Small-molecule semiconductors containing dithienylacrylonitrile for high-performance organic field-effect transistors

Article abstract of DOI:10.1039/c9tc03726h

We designed and synthesized four donor-acceptor-type conjugated small-molecule compounds DPP-CN-DTE-1, DPP-CN-DTE-2, DPP-DTE-CN-1 and DPP-DTE-CN-2. The four compounds contained long alkyl side chains on the diketopyrrolopyrrole acceptor unit and cyano (CN) groups substituted on the dithiophene ethylene donor unit at different positions. The four small molecules exhibited good thermal stability and solution dispersibility. The bottom gate-bottom contact OFET devices based on these compounds showed excellent p-type performances. The relationship between molecular structures and field-effect performances indicated that the alkyl side-chain length and the CN substituted position significantly affected their charge carrier transport properties. The DPP-CN-DTE-1 with side-chain 2-mercaptotetradecyl side-chains and inner-side substituted CN groups exhibited the highest hole mobility of 2.52 cm² V^-1 s^-1. This work provided a promising approach to develop excellent p-type small-molecule semiconductors with high performance, good solution processability and thermal stability for device fabrications.

Full text of DOI:10.1039/c9tc03726h

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Page 1 of 9
J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
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DOI: 10.1039/C9TC03726H
ARTICLE
Small-molecule semiconductors containing dithienylacrylonitrile
for high-performance organic field-effect transistors
Received 00th January 20xx,
Accepted 00th January 20xx
a
ab
ac
ab
*b
a
Dizao Li, Jiabin Zou, Congyuan Wei, Yankai Zhou, Liping Wang, Weifeng Zhang and Gui
DOI: 10.1039/x0xx00000x
*ac
Yu
We designed and synthesized four donor–acceptor-type conjugated small-molecule compounds DPP-CN-DTE-1, DPP-CN-
DTE-2, DPP-DTE-CN-1 and DPP-DTE-CN-2. The four compounds contained long alkyl side chains on the
diketopyrrolopyrrole acceptor unit and cyano (CN) groups substituted on the dithiophene ethylene donor unit at different
positions. The four small molecules exhibited good thermal stability and solution dispersibility. The bottom gate-bottom
contact OFET devices based on these compounds showed excellent p-type performances. The relationship between
molecular structures and field-effect performances indicated that the alkyl side-chain length and the CN substituted
position significantly affected their charge carrier transport properties. The DPP-CN-DTE-1 with side-chain 2-
2
‒1
mercaptotetradecyl side-chains and inner-side substituted CN groups exhibited the highest hole mobility of 2.52 cm V
‒
1
s . This work provided a promising approach to develop excellent p-type small-molecule semiconductors with high
performance, good solution processability and thermal stability for device fabrications.
substituted dithiophene ethylene (DTE) donor units were
designed and synthesized. The four target conjugated
compounds, DPP-CN-DTE-1, DPP-CN-DTE-2, DPP-DTE-CN-1 and
Introduction
Although p-type organic semiconductor materials research has
DPP-DTE-CN-2, respectively, contain DPP units with different
side chains and the DTE units substituted by CN groups in
different sites. These four conjugated compounds exhibited
good solubility and good thermal stability, providing an
important guarantee for the solution processing and
performance's annealing optimization of their OFET devices.
Based on these D–A type organic small-molecule materials, we
fabricated bottom-gate bottom-contact (BGBC) OFET devices,
which showed excellent p-type charge carrier transport
performance. The structure-performance relationship
indicated that both the length of the alkyl side chain on the
acceptor moiety DPP and the substituting position of CN group
on the donor moiety DTE in the conjugated skeleton of the D–
A type organic small molecule have different degrees of
influence on their charge carrier transport properties. The
longer side chain group 2-mercaptotetradecyl and the inside
CN substituting positions on DTE are more conducive to the
hole transport, thus organic small molecule DPP-CN-DTE-1
exhibited high p-type OFET performance with a maximum hole
reached an unprecedented height, and more and more high-
1
-4
performance materials have been developed, still many
improvements and ameliorations should be obtained in the
controllability of material structures, purity and so on. Organic
conjugated small molecules have important significance for
the fabrication of organic field-effect transistors (OFETs)
because of their structural certainty, purity and solubility
controllability. Molecular engineering by introducing side
chains and modifying conjugated skeleton structures has been
widely used to develop high-performance p-type organic
5
-11
conjugated semiconductors. In this work, the length of side
chain on the acceptor unit and the relative position of the
cyano (CN) groups on the donor unit of the conjugated
backbone were respectively adjusted. These adjustments' aim
was to obtain p-type donor–acceptor (D‒A) type conjugated
compounds with excellent thermal stability and solution
processability. Here, four D–A conjugated organic compounds
a. Beijing National Laboratory for Molecular Sciences, CAS Research/Education
2
‒1 ‒1
mobility (μhmax) of 2.52 cm V s .
Center for Excellence in Molecular Sciences, Institute of Chemistry, Chinese
Academy of Sciences, Beijing 100190, P. R. China. E-mail: yugui@iccas.ac.cn
School of Materials Science and Engineering, University of Science and Technology
b.
Beijing, Beijing 100083, P. R. China. E-mail: lpwang@mater.ustb.edu.cn
School of Chemical Sciences, University of Chinese Academy of Sciences, Beijing
Experimental
c.
1
00049, P. R. China.
Reagents and reactions
Electronic Supplementary Information (ESI) available: [The Device Fabrication and
Performance of the OFETs, NMR spectra of the small molecules]. See
DOI: 10.1039/x0xx00000x
All chemicals were purchased from Acros, Alfa Aesar,
Innochem, J&K Scientific, Sigma-Aldrich, etc. The chemicals
including diketopyrrolopyrrole (DPP) acceptor units and CN were used directly if no specified requirement was needed. If
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
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Journal Name
necessary, anhydrous toluene and tetrahydrofuran (THF) were microscope (AFM) was adopted to analyzeViewtAhrtiincle Ofnillimne
freshly distilled using sodium as scavenger and using morphologies. The small-molecule thin fDilOmI:s10w.1e0r3e9/iCll9uTmC0in3a72te6Hd
benzophenone as indicator according to the standard at a constant incidence angle of 0.2° to obtain their grazing
procedures. P
similarly.
O
2 5
and CaH
2
could be used to treat acetonitrile incidence X-ray diffraction (GIXRD) data. The thin film samples
used in AFM, GIXRD and FET performance analysis were same.
Measurements and characterization of compounds
1
Proton nuclear magnetic resonance ( H NMR) spectra and Synthetic procedure
1
3
carbon nuclear magnetic resonance ( C NMR) spectra of The synthetic route to conjugated small molecules DPP-CN-
synthetic intermediates were recorded on a Bruker Avance III DTE-1, DPP-CN-DTE-2, DPP-DTE-CN-1 and DPP-DTE-CN-2 is
4
00 HD NMR spectrometer. Target compounds were offered as Scheme 1. Intermediate compounds 1‒6 were
1
2-18
characterized at 100 °C by using a Bruker Avance III 500 WB prepared according to the methods reported in literatures.
NMR spectrometer. A 9.4T Solarix FT-ICR mass spectrometer
or an APEX II FT-ICR mass spectrometer was used to collect the General synthetic and purification procedure of DPP-CN-DTE-1,
DPP-CN-DTE-2, DPP-DTE-CN-1 and DPP-DTE-CN-2.
The monomer 2 or 4 (0.60 mmol), bisborate-DPP (5 or 6) (0.20
data of high resolution mass spectroscopy (HRMS)
measurements for all the compounds. A PerkinElmer Pyris
series TGA8000 thermal analysis system was adopted to carry
out the thermaogravimetric analysis (TGA) measurements of
mmol), Na
2
CO
3
aqueous solution (2 M, 6 mL), and toluene (15
(0.06
mL) were added to a 50 mL Schlenk flask. Then Pd(PPh )
3 4
mmol) and KF (0.4 mmol) were added quickly in one portion
after the Schlenk flask was strictly charged with Ar. The
mixture was stirred under Ar protection with being heated at
2
target small molecules under N at a heating rate of 10 °C
−1
min . The ultraviolet-visible-near-infrared (UV–Vis–NIR)
absorption spectra of all synthesized small molecules were
recorded by using a Hitachi U-3010 spectrophotometer. The
1
10 °C for 48–96 h. The reaction mixture was poured on a
short silica gel pad after being cooled to room temperature
electrochemical properties were characterized by using cyclic (RT) to remove the catalyst and most of salts by using ethyl
voltammetry (CV) on a conventional three-electrode type acetate as an eluent. The filtration was concentrated in vacuo
electrochemistry workstation. The HOMO and LUMO energy and then purified by silica gel chromatography with eluent of
dichloromethane/hexane followed a recrystallization from
chloroform/methanol to give the titled compound as a dark
green solid.
levels were estimated with the onset of corresponding
oxidative and reductive peaks by adopting the equations EHOMO
onset
onset
=
― (퐸ox + 4.4) eV and ELUMO = ― (퐸re + 4.4) eV. A tapping
mode Digital Instruments Nanoscope
V
atomic force
O
NC
(
a)
b)
S
NBS / DMF
CN
O
S
Br
CN
Br
S
t-BuOK / MeOH
S
S
S
1
2
CN
(
NC
Br2 / NaHCO3 / CHCl3
S
S
O
Br
S
Br
t-BuOK / MeOH
S
3
4
R
O
(c)
NC
H
N
S
S
S
S
S
S
CN
R
N
O
H
O
O
R
N
S
O
B
DPP-CN-DTE-1: R = 2-decyltetradecyl
DPP-CN-DTE-2: R = 2-hexyldecyl
2
or 4 Pd(PPh ) ,
3 4
O
S
B
N
O
2M K2CO3, Toluene
O
R
O
R
H
CN
N
5
: R = 2-decyltetradecyl
: R = 2-hexyldecyl
S
S
S
6
S
S
S
CN
N
H
O
R
DPP-DTE-CN-1: R = 2-decyltetradecyl
DPP-DTE-CN-2: R = 2-hexyldecyl
Scheme 1 Synthetic routes of DPP-CN-DTE-n and DPP-DTE-CN-n (n = 1 and 2).
2
| J. Name., 2012, 00, 1-3
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DOI: 10.1039/C9TC03726H
ARTICLE
DPP-CN-DTE-1: (30% yield). 1H NMR (500 MHz, 373K, of a strong base potassium t-butoxide. For the preparation of
CDCl
.48(d, J = 5.0 Hz, 2H), 7.38 (s, 2H), 7.26(d, J = 4.1 Hz, 2H), 7.21
d, J = 3.9 Hz, 2H), 7.18 (s, 2H), 7.08 (t, J = 5.0 Hz, 2H), 3.95 (d, J
10.0 Hz, 4H), 1.91 (s, 2H), 1.27–1.16 (br, 80H), 0.80–0.77 (dt,
2 2
CDCl , TMS): δ 8.69 (s, 2H), 7.58 (d, J = 3.7 Hz, 2H),
the necessary intermediates 1 and 3, we respectively adopted
7
(
=
20
the method of NBS radical reaction and the method of liquid
21
bromine bromination under alkaline conditions. The DPP
acceptor units (intermediate compounds 5 and 6) were
1
3
J = 5.0 Hz, J = 5.0 Hz, 12H). C-NMR (126 MHz, 373K,
CDCl CDCl , TMS): δ 161.63, 141.39, 139.45, 137.63, 136.78,
prepared by the method of extracting hydrogen with lithium
2
2
1
2-18
diisopropylamide (LDA) according to the literatures.
1
1
3
Finally, CN-substituted DTE donor units 2 or 4 were coupled
with DPP receptor units 5 or 6 using the Suzuki coupling
(MALDI): calcd. for C84
)
3 4
1
C
of the target compounds and intermediates is shown in
Scheme 1. The final products DPP-CN-DTE-1, DPP-CN-DTE-2,
DPP-DTE-CN-1 and DPP-DTE-CN-2 were structurally confirmed
by the NMR spectra and HRMS data. At the same time, in
order to ensure the feasibility of annealing in subsequent OFET
device processing to optimize carrier transport performance,
the good thermal stability of the organic compounds is
necessary. It is considered that thermogravimetric analysis
(
d, J = 5.0 Hz, 2H), 7.10 (s, 2H), 7.01 (s, 2H), 6.99 (s, 2H), 6.92 (s,
4
0
1
1
1
3
1
H), 3.95 (d, J = 10.0 Hz, 4H), 1.94 (s, 2H), 1.27–1.06 (br, 48H),
.64 (s, 12H). 13C-NMR (126 MHz, 373K, C
Cl , TMS): δ
6
2 4
D
61.27, 141.12, 139.38, 139.02, 137.51, 136.65, 136.06,
31.83, 131.50, 129.89, 129.38, 127.70, 127.41, 125.49,
25.11, 115.90, 109.30, 102.88, 46.50, 38.27, 31.72, 31.72,
1.64, 29.99, 29.58, 29.42, 29.14, 26.46, 26.40, 22.45, 22.43,
+
3.68. HRMS (MALDI): calcd. for
C H N O S
68 83 4 2 6
[M+H]
(1179.4835); found: 1179.4839.
(TGA) can usually be used to detect the thermal properties of
DPP-DTE-CN-1: (28% yield). 1H NMR (500 MHz, 373K, organic semiconductors. TGA tests of these conjugated
22
C
6
Cl
2 4
D , TMS): δ 8.84 (d, J = 5.0 Hz, 2H), 7.18 (s, 2H), 7.03 (d, J = compounds were performed with results shown in Fig. S1 and
.0 Hz, 6H), 6.98 (d, J = 5.0 Hz, 2H), 6.91 (d, J = 5.0 Hz, 2H), 6.67
the corresponding data are listed in Table 1. The four
conjugated compounds DPP-CN-DTE-1, DPP-CN-DTE-2, DPP-
DTE-CN-1 and DPP-DTE-CN-2 showed their 5% weight loss at
1
3
1
3
1
1
3
.03 (br, 80H), 0.65 (t, J = 5.0 Hz, 12H). C-NMR (126 MHz,
73K, C Cl , TMS): δ 161.25, 140.99, 139.96, 139.02, 138.81,
37.90, 136.13, 132.68, 130.29, 129.99, 127.86, 127.01,
26.05, 125.63, 125.23, 116.33, 109.49, 103.83, 46.53, 38.30,
1.74, 30.02, 29.58, 29.51, 29.17, 26.48, 22.45, 13.68. HRMS
6
2 4
D
4
04.7, 396.0, 402.0 and 396.3 °C, respectively. These
temperature data indicated that these compounds showed
good thermal stability. It provides good stability guarantee for
the optimization of annealing in the preparation of their OFET
devices.
[M+Na]+ (1425.7158);
(MALDI): calcd. for C84H N NaO S
114 4 2 6
found: 1425.7162.
DPP-DTE-CN-2: (20% yield). 1H NMR (500 MHz, 373K,
Optical properties
2 2
CDCl CDCl , TMS): δ 8.69 (d, J = 3.2 Hz, 2H), 7.48 (d, J = 3.6 Hz,
We measured the photophysical properties of four DPP-DTE-
based conjugated compounds DPP-CN-DTE-1, DPP-CN-DTE-2,
DPP-DTE-CN-1 and DPP-DTE-CN-2 by using UV-Vis-NIR
absorption spectroscopy. The UV-Vis-NIR absorption spectra of
the four compounds in a chloroform solution (concentration
2
2
7
1
1
1
1
H), 7.34 (d, J = 3.8 Hz, 2H), 7.31 (s, 2H), 7.27 (d, J = 3.0 Hz,
H), 7.25 (d, J = 4.2 Hz, 4H), 6.99 (d, J = 4.0 Hz, 2H), 3.93 (d, J =
.4 Hz, 4H), 1.88 (s, 2H), 1.36–1.06 (br, 48H), 0.77 (t, J = 5.0 Hz,
2H). 1 C NMR (126 MHz, 373K, CDCl
3
CDCl , TMS): δ 160.68,
2 2
40.32, 139.31, 138.54, 137.94, 137.14, 135.19, 132.10,
30.11, 129.02, 127.42, 126.25, 125.64, 125.18, 124.86,
15.82, 108.60, 103.04, 45.81, 37.22, 30.87, 30.76, 29.05,
8.69, 28.66, 28.50, 28.25, 25.61, 25.57, 21.62, 21.58, 13.00.
-5
1
0 M) and on a quartz plate are shown in Figs. 1 and S2. In
chloroform solution, the maximum absorption wavelengths of
DPP-CN-DTE-1, DPP-CN-DTE-2, DPP-DTE-CN-1 and DPP-DTE-
CN-2 were 624, 632, 632 and 623 nm, respectively, with
almost no significant difference. In the thin films, the
maximum absorption wavelengths of DPP-CN-DTE-1, DPP-CN-
DTE-2, DPP-DTE-CN-1 and DPP-DTE-CN-2 were 760, 753, 762
and 752 nm, respectively, also without significant difference.
However, by comparing the absorption in solution and thin
film, we found two differences. The one difference was that
the corresponding absorption peak of the maximum
2
+
HRMS (MALDI): calcd. for
C H N NaO S
68 82 4 2 6
[M+Na]
(1201.4654); found: 1201.4646.
Results and discussion
Synthesis and thermal properties
In order to obtain CN-substituted DTE donor units, key
intermediates 2 and 4, we used the Knoevenagel condensation absorption wavelength of each material in solution was found
reaction method reported in the literature, under the action close to the Gaussian distribution while those in films
1
9
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J Po lue ran sael od fo Mn aot te rai ad l jsu Cs ht emm ai rs gt ri yn sC
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exhibited obvious shoulder peaks. The maximum absorption The absorption onsets of DPP-CN-DTE-1, DPP-CNV-iDewTAEr-ti2cl,e DOnPliPne-
wavelength of the thin films showed red shifted above 120 nm DTE-CN-1 and DPP-DTE-CN-2 are 842, 865
121‒136 nm) compared to those in the respective solution. It
D
,
O
8
I:
7
1
8
0.1
a
0
n
3
d
9/
8
C
7
9
2
TC
n
0
m
3726H
,
(
can be seen that the aggregation of the four materials in the
film is much higher than that in the corresponding solution. It
can be also reflected from the side angle that there was a high
degree of dispersion for this series of materials in the
chloroform solution. And there is almost no pre-aggregation
phenomenon for these four materials in solution, which should
be beneficial for the processing of corresponding OFET devices
by solution method. The peak shapes of the absorption peaks
at the maximum absorption wavelength of the four materials
are almost identical for each both in the solution and film
state. It is reflecting to some extent that the dispersion degree
in chloroform solution and the aggregation degree in film state
are almost the same for each of the four materials.
Fig. 1 UV-Vis-NIR absorption spectra of the conjugated
compounds (a) DPP-CN-DTE-1, (b) DPP-CN-DTE-2, (c) DPP-DTE-
CN-1 and (d) DPP-DTE-CN-2 in chloroform solutions and thin
films.
In addition, the onset of the UV-Vis-NIR absorption
spectrum (λonset) of the films was used to calculate the optical
band gap E (opt) based on the formula E (opt) = 1240/λonset.
g g
Table 1 Thermal, optical and electrochemical properties of small molecules based on DPP-DTE
a
o
b
b
c
Compd
T
d
( C)
λ
max (solution)(nm)
λ
max (film)(nm)
E
g
(opt) (eV)
EHOMO (eV)
ELUMO (eV)
DPP-CN-DTE-1
DPP-CN-DTE-2
DPP-DTE-CN-1
DPP-DTE-CN-2
404.7
396.0
402.0
396.3
624
632
632
623
760
753
762
752
1.47
1.43
1.41
1.42
-5.18
-3.65
-5.25
-3.72
-4.86
-3.70
-4.85
-3.71
a
Temperature at 5% weight loss. b Maximum absorption wavelengths in chloroform solution and film state. Calculated according to the
c
wavelength at the peak onset in the UV-Vis-NIR absorption spectra in the film state.
respectively, which were brought into the above formula to 4.4) eV at the starting point of the respective oxidation peaks
2
3
obtain the optical band gap of the compounds. Their optical and reduction peaks.
The initial oxidation/reduction
band gaps of 1.47, 1.43, 1.4, and 1.42 eV (Table 1) from DPP- potentials of DPP-CN-DTE-1, DPP-CN-DTE-2, DPP-DTE-CN-1,
CN-DTE-1, DPP-CN-DTE-2 to DPP-DTE-CN-1, and DPP-DTE-CN-2 and DPP-DTE-CN-2 are located at 0.78/-0.75 eV, 0.85/-0.68 eV,
show a gradual narrowing trend. The trend of band gap 0.46/−0.70 eV and 0.45/−0.69 eV, respectively (Fig. 2). As
narrowing from DPP-CN-DTE-1 to DPP-CN-DTE-2 is slightly shown in Table 1, based on these initial potential values and
more pronounced, while DPP-DTE-CN-1 and DPP-DTE-CN-2 calculated according to the above equations, the
showed almost no significant difference. This phenomenon can HOMO/LUMO energy levels of the compounds DPP-CN-DTE-1,
reflect a fact that for small molecules, when the CN group is DPP-CN-DTE-2, DPP-DTE-CN-1 and DPP-DTE-CN-2 were
close to the DPP acceptor unit, the length of the alkyl side ‒5.18/‒3.65, ‒5.25/‒3.72, ‒4.86/‒3.70 and ‒4.85/‒3.71 eV,
chain on the acceptor unit generated a relatively significant respectively. These observations indicate that the position of
effect impacting on the optical band gap. The above results the CN substitution of the conjugated backbone has a
indicated that the aggregation state's difference of these
conjugated compounds in the solution and film states is
significant. But on the conjugated backbone, neither the CN
substitution position of the donor unit nor the different length
of the alkyl side chain on the acceptor unit shows significant
effect impacting on the absorption spectra.
Electrochemical Properties
We used cyclic voltammetry (CV) to study the electrochemical
performance of the four conjugated compounds based on
DPP-DTE. In the CV test, silver/silver chloride (Ag/AgCl) was
used as a reference electrode, trace ferrocene as an internal
standard, and a Pt electrode coated with a thin film of the
conjugated compound as
a
working electrode. All
measurements were carried out at room temperature under a
nitrogen atmosphere. The HOMO and LUMO energy levels of
the conjugated compounds were estimated by using the
onset
onset
equations EHOMO = ― (퐸ox + 4.4) eV and ELUMO = ― (퐸re
+
4
| J. Name., 2012, 00, 1-3
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ARTICLE
Fig. 2 Cyclic voltammetry curves of the thin films for the DPP- configurations were fabricated. We annealed theVitehwinArtficillemOsnlionef
DTE-based compounds in an acetonitrile solution containing the DPP-DTE-based compounds DPP-CN-
.1 M electrolyte n-Bu NPF and trace ferrocene as internal DPP-DTE-CN-1 and DPP-DTE-CN-2 at their own optimal
standard.
D
D
O
T
I
E
:
-
1
1
0.
,
10
D
3
P
9
P
/C-C9T
N
C
-
0
D
3
T
7
E-2,
2
6
H
0
4
6
o
annealing-temperatures of 140, 180, 100 and 100 C,
respectively. All OFET devices based on the compounds DPP-
significant effect on their HOMO energy levels, while the alkyl CN-DTE-1, DPP-CN-DTE-2, DPP-DTE-CN-1 and DPP-DTE-CN-2
side chain has no significant effect. In addition, the differences exhibited p-type field-effect properties under air conditions.
between the electrochemical band gaps and the optical band Typical transfer and output curves for OFET devices based on
gaps of these four small-molecule compounds are 0.06–0.28 the four compounds are shown in Fig. 3, and the
eV, which is within the acceptable experimental error range corresponding parameters are collected in Table 2. The listed
2
4
according to the literature.
saturation mobilities were obtained from the transfer curves
of the OFET devices. Among the four compounds, DPP-CN-
DTE-1 showed much higher hole mobility than those of the
Theoretical calculations
To further understand the frontier molecular orbital features other three materials. The highest hole mobility of DPP-CN-
2
‒1 ‒1
DTE-1 reached 2.52 cm
V
s , which was two orders of
the molecular geometries, we replaced the alkyl side chain
with methyl group to simply the two small molecules DPP-DTE-
CN-1 and DPP-CN-DTE-1 before theoretically calculated them
using Guassian 09 software at the density functional theory
magnitude higher compared with the other three compounds.
The highest hole mobility of the materials DPP-CN-DTE-2, DPP-
-2
-2
DTE-CN-1 and DPP-DTE-CN-2 were 1.92×10 , 2.30×10 and
2
2
‒1 ‒1
2
.17×10- cm V s , respectively. The above results indicated
(DFT)/B3LYP/6-31G (d) level. The theoretical calculation results
that the CN groups on the inner side with a larger alkyl side
chain substituted on the DPP were beneficial for greatly
increasing the carrier transport properties and obtaining
higher hole mobility.
(Fig. S3) show that both the molecules possess very good
planarity, the introduction of the CN unit does not cause the
distortion of the molecular backbone, and their HOMO and
LUMO are all delocalized throughout the molecular backbone.
The difference in the position of the CN unit does not cause a Characterization of thin film microstructure
significant difference in the HOMO and LUMO energy levels of To further understand the relationship between the field-
effect properties of DPP-DTE-based compounds and their
molecular structures, the intermolecular stacking and surface
topography of their thin films were studied by means of 2D-
GIXRD and AFM experiments. Figure 4 shows the 2D-GIXRD
patterns of the thin films for the four compounds DPP-CN-DTE-
the two molecules. It is speculated that the significant
difference of their HOMO energy levels obtained from the
above CV detections maybe due to the influence of the inter-
molecular arrangement and crystallization caused by the
interaction of the alkyl chain and the inner CN group.
1
, DPP-CN-DTE-2, DPP-DTE-CN-1 and DPP-DTE-CN-2 before and
after annealing at their own optimal annealing-temperatures
Charge carrier transport performance.
In order to study the field-effect characteristics of the four
DPP-DTE-based compounds, the OFET devices with the BGBC
o
1
40, 180, 100 and 100 C, respectively. We found through the
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Fig. 3 Transfer and output curves of the OFET devices based on the compounds (a,b) DPP-CN-DTE-1, (c,d) DPP-CN-DTE-2, (e,f)
View Article Online
DOI: 10.1039/C9TC03726H
o
DPP-DTE-CN-1 and (g,h) DPP-DTE-CN-2 after annealing at 140, 180, 100 and 100 C, respectively.
Table 2 The performances of OFET devices with BGBC configurations and relevant crystallographic parameters of thin films for
the DPP-DTE-based compounds
2
‒1 ‒1
a
a
Compd
µ
hmax (rt/annealed) (cm V s )
I
ON/IOFF
Vth (V)
d‒d (Å)
π‒π (Å)
4
5
6
8
8
DPP-CN-DTE-1
DPP-CN-DTE-2
DPP-DTE-CN-1
DPP-DTE-CN-2
0.96 / 2.52
10 ‒10
2.32
17.4
15.0
24.7
17.7
3.48
3.50
3.98
3.56
-3
‒2
5
8.26×10 / 1.92×10
10 ‒10
‒4.57
‒42.55
‒18.30
1.08×10‒ / 2.30×10‒2
2
10 ‒10
7
1.04×10‒ / 2.17×10‒2
2
10 ‒10
7
a
The stacking distances calculated from the annealed films.
Fig. 4 GIXRD patterns of the (a) DPP-CN-DTE-1, (b) DPP-CN-DTE-2, (c) DPP-DTE-CN-1 and (d) DPP-DTE-CN-2 thin films before and
o
after annealing at 140, 180, 100 and 100 C, respectively.
Fig. 5 AFM height maps of the (a) DPP-CN-DTE-1, (b) DPP-CN-DTE-2, (c) DPP-DTE-CN-1 and (d) DPP-DTE-CN-2 thin films before
o
and after annealing at 140, 180, 100 and 100 C, respectively.
corresponding processing and analysis of Fig. 4 that d‒d peaks of the DPP-CN-DTE-1, DPP-CN-DTE-2, DPP-DTE-CN-1 and
separation distance values of 17.4, 15.0, 24.7 and 17.7 Å were DPP-DTE-CN-2 thin films, respectively. In the in-plane (qxy
)
corresponding to the out-of-plane (q )-oriented (100) Bragg orientation, the four thin films had distinct (010) Bragg in-
z
6
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ARTICLE
plane peaks, in which DPP-CN-DTE-1 and DPP-CN-DTE-2 were morphology, molecular packing mode and carrieVriemw oArbticilleitOyn.liInne
particularly significant. The corresponding π‒π stacking other words, the position of the CN play ta
D
e
O
d
I: 1
a
0
n
.10im39
p
/C
o
9
r
T
C
n
0
t
37
role
2
6
H
distances of DPP-CN-DTE-1, DPP-CN-DTE-2, DPP-DTE-CN-1 and in regulating the electronic structure of the molecule, the
DPP-DTE-CN-2 were 3.48, 3.50, 3.98, and 3.56 Å, respectively. accumulation between the conjugated backbones, and the
All of the above related parameters can be found in Table 2. intermolecular interaction, and thus affecting the
According to the (010) Bragg peaks in the in-plane (qxy) and microstructure of the thin film and carrier transport
2
5-28
out-of-plane (q
z
) directions provided by the 2D-GIXRD spectra, performance.
The CN groups on the inner-side of the
we can infer that among the four compounds, both DPP-CN- molecule backbone was beneficial to lower the HOMO energy
DTE-1 and DPP-CN-DTE-2 tend to adopt edge-on packing levels, and their corresponding thin films were advantageous
mode, while the DPP-DTE-CN-1 and DPP-DTE-CN-2 are for adopting a more orderly layered stacking pattern. Under
amorphous in Fig. 4. In this mode, the thin films of DPP-CN- the combination of the inner-side substituted CN groups and
DTE-1 and DPP-CN-DTE-2 with the electron-absorbing CN the larger 2-mercaptotetradecyl group on the DPP unit, the
groups on the donor unit DTE and near to the acceptor unit DPP-CN-DTE-1 was more favourable to exhibit a continuous
DPP (inner-side) showed a more obvious edge-on-based film morphology and thus was more conducive for charge
molecular packing pattern. Interestingly, the DPP-CN-DTE-1 carrier transport to achieve higher p-type field-effect
thin film showed the strongest (h00) diffraction peaks from performance.
(
100) up to (400) (Fig. 4a). The DPP-CN-DTE-2 thin film
exhibited strong (h00) diffraction peaks from (100) up to (300)
(
Fig. 4b). Meanwhile, the thin films of DPP-DTE-CN-1 and DPP- Conclusions
DTE-CN-2 with CN groups substituted on outer-side only
showed diffraction peaks of (100) (Fig. 4c and 4d). This
phenomenon indicated that among these four DPP-DTE-based
small-molecule compounds, DPP-CN-DTE-1 and DPP-CN-DTE-2
Four DPP-DTE-based D–A type conjugated small-molecule
compounds DPP-CN-DTE-1, DPP-CN-DTE-2, DPP-DTE-CN-1 and
DPP-DTE-CN-2 were designed and synthesized by tuning alkyl
with the CN groups substituted on the inner-side exhibited side chain size and electron-withdrawing group CN
better crystallinity and more ordered layer-structure than substitution position. Their thermal properties, optical
those of DPP-DTE-CN-1 and DPP-DTE-CN-2 with CN substituted absorption spectra, electrochemical properties, carrier
on the outer-side. In addition, from Fig. 4, we also observed
that both the length of the alkyl side chain on the DPP unit and
the annealing treatment of the films exhibited no obvious
influence on the ordering of the molecular layer-structure.
For the surface morphology of thin films of the four DPP-
DTE-based compounds, we used the Tapping mode AFM for
detection. The height profiles of the DPP-CN-DTE-1, DPP-CN-
DTE-2, DPP-DTE-CN-1 and DPP-DTE-CN-2 thin films before and
transport properties, microscopic arrangement and surface
morphology of the films were systematically studied. The
compounds show good thermal stabilities and solution
dispersibility, which provided guarantees for the solution
processing and annealing optimization of their OFET devices.
The substituted position of CN had a great influence on the
electronic structure, film surface morphology, molecular
packing mode and carrier mobility of these compounds. The
after annealing at their own optimal annealing-temperatures
o
1
40, 180, 100 and 100 C, respectively, are shown in Fig. 5. The CN on the inner-side was favorable for lowering the HOMO
temperatures before and in annealing were room temperature energy levels and adopting orderly layered packing mode in
rt) and the optimum annealing ones, respectively. The thin film. The structure-performance relationship indicated
(
morphologies of the four thin films were improved to some
extent after annealing. The morphology of the DPP-CN-DTE-1
film both before and after annealing showed obvious fish bone
combined with the mesh shape. This kind of surface
morphology of the film is generally favourable for the charge
carrier transport, which can prove the high mobility of the
compound DPP-CN-DTE-1 from a certain angle. The films of the
other three compounds DPP-CN-DTE-2, DPP-DTE-CN-1 and
DPP-DTE-CN-2 showed a granular morphology before and after
that the alkyl side-chain length and the CN substituted position
significantly affected the carrier transport properties.
Combined with inner-side substituted CN and longer side-
chain 2-mercaptotetradecyl, the DPP-CN-DTE-1 exhibited a
more continuous film morphology, which was more conducive
for charge carrier transport to obtain higher p-type OFET
performance than those of other three compounds. Among
these four compounds, DPP-CN-DTE-1 showed the highest
2
annealing. This granular morphology reflected the OFET performance with its maximum hole-mobility of 2.52 cm
‒
1
‒1
arrangement continuity among the molecules of the material
s . The above results provided a promising approach to
was relatively poor, and even there were relatively obvious develop excellent small-molecular OFET materials with high
V
grain boundaries, which were obviously not conducive to
charge carrier transport. The apparent difference in
morphology of the above-mentioned four thin films may lead
to the difference in their charge carrier mobility. It can be
reflected from the side for the inevitability that the compound
DPP-CN-DTE-1 exhibited a higher hole-mobility than DPP-CN-
DTE-2, DPP-DTE-CN-1 and DPP-DTE-CN-2 did.
hole-mobility, good solution processability and good thermal
stability.
Conflicts of interest
There are no conflicts to declare.
These 2D-GIXRD and AFM results of the four DPP-DTE-
based compounds were combined with charge carrier
transport mobilities. We found that the CN substitution Acknowledgements
position on the DTE donor unit had a great influence on the
compound's electronic structure, the film's surface
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This work was supported under the financial support from the 23. Y. Cui, X. Zhang and S. A. Jenekhe, MacromolecuVlieews,A1rti9c9le9O,n3lin2e,
824-3826.
3
DOI: 10.1039/C9TC03726H
National Key Research and Development Program of China
2017YFA0204703 and 2016YFB0401100) and the National
2
2
2
2
2
4. D. Gao, Z. Chen, Z. Mao, J. Huang, W. Zhang, D. Li and G. Yu,
RSC Adv., 2016, 6, 78008-78016.
5. J. Mei, D. H. Kim, A. L. Ayzner, M. F. Toney and Z. Bao, J. Am.
Chem. Soc., 2011, 133, 20130-20133.
6. J. Lee, A. R. Han, J. Kim, Y. Kim, J. H. Oh and C. Yang, J. Am.
Chem. Soc., 2012, 134, 20713-20721.
7. J. Yao, C. Yu, Z. Liu, H. Luo, Y. Yang, G. Zhang and D. Zhang, J.
Am. Chem. Soc., 2016, 138, 173-185.
(
Natural Science Foundation of China (51773016, 21673258,
and 21774134). The scientists from 1W1A station of Beijing
Synchrotron Radiation Facility (BSRF) and the BL14B1 Station
of Shanghai Synchrotron Radiation Facility (SSRF) gave much
assistance during the GIXRD tests for this work. The authors
sincerely thank them all.
8. W. Zhang, Z. Chen, Z. Mao, D. Gao, C. Wei, Z. Lin, J. Huang, L.
Wang and G. Yu, Dyes Pigments, 2018, 149, 149-157.
Notes and references
1
2
3
.
.
.
D. X. Long, E. Y. Choi and Y. Y. Noh, ACS Appl. Mater.
Interfaces, 2017, 9 , 24763-24770.
M. Wang, M. J. Ford, A. T. Lill, H. Phan, T. Q. Nguyen and G. C.
Bazan, Adv. Mater., 2017, 29, 1603830.
B. Fu, J. Baltazar, A. R. Sankar, P. H. Chu, S. Zhang, D. M.
Collard and E. Reichmanis, Adv. Funct. Mater., 2014, 24, 3734-
3
744.
4
5
.
.
J. Y. Back, H. Yu, I. Song, I. Kang, H. Ahn, T. J. Shin, S. K. Kwon,
J. H. Oh and Y. H. Kim, Chem. Mater., 2015, 27, 1732-1739.
S. Ghosh, R. Raveendran, A. Saeki, S. Seki, M. A. Namboothiry
and A. Ajayaghosh, ACS Appl. Mater. Interfaces, 2019, 11,
1
088-1095.
6
.
T. He, P. Leowanawat, C. Burschka, V. Stepanenko, M. Stolte
and F. Wurthner, Adv. Mater., 2018, 1804032.
7
8
9
.
.
.
B. Lim, H. Sun and Y. Y. Noh, Dyes Pigments, 2017, 142, 17-23.
B. Lim, H. Sun, J. Lee and Y. Y. Noh, Sci. Report., 2017, 7, 164.
G. Zhang, Y. Zhao, B. Kang, S. Park, J. Ruan, H. Lu, L. Qiu, Y.
Ding and K. Cho, Chem. Mater., 2019, 31, 2027-2035.
1
1
0. K. Hyodo, S. Nishinaga, Y. Sawanaka, T. Ishida, H. Mori and Y.
Nishihara, J. Org. Chem., 2019, 84, 698-709.
1. T. Delouche, A. Mocanu, T. Roisnel, R. Szucs, E. Jacques, Z.
Benko, L. Nyulaszi, P. A. Bouit and M. Hissler, Org. Lett., 2019,
2
1, 802-806.
1
1
2. K. Shi, W. Zhang, C. Wei, Z. Lin, X. Liu and G. Yu, J. Polym. Sci.,
Part A: Polym. Chem., 2018, 56, 1012-1019.
3. G. Conboy, R. G. D. Taylor, N. J. Findlay, A. L. Kanibolotsky, A.
R. Inigo, S. S. Ghosh, B. Ebenhoch, L. K. Jagadamma, G. K. V. V.
Thalluri, M. T. Sajjad, I. D. W. Samuel and P. J. Skabara, J.
Mater. Chem. C, 2017, 5, 11927-11936.
1
1
1
1
4. W. Zhang, Z. Mao, N. Zheng, J. Zou, L. Wang, C. Wei, J. Huang,
D. Gao and G. Yu, J. Mater. Chem. C, 2016, 4, 9266-9275.
5. H. Burckstummer, A. Weissenstein, D. Bialas and F. Wurthner,
J. Org. Chem., 2011, 76, 2426-2432.
6. J. Lee, S. Cho, J. H. Seo, P. Anant, J. Jacob and C. Yang, J.
Mater. Chem., 2012, 22, 1504-1510.
7. D. Cortizo-Lacalle, S. Arumugam, S. E. T. Elmasly, A. L.
Kanibolotsky, N. J. Findlay, A. R. Inigo and P. J. Skabara, J.
Mater. Chem., 2012, 22, 11310-11315.
1
1
2
2
2
8. J. Lee, A. R. Han, J. Hong, J. H. Seo, J. H. Oh and C. Yang, Adv.
Funct. Mater., 2012, 22, 4128-4138.
9. H. J. Yun, S. J. Kang, Y. Xu, S. O. Kim, Y. H. Kim, Y. Y. Noh and S.
K. Kwon, Adv. Mater., 2014, 26, 7300-7307.
0. N. S. Cho, D. H. Hwang, B. J. Jung, E. Lim, J. Lee and H. K. Shim,
Macromolecules, 2004, 37, 5265-5273.
1. F. Yang, X. L. Xu, Y. H. Gong, W. W. Qiu, Z. R. Sun, J. W. Zhou,
P. Audebert and J. Tang, Tetrahedron, 2007, 63, 9188-9194.
2. Y. Li, S. P. Singh and P. Sonar, Adv. Mater., 2010, 22, 4862-
4
866.
8
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Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C9TC03726H
Small-molecule compounds based on diketopyrrolopyrrole and cyano substituted
dithiophene-ethylene were synthesized and their properties were systematically studied.