Synthesis, properties, crystal structures, and semiconductor characteristics of naphtho[1,2-b:5,6-b′]dithiophene and -diselenophene derivatives

Article abstract of DOI:10.1021/jo902545a

(Chemical Equation Presented) In this paper we present the synthesis, structures, characterization, and applications to field-effect transistors (FETs) of naphtho[1,2-b:5,6-b′]dithiophene (NDT) and -diselenophene (NDS) derivatives. Treatment of 1,5-dichloro-2,6-diethynylnaphthalenes, easily derived from commercially available 2,6-dihydroxynaphthalene, with sodium chalcogenide afforded a straightforward access toNDTsand NDSsincluding the parent and dioctyl and diphenyl derivatives. Physicochemical evaluations ofNDT and NDS derivatives showed that these heteroarenes have a similar electronic structure with isomeric [1]benzothieno[2,3-b][1]benzothiophene (BTBT) and [1] benzoselenopheneno[2,3-b][1]benzoselenophene (BSBS) derivatives, respectively. Although attempts to fabricate solution-processed field-effect transistors (FETs) with soluble dioctyl-NDT (C₈-NDT) and -NDS (C₈-NDS) failed, diphenyl derivatives (DPh-NDTand DPh-NDS) afforded vapor-processed FETs showing field-effect mobility as high as 0.7 cm² V^-1 s^-1. These results indicated that NDT and NDS are new potential heteroarene core structures for organic semiconducting materials. 2010 American Chemical Society.

Full text of DOI:10.1021/jo902545a

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Synthesis, Properties, Crystal Structures, and Semiconductor
Characteristics of Naphtho[1,2-b:5,6-b0]dithiophene and -diselenophene
Derivatives
Shoji Shinamura,† Eigo Miyazaki,† and Kazuo Takimiya*,†,‡
†Department of Applied Chemistry, Graduate School of Engineering, Hiroshima University,
Higashi-Hiroshima 739-8527, Japan, and Institute for Advanced Materials Research, Hiroshima
University, Higashi-Hiroshima 739-8530, Japan
‡
ktakimi@hiroshima-u.ac.jp
Received December 1, 2009
In this paper we present the synthesis, structures, characterization, and applications to field-effect
transistors (FETs) of naphtho[1,2-b:5,6-b0]dithiophene (NDT) and -diselenophene (NDS) derivatives.
Treatment of 1,5-dichloro-2,6-diethynylnaphthalenes, easily derived from commercially available
2,6-dihydroxynaphthalene, with sodium chalcogenide afforded a straightforward access to NDTs and
NDSs including the parent and dioctyl and diphenyl derivatives. Physicochemical evaluations of NDT
and NDS derivatives showed that these heteroarenes have a similar electronic structure with isomeric
[1]benzothieno[2,3-b][1]benzothiophene (BTBT) and [1]benzoselenopheneno[2,3-b][1]benzoseleno-
phene (BSBS) derivatives, respectively. Although attempts to fabricate solution-processed field-effect
transistors (FETs) with soluble dioctyl-NDT (C8-NDT) and -NDS (C8-NDS) failed, diphenyl
derivatives (DPh-NDT and DPh-NDS) afforded vapor-processed FETs showing field-effect mobility
as high as 0.7 cm2 V-1 s-1. These results indicated that NDT and NDS are new potential heteroarene
core structures for organic semiconducting materials.
Introduction
(Figure 1). In sharp contrast, heteroarenes consisting of
one naphthalene and two thiophenes in a cata-condensed
Thiophene-containing fused aromatics, often called hete-
roarenes, have been important core structures for the devel-
opment of novel electronic materials.1 Among numbers of
heteroarene systems developed so far, benzodithiophenes
(BDTs)2 and anthradithiophenes (ADTs)3 have been repre-
sentatives and used as core structures for organic semicon-
ductors applicable to superior organic field-effect transistors
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Otsubo, T. J. Am. Chem. Soc. 2004, 126, 5084–5085. (d) Takimiya, K.; Konda,
Y.; Ebata, H.; Niihara, N.; Otsubo, T. J. Org. Chem. 2005, 70, 10569–10571.
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B. S.; Zhu, S.; Xu, G. J. Am. Chem. Soc. 2007, 129, 4112–4113. (h) Pan, H.;
Wu, Y.; Li, Y.; Liu, P.; Ong, B. S.; Zhu, S.; Xu, G. Adv. Funct. Mater. 2007, 17,
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Published on Web 01/25/2010
DOI: 10.1021/jo902545a
r
2010 American Chemical Society

Shinamura et al.
JOCArticle
FIGURE 3. Molecular structure of naphtho[1,2-b:5,6-b0]dithiophe-
nes and -diselenophenes.
FIGURE 1. Some heteroarene cores for organic semiconductors.
SCHEME 1. Synthesis of NDT and NDS Derivatives
FIGURE 2. C2h symmetrical naphthodichalcogenophene isomers
(X = S or Se) as potential organic semiconductor cores.
manner, i.e., naphtodithiophenes (NDTs, Figure 2), have
not been examined as organic semiconductors,4 although
several isomeric NDTs have been known5 and they seem to
be promising as core structures for organic semiconductors.6
This is mainly due to the lack of practical methods for the
scalable synthesis of NDTs for further investigation.
We have recently reported a straightforward protocol for
thiophene-annulation reactions on a benzene ring to give
various benzo[b]thiophene derivatives, not only monoannu-
lated ones (benzo[b]thiophenes), but also bis-(benzodithio-
phenes) and tris-annulated derivatives (benzotrithiophe-
nes).7 One of the merits of this protocol is that one can use
easily available o-chloro- or o-bromo-substituted ethynyl-
benzenes as a precursor. Taking advantage of the protocol,
we examined the syntheses of one of the NDT isomers,
naphtho[1,2-b:5,6-b0]dithiophenes (2, Figure 2), and its sele-
nium analogues from 1,5-dichloro-2,6-diethynylnaphtha-
lenes and found that these heteroarenes are easily synthe-
sizable. Since the parent heteroarenes have an isoelectronic
structure with [1]benzothieno[2,3-b][1]benzothiophene (BTBT,
Figure 1)8 and its selenium analogue (BSBS)9 that can serve as
cores for superior organic semiconductors, it is very interesting
to compare the physicochemical properties between NDT/NDS
and BTBT/BSBS and to examine NDT and NDS derivatives
(Figure 3) as organic semiconducting materials. We here report
their synthesis, properties, crystal structure, and semiconductor
characteristics.
Results and Discussions
Synthesis. Successful synthetic routes to NDTs and NDSs
were shown in Scheme 1. Starting from commercially avail-
able 2,6-dihydroxynaphthalene (4), selective chlorination at
1- and 5-positions to give 510 followed by a reaction with
trifluoromethanesulfonic anhydride gave a key intermediate,
1,5-dichloro-2,6-bis(trifluoromethanesulfonyloxy)naphthalene
(6). Under the typical Sonogashira coupling conditions,
reaction with various terminal acetylenes, e.g., trimethylsi-
lylacetylene, 1-octyne, and phenylacetylene, took place che-
moselectively at the triflate sites (2- and 6- positions) on 6
to give the precursors (7a-c) in moderate to high yields.
Final ring-closing reactions that construct fused-thiophene
or -selenophene rings were easily accomplished in reasonable
yields with sodium chalcogenide reagents as previously
reported.7 All the new materials were fully characterized
with spectroscopic analyses and combustion elemental ana-
lysis. We also carried out single-crystal X-ray analysis for the
parent NDT and NDS, C8-NDT, and DPh-NDT. All these
structural analyses also gave unambiguous identification of
the desired compounds in the present synthesis.
(4) Peri-condensed naphthodithiophene derivatives have been reported:
(a) Takimiya, K.; Yashiki, F.; Aso, Y.; Otsubo, T.; Ogura, F. Chem. Lett.
1993, 22, 365–368. (b) Takimiya, K.; Otsubo, T.; Ogura, F. J. Chem. Soc.,
Chem. Commun. 1994, 1859–1860. (c) Takimiya, K.; Kato, K.-i.; Aso, Y.;
Ogura, F.; Otsubo, T. Bull. Chem. Soc. Jpn. 2002, 75, 1795–1805. (d)
Takimiya, K.; Kunugi, Y.; Toyoshima, Y.; Otsubo, T. J. Am. Chem. Soc.
2005, 127, 3605–3612.
(5) Synthesis of 2 and 3 (X = S) via flash vacuum pyrolysis (FVP) was
recently reported: (a) Umeda, R.; Fukuda, H.; Miki, K.; Rahman, S. M. A.;
Sonoda, M.; Tobe, Y. C. R. Chim. 2009, 12, 378-384. See also: (b) Tilak, B.
D. Proc. Indian Acad. Sci., Sect. A 1951, 33A, 71–77.
(6) Coropceanu, V.; Kwon, O.; Wex, B.; Kaafarani, B. R.; Gruhn, N. E.;
Durivage, J. C.; Neckers, D. C.; Bredas, J.-L. Chem.;Eur. J. 2006, 12, 2073–
2080.
Molecular structures of the parent NDT and NDS are
depicted in Figure 4a. Both molecules have almost planar
structure as expected. In the crystal packing, the molecules of
both NDT and NDS form similar layered structures and
arrange in herringbone manner in each layer (Figure 4b).
(7) Kashiki, T.; Shinamura, S.; Kohara, M.; Miyazaki, E.; Takimiya, K.;
Ikeda, M.; Kuwabara, H. Org. Lett. 2009, 11, 2473–2475.
(8) (a) Takimiya, K.; Ebata, H.; Sakamoto, K.; Izawa, T.; Otsubo, T.;
Kunugi, Y. J. Am. Chem. Soc. 2006, 128, 12604–12605. (b) Ebata, H.; Izawa,
T.; Miyazaki, E.; Takimiya, K.; Ikeda, M.; Kuwabara, H.; Yui, T. J. Am.
Chem. Soc. 2007, 129, 15732–15733. (c) Izawa, T.; Miyazaki, E.; Takimiya,
K. Adv. Mater. 2008, 20, 3388–3392. (d) Izawa, T.; Mori, H.; Shinmura, Y.;
Iwatani, M.; Miyazaki, E.; Takimiya, K.; Hung, H.-W.; Yahiro, M.; Adachi,
C. Chem. Lett. 2009, 38, 420–421.
(9) (a) Takimiya, K.; Kunugi, Y.; Konda, Y.; Ebata, H.; Toyoshima, Y.;
Otsubo, T. J. Am. Chem. Soc. 2006, 128, 3044–3050. (b) Izawa, T.; Miyazaki,
E.; Takimiya, K. Chem. Mater. 2009, 21, 903–912.
(10) (a) Nakasuji, K.; Sugiura, K.; Kitagawa, T.; Toyoda, J.; Okamoto,
H.; Okaniwa, K.; Mitani, T.; Yamamoto, H.; Murata, I. J. Am. Chem. Soc.
€
1991, 113, 1862–1864. (b) Willstatter, R.; Parnas, J. Ber. Dtsch. Chem. Ges.
1907, 40, 3971–3978.
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FIGURE 5. Cyclic voltammograms of NDT, NDS, BTBT, and
chrysene.
FIGURE 4. Molecular (a) and packing structures (b) of NDT (left)
and NDS (right).
Physicochemical Properties. The parent NDT is formally
isoelectronic with BTBT and chrysene.11 Thus, it is interesting
tocomparethe electronic structureofthese fused-aromaticsto
elucidate the structure-property correlations. Figure 5 shows
cyclic volatmmograms of NDT, NDS, BTBT, and chrysene,
whereall fourcompoundsshow oxidation peaks ina relatively
high potential regime (ca. þ1.3-1.5 V vs. Ag/AgCl). Their
HOMO energy levels estimated from the onsets of the oxida-
tion peaks are summarized in Table 1.12 The chalcogen-
ophene-containing compounds tend to have slightly higher
HOMO energy levels than chrysene does. In contrast to the
quasi-reversible oxidation peak of BTBT, the peaks of NDT
and NDS are irreversible without clear reduction processes. In
addition, receptive voltammetricscan for the parent NDT and
NDS deposited polymer-like film on the working electrode,
probably owing to electrochemical homopolymerization at
the electrochemically active R-position of thiophene or sele-
nophene at both ends of the molecules (Figure S3, Supporting
Information). Although individual features for each com-
pound are observed in the voltammogram, the HOMO energy
level is almost the same for the four compounds, reflecting
their isoelectronic structures as expected.11
FIGURE 6. UV-vis spectra of NDT, NDS, BTBT, and chrysene in
dichloromethane.
TABLE 1. Oxidation Potential, Absorption Edge in UV-Vis Spectra
of NDT and NDS Derivatives
compd
Eonset/Va
HOMO/eVb
λedge/nm
Eg/eVd
NDT
NDS
BTBT
chrysene
1.38
1.36
1.38
1.46
-5.8
-5.7
-5.8
-5.9
320c
335c
340
3.9
3.7
3.7
3.8
330
C8-NDT
C8-NDS
DPh-NDT
DPh-NDS
1.25
1.23
1.15
1.18
-5.6
-5.6
-5.5
-5.6
325c
340c
395
3.8
3.6
3.1
3.1
405
a V vs. Ag/AgCl. All the potentials were calibrated with the Fc/Fcþ
(E1/2 =þ0.43 V measured under identical conditions). bEstimated with
the following equation: EHOMO (eV) = -4.4 - Eonset. cForbidden triplet-
Their UV-vis spectra depicted in Figure 6 clearly indi-
cated that all four materials have largely blue-shifted absorp-
tions (up to ca. 350 nm) compared with that of naphthacene
triplet bands were not considered. dCalculated from λedge
.
(∼490 nm, not seen in Figure 6),11 an acene consisting of four
benzene rings, indicating that the electronic structures of
NDT and BTBT are rather phene-like. Despite their overall
similarity in UV-vis spectra, small differences are observed:
(11) Takimiya, K.; Yamamoto, T.; Ebata, H.; Izawa, T. Sci. Technol.
Adv. Mater. 2007, 8, 273–276.
€
(12) Pommerehne, J.; Vestweber, H.; Guss, W.; Mahrt, R. F.; Bassler, H.;
Porsch, M.; Daub, J. Adv. Mater. 1995, 7, 551–554.
1230 J. Org. Chem. Vol. 75, No. 4, 2010

Shinamura et al.
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FIGURE 7. Molecular arrangement in a single crystal of C8-NDT.
FIGURE 9. Output and transfer characteristics of DPh-NDT-
based OFET fabricated on HMDS-treated Si/SiO2 substrate.
FIGURE 8. XRD pattern of the evaporated thin film of DPh-NDT.
devices via solution deposition processes using highly soluble
C8-NDT and C8-NDS unfortunately failed. All the devices
showed no filed effect, owing to the poor quality of the films
on Si/SiO2 substrates: only noncontinuous films were depo-
sited and could not cover the channel region of the devices.
Besides poor thin film forming properties, the molecular
arrangement of C8-NDT missing effective intermolecular
interactions between the NDT cores would not be suitable
for effective carrier transport (Figure 7). Thus, it can be
concluded that alkylated NDT and NDS are significantly
different from their isomeric alkylated BTBTs and BSBSs in
terms of film-forming nature and molecular arrangement in
the thin film state and the bulk single crystals,8b,c,9b although
the molecular electronic properties are very similar to each
other as discussed above.
in particular, NDT and NDS have weak, but red-shifted
absorption bands up to 360 nm, which reflects marginal
difference in their electronic structure. At the present mo-
ment, the origin of the red-shifted absorption bands for NDT
and NDS is not clear. To help to understand, we carried out
time-dependent differential functional theory (TD-DFT)
MO calculations13 for NDT, which suggests that these
absorptions can be ascribed to triplet transitions between
orbitals near the HOMO-LUMO gaps that are normally
forbidden (see the Supporting Information).
Oxidation onsets extracted from CVs and absorption edge
from UV-vis spectra of C8-NDT, DPh-NDT, C8-NDS,
and DPh-NDS were also summarized in Table 1. C8-NDT
and -NDS showed lower oxidation onsets than those of the
parent ones, reflecting the electron-donating nature of the
alkyl groups. Introduction of phenyl groups not only lowered
the oxidation onsets by more than 0.2 V but also caused a
large red shift in UV-vis spectra, indicative of extension of
π-conjugation. The HOMO energy levels and energy gaps
estimated from the oxidation onsets and absorption edges,
respectively, for the dialkyl and diphenyl derivatives of NDT
and NDS are also similar to those of the corresponding BTBT
and BSBS derivatives.8,9 The similarity in physicochemical
properties can be understood by the consideration that the
molecular electronic structures of the NDT and NDS deriva-
tives are basically the same as those of the BTBT and BSBS
derivatives.
In contrast, physical vapor deposition of DPh-NDT
and DPh-NDS gave homogeneous thin films on Si/SiO2
substrates, which also showed crystalline peaks in XRD
patterns assignable to layered structure on the substrate
(Figure 8). Calculated interlayer spacing for the DPh-NDT
˚
thin film (∼19 A) is almost the same as that with the
crystallographic c-axis of its bulk single crystal and with its
molecular length (vide infra).
FET devices with a top contact configuration (W/L = 30)
were evaluated under ambient conditions. In the case of DPh-
NDT-based devices, devices fabricated at any substrate tem-
peratures (Tsub) showed typical p-channel FET responses.
The field-effect mobilities extracted from the saturation re-
gime for DPh-NDT-based devices were up to 0.2 cm2 V-1 s-1
with a Ion/Ioff ratio of 106 (Figure 9). The relatively good
device performances of the DPh-NDT-based FETs can be
rationalized by the molecular arrangement of DPh-NDT:
single-crystal X-ray analysis of DPh-NDT clearly indicated
that the DPh-NDT molecules arranged in a herringbone
manner (Figure 10), which is an optimal molecular arrange-
ment to give a two-dimensional electronic structure suitable
FET Devices. To examine the present NDT and NDS
derivatives as organic semiconductors, we fabricated and
evaluated their FET devices. Attempts to fabricate FET
(13) MO calculations were carried out with the DFT/TD-DFT method at
the B3LYP/6-31g(d) level, using the Gaussian 03 program package . Frisch,
M. J. et al. Gaussian 03, revision C.02; Gaussian, Inc., Wallingford, CT,
2004.
J. Org. Chem. Vol. 75, No. 4, 2010 1231

Shinamura et al.
JOCArticle
packing structure with that of DPh-NDT, since their thin
˚
film XRDs with d-spacings of ca. 20 A are similar to each
other (Figure S4, Supporting Information). Therefore, we
concluded at this moment that the well-ordered molecular
array for DPh-NDS similar to that for DPh-NDT also
accounted for their relatively high μFET values. These results
indicated that the NDT and NDS frameworks are potential
core structures for further development of superior organic
semiconductors, provided that suitable molecular modifica-
tions for the thin film deposition are made.
Conclusions. In summary, we have successfully established
practical syntheses of naphtho[1,2-b:5,6-b0]dithiophene (NDT)
and -diselenophene (NDS) derivatives, taking advantage of the
thiophene- and selenophene-annulation protocol recently
developed in our group. Physicochemical evaluation of the
NDT and NDS derivatives indicated that they are isostruc-
tural with corresponding BTBT and BSBS derivatives, re-
spectively. Through the present screening research of the
NDT and NDS derivatives as organic semiconductors for
OFET devices, we found that the dipheneyl derivatives, DPh-
NDT and DPh-NDS, are promising materials for high-
performance organic semiconductors with relatively high
mobility up to 0.7 cm2 V-1 s-1. These results indicate that
NDT and NDS are potential cores for the development of
organic semiconductors similar to their isoelectronic heteroa-
rens, BTBT and BSBS. Different from BTBT and BSBS, an
interesting feature of the NDT/NDS system is that they have
vacant R positions of thiopheneorselenophene rings, atwhich
various chemical or electrochemical reactions can take place
easily and selectively. Thus, NDT and NDS will be useful
cores not only for small molecule-based organic semiconduc-
tors but also polymer semiconductors. Further investigations
to develop new materials via chemical modifications are now
actively being conducted in our research group.
FIGURE 10. Molecular arrangement in a bulk single crystal of
DPh-NDT.
TABLE 2. FET Characteristicsa of DPh-NDT- and DPh-NDS-Based
OFETs
μFETc/cm2 V-1 s-1
Ion/Ioff
Vth/V
d
compd
Tsubb/°C
DPh-NDT
25
60
100
25
60
100
0.2
0.3
0.3
0.7
0.3
0.4
105
106
106
106
106
107
-19
-19
-32
-15
-30
-31
DPh-NDS
Experimental Section
a FET devices were fabricated on HMDS-treated substrates with
W/L = 30. bSubstrate temperature during vapor deposition of the semi-
conductors. cExtracted from the saturation regime. dIon and Ioff were the
source-drain current measured at Vg = -60 and 0 V, respectively.
Synthesis: General. All chemicals and solvents are of reagent
grade unless otherwise indicated. Triethylamine, ethanol, tetra-
hydrofuran (THF), and N-methyl-2-pyrrolidone (NMP) were
purified with standard distillation procedures prior to use. All
reactions were carried out under nitrogen atmosphere. Melting
points were uncorrected. Nuclear magnetic resonance spectra
were obtained in deuterated chloroform with TMS as internal
reference; chemical shifts (δ) are reported in parts per million.
EI-MS spectra were obtained with use of an electron impact
ionization procedure (70 eV). The molecular ion peaks of the
chlorine-, sulfur-, or selenium-containing compounds showed a
typical isotopic pattern, and all the mass peaks are reported
based on 35Cl, 32S, or 80Se, respectively.
for thin film-based OFETs as was observed for the pentacene
thin films.14 However, compared to the device characteristics
of DPh-BTBT, which is isoelectronic with DPh-NDT, the
mobility of DPh-NDT-based devices is lower by one order
of magnitude than that of the best DPh-BTBT device ( μ =
2.0 cm2 V-1 s-1).8a At the moment the reasons for the reduced
device characteristics are not clear, but we speculate that the
extent of intermolecular interaction in the solid state is
different between these two compound, since nonbonded
sulfur-sulfur contact does not exist in the present DPh-
NDT, whereas in general the BTBT-based molecules tend to
have effective intermolecular interaction though nonbonded
sulfur-sulfur contacts.8c
With the selenium analogue, DPh-NDS, the OFETs fab-
ricated under various processing conditions also showed
comparable FET characteristics to those of DPh-NDT-
based ones, showing μFET values of up to 0.7 cm2 V-1 s-1
(Table 2). Although the exact molecular arrangement in the
solid state is not clear, DPh-NDS seems to have a similar
1,5-Dichloro-2,6-dihydroxynaphthalene (5)10. To a solution of
2,6-dihydroxynaphthalene (4, 3.0 g, 18.7 mmol) in glacial acetic
acid (90 mL) was slowly added sulfuryl chloride (3.0 mL, 37.5
mmol) at 0 °C. After the mixture was stirredfor 5 h, water (50mL)
was added, andthe resulting precipitatewas collected byfiltration
and washed with water to give 1,5-dichloro-2,6-dihydroxy-
naphthalene as a white solid (3.3 g, 78%). Mp 230.0-230.5 °C
(lit.10 mp 223.5 °C); 1H NMR δ 5.79 (s, 2H), 7.35 (d, J = 8.9 Hz,
2H), 7.96 (d, J = 8.9 Hz, 2H); EIMS m/z 228 (Mþ).
1,5-Dichloro-2,6-bis(trifluoromethanesulfonyloxy)naphthalene
(6). To a suspension of 1,5-dichloro-2,6-dihydroxynaphthalene
(5, 2.3 g, 10 mmol) and pyridine (4.8 mL, 60 mmol) in dichloro-
methane (100 mL) was slowly added trifluoromethanesulfonic
anhydride (3.6 mL, 22 mmol) at 0 °C.After the mixture wasstirred
for 18 h, water (10 mL) and hydrochloric acid (1 M, 10 mL) were
(14) Cornil, J.; Calbert, J. P.; Bredas, J. L. J. Am. Chem. Soc. 2001, 123,
1250–1251.
1232 J. Org. Chem. Vol. 75, No. 4, 2010

Shinamura et al.
JOCArticle
added. The resulting mixture was extracted with dichloromethane
(3 ꢀ 20 mL), and the combined organic layer was dried (MgSO4)
and concentrated in vacuo. The residue was purified by column
chromatography on silica gel eluted with dichloromethane (Rf
0.95) to give 1,5-dichloro-2,6-bis(trifluoromethanesulfonyloxy)-
added 1,5-dichloro-2,6-bis(phenylethynyl)naphthalene (7c, 250
mg, 0.63 mmol), and the resulting mixture was heated at 185 °C
for 12 h. After cooling, the mixture was poured into saturated
aqueous ammonium chloride solution (50 mL). The resulting
precipitate was collected by filtration and washed with water.
The crude solid was purified by vacuum sublimation to give
analytical 2,7-diphenylnaphtho[1,2-b:5,6-b0]dithiophene (147 mg,
60%) as a pale yellow solid. Mp >300 °C; 1H NMR δ 7.34-7.40
(m, 2H), 7.45-7.57 (m, 4H), 7.71 (s, 2H), 7.79-7.82 (m, 4H), 7.91
(d, J = 8.6 Hz, 2H), 8.05 (d, J = 8.6 Hz, 2H); 13C NMR δ 121.4,
122.8, 125.3, 125.4, 126.2, 137.4, 138.6; EIMS m/z 392 (Mþ). Anal.
Calcd for C26H16S2: C, 79.55; H, 4.11. Found: C, 79.31; H, 3.81.
Naphtho[1,2-b:5,6-b0]diselenophene (NDS, 2d). To a suspen-
sion of selenium powder (72 mg, 0.91 mmol) in ethanol (3 mL)
was added sodium borohydride (NaBH4, 34 mg, 0.91 mmol) at
ice-bath temperature. After the mixture was stirred for 40 min at
the same temperature, NMP (10 mL) and 1,5-dichloro-2,6-
bis(trimethylsilylethynyl)naphthalene (7a, 100 mg, 0.26 mmol)
were added. The mixture was heated at 185 °C with distilling out
ethanol with use of a Dean-Stark condenser for 12 h. After
cooling, the mixture was poured into saturated aqueous ammo-
nium chloride solution (50 mL). The resulting precipitate was
collected by filtration and purified by column chromatography
on silica gel eluted with hexane (Rf 0.2) to give naphtho[1,2-
b:5,6-b0]diselenophene (70 mg, 81%) as a white solid. Mp
193.0-193.5 °C; 1H NMR δ 7.73 (d, J = 5.8 Hz, 2H), 7.92 (s,
4H), 8.08 (d, J = 5.86 Hz, 2H); 13C NMR δ 123.6, 124.4, 128.4,
128.4, 129.2, 140.0, 142.2; EIMS m/z 336 (Mþ). Anal. Calcd for
C14H8Se2: C, 50.32; H, 2.41. Found: C, 50.34; H, 2.14.
2,7-Dioctylnaphtho[1,2-b:5,6-b0]diselenophene (C8-NDS, 2e).
A similar procedure as above with 1,5-dichloro-2,6-di(decyn-1-
yl)naphthalene (7b) gave the title compound in 89% yield. Mp
130.5-131.0 °C; 1H NMR δ 7.73 (d, J = 5.8 Hz, 2H), 7.92 (s, 4H),
8.08 (d, J = 5.86 Hz, 2H); 13C NMR δ 14.2, 22.8, 29.2, 29.3, 29.5,
32.0, 32.3, 33.4, 123.1, 123.7, 125.5, 128.0, 139.9, 141.1, 151.0;
EIMSm/z 560 (Mþ). Anal.Calcdfor C30H40Se2:C, 64.51; H, 7.22.
Found: C, 64.56; H, 7.27.
2,7-Diphenylnaphtho[1,2-b:5,6-b0]dithiophene (DPh-NDS, 2f).
To a suspension of selenium powder (141 mg, 1.8 mmol) in
ethanol (4 mL) was addedsodiumborohydride (68mg, 1.8mmol)
at ice-bath temperature. After the mixture was stirred for 40 min
at the same temperature, NMP (20 mL) and 1,5-dichloro-2,6-
bis(phenylethynyl)naphthalene (7c, 200 mg, 0.5 mmol) were
added. Then, the mixture was heated at 185 °C with distilling
out ethanol withuse ofa Dean-Starktrap for 12h. After cooling,
the resulting mixture was added into saturated aqueous ammo-
nium chloride solution (50 mL). The resulting precipitate was
collected by filtration, washed with water, and dried. Continuous
extraction from the solid with boiling chloroform afforded 2,7-
diphenylnaphtho[1,2-b:5,6-b0]dithiophene as a pale yellow solid
(230 mg, 94%). For device fabrication, DPh-NDS was further
purified by vacuum sublimation. Mp >300 °C; EIMS m/z 488
(Mþ). Anal. Calcd for C26H16Se2: C, 64.21; H, 3.32. Found: C,
63.84; H, 3.16.
1
naphthalene as a white solid (4.9 g, 99%). H NMR δ 7.68 (d,
J=9.3 Hz, 2H), 8.40 (d, J=9.3 Hz, 2H); 13C NMR δ 118.8 (q,
2JC-F=322.5 Hz), 122.9, 125.6, 126.2, 131.4, 144.9; EIMS m/z
492 (Mþ); mp 127.2-128.0 °C. Anal. Calcd for C12H4Cl2F6O6S2:
C, 29.22; H, 0.82. Found: C, 29.44; H, 0.76.
General Procedure for the Palladium-Catalyzed Sonogashira
Coupling of 1,5-Dichloro-2,6-bis(trifluoromethanesulfonyloxy)-
naphthalene (6) with Terminal Alkynes. To a deaerated solution
of 1,5-dichloro-2,6-bis(trifluoromethanesulfonyloxy)naphthalene
(6, 493 mg, 1.0 mmol) and triethylamine (0.42 mL, 3.0 mmol) in
THF (10 mL) were added Pd(PPh3)2Cl2 (70 mg, 0.05 mmol,
10 mol %), CuI (38 mg, 0.1 mmol, 20 mol %), and terminal
alkyne (3.0 mmol). After the mixture was refluxed for 20 h, water
(1 mL) and hydrochloric acid (1 M, 1 mL) were added. The
resulting mixture was extracted with dichloromethane (3 ꢀ 5 mL),
and the combined organic layer was dried (MgSO4) and concen-
trated in vacuo. The residue was purified by column chromato-
graphy on silica gel eluted with hexane to give 1,5-dichloro-2,6-
dietynylnaphthalene analogue (7) as a white solid.
1,5-Dichloro-2,6-bis(trimethylsilylethynyl)naphthalene (7a): 52%
yield; Mp 217.0-218.0 °C; 1H NMR δ 0.31 (s, 18H), 7.61 (d, J =
8.8 Hz, 2H), 8.12 (d, J = 8.8 Hz, 2H); 13C NMR δ 0.1, 101.8, 103.0,
122.0, 123.7, 130.7, 131.3, 134.8; EIMS m/z 388 (Mþ). Anal. Calcd
for C20H22Cl2Si2: C, 61.68; H, 5.69. Found: C, 61.45; H, 5.51.
1,5-Dichloro-2,6-di(decyn-1-yl)naphthalene (7b): 90% yield; Mp
44.0-44.5 °C; 1H NMR δ 0.89 (t, J = 7.0 Hz, 6H), 1.23-1.71 (m,
24H), 2.53 (t, J = 7.0 Hz, 4H), 7.56 (d, J = 8.5 Hz, 2H), 8.13 (d,
J = 8.5 Hz, 2H); 13CNMR δ14.2, 19.9, 22.8, 28.7, 29.0, 29.2, 29.3,
32.0, 78.5, 98.6, 122.5, 123.5, 130.7, 131.0, 133.8; EIMS m/z 468
(Mþ). Anal. Calcd for C30H38Cl2: C, 76.74; H, 8.16. Found: C,
76.74; H, 8.31.
1,5-Dichloro-2,6-bis(phenylethynyl)naphthalene (7c): 70% yield;
Mp 200.5-201.0 °C; 1H NMR δ 7.39-7.42 (m, 6H), 7.63-7.67
(m, 4H), 7.74 (d, J = 8.6 Hz, 2H), 8.25 (d, J = 8.6 Hz, 2H); EIMS
m/z 396 (Mþ). Anal. Calcd for C26H14Cl2: C, 78.60; H, 3.55.
Found: C, 78.39; H, 3.34.
Naphtho[1,2-b:5,6-b0]dithiophene (NDT, 2a). A suspension of
Na2S 9H2O (615 mg, 2.56 mmol) in NMP (15mL) was stirred for
3
15 min at room temperature. To the mixture was added 1,5-
dichloro-2,6-bis(trimethylsilylethynyl)naphthalene (7a, 250 mg,
0.64 mmol), and the resulting mixture was heated at 185 °C for
12 h. After cooling, the mixture was poured into saturated
aqueous ammonium chloride solution (50 mL). The resulting
precipitate was collected by filtration and purified by column
chromatography on silica gel eluted with hexane (Rf 0.2) to give
naphtho[1,2-b:5,6-b0]dithiophene (NDT, 139mg, 90%) as a white
solid. Mp 150.4-150.8 °C; 1H NMR δ 7.50 (d, J = 5.3 Hz, 2H),
7.54 (d, J = 5.3 Hz, 2H), 7.95 (d, J = 8.6 Hz, 2H), 8.07 (d, J = 8.6
Hz, 2H); 13C NMR δ 121.3, 122.8, 125.3, 125.4, 126.2, 137.4,
138.6; EIMS m/z 240 (Mþ). Anal. Calcd for C14H8S2: C, 69.96; H,
3.35. Found: C, 69.95; H, 3.26.
X-ray Crystallographic Analysis. Recrystallization from ap-
propriate solvents for respective compounds gave single crystals
suitable for X-ray crystallographic analysis: NDT (hexane), NDS,
(hexane), C8-NDT (chloroform), and DPh-NDT (NMP). The
X-ray crystal structure analysis was made on a Rigaku RAPID-IP
2,7-Dioctylnaphtho[1,2-b:5,6-b0]dithiophene (C8-NDT, 2b). A
similar procedure as above with use of 1,5-dichloro-2,6-di(decyn-
1-yl)naphthalene (7b) gave the title compound in 89% yield. Mp
92.0-93.0 °C; 1H NMR δ 0.88 (t, J = 6.8 Hz, 6H), 1.21-1.83 (m,
24H), 2.97 (t, J = 7.4 Hz, 4H), 7.14 (s, 2H), 7.77 (d, J = 8.6 Hz,
2H), 7.91 (d, J = 8.6 Hz, 2H); 13C NMR δ 14.2, 22.8, 29.3, 29.4,
29.5, 30.9, 31.5, 32.0, 120.9, 122.0, 122.1, 125.7, 137.4, 137.6,
145.8; EIMS m/z 464 (Mþ). Anal. Calcd for C30H40S2: C, 77.53;
H, 8.67. Found: C, 77.46; H, 8.71.
˚
(Mo KR radiation, λ = 0.71069 A, graphite monochromator,
T = 296 K, ω scan, 2θmax = 55.0°) or on a Rigaku Mercury-CCD
˚
(Mo KR radiation, λ = 0.71069 A, graphite monochromator,
T = 296 K, 2θmax = 55.0°). The structure was solved by the direct
methods.15 Non-hydrogen atoms were refined anisotropically,
and hydrogen atoms were included in the calculations but not
2,7-Diphenylnaphtho[1,2-b:5,6-b0]dithiophene (DPh-NDT, 2c). A
suspension of Na2S 9H2O (608 mg, 2.53 mmol) in NMP (15 mL)
3
(15) SHELXL (SHELX97): Schldric, G. M. Programs for the refinement
of crystal structures; University of Goettingen, Goettingen, Germany, 1997.
was stirred for 15 min at room temperature. To the mixture was
J. Org. Chem. Vol. 75, No. 4, 2010 1233

Shinamura et al.
JOCArticle
refined. All calculations were performed with the crystallographic
software package TeXsan 1.2.16 Crystallographic data are sum-
marized in Table S1 (Supporting Information).
Physicochemical Studies. UV-vis spectra were measured in
dichloromethane or THF solution (concentration: 10-5-10-6 M).
Cyclic voltammograms (CVs) were recorded on a Hokuto
Denko HA-301 potentiostat and a Hokuto Denko HB-104
function generator in benzonitrile containing tetrabutylammo-
nium hexafluorophosphate (Bu4NPF6, 0.1 M) as supporting
electrolyte at a scan rate of 100 mV/s. Counter and working
electrodes were made of Pt, and the reference electrode was
Ag/AgCl. All the potentials were calibrated with the standard
ferrocene/ferrocenium redox couple (Fc/Fcþ: E1/2 = þ0.43 V
measured under identical conditions). X-ray diffractions of
thin films deposited on the Si/SiO2 substrate were obtained
with a Rigaku Ultima IV diffractometer with a Cu KR source
Device Fabrication. Si/SiO2 substrates were exposed to HMDS
(hexamethyldisilazane) vapor at room temperature in a closed
desiccator under nitrogen overnight.17 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).
A thin film (50 nm thick) of DPh-NDT or DPh-NDS as an active
layer was vacuum-deposited on the Si/SiO2 substrate maintained
-1
˚
at various temperatures (Tsub) at a deposition rate of ca. 1 A s
under a pressure of ∼10-3 Pa. On top of the organic thin film,
gold films (80 nm) as drain and source electrodes were deposited
through a shadow mask. For a typical device, the drain-source
channel length (L) and width (W ) are 50 μm and 1.5 mm,
respectively. Characteristics of the OFET devices were measured
at room temperature under vacuum or in the air with a Keithley
4200 semiconducting parameter analyzer. Field-effect mobility
( μFET) was calculated in the saturation regime (Vd = -60 V) of
the Id, using the following equation:
˚
(λ = 1.541 A) in the air. AFM images of thin films on Si/SiO2
were obtained by using a Molecular Imaging PicoPlus micro-
scope in air.
Acknowledgment. This work was partially supported by a
Grant-in-Aid for Scientific Research (No. 20350088) from
the Ministry of Education, Culture, Sports, Science and
Technology, Japan.
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. The current on/off
ratio (Ion/Ioff) was determined from the Id at Vg = 0 (Ioff) and -60
V (Ion). The μFET data reported in Table 2 are typical values from
more than five different devices.
Supporting Information Available: 1H and 13C NMR spec-
tra of reported compounds including the intermediates, crystal-
lographic information files (CIFs) for NDT, NDS, C8-NDT,
and DPh-NDT, complete ref 13, results on MO calculations,
XRD patterns, and AFM images of evaporated thin films of
DPh-NDT and DPh-NDS, and output and transfer character-
istics of DPh-NDS-based OFETs. This material is available free
of charge via the Internet at http://pubs.acs.org.
(16) teXsan: Single Crystal Structure Analysis Software, Version 1.19;
Molecular Structure Corporation and Rigaku Corporation, 2000.
(17) Yoon, M.-H.; DiBenedetto, S. A.; Facchetti, A.; Marks, T. J. J. Am.
Chem. Soc. 2005, 127, 1348–1349.
1234 J. Org. Chem. Vol. 75, No. 4, 2010