Functionalized dithieno[2,3-b:3′,2′-d]thiophenes (DTTs) for organic thin-film transistors

Article abstract of DOI:10.1016/j.orgel.2010.01.022

A series of dithieno[2,3-b:3′,2′-d]thiophene (DTT; 1) derivatives were synthesized and characterized. Facile, one-pot [2 + 1] and [1 + 1 + 1] synthetic methods of DTT were developed, which enabled the efficient realization of a new DTT-based semiconductor series for organic thin-film transistors (OTFTs). These DTTs are end-functionalized with perfluorophenyl (FP-), perfluorobenzoyl (FB-), benzoyl (B-), 2-naphthylcarbonyl (Np-), 2-benzothiazolyl (BS-), 2-thienylcarbonyl (T-), and 2-(5-hexyl)thienylcarbonyl (HT-) groups. The molecular structures of DFP-DTT (3), DFB-DTT (4), FBB-DTT (5), DB-DTT (6), and DNp-TT (7) were determined via single-crystal X-ray diffraction. Our studies reveal that the majority of these carbonyl-containing derivatives exhibit p-channel transport with hole mobilities of up to 0.01 cm²/Vs for DB-DTT and DBS-DTT, while perfluorobenzoyl and perfluorophenyl-substituted compounds exhibit n-channel transport with mobilities up to 0.002 cm²/Vs for DFB-DTT, 0.03 cm²/Vs for FBB-DTT, and 0.07 cm²/Vs for DFP-DTT, rendering the latter the DTT derivative currently having the highest electron mobility in OTFT devices. Within this family, the carrier mobility values are strongly dependent upon the semiconductor growth temperature and the dielectric surface treatment.

Full text of DOI:10.1016/j.orgel.2010.01.022

Organic Electronics 11 (2010) 801–813
Contents lists available at ScienceDirect
Organic Electronics
journal homepage: www.elsevier.com/locate/orgel
Functionalized dithieno[2,3-b:30,20-d]thiophenes (DTTs) for organic
thin-film transistors
b
b
a
Choongik Kim a, Ming-Chou Chen b, , Yen-Ju Chiang , Yue-Jhih Guo , Jangdae Youn ,
*
Hui Huang a, You-Jhih Liang b, Yu-Jou Lin b, Yu-Wen Huang b, Tarng-Shiang Hu b,c
,
Gene-Hsiang Lee d, Antonio Facchetti a, , Tobin J. Marks
a,
*
*
a Department of Chemistry and the Materials Research Center, Northwestern University, 2145 Sheridan Rd., Evanston, IL 60208-3113, USA
b Department of Chemistry, National Central University, Jhong-Li, Taiwan 32054, ROC
c Industrial Technology Research Institute, Taiwan, ROC
d Instrumentation Center, National Taiwan University, Taipei 10660, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
A series of dithieno[2,3-b:30,20-d]thiophene (DTT; 1) derivatives were synthesized and
characterized. Facile, one-pot [2 + 1] and [1 + 1 + 1] synthetic methods of DTT were devel-
oped, which enabled the efficient realization of a new DTT-based semiconductor series for
organic thin-film transistors (OTFTs). These DTTs are end-functionalized with perfluor-
ophenyl (FP-), perfluorobenzoyl (FB-), benzoyl (B-), 2-naphthylcarbonyl (Np-), 2-benzo-
thiazolyl (BS-), 2-thienylcarbonyl (T-), and 2-(5-hexyl)thienylcarbonyl (HT-) groups. The
molecular structures of DFP-DTT (3), DFB-DTT (4), FBB-DTT (5), DB-DTT (6), and DNp-
TT (7) were determined via single-crystal X-ray diffraction. Our studies reveal that the
majority of these carbonyl-containing derivatives exhibit p-channel transport with hole
mobilities of up to 0.01 cm2/Vs for DB-DTT and DBS-DTT, while perfluorobenzoyl and per-
fluorophenyl-substituted compounds exhibit n-channel transport with mobilities up to
0.002 cm2/Vs for DFB-DTT, 0.03 cm2/Vs for FBB-DTT, and 0.07 cm2/Vs for DFP-DTT, render-
ing the latter the DTT derivative currently having the highest electron mobility in OTFT
devices. Within this family, the carrier mobility values are strongly dependent upon the
semiconductor growth temperature and the dielectric surface treatment.
Article history:
Received 7 December 2009
Received in revised form 19 January 2010
Accepted 20 January 2010
Available online 2 February 2010
Keywords:
Organic thin-film transistor
Fused thiophene
Organic semiconductor
Ó 2010 Elsevier B.V. All rights reserved.
1. Introduction
p-channel materials due to the relatively air-stable hole-
transporting characteristics of the cores; the HOMO energy
Over the past two decades, organic semiconducting
materials have been extensively developed and employed
in organic thin-film transistors (OTFTs) for potential appli-
cations in low cost/printable electronics, such as flexible
displays, RF-ID components, and e-papers [1,2]. Most of
the previously developed organic semiconductors are
pentacene [3], oligothiophene [4], fused thiophene [5],
and anthradithiophene derivatives [6]. These are mostly
levels align well with the work functions of the air-stable
electrodes (e.g., Au = 5.1 eV). The development of efficient
n-channel (electron-transporting) semiconductors is more
recent and relatively rare [7]. However, to realize comple-
mentary circuit designs that would enable simpler circuit
design and higher operating speeds [8], further develop-
ment of n-channel organic semiconductors is essential.
Fused thiophene-based materials are some of the most
promising organic semiconductors for applications in elec-
tronic and optical devices [5,9]. Several p-channel materi-
als based on 3-ring (dithieno[2,3-b:30,20-d]thiophene,
DTT; 1) [10] fused thiophene derivatives with hole mobil-
ities of 0.1–0.6 cm2/Vs have been reported. For example,
* Corresponding authors. Tel.: +1 1886 34273253; fax: +1 1886
34227664.
E-mail addresses: mcchen@ncu.edu.tw (M.-C. Chen), a-facchetti@
northwestern.edu (A. Facchetti), t-marks@northwestern.edu (T.J. Marks).
1566-1199/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.orgel.2010.01.022

802
C. Kim et al. / Organic Electronics 11 (2010) 801–813
DP-DTT (2) exhibit excellent p-channel transport with hole
mobilities of 0.42 cm2/Vs [10a]. However, n-channel DTT-
based semiconductors have been unknown until recently
[11]. One approach to realizing electron transport in OTFTs
is to functionalize p-channel semiconductors with strong
electron-withdrawing and/or perfluorinated substituents,
such as fluoro- [7a], perfluoroalkyl- [7b,12], perfluoroaryl-
[7c,13], carbonyl- [14], cyano- [15], and trifluoromethyl-
phenyl- [16] groups. Perfluorobenzoyl (COC6F5)-substi-
tuted quarter thiophenes (DFCO-4T) exhibit especially
high electron mobilities of 0.45 cm2/Vs for vapor-deposited
films and 0.21 cm2/Vs for solution-cast films [14a].
13C NMR spectra were recorded on a Bruker 500, 300, or a
Bruker DRX-200 instrument. Chemical shifts for 1H and 13
C
spectra were referenced to solvent peaks. 19F NMR spectra
were referenced to external CFCl3. Differential scanning
calorimetry (DSC) was carried out on a Mettler DSC 822
instrument, and calibrated with a pure indium sample at
a
scan rate of 10 K/min. Thermogravimetric analysis
(TGA) was performed on a Perkin–Elmer TGA-7 thermal
analysis system using dry nitrogen as a carrier gas at a flow
rate of 40 mL/min. The UV–Vis absorption and fluorescence
spectra were obtained using JASCO V-530 and Hitachi F-
4500 spectrometers, respectively, and all spectra were
measured in a specified solvent at room temperature. The
IR spectra were obtained using a JASCO FT/IR-4100 spec-
trometer. Differential pulse voltammetry experiments
were performed with a CH Instruments model CHI621C
Electrochemical Analyzer. All measurements were carried
out at a specified temperature with a conventional three-
electrode configuration consisting of a platinum disk work-
ing electrode, an auxiliary platinum wire electrode, and a
non-aqueous Ag reference electrode. The supporting elec-
trolyte was 0.1 M tetrabutylammonium hexafluorophos-
phate (TBAPF6) in a specified dry solvent. All potentials
reported are referenced to an Fc+/Fc internal standard (at
+0.6 V). Elemental analyses were performed on a Heraeus
CHN–O-Rapid elemental analyzer. Mass spectrometric
data were obtained with a JMS-700 HRMS instrument.
Prime grade silicon wafers (p+-Si) with ꢁ300 nm ( 5%)
thermally grown oxide (from Montco Silicon) were used
as device substrates. Preparation of DTT (1) and TTA (via
one-pot [1 + 1 + 1] synthesis), DFB-DTT (4), FBB-DTT (5),
DB-DTT (6), and DT-DTT (9) as well as X-ray crystal struc-
ture determinations of compounds 4, 5, and 6 see support-
ing information of Ref. [11].
O
F
F
F
F
F
O
F
S
S
S
S
F
F
F
F
DFCO-4T
Following a similar molecular design strategy, we partly
communicated synthetic approaches to several DTT-based
compounds and their physicochemical properties [11]. Ini-
tial TFT results showed that two of these materials are n-
channel semiconductors with electron mobilities of 10ꢀ3
–
0.03 cm2/Vs, and these were the first reports on DTT-based
semiconductors. Although perfluorophenyl-substituted
DFP-DTT (3) has been reported [17], its OTFT performance
has not been explored. Herein, we report in full on the syn-
thesis, characterization, and OTFT performance of DTT-
based (3–10) organic semiconductors with appropriate
electron-withdrawing groups, as shown in Fig. 1.
2. Experimental section
2.1. Materials and methods
2.2. Synthesis
All chemicals and solvents were of reagent grade and
were obtained from Aldrich, Arco, or TCI Chemical Co. Sol-
vents for reactions (toluene, benzene, ether, and THF) were
distilled under nitrogen from sodium/benzophenone ketyl,
and halogenated solvents were distilled from CaH2. 1H and
2.2.1. One-pot [2 + 1] synthesis of dithieno[2,3-b:30,20-d]thio-
phene (DTT; 1)
Under nitrogen at ꢀ78 °C, 2.5 M n-BuLi (48 mL in hex-
anes, 0.12 mol) was slowly added to an ether solution
F
F
F
F
O
F
F
F
F
F
F
O
F
O
F
F
F
S
S
S
S
F
F
F
F
S
S
F
F
S
S
S
DP-DTT (2)
DFP-DTT (3)
DFB-DTT (4)
F
F
O
F
O
O
O
O
S
S
S
S
S
S
F
F
S
S
S
DNp-DTT (7)
FBB-DTT (5)
DB-DTT(6)
O
O
O
O
N
S
N
S
S
S
S
S
S
S
S
S
S
S
C6H13
C6H13
S
S
S
DT-DTT (9)
DHT-DTT (10)
DBS-DTT (8)
Fig. 1. Chemical structures of dithieno[2,3-b:30,20-d]thiophene (DTT) derivatives employed in this study.

C. Kim et al. / Organic Electronics 11 (2010) 801–813
803
(48 mL) of 3-bromothiophene (12 mL, 0.12 mol), and the
mixture was stirred for 40 min. This solution was then
warmed to 0 °C to vacuum remove C4H9Br, and then ether
(48 mL) was added. (Note: without removing C4H9Br, 3-
butyl-S-thiophene will be generated as a major side prod-
uct after the S addition in the next step.) At ꢀ78 °C, sulfur
(1.92 g, 0.06 mol) was added into this ether solution, stir-
red for 30 min, warmed to 0 °C, and stirred for another
30 min. p-Toluenesulfonyl chloride (TsCl, 11.42 g,
0.06 mol) was added to this solution at 0 °C, stirred for
30 min, then warmed up to 40 °C for 4 h. Next, at 0 °C,
2.5 M n-BuLi (52.8 mL in hexanes, 0.132 mol) was slowly
added to this mixture, stirred for 30 min, and then refluxed
for 1 h. CuCl2 (18.32 g, 0.138 mol) was added to this mix-
ture at 0 °C, stirred for 1 h, warmed to room temperature,
and stirred overnight. Solids were removed by filtration,
and the organic + ether portion was collected, and then
chromatographed (silica gel; hexanes as the eluent). The
DTT product was recrystallized from hexanes as light-yel-
low powder to give a total of 2.94 g in a yield of ꢁ25.0%. 1H
NMR (CDCl3): d 7.36 (d, J = 5.4 Hz, 2H, 2,6-CH), 7.29 (d,
J = 5.1 Hz, 2H, 3,5-CH).
giving a bright-yellow solid (0.736 g) in a yield of 30%. 1H
NMR (CDCl3): d 8.46, (s, 1H), 8.02–7.94 (m, 4H), 7.98 (s,
1H), 7.66–7.62 (m, 2H), 7.55–7.52 (m, 2H). 13C NMR
(CDCl3): not sufficiently soluble to obtain a spectrum. Anal.
calcd. for C30H16O2S3: C, 71.40; H, 3.20; S, 19.06. Found: C,
71.58; H, 2.98; S, 19.38. Orange crystals of the title com-
pound suitable for X-ray diffraction were obtained by slow
diffusion of hexanes into CH2Cl2 solution. The molecular
structure of 7 has been confirmed by X-ray diffraction as
shown in Fig. 4 (cif file of 7 is in SI).
2.2.5. Synthesis of DBS-DTT (8)
Under nitrogen, 3 eq. of 2-aminothiophenol (0.25 g,
1.96 mmol) was added to a 50 mL C6H5Cl solution of
DTT-(COCl)2 (0.21 g, 0.65 mmol, generated from DTT-
(COOH)2 with SOCl2) and the mixture refluxed for 3 days.
The desired solid product was collected by filtration,
washed with ether, and then purified by gradient sublima-
tion at pressures of <10ꢀ4 Torr, giving a bright-yellow solid
(0.13 g) in a yield of 42%. 1H NMR (C2D2Cl4): not suffi-
ciently soluble to obtain a spectrum. Anal. calcd. for
C22H10N2S5: C, 57.11; H, 2.18; N, 6.05, S, 34.65. Found: C,
56.55; H, 2.25; N, 5.96, S, 34.19. MS (FAB) m/z) calcd. for
C22H10N2S5: 462 (M+). Found: 462.
2.2.2. One-pot [1 + 1 + 1] synthesis of pentathienoacene (PTA)
[5a]
Follow the one-pot [1 + 1 + 1] synthetic procedure [11],
3-bromothieno[3,2-b]thiophene [18] was employed to give
pentathienoacene (PTA) [5a] as yellow–orange powder in
2.2.6. Synthesis of DHT-DTT (10)
Under nitrogen,
a CH2Cl2 solution of DTT-(COCl)2
12% yield. 1H NMR (300 Hz; DMSO-d6):
J = 5.1 Hz, 2H, CH), 7.43 (d, J = 5.1 Hz, 2H, CH).
d 7.68 (d,
(0.35 g, 1.1 mmol), 2-hexylthiophene (0.39 g, 2.3 mmol),
and AlCl3 (1.47 g, 11.0 mmol) was stirred at room temper-
ature for 2 days. Water was added to quench the reaction
and the solvent was removed under vacuum. The solid
product was collected by filtration and washed with ether.
The product was purified by gradient sublimation at pres-
sures of <10ꢀ4 Torr, giving a bright-yellow solid (0.22 g) in
a yield of 35%. 1H NMR (CDCl3): d 8.12 (s, 2H), 7.81 (d,
J = 3.9 Hz, 2H), 6.91 (d, J = 3.9 Hz, 2H), 2.90 (t, J = 7.5 Hz,
4H), 1.75 (m, 4H), 1.42 – 1.30 (m, 12H), 0.90 (t, J = 7.5 Hz,
6H) Anal. calcd. for C30H32O2S5: C, 61.60; H, 5.51; S,
27.41. Found: C, 61.8; H, 5.82; S, 27.11. MS (EI) m/z) calcd.
for C30H32O2S5: 584(M+). Found: 584.
2.2.3. Synthesis of DP-DTT(2) [10a] and DFP-DTT (3) [19]
Under nitrogen at 0 °C, n-BuLi (2.5 M, 0.87 mL in hex-
anes, 2.18 mmol) was added to a 20 mL ether solution of
DTT (0.195 g, 0.99 mmol) and the mixture was stirred at
this temperature for 1 h. Tri-n-butylstannyl chloride
(0.60 mL, 2.18 mmol) in 10 mL ether was then added into
the mixture and stirred for 30 min at 0 °C. The mixture
was then stirred at room temperature for 12 h. Ether was
next removed under vacuum and 10 mL toluene solution
of dry bromopentafluorobenzene (0.30 mL, 2.11 mmol) as
well as 20 mL toluene solution of tetrakis(triphenylphos-
phine)palladium (50 mg, 0.04 mmol) were added and the
mixture was refluxed for 24 h. Water was added to quench
the reaction and the solid product was collected/filtered
and was washed with hexanes, which was further purified
by gradient sublimation at a pressure of <10ꢀ4 Torr, giving
a bright-yellow solid DFP-DTT (3; 259 mg) in a yield of
49.2%. 1H NMR (CDCl3): d 7.77, 19F NMR (CDCl3): d ꢀ139,
ꢀ154, and ꢀ161.
2.3. X-ray crystal structure determinations of compounds 3
and 7 [20]
The chosen crystal was mounted on a glass fiber. Data
collection for compound 3 was carried out on a Bruker
Smart Apex CCD diffractometer and compound 7 on a Non-
ius Kappa CCD diffractometer with Mo radiation
(k = 0.71073 Å) at 100(2) K and 200(2) K, respectively.
After data collection, the frame was integrated and absorp-
tion correction was applied. The initial crystal structure
was solved by direct methods, the structure solution was
expanded through successive least-squares cycles, and
the final solution was determined. All of the non-hydrogen
atoms were refined anisotropically. Hydrogen atoms at-
tached to carbon atoms were fixed at calculated positions
and refined using a riding mode. Crystal data, data collec-
tion, and refinement parameters are summarized in Table
S1.
DP-DTT (2) [10a] was prepared ꢁ50% yield via similar
procedure except using C6H6Br in the coupling reaction.
2.2.4. Synthesis of DNp-DTT (7)
Under nitrogen, AlCl3 (6.47 g, 47.8 mmol) was added to
a 100 mL CS2 solution of DTT (0.939 g, 4.78 mmol) and 2-
naphthalenecarbonyl chloride (2.03 g, 10.5 mmol), and
the mixture was stirred at 40 °C for 3 days. Water was then
added to quench the reaction, and the solid product was
washed with ether and ethyl acetate, which was then puri-
fied by gradient sublimation at a pressure of <10ꢀ4 Torr,

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C. Kim et al. / Organic Electronics 11 (2010) 801–813
2.4. Film deposition and characterization
in DTT in a much shorter synthetic time [21]. For this
one-pot [2 + 1] synthesis, 3-bromo-thiophene (2 eq.) was
first lithiated with n-BuLi (2 eq.), followed first by S8
(1 eq.) and then by TsCl (1 eq.) additions, as shown in
Scheme 1. Without isolating the product, the crude mix-
ture was dilithiated with n-BuLi and ring closure was
achieved with CuCl2. Finally, DTT was isolated in a yield
of about 25%. An alternative one-pot [1 + 1 + 1] synthesis
of DTT was also achieved and offered a higher yield (about
30%). The former [2 + 1] route is simpler, but the latter
[1 + 1 + 1] route enables the synthesis of fused thiophenes
with more rings (e.g., pentathienoacene (PTA) was ob-
tained in 12% yield) [5a] and asymmetric fused thiophenes
(e.g., DS-DTT) that are not feasible using previous methods,
as shown in Scheme 2 [11].
All p+-Si/SiO2 substrates were cleaned via sonication in
absolute ethanol for 3 min and then by oxygen plasma
treatment for 5 min (20 W, 0.5 Torr). For the SiO2 coating
layer, –SiMe3 groups were introduced using hexamethyldi-
silazane (HMDS) and were deposited by placing the clean
SiO2 substrates in a N2-filled chamber saturated with
HMDS vapor for 48–72 h. All of the semiconducting mate-
rials were vacuum deposited at ꢁ6 ꢂ 10ꢀ6 Torr (ꢁ500 Å,
0.2–0.3 Å/s) at the preset deposition temperatures (TD).
Thin films of organic semiconductors were analyzed by
atomic force microscopy (AFM) (JEOL-5200 Scanning Probe
Microscope) in the tapping mode, scanning electron
microscopy (Hitachi S-4800 FE-SEM), and wide angle h–
2h X-ray diffraction (XRD) (Rigaku ATXG) using monochro-
The synthesis of functionalized dithieno[2,3-b:30,20-
d]thiophene was achieved and is shown in Schemes 3–
6. Perfluorophenyl and perfluorobenzoyl functionalization
of the DTT core should result in good candidates of n-
channel semiconductors 3 (DFP-DTT) [17] and 4 (DFB-
DTT). Since the electronic performance of 3 has not been
examined, it was explored via the Stille coupling of the
DTT core with C6F5Br in ꢁ49% yield as shown in Scheme
3, which is comparable to the Suzuki coupling method.
For comparison DP-DTT (2) [10a] was also achieved via
similar synthetic route. Preparation of 4 was explored
using three different routes shown in Scheme 4. Route I,
via the double deprotonation of DTT and then double
acylation, provided the most efficient path to 4 (36%
yield). Route II, via the thermal acylation of DTT, pro-
duced the double acylation product 4 in a yield of <30%
with a considerable amount of mono-acylated FB-DTT
mated Cu K radiation. For TFT device fabrication, top-con-
a
tact electrodes (ꢁ70 nm) were deposited by evaporating
gold (ꢁ1 ꢂ 10ꢀ6 Torr) through a shadow mask with a chan-
nel length (L) of 100 lm and a channel width (W) of
5000 lm.
3. Results and discussion
3.1. Synthesis
Since the key building block is the DTT core, a conve-
nient, efficient, and cheap one-pot [2 + 1] synthesis of
DTT was explored. Our new route from inexpensive, com-
mercially available materials dispenses with the require-
ment for expensive bis(phenylsulfonyl)sulfide, and results
1. 2 eq. n-BuLi
2. 1 eq. S8
Br
Br
S
S
4. n-BuLi
5. CuCl2
2
S
S
3. 1 eq. TsCl
S
S
S
S
S
DTT
Li
4.
S
S
Ts
1. n-BuLi
S
2. S8
5. n-BuLi
6. CuCl2
S
S
3. TsCl
DTT
Scheme 1. One-pot [2 + 1] and [1 + 1 + 1] syntheses of the DTT core.
Li
Li
Li
Li
Li
Li
S
S
S
TTA
S8
S8
S8
+
+
+
+
+
+
S
S
S
S
S
S
S
S
S
S
S
S
S
PTA
S
S
SMe
SMe
S
DS-DTT
SMe
SMe
S
S
Scheme 2. One-pot syntheses of tetrathienoacene (TTA), pentathienoacene (PTA) and asymmetric DTT.

C. Kim et al. / Organic Electronics 11 (2010) 801–813
805
S
S
R5
R5
1) n-BuLi, Bu3SnCl / ether
2) Ar-Br, Pd(PPh3)4
Toluene
S
S
S
S
R = H; DP-DTT (2)
R = F; DFP-DTT (3)
DTT
Scheme 3. Synthetic route to DP-DTT (2) and DFP-DTT (3).
F
F
F
S
F
F
F
F
F
F
1. n-BuLi (2eq)
I
2. C6F5COCl (2 eq)
S
S
F
DFB-DTT; 4 O
O
S
1. n-BuLi (1eq)
FB-DTT
2. C6F5COCl (1 eq)
S
S
DTT; 1
F
S
F
F
F
C6F5COCl
AlCl3
+
II
4
S
S
F
O
FB-DTT
S
III
Cl
Cl
4
C6F5Li
S
S
O
O
F
H
H
F
S
S
H
F
F
F
F
II
C6H5COCl
F
H
F
S
S
S
S
F
AlCl3
H
F
O
O
FBB-DTT; 5 O
FB-DTT
Scheme 4. Synthetic routes to DFB-DTT (4) and FBB-DTT (5).
side product, even after refluxing for one week. Presum-
ably, compound 4 could also be generated from route
III, the reverse of route I; however, a yield of less than
10% was obtained. Unprecedentedly, since mono-acylated
FB-DTT could also be obtained as the major product
(>80%) via mono-deprotonation of DTT with 1 eq. of n-
BuLi and then mono-acylation with 1 eq. C6F5COCl, asym-
metric FBB-DTT (5) was developed from the thermal
mono-acylation of FB-DTT with benzoyl chloride via route
II in a yield of 57% as shown in Scheme 4. Benzoyl-, 2-
naphthylcarbonyl (Np-), and 2-thienoyl-substituted deriv-
atives 6, 7, and 9 were also obtained in good yields via
Route II (shown in Scheme 5). DBS-DTT (8) and DHT-
DTT (10) can be obtained from refluxing DTT-(COCl)2
[22] with 2-aminothiophenol and 2-hexylthiophene in a
yield of ꢁ40%, as shown in Scheme 6.
3.2. Thermal and optical properties
For these DTT derivatives, differential scanning calorim-
etry (DSC) scans exhibit a sharp endotherm above 214 °C,
and thermogravimetric analysis plots demonstrate weight
loss (5%) only on heating above 241 °C, as summarized in
Table 1. For compounds 4–6, lower melting points and
lower weight loss temperatures were observed for DTT
derivatives with a greater number of perfluorophenyl
groups, which indicates a higher volatility contributed by
the F-substituents, as reported in the literature [23]. Simi-
lar trend was observed for DFP-DTT (3) compared to its
non-fluorinated derivative DP-DTT (2) [10a].
The optical absorption spectra of DTTs 2–10 in o-
C6H4Cl2 are significantly red-shifted compared to 1 (kmax
ꢁ300 nm), as shown in Fig. 2, and the DTTs with the
S
S
R = C6H5; DB-DTT; 6; 63%
II
RCOCl
AlCl3
R
R
R = 2-C10H7; DNp-DTT; 7; 30%
S
S
S
S
O
O
R = C4H3S; DT-DTT; 9; 41%
DTT
Scheme 5. Synthetic routes to DTTs (6, 7, and 9).

806
C. Kim et al. / Organic Electronics 11 (2010) 801–813
SH
S
NH2
S
S
N
AlCl3
S
N
S
S
DBS-DTT; 8; 42%
Cl
Cl
S
S
S
C6H13
AlCl3
O
O
S
C6H13
S
C6H13
S
S
S
O
O
DHT-DTT; 10; 35%
Scheme 6. Synthetic routes to DTTs (8 and 10).
Table 1
Thermal, optical absorption, and electrochemical data for compounds 2–10.
Compound
DS C Tm (°C)
TGA (°C; 5%)
UV–Visb kmax (nm)
Reductive potential (V)c
Oxidative potential (V)c
DEgap (eV)
(UV)b
(DPV)c
2
3
4
5
6
7
8
9
290a
258
214
239
262
291
262
320
238
394a
270
241
265
298
384
388
342
334
374
367
ꢀ1.95
ꢀ1.62
ꢀ0.81
ꢀ1.00
ꢀ1.12
ꢀ1.14
ꢀ1.46
ꢀ1.06
ꢀ1.12
1.21
1.64
2.16
2.07
1.96
1.93
1.47
1.93
1.88
3.00
3.07
2.89
2.93
2.94
2.91
2.69
2.85
2.84
3.17
3.26
2.97
3.07
3.08
3.06
2.93
2.99
3.00
403, 383
399, 382
395, 378
384, 399
441, 417
406, 391
409, 399
10
a
b
c
See Ref. [10a].
In o-C6H4Cl2.
By DPV in o-C6H4Cl2 at 25 °C (using ferrocene/ferrocenium as internal standard at +0.6 V).
DP-DTT;2
DFP-DTT;3
DB-DTT;6
FBB-DTT; 5
1.0
DNp-DTT; 7
DFB-DTT; 4
DT-DTT; 9
DHT-DTT; 10
DBS-DTT; 8
0.8
0.6
0.4
0.2
0
300
350
400
Wavelength (nm)
450
500
Fig. 2. Optical spectra of DTTs (2–10) in o-C6H4Cl2 solution.
carbonyl substituents exhibit further red-shifted absorp-
tions (kmax >400 nm) than those without carbonyl substit-
uents DP-DTT and DFP-DTT (kmax ꢁ360 nm). For
compounds 4–6, note that the absorption is slightly red-
shifted in the compound having the greater number of F
atoms. This result is in line with established substituent
group directing effects [6c,24]. Compared to benzoyl-
delocalization extending from the DTT core to the two
benzothiazolyl substituents. The HOMO–LUMO energy
gaps calculated from the onset of the optical absorption
(2.6–3.1 eV) increase in the order: 8 < 9 ꢃ 10 < 4 < 7 < 5
< 6 < 2 < 3, as shown in Table 1.
The photooxidative stability of the DTT derivatives was
investigated by monitoring the absorbance decay at kmax of
2–10 in aerated CHCl3 solutions exposed to white light
(fluorescent lamp) at room temperature. Under these con-
ditions for 4–5 days, no decomposition is observed for any
of these compounds, demonstrating the favorable stability
of these materials.
substituted 6, more
p-electron delocalization is observed
for the 2-naphthylcarbonyl (7), and 2-thienoyl-substi-
tuted thienyl (9/10) or benzothiazolyl (8) substituted
compounds, giving the latter the lowest energy gap
among the compounds in this study. This result indicates

C. Kim et al. / Organic Electronics 11 (2010) 801–813
807
3.3. Electrochemical characterization
ranked in the order 8 < 4 < 9 ꢃ 10 < 7 < 5 < 6 < 2 < 3 (Table
1), which is consistent with the values obtained from opti-
cal spectroscopy.
Differential pulse voltammograms (DPVs; using ferro-
cene/ferrocenium as internal standard at +0.6 V) of DTTs
2–10 were recorded in dichlorobenzene at 25 °C, and the
resulting reductive and oxidative potentials are summa-
rized in Table 1 [25]. As expected, the non-carbonyl substi-
tuted DTTs exhibit the largest band gap of all the
compounds in this study revealing relatively small -elec-
tron delocalization. Furthermore, the electron affinity in-
creases with an increase in the number of fluoroaryl
rings, where fluoroaryl substitution in DFP-DTT (3)
strongly lowers both the HOMO and LUMO energies com-
pared to those in DP-DTT (2). Similar trend was observed
for DFB-DTT (4) compared to its non-fluorinated derivative
DB-DTT (6) and half fluorinated asymmetric FBB-DTT (5).
The HOMO–LUMO energy gaps obtained from the DPV
data are 2.97 eV for DFB-DTT, 3.07 eV for FBB-DTT, and
3.08 eV for DB-DTT (Fig. 3; assuming ferrocene/ferroce-
nium oxidation at 4.8 eV) and the ordering is consistent
with that obtained by optical absorption data. Compared
to compound 6, the HOMO and LUMO energies of the 2-
naphthylcarbonyl (7), thienyl- (9) and hexylthienyl- (10)
substituted compounds showed no significant change. In
contrast, the benzothiazolyl substitution in compound 8
strongly shifts both the HOMO and LUMO levels to higher
values, causing the compound to exhibit the most exten-
3.4. Crystal structure
The diffraction-derived crystal structures of compounds
3 and 7 are shown in Figs. 4 and 5, and the crystal structure
data are summarized in Table S1 [27]. Similar to DFCO-4T
[14], compound 3 with F-substituents on both ends exhib-
its intramolecular and intermolecular ortho-F (perfluor-
ophenyl)-H (DTT core) contacts [28], as shown in Fig. 4A
and B. Like other non-carbonyl diaryl substituted DTTs
[10], compound 3 exhibits typical herringbone packing
with an interplanar angle of ꢁ43.7° and the perfluorophe-
nyl groups are only slightly deviated at angles of ꢁ11° to
the DTT core (Fig. 4B). The distances between the planar
DTT cores are ꢁ3.60 Å (Fig. 4B) with the shortest sulfur–
sulfur distance of ꢁ3.48 Å (Fig. 4C). Similar to compounds
4, 5, and 6, the functionalized 2-naphthylcarbonyl moieties
in compound 7 are not coplanar with the DTT cores, but are
with a less acute torsional angles of about 36.4° (Fig. 5C)
[29]. However, without the H–F intermolecular interac-
tions, the molecular packings are considerably different
for compound 7 (compared to 4 and 5). Compound 7
exhibits typical herringbone structure (Fig. 5D) and adopt
an edge-to-face packing motif [30] with an smaller inter-
planar angle of ꢁ23.0° for 7 (Fig. 5E) [31] with the shortest
sulfur–sulfur distance of ꢁ3.25 Å (Fig. 5D). Comparing the
carbonyl substituted DTT derivatives 4–6, the distances
sive
p-electron delocalization among the DTT series with
the smallest band gap (about 2.93 eV) [26]. Overall, the
electrochemically-derived HOMO–LUMO energy gaps are
-1
2
3
4
5
6
7
8
9
10
-2
-3
-4
-5
-6
3.17
2.93
3.26
3.08
3.07
3.00
2.99
3.07
2.97
Fig. 3. The electrochemically-derived HOMO and LUMO energy levels of DTTs 2–10.
Fig. 4. Single-crystal structure of compound 3. (A) Top view. Intramolecular (2.22 Å) and intermolecular (2.58 Å) F–H interactions between DTT cores. (B)
Side view. The two DTT units with a 3.60 Å planar distance and an interplanar angle of 43.7 °. (C) S–S distances in DTTs.

808
C. Kim et al. / Organic Electronics 11 (2010) 801–813
Fig. 5. Single-crystal structure of 7. (A) Front view of 7. (B) Top view. (C) Side view. (D) DTT cores with a herringbone arrangement and the S–S distances in
DTTs. (E) DTT cores with an interplanar angle of 23.0°. (F) 2-Naphthyl with a torsional angle of about 36.4° to the DTT core.
between the planar DTT cores and the shortest S–S dis-
tances among DTT cores are 5 (ꢁ3.50 Å) < 6 (3.68 Å) < 4
(3.74 Å) and 5 (3.20 Å) < 6 (3.23 Å) < 4 (3.42 Å), respec-
tively, demonstrating the tightest molecule-packing of 5
in the solid state, which is in accord with the OTFT device
performance trends (vide infra).
charge carrier types and device performance. TFT data
are summarized in Table 2, and representative transfer
and output plots are shown in Fig. 6.
Devices fabricated with DTT-based compounds all exhi-
bit TFT activity, with compounds 3 –5 performing as n-
channel semiconductors, and the rest of the compounds
performing as p-channel semiconductors. Derived field-ef-
fect mobilities of the DTT derivatives strongly depend
upon both the dielectric surface treatment and the deposi-
tion temperature (TD). In general, enhanced device perfor-
mance is observed at higher deposition temperatures and
on HMDS-treated SiO2 substrates. Compounds 3–5 exhibit
electron mobilities as high as 0.07, 0.002 and 0.03 cm2/Vs,
respectively. Compound 4 is active both under vacuum
3.5. Thin-film transistor characterization
Top-contact/bottom gate OTFT devices were fabricated
by vacuum deposition (5 ꢂ 10ꢀ6 Torr) of each compound
on bare and HMDS-treated SiO2/p+-Si substrates at preset
deposition temperatures (TD). Gold source and drain con-
tacts were patterned by thermal evaporation using shadow
(
l
= 3 ꢂ 10ꢀ5–0.002 cm2/Vs) and under ambient condi-
masks that gave a channel length of 100
lm and a width of
tions (
l
= 1 ꢂ 10ꢀ4 cm2/Vs), exhibiting high current on/off
5000 m. The TFT properties were tested under positive or
l
ratios of 105–106. Compounds 3 and 5, on the other hand,
negative gate bias under vacuum to explore the major
Table 2
Majority charge carrier types, field-effect mobilities (l
, cm2/Vs),a current on/off ratios (Ion/Ioff), and threshold voltages (VT, V) for thin-film OTFTs fabricated by
vacuum deposition of compounds 3–10 on bare and HMDS-treated p+-Si/SiO2 substrates at the indicated deposition temperatures (TD, °C). Device performance
measured under vacuum unless otherwise indicated.
Compound
Polarity
TD
Bare
HMDS
l
Ion:Ioff
VT
l
Ion:Ioff
VT
3
4
5
6
N
N
N
P
25
50
25
25b
25
70
25
70
90
25
90
25
70
90
25
70
25
50
3 ꢂ 10ꢀ4
3 ꢂ 10ꢀ4
3 ꢂ 10ꢀ5
Not active
4 ꢂ 10ꢀ6
3 ꢂ 10ꢀ6
3 ꢂ 10ꢀ4
0.006
105
105
104
+74
+62
+74
0.07
0.06
107
107
105
105
107
107
106
107
107
103
106
105
107
105
104
105
105
105
+62
+54
+35
+28
+46
+31
ꢀ65
ꢀ49
ꢀ53
ꢀ66
ꢀ67
ꢀ24
ꢀ26
ꢀ23
ꢀ58
ꢀ64
ꢀ78
ꢀ77
0.002
1 ꢂ 10ꢀ4
104
104
106
107
107
+60
+38
ꢀ66
ꢀ66
ꢀ40
0.003
0.03
0.001
0.005
0.01
Not active
0.001
0.01
7
8
P
P
3 ꢂ 10ꢀ5
107
105
104
105
ꢀ45
ꢀ17
ꢀ18
ꢀ10
0.004
5 ꢂ 10ꢀ6
4 ꢂ 10ꢀ6
4 ꢂ 10ꢀ4
Not active
2 ꢂ 10ꢀ4
3 ꢂ 10ꢀ6
1 ꢂ 10ꢀ5
0.005
0.008
0.01
9
P
P
1 ꢂ 10ꢀ5
1 ꢂ 10ꢀ5
6 ꢂ 10ꢀ6
4 ꢂ 10ꢀ6
106
104
105
ꢀ50
ꢀ77
ꢀ76
10
a
Device performance is the averaged value of at least four samples. (Standard deviation between devices is <10%.)
Measured in ambient.
b

C. Kim et al. / Organic Electronics 11 (2010) 801–813
809
10-3
10-5
10-7
10-9
10-11
10-13
A.
VG = 120 V
100 V
2.0
1.5
S (Au)
D (Au)
1.0
0.5
0.0
80 V
Semiconductor
Dielectric
Gate (p+-Si)
0 – 60 V
0
50
VDS (V)
100
0
50
VG (V)
100
1.5
1.0
0.5
0.0
B.
VG = -100 V
10-5
10-7
10-9
-80 V
-60 V
-40 – 0 V
-100
-50
VG (V)
0
-100
-50
VDS (V)
0
Fig. 6. OTFT plots of devices fabricated with compounds 3 and 8 on HMDS-treated SiO2 substrates. (A) Transfer (VDS = 100 V) and output plots of 3
(TD = 25 °C), (B) transfer (VDS = ꢀ100 V) and output plots of 8 (TD = 90 °C). The general OTFT device structure (inset).
are only active under vacuum. Compound 3 exhibits the
highest electron mobility, 0.07 cm2/Vs, of all the DTT deriv-
atives on HMDS-treated SiO2 substrates (TD = 25 °C) with
an Ion/Ioff of ꢁ107 (Fig. 6A). The end-substitution with elec-
tron-withdrawing perfluorophenyl groups promotes
majority carrier sign inversion in this family, as previously
demonstrated for other materials [13]. The non-fluorinated
DTT derivatives 6–10 exhibits p-channel transport with
hole mobilities of 4 ꢂ 10ꢀ6–0.01 cm2/Vs. Among the p-
channel DTT-based compounds, 6 and 8 exhibit relatively
high mobilities, up to 0.01 cm2/Vs, with Ion/Ioff of 105–107
on HMDS-treated SiO2 substrates (Fig. 6B). For these com-
the source and drain electrodes. In this study, conventional
h/2h scans were utilized to obtain out-of-plane d-spacings
in the vacuum-deposited thin films on HMDS-treated Si/
SiO2 substrates at various TDs. The thicknesses of all films
were determined to be 50–70 nm by profilometry. Repre-
sentative XRD scans are shown in Fig. 7, and the data are
presented in Table 3.
The h/2h out-of-plane XRD scans show that all of com-
pounds except 4 and 10 were highly textured and exhibit
high intensities with multiple reflections (Fig. 7). For all
of the films except compound 6 (vide infra), a single set
of diffraction peaks is observed without the presence of
pounds, there is a clear correlation between
l
and TD,
any reflections corresponding to p–p stacking distances,
which is also evident in the XRD and AFM characterization
and d-spacing values are estimated from the nominal
(1 0 0) reflection peaks as 18.2–24.4 Å, suggesting the pres-
ence of a crystalline polymorph where the majority of the
molecules have an edge-on orientation with respect to the
data (vide infra). The other DTT (7, 9, and 10) derivatives
exhibit relatively low hole mobilities of 4 ꢂ 10ꢀ6
–
0.004 cm2/Vs and Ion/Ioff of 103–107.
substrate surface, with the p–p stacking direction roughly
3.6. Thin-film microstructure and morphology
parallel to the substrate surface. This molecular orientation
promotes in-plane charge transport from the source to the
drain. Compounds 3–8 (except 4) exhibit strong XRD peak
intensities and multiple reflections, consistent with good
TFT mobility, as described above. Compound 10 with poor
TFT mobility exhibits only a single Bragg reflection, indi-
cating low film texturing. This low texturing is possibly
due to hindered molecular packing by the n-hexyl side
groups. Interestingly, films of compound 4, having reason-
able carrier mobility (60.002 cm2/Vs), also exhibits only a
single reflection and modest peak intensity. This indicates
the presence of an interface mismatch between the HMDS-
Vacuum-deposited film crystallinity and morphology
are known to affect TFT performance. Thin-film micro-
structures and morphologies for this new class of materials
were studied by h–2h XRD, AFM, and SEM. X-ray diffraction
experiments provide useful information to understand the
crystallinity of the semiconductors as thin films and the
molecular orientation relative to the substrate surface. In
general, high crystallinity and preferential alignment of
the
p-conjugated core (perpendicular to the dielectric sur-
face) are beneficial to efficient charge transport between

810
C. Kim et al. / Organic Electronics 11 (2010) 801–813
106
105
104
103
102
101
Compound 3
TD = 25 oC
Compound 7
TD = 90 oC
105
104
103
102
101
105
Compound 8
TD = 90 oC
Compound 4
TD = 25 oC
103
102
104
103
102
101
104
101
104
Compound 9
TD = 70 oC
Compound 5
TD = 70 oC
103
102
101
103
102
101
105
104
103
102
101
Compound 10
TD = 50 oC
Compound 6
TD = 90 oC
104
103
102
101
5
10
15
20
25
3
5
10
15
20
25
3
2 Theta (degrees)
Fig. 7. Representative h–2h XRD scans on a logarithmic scale of DTT (3–10) films vapor-deposited at the indicated TDs on HMDS-treated SiO2 substrates.
Table 3
compound 8 films does not change at different TDs. Similar
behavior is also observed for compound 5-based TFTs (not
shown). Interestingly, compound 6-derived films show
somewhat different XRD patterns. As the TD increased, the
XRD peak intensity for compound 6 films decreases slightly
(Fig. 8B). However, the XRD peak position shifts to slightly
higher angle, from 2h = 4.53° to 4.60°, at higher TD values,
suggesting some structural reorganization (from 19.5 to
19.2 Å of d-spacing). Enhanced mobility at higher TD values
for compound 6-based TFTs appears to be associated with
this reduced d-spacing.
The reflections and d-spacings calculated from (1 0 0) reflection for
vacuum-deposited films of compounds 3–10 on HMDS-treated SiO2
substrates at the indicated TDs.
Compound
Reflections TD (°C) 2h (°) (1 0 0)
d-spacing (Å)
3
4
5
6
7
8
9
10
100–600
100
25, 50
25
4.70
4.84
4.06
4.57
3.61
4.20
4.80
3.83
18.8
18.2
21.7
19.2–19.5
24.4
21.0
18.4
23.0
100–700
100–600
100–800
100–700
100–600
100
25, 70
25–90
25, 90
25–90
25, 70
25, 50
Since microstructure characterization at the dielectric-
semiconductor interface, where charge transport in TFTs
occurs, is challenging by conventional techniques, we stud-
ied the morphology of the semiconductor surfaces via AFM
and SEM, assuming that the microstructure at the surface
conveys information about the underlying microstructure
at the interface. From the film morphologies, it is clear that
the film growth patterns depend significantly on the sub-
strate temperature and surface treatment, which are
strongly correlated with the device performance (vide su-
pra). Figs. 9 and S1 show representative surface morpholo-
gies of the films of compounds 3–10. For example, films
exhibit ribbon-like grains (compounds 4 and 5 at 25 °C),
plate-like faceted films (3, 5–8 at high TD), or small grains
(compounds 9 and 10).
treated SiO2 dielectric and the fluorinated semiconductor
layers, which prevents ordered crystal growth in the semi-
conductor layer. Similar results have been observed for
end-fluorinated perylene- and naphthalene-based com-
pounds [1c,32].
Since the TFT performance for several compounds is
quite sensitive to the deposition temperature (vide supra),
TD-dependent XRD patterns were also examined. Fig. 8A
shows field-effect mobilities and XRD data for films of com-
pound 8 on HMDS-treated substrates at various TDs. As
shown, there is a clear correlation between mobility values
and XRD peak intensity. Note that XRD peak position for

C. Kim et al. / Organic Electronics 11 (2010) 801–813
811
correlation with the device performance. Fig. 9A and B
shows AFM and SEM images of the films from compounds
6 and 8, respectively, grown at different TDs. The films
from compound 6 on bare SiO2 substrates exhibit small
grains with a few plate-like grains at TD = 25 °C, but much
larger, well-faceted grains are observed at higher TDs, as
assessed by AFM (Fig. 9A). Films from compound 8 on
HMDS-treated SiO2 substrates show similar behavior,
with lower TD samples having small grains at TD = 25 °C,
but large crystal-like grains protruding from the film sur-
face at higher TDs. The large highly-crystalline surface
microstructural features exhibited by both compounds
at the higher deposition temperature correlates well with
the enhanced TFT performance. Similar TD-dependent
morphological change is also observed for compounds 3,
5, and 7 (Fig. S1).
A.
10.0
8.0
6.0
4.0
2.0
0.0
9.0
6.0
3.0
0.0
30
60
90
T
D (oC)
B.
2.5
2.0
1.5
1.0
0.5
0.0
TD (oC)
25
70
90
4. Conclusions
Convenient, efficient, cost-effective, one-pot [2 + 1] and
[1 + 1 + 1] synthesis of DTT were achieved that enables the
efficient realization of a new DTT-based semiconductor
series for organic thin-film transistors (OTFTs). Perfluor-
ophenyl and perfluorobenzoyl substitutions are found to
be effective in promoting n-channel transport. Diperfluor-
ophenyl DFP-DTT (3), diperfluorobenzoyl DFB-DTT (4),
and asymmetric FBB-DTT (5) films exhibit n-type trans-
port with mobilities as high as 0.07 cm2/Vs [33]. Compared
to DFCO-4T [14a], the lower mobilities can be ascribed to
4.0 4.2 4.4 4.6 4.8 5.0
2 Theta (degrees)
Fig. 8. (A) Field-effect mobilities and XRD (h/2h scan; 2h = 3–6°) data for
compound 8-based TFTs on HMDS-treated SiO2 substrates at the
indicated TDs. (B) XRD (h/2h scan) data (2h = 4–5°) for compound 6-
derived films on bare SiO2 substrates grown at the indicated TDs.
the larger interplanar
p–p separation distances (3.74 Å
for 4 and 3.56 Å for 5 vs. 3.5 Å for DFCO-4T) caused by
non-negligible Fꢄ ꢄ ꢄH interactions in compounds 4 and 5
[34]. Interestingly, the intermolecular Hꢄ ꢄ ꢄF interactions
in asymmetric compound 5, the compound having the
shortest interplanar DTT core distances in this study, reveal
the potential utility of this asymmetric design for other n-
channel systems. In contrast, the non-fluorinated aryl car-
bonyl substituted DTT derivatives exhibit exclusively p-
type transport, with the greatest hole mobility of
0.01 cm2/Vs, observed for DB-DTT (6) and DBS-DTT (8).
The carrier mobilities are found to be strongly dependent
on the substrate deposition temperatures and surface
treatments, and these DTT-based OTFTs exhibit excellent
ambient stability over many months (near 1 year). These
results provide new information about the structural char-
acteristics of DTT-based semiconductors and the advanta-
ges of using this stable core for designing more soluble
derivatives.
Acknowledgements
We thank the National Science Council, Taiwan,
Republic of China (Grant Numbers NSC98-2628-M-008-
003, NSC97-2113-M-008-003, and NSC98-2627-E-006-
003) and Industrial Technology Research Institute of
Taiwan for support. Financial assistance for this research
was partially provided by the NSF-MRSEC program
through the Northwestern Materials Research Center
(DMR-0520513).
Fig. 9. (A) AFM images (5 ꢂ 5
l
m2) of films from compound 6 on bare
SiO2 substrates grown at the indicated TDs. (B) SEM images of films from
compound 8 on HMDS-treated SiO2 substrates grown at the indicated TDs.
Similar to the XRD patterns, AFM images also show a
strong dependence of film morphology on the TDs and a

812
C. Kim et al. / Organic Electronics 11 (2010) 801–813
(d) . For 7 fused ring example see:M. He, F. Zhang, J. Org. Chem. 72
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(2006) 426;
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/
j.orgel.2010.01.022.
(b) Y. Sun, Y. Liu, Y. Ma, C. Di, Y. Wang, W. Wu, G. Yu, W. Hu, D. Zhu,
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C. Kim et al. / Organic Electronics 11 (2010) 801–813
813
[30] For compounds 4 and 5, the arrangement of the DTT cores adopt a
nearly face-to-face packing motif, see SI in Ref. [11].
[31] For 6, the interplanar angle is 36.5°.
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[33] Ambipolar transport in these DTT materials was not observed.
[34] In addition to the larger intermolecular core distance, the less
conjugation of DTTs may be responsible for the lower
mobilities.