Linear fused dithieno[2,3- b:3′2′- d ]thiophene diimides

Article abstract of DOI:10.1021/ol103013d

Linear fused dithieno[2,3-b:3′2′-d]thiophene diimides (DTTDIs, 1-4) were synthesized. Physicochemical investigations suggested that these diimides might be used as potential n-channel organic semiconductors. Single-crystal analysis of N-propyl DTTDI (1) r

Full text of DOI:10.1021/ol103013d

ORGANIC
LETTERS
Linear Fused Dithieno[2,3-b:3020-d]-
thiophene Diimides
2011
Vol. 13, No. 6
1410–1413
Wei Hong,† Haihong Yuan,† Hongxiang Li,*,† Xiaodi Yang,§ Xike Gao,† and
Daoben Zhu*,†,‡
Laboratory of Material Science, Shanghai Institute of Organic Chemistry, Chinese
Academy of Sciences, Shanghai 200032, P. R. China, Beijing National Laboratory of
Molecular Sciences, Key Laboratory of Organic Solids, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, P. R. China, and Laboratory of Advanced
Materials, Fudan University, Shanghai 200438, P. R. China
lhx@mail.sioc.ac.cn; zhudb@iccas.ac.cn
Received January 12, 2011
ABSTRACT
Linear fused dithieno[2,3-b:3020-d]thiophene diimides (DTTDIs, 1-4) were synthesized. Physicochemical investigations suggested that these
diimides might be used as potential n-channel organic semiconductors. Single-crystal analysis of N-propyl DTTDI (1) revealed that molecules
adopt a layered herringbone packing motif.
. Aromatic imides are significant organic species that
benefit a wide range of applications as flexible optoelec-
tronic devices,1 chemical sensors,2 and supramolecular
assemblies.3 The properties of aromatic imides are strongly
dependent on their π-conjugated cores. For example, as
organic semiconductors of thin film transistors, anthracene
diimide derivatives (ADIs, Scheme 1) display electron trans-
port properties.4 In contrast, linear dibenzotetrathiafulva-
lene diimide derivatives (DBTTFDIs, Scheme 1) exhibit hole
transport characteristics.5 Until now, aromatic imide stu-
dies are primarily focused on fused phenyl imides, such as
naphthalene6 and perylene diimides7 (NDIs and PDIs,
† Laboratory of Material Science, Shanghai Institute of Organic Chem-
istry, Chinese Academy of Sciences.
§ Fudan University.
‡ Beijing National Laboratory of Molecular Sciences, Key Laboratory of
Organic Solids, Institute of Chemistry, Chinese Academy of Sciences.
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r
10.1021/ol103013d
Published on Web 02/18/2011
2011 American Chemical Society

Scheme 1. Chemical Structures of Some Aromatic Imides
Scheme 2. Synthetic Route to Diimides 1-4
respectively, Scheme 1). To broaden the applications and
further understand the relationship between molecular struc-
ture and properties, it is necessary to synthesize novel types
of aromatic imides with differently π-conjugated cores.
Thiophene-containing compounds are frequently used
in organic electronics.8 Among these molecules, linear
ring-fused thiophenes have attracted particular attention
because they exhibit rigid structures, strong intermolecu-
lar interactions, and usually high device performances.9
Recently, several groups have reported the high power
conversion efficiencies (e6.8%) of thieno[3,4-c]pyrrole-
4,6-dione-based (TPDO, Scheme 1) copolymers in solar
cells.10 Facchetti et al. discovered that N-alkyl-2,2-bithio-
phene-3,30-dicarboximides (BTDI, Scheme 1) were ideal
π-conjugated units for the construction of electron-trans-
porting organic semiconductors.11 All of these results sug-
gested that thiophene-based imides would offer more
significant roles in organic electronics. However, to the best
of our knowledge, there have been no precedents of imide
groups directly attached to the 2,3-position of linear fused
thiophenes. Such a desired structure would enlarge the π-
conjugated system, lower the HOMO-LUMO energy
levels, and improve solubility. Herein, we present the first
examples of linear fused thiophene-based imides, dithieno-
[2,3-b:3020-d]thiophene diimides (DTTDIs, Scheme 2), and
include their general accessible method and photophysical
and electrochemical properties. The single crystal structure
of N-propyl DTTDI 1 is also reported.
The syntheses of DTTDIs 1-4 from commercially
available tetrabromothiophene is outlined in Scheme 2.
Previous approaches to prepare imides from anhydride
have been described.12 Additionally, the dehydration of
the DTT tetracarboxylic acid, 7, was assumed to lead to
the formation of the corresponding anhydride, DTTDA
€
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Org. Lett., Vol. 13, No. 6, 2011
1411

8. Thus, compound 7 was the key intermediate in our
synthetic route. We initially attempted to synthesize 7 via
the hydrolysis of tetracyano-DTT, which was a cyaniza-
tion product of tetrabromo-DTT. However, the full
cyanization of tetrabromo-DTT was unsuccessful be-
cause both the starting materials and products were
extremely insoluble in organic solvents. Our novel strat-
egy to synthesize 7 included three steps. First, ethyloxo-
acetate groups were introduced to the two R positions of
the tetrabromothiophene ring via an efficient CuI-cata-
lyzed coupling reaction that we recently established.13
Fortunately, product 5 could be separated in a satisfying
yield (72%) through simple recrystallization from a sol-
vent mixture composed of petroleum ether and dichloro-
methane (CH2Cl2). Next, the reaction of 5 with ethyl
mercaptoacetate and potassium hydroxide in an ethano-
lic solution afforded DTT tetraethyl ester, 6 (32% yield).
A similar reaction was first reported by Holmes and co-
workers.14 However, their reaction condition (potassium
carbonate as a base suspension in DMF) only led to
complicated byproducts for our reactants, probably due
to the different reactivity of the ethyloxoacetate groups in
5. Basic hydrolysis of 6, followed by refluxing in excessive
concentrated hydrochloric acid overnight, afforded 7 in
high yield (88%).15 Less drastic acidification conditions
produced a mixture of 7 and its poorly water-soluble
lithium salts, resulting in an unsuccessful dehydration,
evident by elemental analysis. Tetracarboxylic acid 7 was
easily dehydrated by refluxing acetic anhydride to afford
DTTDA 8 (75% yield).16 The target diimides 1-4 were
obtained in moderate yields (46-59%) via reacting 8 with
different amines, followed by imidization in SOCl2.17,12
The chemical structures of all novel compounds are clearly
supported by characterizations, such as 1H NMR, 13C
NMR, MS, and elemental analysis (see Supporting Informa-
tion, SI).
Figure 1. (a) Absorption (left) and emission spectra (right) of
DTTDIs 1-4 in diluted CH2Cl2 (10-5 mol L-1). (b) Cyclic voltam-
mograms of DTTDIs 1-4 in CH2Cl2 solutions with the following
condition: 0.1 M Bu4NPF6, supporting electrolyte; AgCl/Ag, refer-
ence electrode; Pt disk, working electrode; Pt wire, counter electrode;
ferrocene, internal potential marker; and scan rate, 50 mV-1
.
which indicated the strong electron-withdrawing prop-
erty of diimide groups. The HOMO-LUMO energy gaps
calculated from the on-set absorption were in the range
2.80 to 2.84 eV for 1-4 and slightly increased in the order
3 < 1 < 2 ≈ 4. No absorption decay was observed for the
solutions of 1-4 after storage in ambient conditions for
one week, indicating the high environmental stability of
these compounds.
The electrochemical properties of DTTDIs 1-4 were
examined by cyclic voltammetry (CV). The measurements
were performed in CH2Cl2, and the data are shown in
Figure 1b. No obvious peaks were observed for DTTDIs
upon oxidation up to 1.8 V, indicating that the substitution
of the imide groups remarkably enhanced the electron
affinity of the DTT core (E1/2ox = þ0.98 V).18 A reversible
and two irreversible reduction waves were observed for 1and
2, while only two reduction waves (one reversible, one irrever-
sible) were seen for 3 and 4. The initial reduction peaks of 3
and 4(E1/2red1 of -0.78 and -0.82 V for 3and 4, respectively)
were shifted to positive values, compared with those of 1 and
2 (E1/2red1 of -0.92 and -0.88 V for 1 and 2, respectively).
These results suggest that the fluoroalkyl substituents in-
duced a stronger electron-accepting ability than that of the
All linear fused thiophene-based diimides 1-4 were
bright yellow crystals or powders and soluble in polar
solvents, such as CH2Cl2, THF, and chlorobenzene. The
absorption and emission spectra of 1-4 in diluted
CH2Cl2 are shown in Figure 1a. The absorptions of the
DTTDIs (λmax ≈ 405-410 nm) were significantly red-
shifted, compared to that of the DTT (λmax ≈ 300 nm).18
Minor red shifts of 2-15 nm were also exhibited, com-
pared to those of the R,R-dicarbonyl substituted DTTs,19
(13) Lin, H.; Xu, W.; Zhu, D. J. Mater. Chem. 2010, 20, 884.
(14) Frey, J.; Proemmel, S.; Armitage, M. A.; Holmes, A. B. Org.
Synth. 2006, 83, 209.
(15) Webster, O. W.; Sharkley, W. H. J. Org. Chem. 1962, 27, 3354.
(16) Niebel, C.; Lokshin, V.; Khodorkovsky, V. Tetrahedron Lett.
2008, 49, 5551.
(17) Attempts to synthesize 1-4 from 7 directly failed due to the low
reactivity of 7.
(18) Sanchez-Carrera, R. S.; Odom, S. A.; Kinnibrugh, T. L.; Sajoto,
T.; Kim, E.-G.; Timofeeva, T. V.; Barlow, S.; Coropceanu, V.; Marder,
ꢀ
S. R.; Bredas, J.-L. J. Phys. Chem. B 2010, 114, 749.
(19) (a) Chen, M.-C.; Chiang, Y.-J.; Kim, C.; Guo, Y.-J.; Chen,
S.-Y.; Liang, Y.-J.; Huang, Y.-W.; Hu, T.-S.; Lee, G.-H.; Facchetti, A.;
Marks, T. J. Chem. Commun. 2009, 45, 1846. (b) Kim, C.; Chen, M.-C.;
Chiang, Y.-J.; Guo, Y.-J.; Youn, J.; Huang, H.; Liang, Y.-J.; Lin, Y.-J.;
Huang, Y.-W.; Hu, T.-S.; Lee, G.-H.; Facchetti, A.; Marks, T. J. Org.
Electron 2010, 11, 803.
1412
Org. Lett., Vol. 13, No. 6, 2011

By slow evaporation of a chloroform solution, large
area (>0.3 cm2), single crystals of compound 1 could be
obtained. The XRD patterns of DTTDI indicated that the
core exhibited a planar structure, as expected (Figure 2a).
The two terminal propyl chains were turned out of the
plane, affording a chairlike configuration (Figure 2b).
Compound 1 displayed a layered herringbone arrange-
ment with two orientations in the crystals (Figure 2c).
S
π and C-O π interactions were observed in each
3 3 3
3 3 3
herringbone packing, with a herringbone angle of ∼55.7°.
Between the two differently orientated herringbone
packages, π-π, C-O S, and S S interactions, as
3 3 3
3 3 3
well as hydrogen bonds between the oxygen atom of the
imides and the atoms in alkyl chains, existed (Figure 2d).
The distance of the π-π interaction was approximately
˚
3.580 A, which was comparable to that of the R,R-dicarbonyl
substituted DTTs.19 All of these intermolecular interactions
would benefit the charge transport in single crystals.9,21
In summary, we report the synthesis and characteriza-
tion of linear fused thiophene-based diimides, termed
DTTDIs. The developed synthetic route was expected to
be feasible for the preparation of novel types of fused
thiophene-2,3-imides to present various functionalities
around the imide rings. The optical, electrochemical,
and thermal properties of the DTTDIs, as well as the
single crystal XRD diffraction pattern results, suggest
that these molecules may have various potential applica-
tions in organic electronics. Further studies on these
avenues are currently underway.
Figure 2. X-ray crystal structure of DTTDI 1. (a,b) The molecular
structure of 1 is represented. (c) The molecular packing of 1 in
crystals with layered herringbone structures is shown. (d) The short
interactions existing between adjacent herringbone packages are
depicted. H atoms were omitted for clarity in (a-c).
alkyl chain substituents. The reduction potentials of the
DTTDIs were larger than those of the unsubstituted ADIs
(E1/2
those of the NDIs (E1/2red1 of -0.67 V for NDI-Cy).20 The
LUMO energy levels of 1-4 were estimated by the reduction
of -1.17 V for ADI-Cy)4 but were smaller than
red1
potentials (ELUMO =-(E1/2 þ 4.44) eV),1a -3.52, -3.56,
red1
-3.66, and -3.62 V for 1-4, respectively. The low-lying
LUMO levels indicated that the DTTDIs might serve as
n-type semiconductor candidates. The frontier orbitals of the
DTTDIs were also estimated through density functional
theory (DFT) calculations (using the Gaussian 03 program
at the B3LYP/6-31G* level), using 3 and methyl diimides of
DTT as models (see SI). The calculations showed that the
extension of the DTT cores with diimides reduced both
HOMO and LUMO levels, and the LUMO energy level of
fluoroalkyl diimide 3was 0.3 eV lower than that of the methyl
diimides. This tendency was in good agreement with the
experimental results.
Acknowledgment. This work was supported by the Na-
tional Natural Science Foundation of China (21002119,
60771031), Shanghai Natural Science Foundation
(10ZR1436900), and Chinese Academy of Sciences.
Supporting Information Available. Synthetic proce-
dures, characterization data for all compounds 1-8,
density functional theory (DFT) calculations of DTTDIs,
and X-ray crystallographic data of compound 1 in CIF
format are presented here. The material is available free
of charge via Internet at http://pubs.acs.org.
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Higuchi, H.; da Silva; Filho, D. A.; Young, V. G.; Bredas, J.-L.; Mann,
K. R. J. Am. Chem. Soc. 2004, 126, 15295.
(20) Erten, S.; Alp, S.; Icli, S. J. Photochem. Photobiol. A 2005,
175, 214.
Org. Lett., Vol. 13, No. 6, 2011
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