One-step synthesis of [1]benzothieno[3,2-b][1]benzothiophene from o-chlorobenzaldehyde

Article abstract of DOI:10.1016/j.tetlet.2010.11.021

Simple one-step synthesis of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) from commercially available o-chlorobenzaldehyde is reported. The procedure is also applicable to the synthesis of dinaphtho[2,3-b:2′,3′-f] thieno[3,2-b]thiophene (DNTT).

Full text of DOI:10.1016/j.tetlet.2010.11.021

Tetrahedron Letters 52 (2011) 285–288
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
One-step synthesis of [1]benzothieno[3,2-b][1]benzothiophene
from o-chlorobenzaldehyde
a
a
a
a,b,
⇑
, Hirokazu Kuwabara , Masaaki Ikeda c
c
Masahiko Saito , Itaru Osaka , Eigo Miyazaki , Kazuo Takimiya
a
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
Functional Chemicals Research Laboratories, Nippon Kayaku Co. Ltd, 3-31-12 Shimo, Kita-ku, Tokyo 115-8588, Japan
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Simple one-step synthesis of [1]benzothieno[3,2-b][1]benzothiophene (BTBT) from commercially avail-
able o-chlorobenzaldehyde is reported. The procedure is also applicable to the synthesis of dinaph-
tho[2,3-b:2 ,3 -f]thieno[3,2-b]thiophene (DNTT).
Received 14 September 2010
Revised 29 October 2010
Accepted 5 November 2010
Available online 11 November 2010
0
0
Ó 2010 Elsevier Ltd. All rights reserved.
The performances of organic field-effect transistors (OFETs)
have been significantly improved in the last decade.1 Particularly,
the p-channel OFET has now achieved many important milestones:
S
S
S
S
2
ꢁ1 ꢁ1
2
3
high mobility (ꢀ5.0 cm V
s ), solution processability, air-sta-
4
BTBT
DTTN
bility, flexibility, low-voltage operation, and so on. For these
achievements, the development of new superior materials, in par-
ticular, new organic semiconductors have contributed signifi-
cantly. Although such new materials are very attracting, their
limited availability often stands in the way of further exploring
their possibility. Commercializing the materials is one way to
Figure 1. Chemical structure of BTBT and DNTT.
N
Scheme 1. The key step for the formation of BTBT is the S Ar-type
sulfuration reaction by the thiolate anion on each benzene ring of
. However, the second sulfuration reaction on the intermediate
2) is relatively slow and is competing with the intramolecular
cyclization to give 4, which ends up to the ill-defined byproducts
via further reaction. We thus speculated that the moderate yield
of BTBT from 1 is ascribed to the competitive reaction path to 4
via 2, owing to the lower reactivity of 2 in the second sulfuration
reaction to form o-dimercaptostilbene (3).
From these considerations, we proposed that alternative syn-
thesis of 3 or its synthetically equivalent compound would enable
another facile synthesis of BTBT, and thus first attempted sulfura-
tion reaction of o-chlorobenzaldehyde (5) to obtain o-mercapto-
5
address this issue, another way is to develop easy and practical
1
(
synthetic methods for the given organic semiconducting materials
and/or their key synthetic intermediates from readily available raw
materials.
6
[
1]Benzothieno[3,2-b][1]benzothiophene (BTBT) derivatives
0
0
and its further
p-extended analogue, dinaphtho[2,3-b:2 ,3 -f]thie-
7
no[3,2-b]thiophene (DNTT) (Fig. 1) are promising organic semi-
2
ꢁ1 ꢁ1
conductors, because of their high mobility (ꢀ5.0 cm V
s
for
8
2
ꢁ1 ꢁ1
9
the BTBT derivatives, ꢀ8.3 cm V
s
for DNTT ) and good air-
stability. However, for the synthesis of the p-extended compounds
of this kind, where two benzo[b]thiophene moieties fused at the
thiophene b-bond, not so many convenient methods, especially
scalable and versatile ones, have been reported so far.10
In this relation, we have recently found that the treatment of
readily available o-dihalostilbenes (1) with combined reagents of
12
benzaldehyde (6), which is supposed to subsequently dimerize
into 3. For the synthesis of 6, we traced the patented procedure,
which claimed that treatment of 5 with NaSHꢂnH
2
O in DMF or
13
NMP at 60 °C gave 6 in ca. 60% yield. Attempted reactions, how-
ever, gave a complex mixture after workup with an aqueous
ammonium chloride solution, and the desired 6 was not obtained
sodium sulfide nonahydrate (Na
2
Sꢂ9H
2
O) or sodium hydrosulfide
hydrate (NaSHꢂnH
2
O) and sulfur gave BTBT in moderate yields up
1
1
to 44% (Scheme 1). To get insight into this intriguing reaction,
(
(
Scheme 2). Instead, 6,12-imino-6H,12H-dibenzo[b,f]-1,5-dithiocin
7) was isolated in 21% yield, which was reported to form via a
reaction of 6 in the presence of ammonium acetate.
of 7 is therefore a strong proof for the formation of 6 in this reac-
tion. We then further examined this reaction under various condi-
tions to isolate 6.
we carefully investigated the possible reaction path from 1 to BTBT
0
by isolating an intermediate, 2-chloro-2 -mercaptostilbene (2)
12,14
Isolation
and a byproduct (4) and examining their reactivity to the reagents.
As a result, a plausible reaction path was proposed as shown in
⇑
Corresponding author. Tel.: +81 82 424 7734; fax: +81 82 424 5494.
E-mail address: ktakimi@hiroshima-u.ac.jp (K. Takimiya).
Among a number of reaction conditions examined, we surpris-
ingly found that the reactions at higher temperature (160–220 °C)
0
040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.11.021

2
86
M. Saito et al. / Tetrahedron Letters 52 (2011) 285–288
HS
X
X
NaSH·nH O/S
2
BTBT
~ 44% from 1)
(
NMP
80 °C
SH
SH
X
1
3 (not isolated)
1
2
X = Cl or Br
X
ill-defined
byproducts
S
4
Scheme 1. Formation of BTBT from o-dihalostilbenes by an action of NaSH/S as a reagent.
1
) NaSH·nH O
NMP, 60 °C
This one-step synthesis of BTBT from 5 should involve the initial
O reagent to give o-merca-
2
CHO
Cl
CHO
SH
S
nucleophilic sulfuration with NaSHꢂnH
2
HN
S
ptobenzaldehyde (6), subsequent dimerization of 6, following
cyclization, and the final aromatization. The dimerization reaction
of 6 in situ generated under acidic conditions from 2-tert-butyl-
2
) aq. NH Cl
4
5
6
7
21%
0
thiobenzaldehyde (6 ) was already reported to give 6,12-epoxy-
1
6
6
H,12H-dibenzo[b,j][1,5]dithiocin (8, Scheme 3). Since 8 is a di-
mer of 6 with loss of one water molecule, it is highly likely that
is a potential precursor for BTBT; an elimination of one more
water molecule from 8 can give BTBT (Scheme 3). This speculation
impelled us to examine the reaction of 8 with NaSHꢂnH O in NMP.
O in
Scheme 2. Reaction of 5 with NaSHꢂnH
2
O.
8
Table 1
Reaction of o-chlorobenzaldehyde (5) with NaSHꢂnH
Oa,b
2
2
Contrary to our expectations, 8 did not react with NaSHꢂnH
2
CHO 2 eq. NaSH·nH O
S
NMP at all and was recovered quantitatively. Another attempted
reactions of 8 with acidic dehydration reagents or neutral deoxy-
gen reagents did not give BTBT. From these results, we concluded
that 8 is neither the precursor nor an intermediate in the formation
of BTBT from 6.
2
Cl
solvent
S
5
BTBT
Entry
Solvent
Temp (°C)
Time (h)
Yield of BTBT (%)c
It was reported that b-mercaptoaldehyde prepared from acro-
lein with hydrogen sulfide in the presence of triethylamine exists
1
2
3
4
DMF
DMSO
NMP
DMI
Reflux
180
180
3
3
3
3
20
28
39
31
CHO dimerization
SH
-H2O
S
-H2O
220
CHO
H+
BTBT
O
a
All the reactions were carried out using 1.0 g (7.1 mmol) of 5 in 10 mL of
solvent.
t
S Bu
S
b
Similar reactions with sodium sulfide nonahydrate (Na
2
Sꢂ9H
2
O) gave no BTBT at
6'
6
8
all.
c
Isolated yield after column chromatography eluted with hexane and recrys-
Scheme 3. Proposed route to BTBT form 6 via 8.
tallization from toluene.
in various aprotic polar solvents (Table 1) gave BTBT. The yields of
BTBT varied depending on the solvent used, but BTBT was repro-
ducibly formed in all the solvents tested. In case of the reaction
in NMP, the yield of BTBT was among the highest (39%, entry 3
in Table 1), and thus we tried to optimize the reaction conditions
using NMP as the solvent.
(
a)
HO
S
SH
+
SH CH2 CH2 CH
OH
S
CH2 CH2 CHO
n
OHC
S
OH
5%
When equimolar amount of NaSHꢂnH
2
O to 5 was used, the yield
4
55%
of BTBT was reduced to 23%. On the other hand, large excess of the
reagent (4 equivalent to 5) also reduced the yield (13%) signifi-
cantly. However, when the reaction was done with two equivalent
(
b)
HO
S
-
2 H O
2
of NaSHꢂnH
regardless of the amount of solvent used (1–20 mL for 1.0 g
7.1 mmol) of 5) and reaction time (0.5–17 h). The best yield of
BTBT was 43%, when the mixture of 5 (1.0 g, 7.1 mmol) and two
O in NMP (20 mL) was first heated at 80 °C
2
O to 5, the yield of BTBT was always around 40%,
BTBT
S
CHO
SH
(
OH
9
equivalent NaSHꢂnH
2
+
for one hour and then at 180 °C for 16 h. Although the yields of
6
the present reactions are almost comparable with that of the pre-
HO
HS
CHO
S
vious BTBT synthesis from o-dihalostilbenes (ꢀ44%), a large advan-
tage of the present synthesis over the previous ones1
1,15
is that
commercially available 5 can be directly converted into BTBT in
one-step reaction. An additional advantage is that the present pro-
cedure is easily scalable; 100 g of 5 gave more than 30 g of BTBT
easily in one batch (see Supplementary data).
n
Scheme 4. (a) Dimerization and oligomeriation of b-mercaptoaldehyde17 and (b)
possible reaction path from 6 to BTBT via 9.

M. Saito et al. / Tetrahedron Letters 52 (2011) 285–288
287
as a mixture of dimer and oligomer (Scheme 4a).17 It is therefore
rational to consider that 6 with a b-mercaptoaldehyde substruc-
ture can also be dimerized and oligomerized under the basic con-
dition to form the corresponding dimer (9) and oligomers, the
former of which can be a potential precursor for BTBT, when two
water molecules from 9 are lost (Scheme 4b). Since the formation
of BTBT from 5 (Table 1) requires high reaction temperature, which
can facilitate the dehydration from 9, we speculate that the BTBT
thieno[3,2-b][1]benzothiophene (BTBT) having four fused aromatic
rings. This simple reaction must involve the initial sulfuration to
form o-mercaptobenzaldehyde (6), the subsequent dimerization
of 6, and the final dehydration reaction to give BTBT. Although
the yield of BTBT is moderate, the present one-step synthesis is
quite useful, because both the substrate, that is, 5 and the reagent,
2
NaSHꢂnH O, are cheap, commercially available chemicals. In addi-
tion, the present BTBT synthesis is readily scalable, as the reaction
of 100 g of 5 affords more than 30 g of BTBT in one batch. The par-
ent BTBT is a key intermediate for the synthesis of alkylated-BTBTs
that affords high-performance solution-processable OFETs with
very high mobility. Therefore, the present practical synthesis of
BTBT would contribute to the researches based on the alkylated
BTBTs and related materials. Furthermore, we also demonstrated
that the one-step thermal reaction could be applicable to the syn-
2
formation from 5 by the action of the NaSHꢂnH O reagent involves
following reactions: the initial sulfuration to form 6 and the dimer-
ization of 6 to afford the dimer 9, which thermally loses two water
molecules simultaneously to from BTBT. This plausible reaction
path from 5 to BTBT via 6 well explains the experimental results,
including the moderate yield of BTBT, owing to the coexistences
of the dimer and oligomeric mixture of 6. However, neither the ra-
tio of 9 to the oligomers in the reaction nor the actual mechanism
at the final step (from 9 to BTBT), whether it involves ionic reac-
tions or carben-like transient intermediates, is not clear.
0
0
thesis of dinaphtho[2,3-b:2 ,3 -f]thieno[3,2-b]thiophene (DNTT).
Since the yield of DNTT after purification was not excellent but
quite acceptable (ꢀ21%), the simple synthetic operation of the
present method in combination with ready availability of the pre-
cursor makes it attractive as a practical synthesis of this important
Although the yield is moderate, this one-step synthesis of BTBT
is attractive in the synthesis of the related heteroarene-based or-
ganic semiconductors. Among such organic semiconductors, DNTT
that gives excellent OFETs is one of the most important materials
and the development of convenient synthesis is highly desirable.
We thus applied the present method to the synthesis of DNTT (Ta-
ble 2). Treatment of 3-chloro-2-naphthaldehyde (10)18 in similar
reaction conditions to those for the synthesis of BTBT, however, re-
sulted in very poor yield of DNTT (entry 1). This is partially due to
the lower reactivity of 10 than that of 5: when 5 was mixed with
1
9
organic semiconductor. We thus believe that the present method
as well as the materials, that is, BTBT and DNTT, would contribute
to the further development of the material science based on the or-
ganic semiconductors.
Acknowledgments
This work was partially supported by a Grant-in-Aid for Scien-
tific Research from the Ministry of Education, Culture, Sports, Sci-
ence and Technology, Japan (No. 20350088) and Promoting R & D
program from Japan Science and Technology Agency (JST) of Japan.
The measurements of HRMS were made at the Natural Science
Center for Basic Research and Development (N-BARD), Hiroshima
University.
2
NaSHꢂnH O in NMP at room temperature, a spontaneous exother-
mic reaction took place immediately without external heating,
whereas 10 did not show any such exothermic reaction. Thus,
the reaction of 10 was carried out at high temperature from the
beginning (bath temperature: 200 °C), but the yield of DNTT was
not improved significantly (entry 2). In contrast, the amount of sol-
vent used, that is, the concentration, in the reaction was found to
be critical: when the slurry-like mixture of 10 and the reagent with
a small amount of NMP was heated at 200 °C, DNTT was formed
with good reproducibility (entry 3 and 4).19 Although the yields
of DNTT after purification by the gradient sublimation and recrys-
tallization (ꢀ21%) are not excellent, this one-step procedure is
quite useful for easy synthesis of this important organic semicon-
Supplementary data
Supplementary data (experimental procedures and spectro-
scopic data for 7 and 8) associated with this article can be found,
in the online version, at doi:10.1016/j.tetlet.2010.11.021.
20
ductor from a readily available precursor (10).
In summary, we have found that a one-step thermal reaction of
References and notes
o-chlorobenzaldehyde (5) with NaSHꢂnH
2
O in NMP gave [1]benzo-
1. (a) Dimitrakopoulos, C. D.; Malenfant, P. R. L. Adv. Mater. 2002, 14, 99–117; (b)
Rogers, J. A.; Bao, Z.; Katz, H. E.; Dodabalapur, A. In Thin-Film Transistors; Kagan,
C. R., Andry, P., Eds.; Marcel Dekker: New York, 2003; p 377; (c)Klauk, H.,
Ed.Organic Electronics, Manufacturing and Applications; Wiley-VCH:
Weinheim, 2006; (d)Organic Field-Effect Transistors; Bao, X., Locklin, J., Eds.;
CRC Press, 2007; (e) Anthony, J. E. Chem. Rev. 2006, 106, 5028–5048; (f)
Murphy, A. R.; Frechet, J. M. J. Chem. Rev. 2007, 107, 1066–1096.
Table 2
a
Synthesis of DNTT from 3-chloro-2-naphtaldehyde (10)
2. (a) Lin, Y. Y.; Gundlach, D. J.; Nelson, S. F.; Jackson, T. N. IEEE Electron Device Lett.
CHO 2 eq. NaSH·nH O
S
2
1
2
997, 18, 606–608; (b) Kitamura, M.; Arakawa, Y. J. Phys.: Condens. Matter.
008, 20, 184011; (c) Tan, H. S.; Mathews, N.; Cahyadi, T.; Zhu, F. R.;
Cl
NMP
Mhaisalkar, S. G. Appl. Phys. Lett. 2009, 94, 263303; (d) Halik, M.; Klauk, H.;
Zschieschang, U.; Schmid, G.; Ponomarenko, S.; Kirchmeyer, S.; Weber, W. Adv.
Mater. 2003, 15, 917–922; (e) Okamoto, H.; Kawasaki, N.; Kaji, Y.; Kubozono, Y.;
Fujiwara, A.; Yamaji, M. J. Am. Chem. Soc. 2008, 130, 10470–10471; (f)
Kawasaki, N.; Kubozono, Y.; Okamoto, H.; Fujiwara, A.; Yamaji, M. Appl. Phys.
Lett. 2009, 94, 043310; (g) Meng, H.; Sun, F.; Goldfinger, M. B.; Gao, F.; Londono,
D. J.; Marshal, W. J.; Blackman, G. S.; Dobbs, K. D.; Keys, D. E. J. Am. Chem. Soc.
S
1
0
DNTT
Entry Amount of
solvent used
Conditions
Yield of DNTT
(%)
b
(mL)
2
006, 128, 9304–9305; (h) Klauk, H.; Zschieschang, U.; Weitz, R. T.; Meng, H.;
Sun, F.; Nunes, G.; Keys, D. E.; Fincher, C. R.; Xiang, Z. Adv. Mater. 2007, 19,
882–3887; (i) Gao, P.; Beckmann, D.; Tsao, H. N.; Feng, X.; Enkelmann, V.;
1
6
80 °C (1 h) then 200 °C
10 h)
Trace
3
(
Baumgarten, M.; Pisula, W.; Müllen, K. Adv. Mater. 2009, 21, 213–216; (j)
Zhang, L.; Tan, L.; Wang, Z.; Hu, W.; Zhu, D. Chem. Mater. 2009, 21, 1993–1999;
2
3
6
0.5
200 °C (10 h)
80 °C (1 h) then 200 °C
3.0
12
(
5
k) Yamada, T.; Kumai, R.; Takahashi, Y.; Hasegawa, T. J. Mater. Chem. 2010, 20,
810–5812; (l) Kang, M. J., Doi, I., Mori, H., Miyazaki, E., Takimiya, K., Ikeda, M.,
Kuwabara, H., Adv. Mater. in press, doi:10.1002/adma.201001283.
(
10 h)
4
0.5
200 °C (10 h)
21
a
3. (a) Sirringhaus, H. Adv. Mater. 2005, 17, 2411–2425; (b) Allard, S.; Forster, M.;
Souharce, B.; Thiem, H.; Scherf, U. Angew. Chem., Int. Ed. 2008, 47, 4070–4098.
All the reactions were carried out using 760 mg (4.0 mmol) of 10 and 640 mg of
O.
NaSHꢂnH
2
4
5
.
.
Klauk, H.; Zschieschang, U.; Pflaum, J.; Halik, M. Nature 2007, 445, 745–748.
Several recently developed organic semiconducting materials, for example,
b
Yield after purification with gradient vacuum sublimation followed by recrys-
tallization from chlorobenzene.
6,13-bis(triisopropylsilylethynyl)pentancene
(TIPS-pentacene),
2,7-

2
88
M. Saito et al. / Tetrahedron Letters 52 (2011) 285–288
diphenyl[1]benzothieno[3,2-b][1]benzothiophene (DPh-BTBT), are now
commercially available from chemical suppliers.
11. Saito, M.; Yamamoto, T.; Osaka, I.; Miyazaki, E.; Takimiya, K.; Kuwabara, H.;
Ikeda, M. Tetrahedron Lett. 2010, 51, 5277–5280.
6
.
(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,
12. o-Mercaptobenzaldehyde was reported to be prepared from thiophenol via o-
lithiation and the subsequent reaction with DMF (or other carboration
reagents). See: Toste, F. D.; Lough, A. J.; Still, I. W. J. Tetrahedron Lett. 1995,
36, 6619–6622.
13. Kagano, H.; Itsuda, H.; Yamashita, K.; Yoshida, K. (Sumitomo Seika KK, Japan),
Jpn. Kokai Tokyo Koho JP0515881, 1993; Chem. Abstr. 1993, 119, 249828.
14. Still, I. W. J.; Natividat-Preyra, R.; Toste, F. D. Can. J. Chem. 1999, 77, 113–121.
15. Košata, B. K.; Svoboda, J. Collect. Czech. Chem. Commun. 2002, 67, 645–664.
16. Dickman, D. A.; Chemburkar, S.; Konopacki, D. B.; Elisseou, E. M. Synthesis 1993,
1993, 573–574.
1
3
5732–15733; (c) Izawa, T.; Miyazaki, E.; Takimiya, K. Adv. Mater. 2008, 20,
388–3392.
7
.
(a) Yamamoto, T.; Takimiya, K. J. Am. Chem. Soc. 2007, 129, 2224–2225; (b)
Yamamoto, T.; Takimiya, K. J. Photopolym. Sci. Tech. 2007, 20, 57–59; (c) Uno,
M.; Doi, I.; Takimiya, K.; Takeya, J. Appl. Phys. Lett. 2009, 94, 103307; (d)
Zschieschang, U.; Ante, F.; Yamamoto, T.; Takimiya, K.; Kuwabara, H.; Ikeda, M.;
Sekitani, T.; Someya, T.; Kern, K.; Klauk, H. Adv. Mater. 2010, 22, 982–985; (e)
Yamamoto, T.; Shinamura, S.; Miyazaki, E.; Takimiya, K. Bull. Chem. Soc. Jpn
17. Schnabel, H. W.; Grimm, D.; Jensen, H. Liebigs Ann. Chem. 1974, 477–495.
18. (a) Lindley, W. A.; MacDowell, D. W. H. J. Org. Chem. 1982, 47, 705–709;
2
010, 83, 120–130; (f) Kang, M. J.; Yamamoto, T.; Shinamura, S.; Miyazaki, E.;
Takimiya, K. Chem. Sci. 2010, 1, 179–183.
Alternatively, 3-chloro-2-naphthaldehyde was easily prepared via MnO
2
8
.
.
Uemura, T.; Hirose, Y.; Uno, M.; Takimiya, K.; Takeya, J. Appl. Phys. Express 2009,
oxidation of 3-chloro-2-hydroxymethylnaphthalene: see also (b) Parham, W.
E.; Wright, C. D. J. Org. Chem. 1957, 22, 1473–1477.
2, 111501.
9
(a) Uno, M.; Tominari, Y.; Yamagishi, M.; Doi, I.; Miyazaki, E.; Takimiya, K.;
Takeya, J. Appl. Phys. Lett. 2009, 94, 223308; (b) Haas, S.; Takahashi, Y.;
Takimiya, K.; Hasegawa, T. Appl. Phys. Lett. 2009, 95, 022111.
19. Since this reaction requires high concentration of reactants, uniform heating at
such high temperature in large scale synthesis is difficult, resulting in poor
yields of DNTT. Instead of enlargement of synthetic scale, several parallel
reactions at relatively small scale (ꢀ4 mmol) easily afforded more than 1 g of
DNTT after purification.
1
0. (a) Zherdeva, S. Y. B.; Zheltov, A. Y.; Stepanov, B. I. Zh. Org. Khim. 1980, 16, 430–
38; (b) Sashida, H.; Yasuike, S. J. Heterocycl. Chem. 1988, 35, 725–726; (c)
4
Kaszynski, P.; Dougherty, D. A. J. Org. Chem. 1993, 58, 5209–5220; (d) Izawa, T.;
Miyazaki, E.; Takimiya, K. Chem. Mater. 2009, 21, 903–912; (e) Kienle, M.;
Unsinn, A.; Knochel, P. Angew. Chem., Int. Ed. 2010, 49, 4751–4754.
20. The quality of DNTT prepared by the present method was also checked by the
device fabrication and evaluations. The field-effect mobilities greater than
1.0 cm2
V
ꢁ1
s
ꢁ1
were reproducibly observed.