2
1
. Introduction
Organic semiconductors are promising active layers for the
new-generation electronics, attributed to their intriguing
1
, 2
advantages of low-cost, light-weight, and flexibility. Over the
last decades, great progress has been made in the development of
OFETs and a large number of organic semiconductors have been
3
-5
developed for OFET applications.
Previously, acenes have been widely explored as efficient
charge transport semiconductors for OFETs. Meanwhile, a large
6
Reagents and conditions: (a) NBS, CHCl
CuBr, LiBr, oxalyl chloride, THF/ethyl ether, 54%; (c) FeCl , DCM,
3
, AcOH, 83%; (b) n-BuLi,
3
number of thienoacenes with good charge transport mobility have
been developed for OFET applications because of their desirable
close packing in the solid state, which arising from their rigid and
planar structures and the desirable intermolecular S•••S, S•••H,
and S•••interactions. Besides, the OFETs based on
thienoacenes also exhibited relatively higher air stability as
compared to the acene-based devices because of their lower
7
8%; (d) Zn, (CH CO) O, NEt , DCM, 59%; (e) Cs CO , RX (X =
3 2 3 2 3
Br, I), CH CN, 72-75%.
3
The BBBT-n derivatives were synthesized according to the
synthetic route depicted in Scheme 1. Selective bromination of
benzo[b]thiophene by means of NBS produced 3-
bromobenzo[b]thiophene, 1 in a good yield. Double nucleophilic
substitution reaction of oxalyl chloride with freshly prepared
lithium organocuprate of 1 yielded diketone 2. Subsequent ring-
7
,
8
HOMO energy levels.
6,5‑ b:6′,5′‑ f]thieno[3,2‑ b]thiophene (DBTTT) has been
developed by Lee and coworkers, exhibiting a champion hole
For instance, dibenzothiopheno
[
closing reaction catalyzed by FeCl
3 in a good yield. The cascade reaction of reduction and
acetylation led to the formation of acetylated
gave the fused-ring diketone
3
2
−1 −1
mobility of 19.3 cm ·V ·s in OFET fabricated by vacuum
9
deposition. It has also been demonstrated that molecular
engineering strategy using various alkyl chains incorporated onto
the conjugated backbone is an effective means to tune the
solubility and morphology, and thus to enhance the processibility
benzodithienothiophene 4 in a moderate yield. The BBBT-n
series were then synthesized according by the reaction of
acetylated intermediate 4 and the corresponding alkyl halide in
1
0
and the charge carrier mobility of the organic semiconductors.
the presence of Cs CO as a base. All the BBBT-n derivatives
2 3
1 13
Nevertheless, relatively scarce organic semiconductors with alkyl
chains incorporated laterally have been investigated as compared
to those end-capped with alkyl chains.
were fully characterized by H NMR, C NMR, HRMS and the
spectroscopic data are in good agreement with the proposed
structures. All the details are listed in the supporting information.
2
.2. Thermal, optical and electrochemical properties
Figure 2. TGA, UV-vis absorption spectra, and CV traces of BBBTs
Table 1. Summaries of optical and electrochemical
measurements of BBBTs
Figure 1. Molecular structures of laterally alkyl-substituted
thienoacenes for OFET applications.
ꢁ
ꢀ
ꢂꢃꢄ
ꢅꢈꢉꢊꢋꢄꢌꢄ
ꢅꢆꢇ
ꢐ
ꢓ
Compound
(eV)
ꢄ(eV)
ꢄ(eV)
ꢄꢔꢊꢕꢖ
ꢍꢎꢏꢎ
ꢑꢒꢏꢎ
BBBT-2
3.18
3.18
1.3
1.3
1.3
-5.6
-2.4
In our previous studies, several series of thienoacene-based
semiconductors with alkyl side-chains have been synthesized and
investigated including BDTT, NDTT, NBTBT, and NBBT.
BBBT-4
BBBT-6
-5.6
-5.6
-2.4
-2.4
1
1-14
3.17
In these works, the benzo semiconductors show better mobility
performance than the naphtho ones, and the mobility properties
of the semiconductor are affected by the lateral alkoxy groups.
With these conclusions in mind, we reasoned that the mobility
performance of NBBT could be improved by replace the terminal
thiophene with benzene ring. Therefore, in this contribution, a
series of air-stable benzo[2,1-b:3,4-b’]bis[1]benzothiophenes
a
b
Measured in DCM. Estimated from the absorption edge of absorption in
c
DCM, E
g
= (1240/λonset) eV. Ferrocene was used as the external standard, E1/2
+
d
(
Fc/Fc ) = 0.47 V vs. SCE. Calculated from the first oxidation potential with
ꢅꢈꢉꢊꢋꢄ
ꢅꢆꢇ
e
ferrocene (4.8 V vs. vacuum). HOMO = -4.33 -
LUMO = HOMO
g
E .
The thermal stabilities of BBBTs were estimated by
(BBBT-n) derivatives were designed and synthesized, in which
thermogravimetric analysis (TGA). As shown in Figure 2 (a), all
these compounds exhibited good thermal stability with
decomposition temperature of around 295 C. In order to
investigate the effects of different alkoxy groups on the
optoelectronic performance, UV-vis absorption spectra of
BBBTs were measured in CH Cl solution, as shown in Figure 2
different alkoxy groups were employed to tune the morphology
of the semiconductors on the substrate. Their performances in
OFETs have also been investigated, and BBBT-4 was found to
exhibit the best OFET performance with a hole carrier mobility
2
−1 −1
8
of 0.47 cm ·V ·s and an on/off current ratio of 10 . (Figure 1)
. Results and discussion
.1. Materials and Synthesis
2
2
(
b). All these compounds exhibited strong absorption bands in
2
the range of 290-330 nm and weak absorption bands in the range
of 340-380 nm, corresponding to an optical bandgap of 3.28 eV.
Furthermore, these three compounds exhibited approximately
identical absorption bands, indicating that the alkoxy substituents
have negligible effect on the electron distribution of -
2
Scheme 1 Synthesis of BBBT-2, BBBT-4 and BBBT-6