One-pot [1+1+1] synthesis of dithieno[2,3-b:3′,2′-d]thiophene (DTT) and their functionalized derivatives for organic thin-film transistors

Article abstract of DOI:10.1039/b820621j

A facile one-pot [1+1+1] synthesis of dithieno[2,3-b:3′,2′-d] thiophene (DTT; 1) has been achieved, enabling the efficient realization of a new DTT-based semiconductor series for organic thin-film transistors (OTFTs).

Full text of DOI:10.1039/b820621j

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One-pot [1+1+1] synthesis of dithieno[2,3-b:30,20-d]thiophene (DTT)
and their functionalized derivatives for organic thin-film transistorsw
Ming-Chou Chen,*a Yen-Ju Chiang,a Choongik Kim,b Yue-Jhih Guo,a Sheng-Yu Chen,a
You-Jhih Liang,a Yu-Wen Huang,a Tarng-Shiang Hu,c Gene-Hsiang Lee,d Antonio Facchettib
and Tobin J. Marksb
Received (in Cambridge, UK) 18th November 2008, Accepted 16th January 2009
First published as an Advance Article on the web 20th February 2009
DOI: 10.1039/b820621j
A facile one-pot [1+1+1] synthesis of dithieno[2,3-b:30,20-d]-
thiophene (DTT; 1) has been achieved, enabling the efficient
realization of a new DTT-based semiconductor series for organic
thin-film transistors (OTFTs).
with appropriate electron-withdrawing groups to achieve new
DTT (3–6) and TT-based (7, 8) semiconductors. Since the key
building block is the DTT core, a convenient/efficient/cheaper
one-pot [1+1+1] synthesis of DTT has been developed, which
dispenses with the requirement for expensive bis(phenylsulfonyl)
sulfide, and affords yields comparable to those pioneered by
Janssen14a and Hellberg.14b Although an improved synthetic
route via double annelation of tetrabromothiophene was
developed by Holmes et al.,14c this approach requires four
steps, long reaction times (Bone week), and tedious workup
procedures.15 Our one-pot approach is shown in Scheme 1.
3-Bromothiophene was first lithiated with n-BuLi, followed
first by S8 and then TsCl addition. Then, the mixture was
treated with 3-lithiothiophene, dilithiated with n-BuLi and
ring closure was achieved with CuCl2 to afford DTT in
430% yield.16 Furthermore, as shown in Scheme 2, this
simple route enables the synthesis of more fused thiophene
rings (e.g., tetrathienoacene (TTA)17 was obtained in B27%
yield) and particularly asymmetric fused rings (e.g. DS-DTT)16
which can not be easily obtained by the above previous
methods.
Organic thin-film transistors (OTFTs) have attracted attention
for potential applications in flexible displays and inexpensive
electronic paper.1,2 Most of the developed OTFT semiconductors,
such as pentacene derivatives,3 oligo/polythiophenes,4
fused-thiophenes,5 and anthradithiophenes (ADTs)6 are
hole-transporting (p-type) materials, while the development
of efficient electron-transporting (n-type) semiconductors is
more recent.7 Since n-type semiconductors are key components
for the fabrication of organic p–n junctions, bipolar
transistors, and complementary circuits,8 we are particularly
interested in exploring new electron transport candidates.
Fused thiophene-based materials (from two to seven fused
rings)9 have found application in several electronic and optical
device types and are promising OTFT semiconductors.
However, their n-channel semiconductors are unknown. Recently,
fluoro-,7a perfluoroalkyl-,7b,10 perfluoroaryl-,7c,11 carbonyl-12
and cyano-13 modified p-conjugated cores have been synthe-
sized and shown to exhibit excellent n-channel TFT transport.
Particularly, soluble quaterthiophenes bearing the perfluoro-
benzoyl (COC6F5) substitutent (DFCO-4T) exhibit high elec-
Perfluorobenzoyl functionalization of the DTT core should
afford good n-type candidate 3 (DFB-DTT), which was
isolated by two routes as shown in Scheme 3. Route I provides
the most efficient path to 3 (36% yield) whereas route II
produces 3 in lower yields (o30%) with a considerable
amount of mono-acylated FB-DTT side product, even after
refluxing for one week. Nevertheless, asymmetric FBB-DTT
(4) can be obtained from FB-DTT in 57% yield via route II.16
Benzoyl- and 2-thienoyl-substituted derivatives 5–8 were also
obtained in good yields via route II as shown in Scheme 4.
tron mobilities both as solution-cast (up to 0.21 cm2 Vꢀ1 sꢀ1
and vapor-deposited (up to 0.45 cm2 Vꢀ1 ꢀ1) films.12
)
s
Following this molecular design strategy, we report here the
use of dithieno[2,3-b:30,20-d]thiophene (DTT; 1), and for
comparison thienothiophene (TT; 2), cores in combination
a Department of Chemistry, National Central University, Chung-Li,
Taiwan, 32054, ROC. E-mail: mcchen@ncu.edu.tw
Scheme 1 One-pot [1+1+1] synthesis of DTT.
b Department of Chemistry and the Materials Research Center,
Northwestern University, 2145 Sheridan Rd., Evanston, Illinois,
60208-3113, USA. E-mail: t-marks@northwestern.edu
c Industrial Technology Research Institute, Taiwan, ROC
d Instrumentation Center, National Taiwan University, Taiwan,
Taipei 10660, ROC. E-mail: ghlee@ntu.edu.tw
w Electronic supplementary information (ESI) available: Synthetic
procedures, characterization data for all compounds 3–8. CCDC
701639, 701640 and 710106. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/b820621j
Scheme
2 One-pot synthesis of tetrathienoacene (TTA) and
asymmetric DS-DTT.
ꢁc
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Table 1 Physical properties of compounds 3–8
Potentialb
UV-Visa
DEgap/V
lmax/nm
Ered/V
Eox/V
UV
DPVb
3
4
5
6
7
8
403, 383
399, 382
395, 378
406, 391
343
ꢀ0.81
ꢀ1.00
ꢀ1.12
ꢀ1.06
ꢀ1.09
ꢀ1.02
2.16
2.07
1.96
1.93
2.21
2.13
2.86
2.88
2.93
2.82
3.10
3.05
2.97
3.07
3.08
2.99
3.30
3.15
362
a
b
In o-C6H4Cl2. In o-C6H4Cl2 at 25 1C by DPV (see Fig. S10, ESIw
for details).
Scheme 3 Synthetic routes to DFB-DTT (3) and FBB-DTT (4).
The HOMO–LUMO energy gaps calculated from the onset of
the optical absorption (2.8–3.1 eV) increase in the order: 6 B 3
o 4 o 5 o 8 o 7. The photooxidative stability of the DTTs
was investigated by monitoring the absorbance decay at lmax
of 3–8 in aerated CHCl3 solutions exposed to white light
(fluorescent lamp) at 25 1C. Under these conditions for 4 days,
no decomposition was observed for any compound, demons-
trating the favorable stability of these materials.
Differential pulse voltammograms (DPV) of 3–8 were
recorded in o-C6H4Cl2 at 25 1C, and the reductive and
oxidative potentials are summarized in Table 1. The DPV of
3 exhibits an oxidation peak at +2.16 V and a reduction peak
at ꢀ0.81 V (using ferrocene–ferrocenium as internal standard).
In contrast, both the oxidation and reduction potentials
of asymmetric 4 (Eox = +2.07 V, Ered = ꢀ1.00) and 5
(Eox = +1.96 V, Ered = ꢀ1.12) are shifted to more negative
values than those observed for 3, which can be attributed to
the electron-withdrawing effect of the perfluorobenzoyl
substituents. The electrochemically derived HOMO and
LUMO energies are shown in Fig. 2.16 Clearly, fluoroaryl-
carbonyl substitution in 3 and 4 lowers both the HOMO and
LUMO energies compared to 5. The electrochemically derived
Scheme 4 Syntheses of 5–8.
The crystal structures of compounds 3–5 are shown in
Fig. 1.16 As found for other acyl-oligothiophenes,12 the
benzoyl moieties are not coplanar with the DTT cores, but
are twisted at angles of B52/531, 30/551 and 451 for 3, 4 and 5,
respectively. The crystal structures of 3/4 exhibit intra-
molecular and intermolecular ortho-F (perfluorophenyl)ꢂ ꢂ ꢂH
(DTT core) contacts, as shown in Fig. 1A and B. The distances
between the planar DTT cores are 4 (B3.50 A) o 5 (3.68 A) o
3 (3.74 A), which is in line with the mobility values (vide infra).
The molecular packing is considerably different for these three
DTTs, with 3 exhibiting a ‘‘dimer-like/1-D-slipped’’ motif
(Fig. 1A), and 5 a typical herringbone structure (Fig. 1C).
On the other hand asymmetric structure 4, with extensive
intermolecular Hꢂ ꢂ ꢂF interactions, exhibits a tetramer-like
packing with the shortest DTT plane distance of B3.50 A
(Fig. 1B). The Sꢂ ꢂ ꢂS distances among DTT cores are shown in
Fig. 1 with 4 having the shortest distances.
Several physical properties of these new molecules are sum-
marized in Table 1 and Table S1 (ESIw).16 As expected, the
UV-Vis absorption spectra of 3–8 in o-C6H4Cl2 are significantly
red shifted (lmax B400 nm) compared to 1 (lmax B300 nm).
Fig. 2 The electrochemically derived HOMO and LUMO energy of
3–8 by DPV in o-C6H4Cl2 at 25oC.
Fig. 1 Crystal structures of 3 (A), 4 (B) and 5 (C). (A) Dimer-like stacking in 3 and Sꢂ ꢂ ꢂS distances in DTT cores of 3. (B) Tetramer-like stacking
in 4 and side view of DTT cores stacking in 4. (C) The molecular packing of 5 and the herringbone packing and Sꢂ ꢂ ꢂS distances of DTT cores in 5.
ꢁc
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Table
(Ion : Ioff) and threshold voltages (VT) for OTFTs fabricated with
semiconductors 3–8
2
Charge carrier mobilities (m), current on/off ratios
J. M. Fre
´
chet, Chem. Rev., 2007, 107, 1066; (c) B. A. Jones,
A. Facchetti, M. R. Wasielewski and T. J. Marks, J. Am. Chem.
Soc., 2007, 129, 15259.
2 For recent studies, see: (a) S. Subramanian, S. P. Park, S. R. Parkin,
V. Podzorov, T. N. Jackson and E. J. Anthony, J. Am. Chem. Soc.,
2008, 130, 2706; (b) M. L. Tang, A. D. Reichardt, N. Miyaki,
R. M. Stoltenberg and Z. Bao, J. Am. Chem. Soc., 2008, 130,
6064; (c) C. B. Nielsen, A. Angerhofer, K. A. Abboud and
J. R. Reynolds, J. Am. Chem. Soc., 2008, 130, 9734;
(d) M. L. Navacchia, M. Melucci, L. Favaretto, A. Zanelli,
M. Gazzano, A. Bongini and G. Barbarella, Org. Lett., 2008, 10,
3665; (e) P.-L. T. Boudreault, S. Wakim, N. Blouin, M. Simard,
C. Tessier, Y. Tao and M. Leclerc, J. Am. Chem. Soc., 2007, 129,
9125; (f) R. P. Ortiz, J. Casado, V. Hernandez, J. T. L. Navarrete,
P. M. Viruela, E. Orti, K. Takimiya and T. Otsubo, Angew. Chem.,
Int. Ed., 2007, 46, 9057; (g) Y. Wang, S. R. Parkin, J. Gierschner and
M. D. Watson, Org. Lett., 2007, 9, 4499; (h) R. P. Ortiz, J. Casado,
V. Hernandez, J. T. L. Navarrete, E. Orti, P. M. Viruela, B. Milian,
S. Hotta, G. Zotti, S. Zecchin and B. Vercelli, Adv. Funct. Mater.,
2006, 16, 531; (i) A. Berlin, S. Grimoldi, G. Zotti, R. M. Osuna,
M. C. R. Delgado, R. P. Ortiz, J. Casado, V. Hernandez and
J. T. L. Navarrete, J. Phys. Chem. B, 2005, 109, 22308;
(j) N. Drolet, J.-F. Morin, N. Leclerc, S. Wakim, Y. Tao and
M. Leclerc, Adv. Funct. Mater., 2005, 15, 1671.
3 (a) D. H. Kim, D. Y. Lee, H. S. Lee, W. H. Lee, Y. H. Kim, J. I. Han
and K. Cho, Adv. Mater., 2007, 19, 678; (b) Y. Li, Y. Wu, P. Liu,
Z. Prostran, S. Gardner and B. S. Ong, Chem. Mater., 2007, 19, 418.
4 I. Mcculloch, M. Heeney, C. Bailey, K. Genevicius, I. Macdonald,
M. Shkunov, D. Sparrowe, S. Tierney, R. Wagner, W. Zhang,
M. L. Chabinyc, R. J. Kline, M. D. Mcgehee and M. F. Toney,
Nat. Mater., 2006, 5, 328.
5 (a) K. Xiao, Y. Liu, T. Qi, W. Zhang, F. Wang, J. Gao, W. Qiu,
Y. Ma, G. Cui, S. Chen, X. Zhan, G. Yu, J. Qin, W. Hu and
D. Zhu, J. Am. Chem. Soc., 2005, 127, 13281; (b) also see examples
in ref. 9.
Compound Substrate TDa/1C mb/cm2 Vꢀ1 sꢀ1 Ion : Ioff VT/V
3 (n-type)
HMDS
25
50
70
90
70
25
60
1.5 ꢃ 10ꢀ3
1 ꢃ 10ꢀ4
0.03
106
107
107
107
106
106
105
+35
+68
+42
ꢀ53
ꢀ48
ꢀ72
ꢀ84
3 (n-type)c HMDS
4 (n-type)
5 (p-type)
6 (p-type)
7 (p-type)
8 (p-type)
HMDS
HMDS
Bare
Bare
Bare
0.01
2 ꢃ 10ꢀ4
1 ꢃ 10ꢀ4
1 ꢃ 10ꢀ5
a
b
Substrate deposition temperature. Calculated in the saturation
c
regime. Typical standard deviations are o10%. Measured in air.
HOMO–LUMO energy gaps are ranked as 6 B 3 o 4 o 5 o
8 o 7, which is consistent with the values obtained from
optical spectroscopy.
The semiconducting properties of these systems were
assessed in top-contact OTFTs fabricated by vapor-depositing
3–8 films on bare and hexamethyldisilazane (HMDS)-treated
SiO2/p+–Si substrates, followed by Au deposition through a
shadow mask to define the source and drain electrodes. OTFT
characterization was performed under vacuum and pre-
liminary OTFT data are summarized in Table 2. Perfluoro-
benzoyl substitution is found to be effective in promoting
n-type transport in 3 and 4, with an electron mobility of
0.0015 and 0.03 cm2 Vꢀ1 sꢀ1, respectively. To our knowledge,
both are the first DTT-based semiconductors exhibiting
electron transport in OTFT devices.18 Compared to DFCO-4T,12
the lower mobilities could be ascribed to the larger interplanar
p–p separation distance (3.74 A for 3, 3.56 A for 4, vs. 3.5 A
for DFCO-4T) caused by the non-negligible F–H interactions
in 3 and 4.19 Interestingly, the intermolecular Hꢂ ꢂ ꢂF inter-
actions in asymmetric 4, empowering the shortest DTT cores
distance in this study, reveals the potential utility of this
asymmetric design for other n-type systems. In contrast, the
dibenzoyl and di(2-thienyl)carbonyl substituted DTT and TT
derivatives exhibit exclusively p-type transport, with the best
hole mobility of 0.01 cm2 Vꢀ1 sꢀ1 observed for DB-DTT (5),
which is comparable to that of DPCO-4T (0.04 cm2 Vꢀ1 sꢀ1).12
In summary, a convenient/efficient/cost-effective one-pot
[1+1+1] synthesis of DTT has been achieved, which can also
enable the realization of asymmetric and fused thiophenes.
Diperfluorobenzoyl DFB-DTT (3) and asymmetric FBB-DTT
(4) exhibit n-type transport with mobility up to 0.03 cm2 Vꢀ1 sꢀ1
whereas DB-DTT (5) shows only hole transport.19 These
results provide new understanding of the structural character-
istics of DTT-based molecules and the advantages of using this
stable core for designing more soluble derivatives.
6 (a) M. M. Payne, S. R. Parkin, J. E. Anthony, C.-C. Kuo and
T. N. Jackson, J. Am. Chem. Soc., 2005, 127, 4986; (b) M.-C. Chen,
C. Kim, S.-Y. Chen, Y.-J. Chiang, M.-C. Chung, A. Facchetti and
T. J. Marks, J. Mater. Chem., 2008, 18, 1029.
7 (a) Y. Sakamoto, T. Suzuki, M. Kobayashi, Y. Gao, Y. Fukai,
Y. Inoue, F. Sato and S. Tokito, J. Am. Chem. Soc., 2004, 126,
8138; (b) A. Facchetti, M. Mushrush, M.-H. Yoon,
G. R. Hutchison, M. A. Ratner and T. J. Marks, J. Am. Chem.
Soc., 2004, 126, 13859; (c) M.-H. Yoon, A. Facchetti, C. L. Stern
and T. J. Marks, J. Am. Chem. Soc., 2006, 128, 5792;
(d) M.-H. Yoon, C. Kim, A. Facchetti and T. J. Marks, J. Am.
Chem. Soc., 2006, 128, 12851.
8 (a) M.-H. Yoon, S. A. DiBenedetto, A. Facchetti and T. J. Marks,
J. Am. Chem. Soc., 2005, 127, 1348; (b) ref. 7a.
9 (a) For three-fused ring review, see: T. Ozturk, E. Erdal Ertasb and
O. Mert, Tetrahedron, 2005, 61, 11055; (b) for five-fused ring, see:
X. Zhang, A. P. Cote and A. Matzger, J. Am. Chem. Soc., 2005, 127,
10502; (c) For 6 fused ring see: T. Okamoto, K. Kudoh, A. Wakamiya
and S. Yamaguchi, Org. Lett., 2005, 7, 5301; (d) For 7 fused ring see:
M. He and F. Zhang, J. Org. Chem., 2007, 72, 442, and ref. 5.
10 A. Facchetti, M.-H. Yoon, C. L Stern, G. R. Hutchison, M. A.
Ratner and T. J. Marks, J. Am. Chem. Soc., 2004, 126, 13480.
11 A. Facchetti, M.-H. Yoon, C. L. Stern, H. E. Katz and
T. J. Marks, Angew. Chem., Int. Ed., 2003, 42, 3900.
12 J. A. Letizia, A. Facchetti, C. L. Stern, M. A. Ratner and
T. J. Marks, J. Am. Chem. Soc., 2005, 127, 13476.
13 B. A. Jones, A. Facchetti, T. J. Marks and W. R. Wasielewski,
Chem. Mater., 2007, 19, 2703.
We thank the National Science Council, Taiwan, Republic
of China (Grant Numbers NSC95-2113-M-008-008-MY2,
NSC97-2113-M-008-003 and NSC97-2628-M-008-019) for
support. Financial assistance for this research was partially
provided by the NSF-MRSEC program through the
Northwestern Materials Research Center (DMR-0520513).
14 (a) F. De Jong and M. J. Janssen, J. Org. Chem., 1971, 36, 1645;
(b) F. Allared, J. Hellberg and T. Remonen, Tetrahedron Lett.,
2002, 43, 1553; (c) J. Frey, A. D. Bond and A. B. Holmes, Chem.
Commun., 2002, 2424.
15 The average total yield of DTT we obtained following Holmes’
four steps in ref. 14c is o30%.
16 See ESIw for details.
17 Y. Mazaki and K. Kobayashi, Tetrahedron Lett., 1989, 30, 3315.
18 Ambipolar transport in these DTT materials were not observed
and details of the studies will be discussed in the future full paper.
19 In addition to the larger intermolecular core distance, the lower
conjugation of DTTs may be responsible for the lower mobilities.
Notes and references
1 For recent discussions of this topic, see: (a) C. Kim, A. Facchetti
and T. J. Marks, Science, 2007, 318, 76; (b) A. R. Murphy and
ꢁc
This journal is The Royal Society of Chemistry 2009
1848 | Chem. Commun., 2009, 1846–1848