
alkyl chain dependence was not observed for 4b,10 implying
that molecular ordering nature could be affected by the
presence/absence of oxygen atom in the long alkyl groups.
Conclusion
We have successfully developed a new class of oligothieno-
quinoidal derivatives (5) with a newly employed (acyl)cya-
nomethylene terminal group. Although their synthesis were
seemingly easy, it turned out that the analogous methods
successfully applied to the syntheses of dicyanomethylene-
(1) and ((alkyloxy)carbonyl)cyanomethylene-substituted

Article
Chem. Mater., Vol. 23, No. 3, 2011 801
Experimental Section
Synthesis. General. All chemicals and solvents are of re-
agent grade unless otherwise indicated. THF was purified with a
standard distillation procedure prior to use. Melting points were
uncorrected. All reactions were carried out under a nitrogen
atmosphere. Nuclear magnetic resonance spectra were obtained
in deuterated chloroform (CDCl3) with TMS as internal refer-
ence; chemical shifts (δ) are reported in parts per million. IR
spectra were recorded as a neat spectrum for oil samples or using
a KBr pellet for solid samples. EI-MS spectra were obtained
using an electron impact ionization procedure (70 eV). MALDI-
TOF spectra were obtained using dithranol matrix. FAB-MS
spectra were recorded using 3-nitrobenzyl alcohol as a matrix.
Solubilities of 5a and 5b in chloroform were determined as the
saturated concentration (g L-1) at room temperature.
Synthesis of 2-Thienylethanol Derivative (General Proce-
dure)14. 1-(2-Thienyl)butane-2-ol (9, R = C2H5). To a solution
of thiophene (5 mL, 63 mmol) in THF (100 mL) was slowly
added n-butyllithium (1.59 M solution in hexane, 45 mL, 69
mmol) at -78 °C. After stirring for 1 h at room temperature, 1,2-
epoxybutane (11 mL, 126 mmol) was slowly added at -78 °C,
and the mixture was stirred overnight at room temperature. To
the mixture was added hydrochloric acid (1 M, 100 mL), and the
resulting mixture was extracted with ethyl acetate (100 mL ꢀ 3).
The combined extracts were washed with water (100 mL) and
brine (100 mL), dried over magnesium sulfate (anhydrous), and
concentrated in vacuo. The residue was purified by column
chromatography on silica gel eluted with dichloromethane
(Rf = 0.45) to give 9 (R = C2H5) as a pale yellow oil (9.0 g,
91%). 1H NMR (270 MHz) δ 7.18 (d, J = 4.0 Hz, 1H), 6.96 (dd,
J = 4.0 Hz, J = 3.3 Hz, 1H), 6.87 (d, J = 3.3 Hz, 1H), 3.74 (m,
Figure 9. Transfer and output curves of FETs using annealed thin films.
(a) 5b (R = n-C6H13), (b) 5b (R = n-C12H25).
thienoquinoidals (4) were not applicable. Thus, we examined
several potential methods, and finally established a new
synthetic route to the desired oligothienoquinoidals.
The introduced (acyl)cyanomethylene terminal groups
act both as a solublizing group to facilitate solution
processability and an electron-withdrawing group to keep
the LUMO energy levels sufficiently low for n-channel
organic semiconductors. The LUMO energy levels esti-
mated from their reduction potential are ∼4.2 eV below
the vacuum level, which just falls in between those for the
corresponding dicyanomethylene- (1) and ((alkyloxy)-
carbonyl)cyanomethylene-substituted thienoquinoidals
(4). This qualitatively agrees with the electron-withdraw-
ing nature of the terminal groups: the order of the electron
withdrawing nature is cyano- > acyl- > (alkyloxy)carbonyl
groups. The present (acyl)cyanomethylene-substituted
thienoquinoidals (5) gave homogeneous thin films on
the Si/SiO2 substrates by spin coating, and the thin films
based on the terthienoquinoidal derivatives (5b) became
highly crystalline upon thermal annealing. The annealed
film acted as the active semiconducting channel in the
FET devices, and the mobilities extracted from the satu-
ration regime are ∼0.06 cm2 V-1 s-1. These n-channel
FET characteristics are nearly the same as or slightly
higher than those of 4-based FETs. These results indicate
that the (acyl)cyanomethylene moiety is a useful terminal
group on the thienoquinoidals for the development of
soluble n-channel organic semiconductors. Further opti-
mization of the molecular structure of the present thieno-
quinoidal series is now underway in our group. In this
relation, although the present synthetic method is useful
for the synthesis of oligothienoquinoidals, the method
can not be applicable to the synthesis of the fused
thienoquinoidals. Thus, new versatile and efficient methods
for the synthesis of this class of thienoquinoidals are also
intensively investigated.
1H), 3.00 (m, 2H), 1.56 (m, 2H), 1.00 (t, J = 7.4 Hz, 3H). 13
C
NMR (67.8 MHz) δ 10.1, 29.4, 37.5, 73.9, 124.3, 126.1, 127.1,
140.8. MS (EI) m/z = 156 (Mþ). IR (neat) ν = 3381 cm-1 (OH).
Anal. Calcd for C8H12OS: C, 61.50; H, 7.74%. Found: C, 61.16;
H, 7.54%.
1-(2-Thienyl)octan-2-ol (9, R = n-C6H13). Yellow oil, 93%
isolated yield. 1H NMR (400 MHz) δ 7.18 (d, J = 5.2 Hz, 1H),
6.96 (dd, J = 5.2 Hz, J = 3.3 Hz, 1H), 6.86 (d, J = 3.3 Hz, 1H),
3.80 (m, 1H), 3.01 (m, 2H), 1.55-1.29 (m, 10H), 0.89 (t, J = 6.8
Hz, 3H). 13C NMR (67.8 MHz) δ 14.2, 22.7, 25.8, 29.4, 31.9,
36.6, 38.0, 72.5, 124.3, 126.1, 127.1, 140.8. MS (EI) m/z = 212
(Mþ). IR (neat) ν = 3381 cm-1 (OH). Anal. Calcd for C14H24OS:
C, 67.87; H, 9.49%. Found: C, 67.78; H, 9.64%.
1-(2-Thienyl)tetradecan-2-ol (9, R = n-C12H25). Waxy white
solid (mp <30 °C), 95% isolated yield. 1H NMR (270 MHz) δ
7.18 (dd, J = 5.2 Hz, J = 1.2 Hz, 1H), 6.96 (dd, J = 5.2 Hz, J =
3.3 Hz, 1H), 6.86 (d, J = 3.3 Hz, J = 1.2 Hz, 1H), 3.81 (m, 1H),
3.01 (m, 2H), 1.55-1.29 (m, 22H), 0.89 (t, J = 6.8 Hz, 3H). 13
C
NMR (67.8 MHz) δ 14.5, 23.0, 26.0, 29.7, 29.9, 30.0, 32.3, 36.9,
38.3, 72.7, 124.4, 126.3, 127.2, 141.0. MS (EI) m/z = 296 (Mþ).
IR (neat) ν = 3375 cm-1 (OH). Anal. Calcd for C18H32OS: C,
72.91; H, 10.88%. Found: C, 72.77; H, 10.73%.
Synthesis of r-Thienylmethylketone Derivative (General
Procedure). 1-(2-Thienyl)butan-2-one (10, R = C2H5). To a
solution of 9 (R = C2H5, 20.0 g, 128 mmol) in dichloromethane
(800 mL) was portionwise added pyridinium chlorochromate
(30.4 g, 141 mmol) at 0 °C. After stirring overnight at room
temperature, the mixture was filtered through a silica gel pad,
and the filtrate was concentrated in vacuo. The resulting residue
was purified by column chromatography on silica gel eluted with
hexane-ethyl acetate (v/v = 9:1, Rf = 0.3) to give 10 (R = C2H5)
as yellow oil (13.0 g, 66%). Because of its instability, the title

802 Chem. Mater., Vol. 23, No. 3, 2011
Suzuki et al.
compound was immediately used in the next step without fur-
1
being stirred overnight at 60 °C, AgNO3 (859 mg, 5.05 mmol)
and potassium fluoride (293 mg, 5.05 mmol) were again added
and the resulting mixture was further stirred overnight. The
mixture was diluted with ethyl acetate (100 mL) and filtered
through a Celite-pad. The filtrate was diluted with water (100
mL), and the organic layer was separated. The aqueous layer
was then extracted with ethyl acetate (50 mL ꢀ 3), and the
combined organic layer was washed with water (100 mL) and
brine (100 mL), dried over magnesium sulfate (anhydrous), and
concentrated in vacuo. The residue was purified by column
chromatography on alumina eluted with hexane-ethyl acetate
(v/v = 9:1, Rf = 0.3) to give 12 (R = C2H5) as a pale yellow solid
(220 mg, 44%). Mp 87-88 °C. 1H NMR (270 MHz) δ 6.95 (d,
J = 3.6 Hz, 2H), 6.74 (d, J = 3.6 Hz, 2H), 3.84-3.95 (m, 8H),
3.07 (s, 4H), 1.69 (q, J = 7.3 Hz, 4H), 0.95 (t, J = 7.3 Hz, 6H).
13C NMR (67.8 MHz) δ 8.06, 30.4, 38.2, 65.6, 111.1, 122.5,
127.7, 137.3, 137.4. MS (EI) m/z = 394 (Mþ). Anal. Calcd for
C20H26O4S2: C, 60.88; H, 6.64%. Found: C, 60.95; H, 6.61%.
5,50-Bis(2-oxooctyl)-2,20-bithiophene Ethylene Acetal (12, R =
n-C6H13). The title compound was obtained from 11 (R = C6H13)
with the same manner as 12 (R = C2H5). Pale yellow solid, 44%
isolated yield. Mp 74-75 °C. 1H NMR (400 MHz) δ 6.94 (d, J =
3.8 Hz, 2H), 6.73 (d, J = 3.8 Hz, 2H), 3.84-3.95 (m, 8H), 3.06 (s,
2H), 1.64 (t, J = 7.7 Hz, 4H), 1.27-1.54 (m, 16H), 0.87 (t, J = 6.6
Hz, 6H). 13C NMR (67.8 MHz) δ 14.2, 22.7, 23.7, 29.6, 31.9, 37.6,
38.5, 65.5, 110.9, 122.5, 128.5, 137.3, 137.4. MS (EI) m/z = 506
(Mþ). Anal. Calcd for C28H42O4S2: C, 66.36 H, 8.35%. Found: C,
66.38; H, 8.35%.
5,50-Bis(2-oxotetradecyl)-2,20-bithiophene Ethylene Acetal (12,
R = n-C12H25). The title compound was obtained from 11
(R = n-C12H25) with the same manner as 12 (R = C2H5). Pale
yellow solid, 22% isolated yield. Mp 58-59 °C. 1H NMR
(400 MHz) δ 6.94 (d, J = 3.6 Hz, 2H), 6.74 (d, J = 3.6 Hz,
2H), 3.84-3.95 (m, 8H), 3.06 (s, 4H), 1.24-1.66 (m, 44H), 0.95
(t, J = 7.5 Hz, 6H). 13C NMR (67.8 MHz) δ 14.3, 22.8, 23.8,
29.5, 29.7, 29.8, 29.9, 32.1, 37.6, 38.5, 65.5, 110.9, 122.5, 127.3,
137.3, 137.4. EI MS (70 eV) m/z = 674 (Mþ). Anal. Calcd for
C40H66O4S2: C, 71.17 H, 9.85%. Found: C, 70.97; H, 10.08%.
5,50-Bis(2-oxobutyl)-2,20-bithiophene (13, R = C2H5). A solu-
tion of 12 (R = C2H5, 1.06 g, 2.69 mmol) in THF (12 mL) and
hydrochloric acid (2 M, 1 mL) was refluxed overnight. The result-
ing mixture was extracted with dichloromethane (20 mL ꢀ 3).
The combined extracts were washed with water (10 mL) and
brine (10 mL), dried over magnesium sulfate (anhydrous), and
concentrated in vacuo to give 13 (R = C2H5) as a pale yellow
solid (813 mg, quantitative). Mp 77-79 °C. NMR (270 MHz) δ
6.99 (d, J = 3.9 Hz, 2H), 6.77 (d, J = 3.9 Hz, 2H), 3.85 (s, 4H),
2.59 (q, J = 7.2 Hz, 4H), 0.75 (t, J = 7.2 Hz, 6H). 13C NMR
(67.8 MHz) δ 7.9, 35.2, 43.5, 123.4, 127.5, 134.6, 137.1, 207.3.
MS (EI) m/z = 506 (Mþ). IR (KBr) ν = 1707 cm-1 (CdO);
Anal. Calcd for C16H18O2S2: C, 62.71; H, 5.92%. Found: C,
62.73; H, 5.86%.
ther purification. H NMR (270 MHz) δ 7.22 (d, J = 5.1 Hz,
1H), 6.98 (dd, J = 5.1 Hz, J = 3.2 Hz, 1H), 6.89 (d, J = 3.2 Hz,
1H), 3.89 (s, 2H), 2.54 (q, J = 7.3 Hz, 2H), 1.06 (t, J = 7.3 Hz,
3H). 13C NMR (67.8 MHz) δ 8.0, 35.3, 43.5, 53.9, 125.3,
127.0, 127.3, 135.7, 207.8. MS (EI) m/z = 154 (Mþ). IR (neat)
ν = 1716 cm-1 (CdO).
1-(2-Thienyl)octan-2-one (10, R = n-C6H13). Pale yellow oil,
64% isolated yield. 1H NMR (400 MHz) δ 7.22 (d, J = 5.0 Hz,
1H), 6.98 (dd, J = 5.0 Hz, J = 3.1 Hz, 1H), 6.89 (d, J = 3.1 Hz,
1H), 3.88 (s, 2H), 2.49 (t, J = 5.9 Hz, 2H), 1.30-1.24 (m, 8H),
0.87 (t, J = 6.8 Hz, 3H). 13C NMR (67.8 MHz) δ 14.1, 22.5, 23.7,
28.8, 31.6, 41.8, 43.6, 53.2, 125.0, 126.8, 127.7, 135.5, 207.2. MS
(EI) m/z = 210 (Mþ). IR (neat) ν = 1716 cm-1 (CdO).
1-(2-Thienyl)tetradecan-2-one (10, R = n-C12H25). Pale yel-
1
low solid, 86% isolated yield. Mp 29-30 °C, H NMR (270
MHz) δ 7.22 (dd, J = 5.1 Hz, J = 1.1 Hz, 1H), 6.98 (dd, J = 5.2
Hz, J = 5.1 Hz, 1H), 6.88 (dd, J = 5.2 Hz, J = 1.1, 1H), 3.88 (s,
2H), 2.49 (t, J = 7.5 Hz, 2H), 1.30-1.24 (m, 20H), 0.88 (t, J =
6.5 Hz, 3H). 13C NMR (67.8 MHz) δ 14.5, 23.1, 24.1, 29.4, 29.7,
29.8, 30.0, 42.1, 47.5, 52.8, 125.3, 127.0, 127.3, 1235.7, 207.4. MS
(EI) m/z = 294 (Mþ). IR (neat) ν = 1710 cm-1 (CdO).
Synthesis of r-Thienylmethylketone Acetals (General Proce-
dure). 1-(2-Thienyl)butan-2-one Ethylene Acetal (11, R = C2H5).
A solution of ethylene glycol (8.09 g, 129 mmol) and
p-toluene sulfonic acid monohydrate (60 mg, 0.324 mmol) in
benzene (50 mL) was refluxed for 1 h to remove water with a
Dean-Stark condenser. Then, 10 (R = C2H5, 1.0 g, 6.49 mmol)
was added to the solution, and the resulting mixture was refluxed
overnight. After cooling, the mixture was poured into an ice-cooled
saturated NaHCO3 aqueous solution (50 mL) and extracted with
dichloromethane (30 mL ꢀ 3). The combined extracts were washed
with water (10 mL) and brine (10 mL) and dried over magnesium
sulfate (anhydrous). Concentration in vacuo gave practically pure
11 (R = C2H5) as yellow oil (1.20 g, 93%). 1H NMR (270 MHz) δ
7.17 (dd, J= 1.2 Hz, 5.1 Hz, 1H), 6.93 (dd, J= 3.5 Hz, 5.1 Hz, 1H),
6.88 (m, 1H), 3.12 (s, 2H), 3.80-3.96 (m, 4H), 1.67 (q, J = 7.5 Hz,
2H), 0.94 (t, J = 7.5 Hz, 3H). 13C NMR (67.8 MHz) δ 8.1, 30.4,
38.2, 65.6, 111.1, 122.5, 127.7, 137.3, 137.4. MS (FAB) m/z = 177
([M-H]þ). Anal. Calcd for C10H14O2S: C, 60.57; H, 7.12%.
Found: C, 60.45; H, 7.12%.
1-(2-Thienyl)octan-2-one Ethylene Acetal (11, R = n-C6H13).
Colorless oil, quantitative yield. 1H NMR (270 MHz) δ 7.17 (dd,
J = 1.2 Hz, 5.1 Hz, 1H), 6.93 (dd, J = 3.5 Hz, 5.1 Hz, 1H), 6.88
(m, 1H), 3.11 (s, 2H), 3.79-3.95 (m, 4H), 1.26-1.66 (m, 10H),
0.87 (t, J = 6.9 Hz, 3H); 13C NMR (67.8 MHz) δ 14.4, 22.9, 23.9,
29.8, 32.1, 37.9, 38.4, 65.7, 111.1, 125.0, 126.7, 127.3, 138.8. MS
(FAB) m/z = 253 ([M-H]þ). Anal. Calcd for C14H22O2S: C,
66.10; H, 8.72%. Found: C, 65.95; H, 9.05%.
1-(2-Thienyl)tetradecan-2-one Ethylene Acetal (11, R = n-
C12H25). Waxy white solid, 59% isolated yield. Mp <30 °C.
1H NMR (270 MHz) δ 7.17 (dd, J=1.2 Hz, 5.1 Hz, 1H), 6.93
(dd, J=3.5 Hz, 5.1 Hz, 1H), 6.88 (m, 1H), 3.11 (s, 2H), 3.79-
5,50-Bis(2-oxooctyl)-2,20-bithiophene (13, R = n-C6H13). The
title compound was obtained from 12 (R = n-C6H13). Pale
3.95 (m, 4H), 1.26-1.66 (m, 10H), 0.87 (t, J = 6.9 Hz, 3H). 13
C
1
yellow solid, quantitative yield. Mp 84-85 °C. H NMR (400
NMR (67.8 MHz) δ 14.5, 23.0, 24.0, 29.7, 29.9, 30.0, 30.1, 32.2,
37.8, 38.4, 65.6, 111.0, 124.9, 126.7, 127.3, 138.8. MS (EI) m/z =
336 (Mþ). Anal. Calcd for C20H34O2S: C, 70.95%; H, 10.12.
Found: C, 71.02; H, 9.87%.
5,50-Bis(2-oxobutyl)-2,20-bithiophene Ethylene Acetal (12,
R = C2H5)15 (General Procedure). To a degassed solution of
11 (R = C2H5, 500 mg, 2.53 mmol) in DMSO (12.5 mL) was
added AgNO3 (859 mg, 5.05 mmol), potassium fluoride (293
mg, 5.05 mmol), and Pd(PhCN)2Cl2 (10 mg, 0.025 mmol). After
MHz) δ 6.99 (d, J = 3.7 Hz, 2H), 6.77 (d, J = 3.7 Hz, 2H), 3.84
(s, 4H), 2.51 (q, J = 7.5 Hz, 4H), 1.03-1.76 (m, 20H), 0.87 (t,
J = 6.8 Hz, 6H). 13C NMR (67.8 MHz) δ 14.4, 22.8, 24.0, 29.1,
21.9, 42.2, 44.1, 123.7, 127.7, 134.8, 137.4, 207.2. MS (EI) m/z =
418 (Mþ). IR (KBr) ν = 1707 cm-1 (CdO); Anal. Calcd for
C26H24N2O4S3: C, 61.82; H, 5.19%. Found: C, 61.91; H, 5.15%.
5,50-Bis(2-oxotetradecyl)-2,20-bithiophene (13, R = n-C12H25).
The title compound was obtained from 12 (R = n-C12H25).

Article
Chem. Mater., Vol. 23, No. 3, 2011 803
Pale yellow solid, 85% isolated yield. Mp 110-111 °C. 1H NMR
(270 MHz) δ 6.98 (d, J = 3.2 Hz, 2H), 6.76 (d, J = 3.2 Hz, 2H),
3.84 (s, 4H), 2.51 (q, J = 7.6 Hz, 4H), 1.16-1.34 (m, 36H), 0.88
(t, J = 7.3 Hz, 6H); 13C NMR (67.8 MHz) δ 14.3, 22.8, 23.9,
29.2, 29.4, 29.5, 29.6, 29.7, 29.8, 32.1, 42.0, 43.9, 123.4, 127.5,
134.5, 137.2, 207.0. EIMS (70 eV) m/z = 586 (Mþ). IR (KBr) ν
1710 cm-1 (CdO). Anal. Calcd for C36H58O2S2: C, 73.66; H,
9.96%. Found: C, 73.90; H, 9.90%.
1H), 3.84-3.94 (m, 4H), 3.04 (s, 2H), 1.65 (q, J= 7.5, 2H), 0.93 (t, J
=7.5Hz, 3H), 13CNMR(67.8MHz) δ8.0, 30.3, 38.4, 65.5, 110.72,
110.83, 127.3, 129.1, 140.4, MS (FAB) m/z= 275 ([M-H]þ), Anal.
Calcd for C10H13O2SBr: C, 43.33; H, 4.73%, Found: C, 43.43; H,
4.74%.
1-(5-Bromo-2-thienyl)octan-2-one Ethylene Acetal (15, R =
n-C6H13). Yellow oil, 86% isolated yield. 1H NMR (400 MHz) δ
6.87 (d, J = 3.8 Hz, 1H), 6.62 (d, J = 3.8 Hz, 1H), 3.82-3.95 (m,
4H), 3.04 (s, 2H), 1.26-1.63 (m, 10H), 0.87 (t, J = 7.0 Hz, 3H).
13C NMR (67.8 MHz) δ 14.4, 22.9, 23.9, 29.8, 32.1, 37.8, 39.0,
65.7, 110.8, 111.1, 127.6, 129.4, 140.7. MS (FAB) m/z = 331
([M-H]þ). Anal. Calcd for C14H21BrO2S: C, 50.45; H, 6.35%.
Found: C, 50.55; H, 6.39%.
(Z,Z)-5,50-Bis(r-cyano-r-propionylmethylene)-5,50-dihydro-
0
Δ2,2 -bithiophene (5a, R = C2H5)16. To a solution of 13 (R =
C2H5, 100 mg, 0.33 mmol) in THF (6 mL) was added LDA (1 M
solution in THF, 0.72 mL, 0.72 mmol) at 0 °C. After the solution
was stirred for 30 min at the same temperature, a solution of o-
chlorobenzylthiocyanate (239 mg, 1.31 mmol) in THF (3 mL) was
slowly added, and stirred overnight at room temperature. To the
mixture was then added hydrochloric acid (1 M, 10 mL), and the
resulting mixture was extracted with dichloromethane (30 mL ꢀ 3).
The combined extracts were washed with water (10 mL) and brine
(10 mL), dried over magnesium sulfate (anhydrous), and concen-
trated in vacuo. The residue was suspended in a mixed solution of
acetonitrile (5 mL) and water (5 mL), and then NIS (174 mg, 0.65
mmol) was added to the suspension at 0 °C. After being stirred for
30 min at the same temperature, the resulting precipitate was
collected by filtration. The solid product was purified with column
chromatography on silica gel eluted with dichloromethane (Rf =
0.15) and recrystallized from chloroform-acetonitrile to give 5a
1-(5-Bromo-2-thienyl)tetradecan-2-one Ethylene Acetal (15,
R = n-C12H25). Colorless oil, 80% isolated yield. 1H NMR
(400 MHz) δ 6.86 (d, J = 3.7 Hz, 1H), 6.61 (d, J = 3.7 Hz, 1H),
3.82-3.95 (m, 4H), 3.04 (s, 2H), 1.26-1.58 (m, 22H), 0.88 (t, J =
6.5 Hz, 3H). 13C NMR (67.8 MHz) δ 14.5, 23.0, 24.0, 29.7, 29.8,
30.0, 30.1, 32.3, 37.8, 39.0, 110.7, 111.1, 127.6, 129.3, 140.7. MS
(FAB) m/z = 415 ([M-H]þ). Anal. Calcd for C20H33BrO2S: C,
57.54; H, 7.97%. Found: C, 57.24; H, 8.10%.
Stille Coupling Reaction of 15 with 2,5-Bis(trimethylstannyl)-
thiophene (General Procedure)19. 5,500-Bis(2-oxobutyl)-2,20;
50,200-terthiophene Ethylene Acetal (16, R = C2H5). To a degassed
solution of 15 (R=C2H5, 1.35 g, 4.88 mmol) and 2,5-bis(trimethyl-
stannyl)thiophene19 (1.0 g, 2.44 mmol) in DMF (25 mL) was added
Pd(PPh3)4, and the mixture was heated at 80 °C overnight. The
resulting mixture was diluted with water (100 mL) and extracted
with dichloromethane (50 mL ꢀ 3). The combined extracts were
washed with water (100 mL) and brine (100 mL), dried over
magnesium sulfate (anhydrous), and concentrated in vacuo. The
residue was purified by column chromatography on alumina eluted
with hexane-dichloromethane (v/v = 2:1, Rf = 0.3) and recrys-
tallized from hexane to give 16 (R = C2H5) as a yellow solid (734
mg, 63%). Mp 54-55 °C. 1H NMR (270 MHz) δ 7.00 (s, 2H), 6.98
(d, J = 3.5 Hz, 2H), 6.77 (d, J = 3.5 Hz, 2H), 3.88-3.95 (m, 8H),
1
(R = C2H5) as a purple solid (18 mg, 17%). Mp >300 °C. H
NMR (400 MHz) δ 7.66 (d, J = 4.0 Hz, 2H), 7.59 (d, J = 4.0 Hz,
2H), 2.95 (m, 4H), 1.23 (m, 6H). MS (EI) m/z = 354 (Mþ). IR
(KBr) ν = 2298 (CN), 1654 cm-1 (CdO). MS (HRMS) m/z =
354.0497 (Mþ, calcd for C18H14N2O2S2, 354.0497). Solubility:
<0.5 g L-1. From 1H NMR spectra, 5a exists as a mixture of E-
and Z-isomers at the bithienoquinoidal part as in the case for 4a (see
Figure S1 in the Supporting Information).10
Alternatively, the same compound was obtained as follows:
To a mixture of 13 (R = C2H5, 100 mg, 0.33 mmol) and NaH (31
mg, 60% oily, 0.72 mmol) in THF (6 mL) was added 1-cyano-
1H-1,2,3-bezotriazole18 (123 mg, 0.72 mmol) at -30 °C. After
the mixture was stirred overnight at the same temperature, a
similar workup and purification procedure described above
3.08 (s, 4H), 1.70 (q, J = 7.5 Hz, 4H), 0.95 (t, J = 7.5 Hz, 6H). 13
C
NMR (67.8 MHz) δ 8.1, 30.4, 38.2, 65.6, 111.0, 123.0, 123.7, 127.9,
136.2, 136.7, 138.0. MS (EI) m/z = 476 (Mþ). Anal. Calcd for
C24H28O4S3: C, 60.47; H, 5.92%. Found: C, 60.38; H, 5.66%.
5,500-Bis(2-oxooctyl)-2,20;50,200-terthiophene Ethylene Acetal
(16, R = n-C6H13). Yellow solid, 58% isolated yield. Mp 74-
75 °C. 1H NMR (400 MHz) δ 7.00 (s, 2H), 6.98 (d, J = 3.5 Hz,
2H), 6.76 (d, J = 3.5 Hz, 2H), 3.86-3.97 (m, 4H), 3.08 (s, 4H),
1.65 (q, J = 7.5 Hz, 4H), 1.03-1.50 (m, 20H), 0.87 (t, J = 6.8
Hz, 6H). 13C NMR (67.8 MHz) δ 14.2, 22.7, 23.7, 29.6, 31.9,
37.6, 38.5, 65.6, 110.8, 123.0, 123.7, 127.9, 136.2, 136.7, 138.0.
MS (EI) m/z = 588 (Mþ). Anal. Calcd for C32H44O4S3: C, 65.27;
H, 7.53%. Found: C, 65.37; H, 7.61%.
5,500-Bis(2-oxotetradecyl)-2,20;50,200-terthiophene Ethylene Acetal
(16, R = n-C12H25). Yellow solid, 62% isolated yield. Mp 66-
67 °C. 1H NMR (400 MHz) δ 7.00 (s, 2H), 6.98 (d, J = 3.5 Hz,
2H), 6.76 (d, J = 3.5 Hz, 2H), 3.86-3.97 (m, 4H), 3.08 (s, 4H),
1.23-1.65 (m, 44H), 0.88 (t, J = 6.3 Hz, 6H). 13C NMR (67.8
MHz) δ 14.3, 22.8, 23.8, 29.5, 29.6, 29.7, 29.8, 29.9, 32.1, 37.6,
38.5, 65.5, 110.8, 122.9, 123.7, 127.9, 136.2, 136.7, 138.0. MS
(EI) m/z = 756 (Mþ); Anal. Calcd for C44H68O4S3: C, 69.79; H,
9.05%. Found: C, 69.61; H, 8.92%.
gave the desired compound (43 mg, 37%).
(Z,Z)-5,50-Bis(R-cyano-R-heptanoylmethylene)-5,50-dihydro-Δ
2,20
-
bithiophene (5a, R = n-C6H13). Purple solid from hexane, 9%
isolated yield (the LDA-o-chlorobenzylthiocyanate method) or
32% isolated yield (the NaH-1-cyano-1H-1,2,3-bezotriazole
method). Mp 194-195 °C (melt with decomposition). 1H NMR
(270 MHz) δ 7.47-7.67 (m, 4H), 2.90 (m, 4H), 1.33-1.76 (m,
16H), 0.89 (m, 6H), 0.88 (t, J = 6.9 Hz, 6H). 13C NMR (100
MHz) δ 14.0, 22.5, 24.2, 28.8, 31.5, 41.1, 99.5, 100.0, 116.7,
116.8, 135.5, 136.4, 146.5, 147.5, 165.2, 165.3. MS (EI) m/z =
466 (Mþ). IR (KBr) ν = 2298 (CN), 1654 cm-1 (CdO). MS
(HRMS) m/z = 489.16411 ([M þ Na]þ, calcd for C26H30N2-
NaO2S2, 489.16409). Solubility: 5.0 g L-1
.
Bromination of 11 (General Procedure). 1-(5-Bromo-2-thienyl)-
butan-2-one Ethylene Acetal (15, R = C2H5). To a solution of 11
(R = C2H5, 3.0 g, 15.2 mmol) in DMF (150 mL) was portionwise
added NBS (2.72 g, 15.2 mmol). After being stirred overnight, an
aqueous NaHCO3 solution (saturated, 100 mL) was added to the
mixture, and the resulting mixture was then extracted with hexane
(50 mL ꢀ 3). The combined extracts were washed with water
(50 mL) and brine (50 mL) and dried over magnesium sulfate
(anhydrous). Concentration of the extract in vacuo gave practically
pure 15 (R = C2H5) as yellow oil (3.68 g, 88%). 1H NMR
(270 MHz) δ 6.86 (d, J = 3.7 Hz, 1H), 6.62 (dd, J = 3.7 Hz,
Deprotectionof the Acetal Moiety (General Procedure). 5,500-
Bis(2-oxobutyl)-2,20;50,200-terthiophene (17, R=C2H5). A solu-
tion of 16 (R = C2H5, 20 mg, 0.042 mmol) in THF (3 mL) and
hydrochloric acid (2 M, 1 mL) was refluxed overnight. The result-
ing mixture was extracted with dichloromethane (20 mL ꢀ 3).
The combined extracts were washed with water (10 mL) and brine

804 Chem. Mater., Vol. 23, No. 3, 2011
Suzuki et al.
(10 mL), dried over magnesium sulfate (anhydrous), and concen-
trated in vacuo to give 17 (R = C2H5) as a pale yellow solid (18 mg,
quantitative). Mp 107-109 °C; 1H NMR (270 MHz) δ7.03 (s, 2H),
7.02 (d, J = 3.7 Hz, 2H), 6.78 (d, J = 3.7 Hz, 2H), 3.87 (s, 2H), 2.56
(q, J= 7.3 Hz, 4H), 1.09 (t, J= 7.3 Hz, 6H). 13CNMR(67.8MHz)
δ 7.8, 35.2, 43.5, 123.5, 124.1, 127.6, 134.8, 136.0, 136.8, 207.2. MS
(EI) m/z=388 (Mþ). IR (KBr) ν=1712 cm-1 (CdO). Anal. Calcd
for C20H20O2S3: C, 61.82; H, 5.19%. Found: C, 61.19; H, 5.15%.
5,500-Bis(2-oxooctyl)-2,20;50,200-terthiophene (17, R = n-
decomposition). 1H NMR (270 MHz) δ 7.38-7.64 (m, 6H), 2.88
(t, J = 8.6 Hz, 4H), 1.33-1.72 (m, 36H), 0.88 (t, J = 6.0 Hz, 6H).
MS (MALDI-TOF) m/z = 716 (M-). IR (KBr) ν = 2291 (CN),
1647 cm-1 (CdO). Anal. Calcd for C42H56N2O2S3:C,70.35;H,7.87;
N, 3.91%. Found: C, 70.62; H, 7.95; N, 3.97%. Solubility: 0.6 g L-1
.
Single-Crystal X-ray Analysis. Single crystals of 14 suitable
for X-ray structural analysis were obtained by careful recrystalliza-
tion from chloroform. The X-ray crystal structure analysis of 14 was
made on a Rigaku RAXIS-RAPID Imaging Plate diffractometer
1
˚
(Mo KR radiation, λ = 0.71069 A, graphite monochromator, T =
C6H13). Orange solid, quantitative yield. Mp 125-127 °C. H
150 K, 2θmax = 54.9°). The structure was solved by the direct
methods.22 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
package TeXsan 1.2.22 Crystallographic data: C24H20ClNO2S2
(453.06), violet block, 0.70 ꢀ 0.25 ꢀ 0.10 mm3, triclinic, space
NMR (270 MHz) δ 7.01 (s, 2H), 7.01 (d, J = 3.6 Hz, 2H), 6.78
(d, J=3.6 Hz, 2H), 3.85 (s, 2H), 1.58 (q, J=7.2 Hz, 4H),
1.25-1.30 (m, 16H), 0.87 (t, J = 6.5 Hz, 6H). 13C NMR (67.8
MHz) δ 14.3, 22.8, 24.0, 29.1, 31.9, 42.2, 42.3, 44.1, 123.8, 124.4,
127.9, 135.0, 136.3, 137.2, 207.1. MS (EI) m/z = 500 (Mþ). IR
(KBr) ν = 1710 cm-1 (CdO); Anal. Calcd for C28H36O2S3: C,
67.15; H, 7.25%. Found: C, 67.41; H, 7.16%.
˚
˚
˚
group, P1 (#2), a = 9.198(1) A, b = 9.549(1) A, c = 13.271(2) A,
3
5,500-Bis(2-oxotetradecyl)-2,20;50,200-terthiophene (17, R = n-
˚
R = 75.930(3)°, β= 75.466(3)°, γ= 82.159(3)°, V = 1091.0(2) A ,
1
Z =2, R= 0.0912 for 2502 observed reflections (I>2σ(I)) and 271
C12H25). Orange solid, 83% yield. Mp 117-120 °C. H NMR
variable parameters, wR2 = 0.290 for all data.
(270 MHz) δ 7.01 (s, 2H), 7.01 (d, J = 3.6 Hz, 2H), 6.78 (d, J =
3.6 Hz, 2H), 3.86 (s, 2H), 2.52 (q, J = 7.3 Hz, 4H), 1.24-1.30 (m,
40H), 0.88 (t, J = 6.5 Hz, 6H). 13C NMR (100 MHz) δ 14.3,
22.8, 23.7, 29.2, 29.5, 29.6, 29.7, 29.8, 32.1, 42.1, 43.9, 123.5,
124.2, 127.6, 134.8, 136.1, 136.9. MS (EI) m/z = 668 (Mþ). IR
(KBr) ν = 1716 cm-1 (CdO). Anal. Calcd for C40H60O2S3: C,
71.80; H, 9.04%. Found: C, 71.84; H, 9.15%.
Fabrication and Evaluation of FET Devices. Si/SiO2 substrates
were treated with octadecyltrichlorosilane (ODTS) by immersing
the silicon wafers to ODTS solution in dry toluene at room
temperature under nitrogen for 12 h.23 OFETs were fabricated in
a “top-contact” configuration on a heavily doped nþ-Si (100) wafer
with a 200 nm thermally grown SiO2 (Ci = 17.3 nF cm-2). Thin film
of 5a or 5b as an active layer was spin-coated on the Si/SiO2
substrate. 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 room temperature under ambient
conditions with a Keithley 4200 semiconducting parameter ana-
lyzer. Field-effect mobility (μFET) was calculated in the saturation
regime (Vd = 60 V) of the Id using the following equation,
(Z,Z)-5,500-Bis(r-cyano-r-propionylmethylene)-5,50-dihydro-
0
0
00
Δ2,2 :5 ,2 -terthiophene (5b, R = C2H5). To a solution of 17 (R =
C2H5, 100 mg, 0.26 mmol) in THF (5 mL) was added NaH
(25 mg, 60% oily, 0.57 mmol) at 0 °C. After this solution was
stirred for 30 min at the same temperature, a solution of
1-cyano-1H-1,2,3-benzotriazole (82 mg, 0.57 mmol) in THF
(3 mL) was slowly added to the mixture, and the resulting
mixture was stirred overnight at 0 °C. To the mixture was added
hydrochloric acid (1 M, 10 mL), and the resulting mixture was
extracted with dichloromethane (30 mL ꢀ 3). The combined
extracts were washed with water (10 mL) and brine (10 mL), dried
over magnesium sulfate (anhydrous), and concentrated in vacuo.
The residue was suspended in a mixed solvent of acetonitrile (5 mL)
and water (5 mL), and then NIS (116 mg, 0.52 mol) was added to
the suspension at 0 °C. After being stirred for 30 min at the same
temperature, the precipitate was collected by filtration. The solid
collected was purified by column chromatography on silica gel
eluted with dichloromethane (Rf = 0.1) to give 5b (R = C2H5) as a
purple solid (76 mg, 61%). Mp>300 °C. MS (MALDI-TOF)
m/z = 436 (M-). IR (KBr) ν = 2294 (CN), 1653 cm-1 (CdO).
Anal. Calcd for C26H24N2O4S3: C, 60.52; H, 3.69; N, 6.42%.
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) 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
five different devices.
Acknowledgment. This work was partially supported by a
Grant-in-Aid for Scientific Research (20350088) from the
Ministry of Education, Culture, Sports, Science and Technol-
ogy, Japan, and the Seeds Excavation Program from Japan
Science and Technology Agency (JST) of Japan. Combustion
elemental analyses and measurements of HRMS were carried
out at the Natural Science Center for Basic Research and
Development (N-BARD), Hiroshima University.
Found: C, 60.27; H, 3.69; N, 6.11%. Solubility: ∼1 ꢀ 10-3 g L-1
.
From 1H NMR spectra, 5b exists as a mixture of E,E-, Z,Z-, and E,
Z-isomers at the terthienoquinoidal part as in the case for 4b (see
Figure S1 in the Supporting Information).10
(Z,Z)-5,500-Bis(R-cyano-R-heptanoylmethylene)-5,50-dihydro-
0
0
00
Δ2,2 :5 ,2 -terthiophene (5b, R = n-C6H13). The title compound
was obtained from 17 (R = n-C6H13) as a purple solid (dichloro-
methane) in 56% isolated yield. Mp 180-182 °C (melt with
decomposition). 1H NMR (400 MHz) δ 7.38-7.64 (m, 6H), 2.88
(m, 4H), 1.33-1.72 (m, 16H), 0.88 (m, 6H). MS (MALDI-TOF)
m/z = 548 (M-). IR (KBr) ν = 2291 (CN), 1647 cm-1 (CdO).
Anal. Calcd for C30H32N2O2S3: C, 65.66; H, 5.88; N, 5.10%.
Supporting Information Available: Instrumentation for the
characterization of compounds and physicochemical evalua-
tion, crystallographic information file (CIF) for 14, complete
entry for ref 12, NMR spectra of compounds (PDF). This
material is available free of charge via the Internet at http://
pubs.acs.org.
Found: C, 65.59; H, 5.88; N, 4.96%. Solubility: 4.1 g L-1
.
(Z,Z)-5,500-Bis(R-cyano-R-tridecanoylmethylene)-5,50-dihydro-
(22) teXsan: Single Crystal Structure Analysis Software, Version 1.2;
Molecular Structure Corporation and Rigaku Corporation: The Woodlands,
TX, 2000.
(23) Ong, B. S.; Wu, Y.; Liu, P.; Gardner, S. J. Am. Chem. Soc. 2004,
126, 3378–3379.
0
0
00
Δ2,2 :5 ,2 -terthiophene (5b, R = n-C12H25). The title compound
was obtained from 17 (R = n-C12H25) as a purple solid (dichloro-
methane) in 62% isolated yield. Mp 185-186 °C (melt with