General synthesis of dinaphtho[2,3- b:2′,3′- f ]thieno[3,2- b ]thiophene (DNTT) derivatives

Article abstract of DOI:10.1021/ol2010837

A new straightforward synthesis of dinaphtho[2,3-b:2′,3′-f] thieno[3,2-b]thiophene (DNTT) derivatives from readily available 2-methoxynaphthalenes is described. Thus, newly developed derivatives of DNTT showed very high field effect mobility in the vapor-

Full text of DOI:10.1021/ol2010837

ORGANIC
LETTERS
2011
Vol. 13, No. 13
3430–3433
General Synthesis of Dinaphtho-
[2,3-b:20,30-f]thieno[3,2-b]thiophene
(DNTT) Derivatives
Kazuki Niimi,† Myeong Jin Kang,† Eigo Miyazaki,† Itaru Osaka,† 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 May 4, 2011
ABSTRACT
A new straightforward synthesis of dinaphtho[2,3-b:20,30-f]thieno[3,2-b]thiophene (DNTT) derivatives from readily available 2-methoxynaph-
thalenes is described. Thus, newly developed derivatives of DNTT showed very high field effect mobility in the vapor-processed field-effect
transistors up to 8 cm2 Vꢀ1 sꢀ1
.
Organic thin-film transistors (OTFTs) have attracted
great interest for their potential use in several electronic
applications, including active-matrix displays, electronic
paper, and chemical sensors.1 The performances of OTFTs
have been significantly improved in the past decade,2 and
in particular, the p-channel OTFT has now achieved many
important milestones: high mobility (>3.0 cm2 Vꢀ1 sꢀ1),3
solution processability,4 air-stability, flexibility, low-vol-
tage operation,5 and so on. For these achievements, the
development of new superior materials, in particular, new
organic semiconductors have contributed significantly.
Among the recently developed materials, dinaphtho[2,
3-b:20,30-f]thieno[3,2-b]thiophene (DNTT)6 (Figure 1) and
its derivatives7 are particularly promising organic semi-
conductors for TFT applications because of high mobility
† Graduate School of Engineering.
‡ Institute for Advanced Materials Research.
(1) (a) Rogers, J. A.; Bao, Z.; Katz, H. E.; Dodabalapur, A. In Thin-
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2003; p 377. (b) Organic Electronics, Manufacturing and Applications;
Klauk, H., Ed.; Wiley-VCH: Weinheim, 2006. (c) Organic Field-Effect
Transistors; Bao, X., Locklin, J., Eds.; CRC Press: Boca Raton, 2007.
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2002, 14, 99–117. (b) Anthony, J. E. Chem. Rev. 2006, 106, 5028–5048.
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IEEE Electron Device Lett. 1997, 18, 606–608. (b) Kitamura, M.;
Arakawa, Y. J. Phys.: Condens. Matter. 2008, 20, 184011. (c) Tan,
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Schmid, G.; Ponomarenko, S.; Kirchmeyer, S.; Weber, W. Adv. Mater.
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Y.; Fujiwara, A.; Yamaji, M. J. Am. Chem. Soc. 2008, 130, 10470–10471.
(f) Kawasaki, N.; Kubozono, Y.; Okamoto, H.; Fujiwara, A.; Yamaji,
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3887. (i) Gao, P.; Beckmann, D.; Tsao, H. N.; Feng, X.; Enkelmann, V.;
(∼3.0 cm2 Vꢀ1 sꢀ1 for DNTT,6 ∼ 7.9 cm2 Vꢀ1
s
ꢀ1 for 2,
9-C10-DNTTs7b) and good air stability. In addition, a recent
investigation on derivatization of DNTT has revealed that
(4) (a) Sirringhaus, H. Adv. Mater. 2005, 17, 2411–2425. (b) Allard,
S.; Forster, M.; Souharce, B.; Thiem, H.; Scherf, U. Angew. Chem., Int.
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2224–2225. (b) Yamamoto, T.; Takimiya, K. J. Photopolymer 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.;
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r
10.1021/ol2010837
Published on Web 05/31/2011
2011 American Chemical Society

dimethyl derivatives (2,9- and 3,10-DMDNTT) can con-
struct intriguing three-dimensional (3D) crystal structures.7a
For this reason, we have examined another synthetic
strategy for the precursor of DNTT, 1,2-bis(3-methylthio-
naphthalen-2-yl)ethenes (Scheme 2); different from the
original DNTT syntheses, where the precursors were
synthesized via the reductive dimerization of the corre-
sponding 3-methylthio-2-naphthaldehydes (red arrow in
Scheme 2), the new strategy involves a cross coupling reac-
tion between two 3-methylthionaphthalene moieties and a
bis-metalated ethene reagent (blue arrow in Scheme 2).
Scheme 2. Retrosynthetic Analysis of 1,2-Bis(3-methylthio-
naphthalen-2-yl)ethene
Figure 1. Structure of DNTT and its derivatives.
For further development of organic semiconducting
materials with the DNTT core, a general and efficient
synthetic method is highly desirable. In the present con-
tribution, we report a newly established synthetic route to
DNTT from commercially available 2-methoxynaphtha-
lene. Since various 2-methoxynaphthalene derivatives are
readily available, the new method allows us to synthesize
various DNTT derivatives. Here, straightforward synth-
eses of the parent DNTT, 2,9-C10-DNTT,7b its 3,10-iso-
mer, and two isomeric 2,9- and 3,10-diphenyl derivatives
(DPhDNTTs) are demonstrated.
The reported synthesis of DNTT and its derivatives is
shown in Scheme 1, which features the double-ring-closing
reaction at the final step to construct the central thieno[3,2-b]-
thiophene moiety from the trans-1,2-bis(3-methylthio-
naphthalen-2-yl)ethenes.6,7 For the synthesis of the pre-
cursors from 2-naphthaldehydes, the first methylthiolation
at the 3-position is the critical step. However, this reaction
is often problematic owing to tedious purification and
moderate yields of the desired 3-functionalized naphtha-
lenes (45ꢀ70% isolated yield depending on substituents on
the 6- or 7-position). This is due to a concomitant compet-
ing reaction at the naphthalene R-position (1-functionaliza-
tion) to form isomeric byproducts (15ꢀ30% yield), which
should be removed by column chromatography and careful
recrystallization processes. Thus, for the large-scale synth-
esis and further derivatization of DNTT, a new synthetic
approach that enables highly selective synthesis from a
readily available starting material should be developed.
After several trials using different combinations of the X
group on the naphthalene moiety and the metal (M) on the
ethene moiety, we have finally found that the combination
of X = OTf (i.e., 3-methylthio-2-naphthyl trifluorometha-
nesulfonate, 4a) and M = SnBu3 (i.e., trans-1,2-bis(tri-
butylstannyl)ethene)8 provides 1,2-bis(3-methylthionaph-
thalen-2-yl)ethene (5a) in a quantitative yield. More
importantly, the synthesis of 4a was demonstrated to be very
easy as shown in Scheme 3. Starting from commercially
available 2-methoxynaphthalene (1a), selective thiomethy-
lation at the 3-position via a lithiation with butyllithium
followed by a reaction with dimethyl disulfide gave 2-meth-
oxy-3-methylthionaphthalene (2a) in 93% isolated yield
after recrystallization.10 Subsequent selective demethyla-
tion on the methoxy group followed by triflation of the
resulting 3-methylthio-2-naphthol (3a)9 proceeded quanti-
tatively to give 4a.
Scheme 3. New Synthetic Route to DNTT from 2-Methoxyn-
aphthalene
Scheme 1. Reported Syntheses of DNTT and Its Derivatives
Although the number of steps are increased, the new
synthetic route to DNTT is superior to the original one in
termsof easyexperimental operation (nochromatographic
separation of the isomer is necessary), cheap starting
Org. Lett., Vol. 13, No. 13, 2011
3431

material, scalability, and total yield (79% for the present vs
39% yield for the previous one). As a result, a very effective
synthetic route to DNTT is now established.
derivative (1d) or in the Suzuki coupling with phenylboro-
nic acid to give the 7-phenyl derivative (1e).
Using these 2-methoxynaphthalene derivatives, the
same synthetic method as in Scheme 3 was applied to
synthesize the corresponding di-n-decyl and diphenyl deri-
vatives of DNTT. The isolated yield in each step summar-
ized in Table 1 is somewhat varied, since the reaction
conditions for each transformation were not fully opti-
mized. However, efficient syntheses of all the derivatives
regardless of either the substituents or the substituted
positions are achieved. Comparedtothe previoussynthesis
of 2,9-C10-DNTT, not only the numbers of steps are
reduced (from 7 to 6 steps)14 but also the total yield is
fairly improved (from 28% to 41%). Furthermore, it
should be again emphasized that the present method does
not require chromatographic separation of the isomeric
byproduct, enabling a scalable synthesis.
Scheme 4. Synthesis of 6- and 7-Substituted 2-Methoxyn-
aphthalene Derivatives
Since DNTT and 2,9-C10-DNTT give high-performance
OTFTs, newly synthesized DNTT derivatives were also
examined as the active semiconducting materials in the
vapor processed OTFTs with the top-contact configura-
tion on ODTS-treated Si/SiO2 (200 nm) substrates. Pre-
liminary measurements revealed unoptimized field-effect
mobilities of ∼8.0 cm2 Vꢀ1 sꢀ1 for 3,10-C10-DNTT, ∼3.4
cm2 cm2 Vꢀ1 sꢀ1 for 2,9-DPh-DNTT, and ∼3.8 cm2 Vꢀ1
sꢀ1 for 3,10-DPh-DNTT (Figure 2, Table 1). These high
mobilities are quite promising, and further optimizations
of the device processing conditions are now underway. In
addition, the isomeric pairs of DNTT derivatives are
suitable for investigating the structure-properties relation-
ship in terms of the molecular ordering in the solid state.
In summary, we have successfully established a general
and improved synthetic route to DNTTs from 2-methox-
ynaphthalene derivatives. Compared to the previous
synthesis of DNTTs, the new method has many advan-
tages including high yield, good selectivity, easy experi-
mental operations, and versatility in derivatization. Using
the new method, facile syntheses of isomeric C10-DNTT
and DPh-DNTT are demonstrated, and these new DNTT
derivatives turn out to be very promising as high per-
formance organic semiconductors. Thus, further device
Another merit of the new method is that various deri-
vatives of 2-methoxynaphthalene are readily available. For
example, commercially available 6-bromo-2-methoxy-
naphthalene (6) can be easily converted into the 6-alkyl
(1b) or 6-phenyl derivative (1c) via the Kumada11 or
Suzuki coupling12 as shown in Scheme 4. Although it is
not easy to prepare 7-halo-2-methoxynaphthalene deriva-
tives, 7-methoxy-2-naphthyl trifluoromethanesulfonate
(7) has been conveniently used for the synthesis of various
7-substituted2-methoxynaphthalene derivatives.13 Thus, 7
was employed either in the Sonogashira coupling with
1-decyne followed by hydrogenation to give the 7-decyl
Table 1. Isolated Yields (%) in the Synthesis of a Series of DNTT Derivatives and Mobilities (μFETs)a of Their Vapor-Processed
Devices
R
2
3
4
5
DNTT derivatives
product
μFETa/cm2 Vꢀ1 sꢀ1
6-n-C10H21 (1b)
7-n-C10H21 (1d)
6-Ph (1c)
quant
93
72
85
73
94
quant
94
quant
quant
57
85
71
89
85
2,9-C10-DNTT
3,10-C10-DNTT
2,9-DPh-DNTT
3,10-DPh-DNTT
7.9b
8.0
3.4
3.8
quant
77
quant
quant
7-Ph (1e)
63
a Extracted from the saturation regime. b Reference 7b.
3432
Org. Lett., Vol. 13, No. 13, 2011

From the viewpoint of synthetic chemistry, the essential
point in the new synthetic method is the selective o-func-
tionalization of methoxy-substituted aromatic rings. Thus,
the present synthetic method may open the door to the
synthesis of DNTT-related materials possessing the benzo-
fused thieno[3,2-b]thiopehene substructure. Further explora-
tions to various π-extend materials using the present
synthetic method are also conducted in our group.
Acknowledgment. This work was partially supported
by a Grant-in-Aid for Scientific Research from the Ministry
of Education, Culture, Sports, Science and Technology,
Japan (No. 20350088, 23245041), Promoting R & D pro-
gram from Japan Science and Technology Agency (JST) of
Japan, NEDO Nanotech Challenge Program, and Japan
Society for the Promotion of Science (JSPS) through its
“Funding Program for World-Leading Innovative R&D
on Science and Technology (FIRST Program).
Supporting Information Available. Experimental pro-
cedures and spectroscopic data. This material is avail-
able free of charge via the Internet at http://pubs.acs.
org.
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1993, 1993, 885–888. In the present reaction, careful inspection of the
products revealed that 1-methoxy-2-methylthionaphthalene was pro-
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3-methylthio isomer by recrystallization.
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Figure 2. Transfer and output curves of (a) 2,9-DPhDNTT-,
(b) 3,10-C10-DNTT-, and (c) 3,10-DPhDNTT-based devices.
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optimizations as well as structural investigation are now
underway for the new DNTT materials.
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Takimiya, K. Chem. Sci. 2010, 1, 179–183. (b) Kang, M. J.; Doi, I.; Mori,
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(14) The previous synthesis of 2,9-C10-DNTT started with methyl
6-bromo-2-naphthalate, which was first reduced to the corresponding
hydroxymethyl compound and then oxidized to 6-bromo-2-naphthalal-
dehyde. Introduction of the n-decyl group on the aldehyde was done via
the palladium-catalyzed Sonogashira coupling followed by dehydro-
genation. As a result, the previous method consists of seven synthetic
reactions from commercially available starting compound.
Org. Lett., Vol. 13, No. 13, 2011
3433