New core-expanded naphthalene diimides with different functional groups for air-stable solution-processed organic n-type semiconductors

Article abstract of DOI:10.1039/c3nj00050h

Among the reported organic n-type semiconductors, naphthalene diimide (NDI) derivatives have received increasing attention. In this paper, we report four non-symmetric core-expanded NDI derivatives 1-4. Electrochemical, absorption spectral and theoretical

Full text of DOI:10.1039/c3nj00050h

New Journal of Chemistry
A journal for new directions in chemistry
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Volume 37 | Number 6 | June 2013 | Pages 1633–1844
ISSN 1144-0546
PAPER
Guanxin Zhang, Deqing Zhang et al.
New core-expanded naphthalene diimides with different functional groups
for air-stable solution-processed organic n-type semiconductors

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New core-expanded naphthalene diimides
with different functional groups for air-stable
solution-processed organic n-type semiconductors†
Cite this: NewJ.Chem., 2013,
37, 1720
Xin Chen, Jianguo Wang, Guanxin Zhang,* Zitong Liu, Wei Xu and Deqing Zhang*
Among the reported organic n-type semiconductors, naphthalene diimide (NDI) derivatives have
received increasing attention. In this paper, we report four non-symmetric core-expanded NDI
derivatives 1–4. Electrochemical, absorption spectral and theoretical calculation studies show that LUMO
energies of 1–4 are lower than that of parent NDI without substitution. OFET devices based on thin
films of 1–4 which can be easily solution-processed are fabricated with conventional techniques and
they show n-type semiconducting behaviours. Moreover, the performance of OFET devices of 1–4
can be significantly improved by annealing their thin films. OFETs of 3 exhibit electron mobility up to
0.17 cm2 VÀ1 sÀ1 with high on/off ratio (under ambient conditions) after annealing.
Received (in Montpellier, France)
13th January 2013,
Accepted 25th March 2013
DOI: 10.1039/c3nj00050h
www.rsc.org/njc
1,4,5,8-Naphthalene diimide (NDI) and its derivatives have
been intensively investigated for n-type semiconductors.9–11
Introduction
Organic semiconducting materials have received increasing
attention in recent years because of their promising applications
in various areas such as organic field-effect transistors (OFETs),
organic light-emitting diodes (OLEDs), organic light-emitting
transistors (OLETs), organic solar cells (OSCs) and sensors.1
Until now, various organic semiconductors bearing p-type,
n-type or ambipolar properties have been disclosed in large
numbers.2–6 For instance, Takimiya et al. described a series of
thiophene-containing conjugated molecules for p-type semi-
conductors which exhibit high hole mobilities and good air
stabilities.7 However, air-stable n-type organic semiconductors
with high electron mobilities are still limited mainly because of
the fact that anions of normal conjugated molecules are
sensitive to oxygen and water.8 Naturally, the OFETs that can
work in air are desirable for future applications. Thus, organic
n-type semiconductors which are stable under OFETs working
conditions are demanding. It is known that organic conjugated
molecules with low LUMO energies are potential candidates for
air-stable n-type semiconductors.
However, the LUMO energy of NDI itself is around À3.9 eV
which is not low enough to enable efficient electron injection
from electrodes and increase the air stability of the NDI
anion.10 In order to lower the LUMO energy, various functional
groups are connected to an NDI core. Previous studies manifest
that the fusion of functional groups at core positions of NDI
can efficiently tune the energy levels of front orbitals.11 For
instance, Gao et al. introduced two 2-(1,3-dithiol-2-ylidene)-
malonitrile (electron withdrawing) groups to the NDI core,
and the LUMO energy was significantly lowered; the resulting
OFETs exhibited electron mobilities up to 1.2 cm2 VÀ1 sÀ1 in
air.12 An alternating NDI–bithiophene polymer was reported by
Facchetti et al., and the top gate bottom contact OFETs showed
electron mobilities up to 0.85 cm2 VÀ1 sÀ1 under ambient
conditions.9 Some of us have very recently described NDI
derivatives entailing 1,3-dithole-2-thione (-one) moieties, and
they showed n-type semiconducting behaviour with electron
mobility up to 0.05 cm2 VÀ1 sÀ1 in air.13 Alternatively, incorporation
of electron donating groups into an NDI core can change the
semiconducting behaviour from n-type to ambipolar and even
to p-type. For instance, we described ambipolar and p-type
semiconductors based on NDI with tetrathiafulvalene groups.14
Wu¨rthner et al. also reported p-type and ambipoar semiconductors
based on core-expanded NDI.15
Beijing National Laboratory for Molecular Sciences, Organic Solids Laboratory,
Institute of Chemistry, Chinese Academy of Sciences, Beijing 100190, China.
E-mail: dqzhang@iccas.ac.cn
† Electronic supplementary information (ESI) available: TGA analysis, cyclic
voltammograms, UV-Vis spectra, DFT calculation data, XRD patterns and AFM
images of thin films of 2 and 4, transfer and output characteristics for OFET of 2
and 4, 1H NMR and 13C NMR spectra of all new compounds. See DOI: 10.1039/
c3nj00050h
In this paper, we report four NDI derivatives 1–4 (Scheme 1)
with thiazole, 1,3-dithole-2-thione and 2-(1,3-dithiol-2-ylidene)-
malonitrile moieties at the core positions. The molecular design
c
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yielded in high yields from 4BrNDI and thioamide derivatives
without catalysts.16 After properly adjusting the reaction conditions,
mono-thiazole-fused NDI derivatives 5 and 6 were obtained in more
than 70% yield. Further separate reactions of 5 and 6 with
(n-Bu4N)2Zn(dmit)2 (dmit = 1,3-dithiole-2-thione-4,5-dithiolate)
or sodium 2,2-dicyanoethene-1,1-bis(thiolate) led to 1, 2, 3
and 4 in 94, 96, 71 and 82% yields, respectively, under mild
conditions.
The chemical structures and purities of compounds 1–4
were established and confirmed by spectroscopic data and
elemental analysis (see Experimental section). Compounds
1–4 show good solubilities (410 mg mLÀ1) in common solvents
such as CH2Cl2, CHCl3, THF and dichlorobenzene. Based on
TGA analysis (see Fig. S1, ESI†) compounds 1 and 2 show an
early weight loss at around 270 1C. This may be due to the
decomposition or loss of the 1,3-dithiole-2-thione moiety
within 1 and 2. However, 3 and 4 are thermally stable below
370 1C.
Cyclic voltammograms of 1–4 were measured and their
reduction potentials were determined (see Table 1). As examples,
Fig. 1 and S2 (ESI†) show cyclic voltammograms of 1–4. 1 and 2
show two quasi-reversible reduction waves, whereas 3 and 4
exhibit three quasi-reduction waves. Based on the respective
onset reduction potentials, the respective LUMO energies of
Scheme 1 Chemical structures of 1, 2, 3 and 4 and their synthetic approaches.
is based on the following considerations: (1) connection of thiazole,
1,3-dithole-2-thione and 2-(1,3-dithiol-2-ylidene)malonitrile moieties
to the NDI core can lower the LUMO energy to different extents
according to previous reports;12–14,16 (2) non-symmetric substitution
of these groups to the NDI core may be able to finely tune the
LUMO/HOMO energies to match well with the work function of
electrodes. Such non-symmetric substitution will allow the
introduction of different functional groups to the NDI core,
and thus the intermolecular interactions can be further tuned;17
(3) connection of these groups to the NDI core may be beneficial
for extending pi-conjugation and increasing intermolecular
interactions; (4) these NDI derivatives are easily accessible as
to be discussed below. The results reveal that new NDI derivates
1–4 behave as air-stable n-type semiconductors and electron
mobility of OFETs based on 3 can reach 0.17 cm2 VÀ1 sÀ1 in air.
1–4 were estimated to be À4.16, À4.15, À4.35 and À4.35 eV,
red1
respectively, by employing the equation:18 LUMO = À(E
+
onset
4.41) eV. Compared to that of unsubstituted NDI, LUMO ener-
gies of 1–4 are obviously lowered. This may be caused by the
following effects: (1) elongation of conjugation; and (2) electron-
induction due to the functional groups in 1–4. Moreover, 3 and 4
exhibit lower LUMO energies than 1 and 2. This is likely due to
the strong electron-withdrawing characteristics of 2-(1,3-dithiol-
2-ylidene)malonitrile moieties in 3 and 4.
Fig. 2 shows the absorption spectra of solutions as well as
thin films of 1 and 3. Compared to those of their solutions, the
onset absorptions of thin films of 1 and 3 were obviously red-
shifted. This is probably owing to the intermolecular inter-
actions within thin films of 1 and 3. The band gaps of 1 and 3
were estimated to be 1.64 and 2.02 eV, respectively, according to
the respective onset absorption wavelengths of thin films of 1
and 3. Therefore, HOMO energies of 1 and 3 were estimated to
be À5.80 and À6.37 eV, respectively. Similarly, band gaps of 2
Results and discussion
Synthesis and characterization
The synthesis of compounds 1–4 started from 2,3,6,7-tetra- and 4 (based on Fig. S3, ESI†) were determined and their
bromo-NDI (4BrNDI), as depicted in Scheme 1. As reported HOMO energies were estimated to be À5.77 and À6.38 eV,
previously by us, dithiazole-fused NDI derivatives could be respectively (see Table 1).
Table 1 Absorption and electrochemical data, HOMO/LUMO energies and band gaps of 1–4
lmax (nm)
Solutiona Film
red1 b
1/2
red2 b
1/2
red3 b
Compounds
E
(V)
E
(V)
E
1/2
(V) LUMO (eV) Expc (Cal)d HOMO (eV) Expc (Cal)d Eg (eV) Expc (Cal)d
1
2
3
4
456, 546
442, 558
334, 546
322, 532
464, 590 À0.35
451, 604 À0.35
356, 578 À0.14
349, 573 À0.15
À0.77
À0.77
À0.30
À0.30
À4.16 (À3.70)
À4.15 (À3.71)
À4.35 (À3.92)
À4.35 (À3.94)
À5.80 (À5.95)
À5.77 (À5.97)
À6.37 (À6.42)
À6.38 (À6.49)
1.64 (2.25)
1.62 (2.26)
2.02 (2.50)
2.03 (2.55)
À0.69
À0.69
a
b
Measured in CH2Cl2 solutions of 1–4 (1.0 Â 10À5 M). Measured in CH2Cl2 solutions containing n-Bu4NPF6 (0.1 M) at a scan rate of 100 mV sÀ1
.
c
red1
onset
d
Estimated from the following equations: LUMO = À(4.41 + E
), HOMO = LUMO À Eg (Exp.). Based on the DFT calculations.
c
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Fig. 1 Cyclic voltammograms of 1 and 3 in CH2Cl2 (1.0 Â 10À3 M) at a scan rate
of 100 mV sÀ1, with Pt as the working and counter electrodes and Ag/AgCl
electrode (saturated KCl) as the reference electrode, and n-Bu4NPF6 (0.1 M) as
supporting electrolyte.
Fig. 3 LUMO, HOMO orbitals and structures of compounds 1 (A) and 3 (B)
obtained by DFT calculations; the alkyl chains were replaced by methyl groups in
the calculations.
À3.70 eV/À5.95 eV, À3.71 eV/À5.97 eV, À3.92 eV/À6.42 eV and
À3.94 eV/À6.49 eV, respectively. The solvent effects were not
included in the theoretical calculations and thus there were
differences between the LUMO/HOMO energies calculated
theoretically and those obtained based on the electrochemical
and spectroscopic data (see Table 1).14,19 But, these results do
indicate that the introduction of functional moieties to the NDI
core can effectively tune their LUMO/HOMO levels.
OFETs based on thin films of 1–4
Bottom gate bottom contact OFETs (organic field effect tran-
sistors) with thin films of 1–4 were fabricated with conventional
techniques. All of the thin films show typical n-type semiconducting
behaviours in the air, and their performances increase after
annealing thin films of 1–4 at different temperatures. Fig. 4
depicts the transfer and output characteristics for OFETs with
thin films of 1 and 3 after annealing at 180 1C. The electron
mobilities and on/off ratios as well as threshold voltages for
OFETs of 1–4 were deduced accordingly and listed in Table 2.
The electron mobility of the OFETs with thin films of 1 is
0.019 cm2 VÀ1 sÀ1 after annealing at 120 1C and it increases to
Fig. 2 The normalized absorption spectra of the solutions and thin films of
1 and 3.
DFT calculations
The chemical structures of 1–4 were investigated with theoretical
calculations based on density functional theory (DFT). The alkyl 0.034 cm2 VÀ1 sÀ1 after annealing at 160 1C. After further
annealing at 180 1C, me reaches 0.043 cm2 VÀ1 À1. Simulta-
s
chains in 1–4 were replaced by methyl groups in the calculations.
As depicted in Fig. 3 and S4 (ESI†), the NDI core and the thiazole
ring are coplanar with each other in 1–4. Also, NDI cores are
coplanar with 2-(1,3-dithiol-2-ylidene)malonitrile moieties in 3
and 4. The 1,3-dithiole-2-thione unit forms a dihedral angle of
about 1281 with the NDI core in 1 and 2. HOMO orbitals of 1 and
2 are mainly localized on the 1,3-dithiole-2-thione moiety, while
neously, the on/off ratio increases, whereas the threshold
voltage decreases for OFETs of 1 after annealing (see Table 2).
The electron mobility and on/off ratio for OFETs of 3 also
increase after annealing the thin films. The maximum mobility
reaches 0.069 cm2 VÀ1 sÀ1 for OFETs of 3 after annealing at
180 1C, as listed in Table 2. As shown in Table 2, electron
the LUMO orbitals are delocalized throughout the NDI core and mobilities of OFETs of 2 and 4 increased from 1.8 Â 10À2
to 3.8 Â 10À2 cm2 VÀ1
s
À1, and from 3.8 Â 10À3 to 8.0 Â
the thiazole ring (see Fig. 3 and S4, ESI†). The corresponding two
10À2 cm2 VÀ1 sÀ1, respectively, after temperature annealing from
120 to 180 1C. This significant increase in me for OFETs of 1–4 after
annealing is in agreement with the respective morphological
changes within their thin films as to be discussed below.
sulfur atoms attached to the NDI core also contribute slightly to
the respective LUMO orbitals. As depicted in Fig. 3 and S4 (ESI†),
both LUMO and HOMO orbitals of 3 and 4 are more delocalized.
LUMO/HOMO energies of 1, 2, 3 and 4 were calculated to be
c
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Table 2 The electron mobilities (me), threshold voltages (Vth), and on/off ratios
(Ion/off) for bottom contact OFET devices based on thin films of 1–4 after
annealing at different temperatures
Compound
T/1C me a/cm2 VÀ1 sÀ1 Vth/V Ion/off
1
120 0.011 (0.019)
160 0.026 (0.034)
180 0.035 (0.043)
120 0.0080 (0.018)
160 0.018 (0.027)
180 0.027 (0.038)
120 0.011 (0.018)
160 0.043 (0.051)
180 0.062 (0.069)
30–36 6.7 Â 105–1.2 Â 106
20–27 3.5 Â 106–8.3 Â 106
14–18 5.7 Â 106–1.0 Â 107
28–32 4.2 Â 104–1.1 Â 105
14–18 2.4 Â 104–1.8 Â 105
14–17 3.6 Â 104–3.1 Â 105
12–18 7.1 Â 104–1.5 Â 105
9–14 2.7 Â 105–5.6 Â 105
4–6 5.8 Â 105–1.0 Â 106
8–15 1.4 Â 105–3.2 Â 105
5–9 6.4 Â 105–3.6 Â 106
À5–0 1.0 Â 106–7.6 Â 106
2
3
3 (modified Au) 120 0.016 (0.031)
160 0.073 (0.083)
180 0.13 (0.17)
4
120 0.0027 (0.0038) 16–18 8.3 Â 103–5.6 Â 104
160 0.009 (0.014)
180 0.073 (0.080)
12–14 3.4 Â 104–7.2 Â 104
0–6 7.4 Â 104–2.1 Â 105
a
The mobilities were provided in ‘‘average (highest)’’ form, and the
performance data were obtained based on more than 10 different
OFETs.
days and then remained almost unaltered after an additional
seven days. The electron mobilities and Ion/off of OFETs of 3 and
4 were decreased to ca. 70% and ca. 80% of the respective initial
ones after 10 days. However, for OFETs of 1 and 2, their electron
mobilities and Ion/off decreased more significantly after being
left in air for 10 days (see Fig. S6, ESI†). Therefore, compounds
3 and 4 show more air-stable semiconducting behavior than 1
and 2. This agrees well with the fact that 3 and 4 exhibit lower
LUMO energies than 1 and 2 (see Table 1).
XRD and AFM investigations
In order to understand the enhancement of electron mobility of
OFETs of 1–4 after annealing their thin films, XRD and AFM
studies were carried out. Thin films of 1–4 exhibit typical
lamellar structures because of the presence of integral multiple
diffraction peaks as depicted in Fig. 5 and S7 (ESI†). As shown
in Fig. 5(A), diffraction peaks at 4.0 and 7.91, corresponding to
d-spacings of 2.2 and 1.1 nm, respectively, were detected for the
thin film of 1 after annealing at 120 1C. After further annealing
at 160 and 180 1C, the intensity of the diffraction peaks
increased. Meanwhile, more diffraction peaks at 11.9 and
Fig. 4 Transfer and output characteristics for OFETs of 1 (A and B) and 3 (C and D)
after annealing at 180 1C; the channel width (W) and length (L) were 1440 and
50 mm, respectively.21
Furthermore, the electron mobility for OFETs of 3 can be 15.91, corresponding to d-spacings of 0.74 and 0.56 nm, respec-
further enhanced after modification of drain-source Au electro- tively, emerged. These XRD data clearly manifest that mole-
des with pentafluorothiophenol, reaching 0.17 cm2 VÀ1 sÀ1 cules of 1 are more orderly arranged and crystallinity is
after annealing at 180 1C. This is probably due to the modifica- improved for the thin film of 1 after annealing. This agrees
tion of interfacial properties and the work function of Au well with the observation that electron mobility of OFETs
electrodes according to previous reports.20 Note that efforts increases after annealing the thin films of 1 (see Table 2).22
were also made to increase the electron mobilities of OFETs Similarly, intensities of diffraction peaks at 3.8 and 7.41
with 1, 2 and 4 by modifying the drain-source Au electrodes (corresponding to d-spacing of 2.3 nm and 1.2 nm, respectively)
with pentafluoro-benzenethiol. However, obvious increases of were largely enhanced and new peaks at 11.1 and 14.71 (corres-
me were not achieved.
ponding to d-spacings of 0.80 and 0.60 nm, respectively)
Additionally, air-stabilities of OFETs of 1–4 were examined appeared after annealing of thin films of 3 at 160 and 180 1C.
by leaving the devices in air and measuring their performances Note that the diffraction patterns of thin films of 1 and 3 after
at different times. As depicted in Fig. S6 (ESI†), their electron annealing at 160 1C are similar to the respective ones after
mobilities decreased by various degrees after the first three annealing at 180 1C. The XRD patterns of thin films of 2 and 4
c
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120 to 160 and 180 1C. Furthermore, as depicted in Fig. S9
(ESI†), the corresponding height variation for the thin film of 3
became less obvious after annealing at 160 and 180 1C. This
indicates the formation of a more continuous and flat thin-film
of 3 after annealing at high temperature. Similar morphological
changes were also observed for the thin films of 2 and 4
(see Fig. S8, ESI†). Such morphological transformation is
beneficial for improving the performances of OFETs of 1–4
according to previous studies.12–14
Conclusions
In summary, we describe four non-symmetric core-expanded
NDI derivatives 1–4 which can be easily synthesized in high
yields. The incorporation of 1,3-dithiole-2-thione-4,5-dithiolate
and 2-(1,3-dithiol-2-ylidene) malonitrile moieties into mono-
thiazole-fused NDIs modifies the electronic structures of the
NDI core significantly, and LUMO energies of 1–4 are lower
than that of NDI which enable them to be used as air-stable
n-type semiconductors. OFET devices based on thin films of
1–4 which can be easily solution-processed are fabricated with
conventional techniques. Interestingly, the performance of
OFET devices of 1–4 can be significantly improved by annealing
their thin films at high temperatures. This is likely due to the
intermolecular rearrangements in thin films of 1–4 based on
the XRD and AFM studies. OFETs of 3 exhibit electron mobility
up to 0.17 cm2 VÀ1 sÀ1 with a high on/off ratio (under ambient
conditions) after annealing. These results and others clearly
indicate that it is possible to generate new air-stable and
solution-processed n-type semiconductors by appropriate
chemical modifications of NDI, and further studies using
thiazole-fused NDI as building blocks are in progress.
Fig. 5 XRD patterns of thin films of 1 (A) and 3 (B) after annealing at 120,
160 and 180 1C, respectively.
vary in a similar way as for those of 1 and 3 after annealing
(see Fig. S7, ESI†).
Fig. 6 and S8 (ESI†) show AFM images of thin films of 1–4
after annealing at different temperatures. The surface morphol-
ogies were changed after annealing. As depicted in Fig. 6, the
surface structure of the thin film of 1 became more uniform
after annealing at 180 1C. The respective height profiles are
displayed in Fig. S9 (ESI†). After annealing at 180 1C, the
corresponding height variation became less frequent across
the thin film of 1. This surface structural change is consistent
with the slight enhancement of mobility after annealing at
180 1C for the thin film of 1 (see Table 2). As shown in Fig. 6,
molecular domains within the thin film of 3 emerged and boundary
areas decreased after increasing the annealing temperatures from
Experimental
General
All chemicals were purchased from Alfa Aesar and Sigma-Aldrich,
and used as received. Solvents and other common reagents were
obtained from Beijing Chemical Co. 4BrNDI, (n-Bu4N)2Zn(dmit)2
and sodium 2,2-dicyanoethene-1,1-bis(thiolate) were synthesized
according to the literature.12,23
Melting points were measured with Bu¨chi B540. 1H NMR
and 13C NMR spectra were recorded on Bruker ADVANCE III
400 MHz and Bruker ADVANCE III 600 MHz spectrometers.
MALDI-TOF MS spectra were recorded with a BEFLEX III
spectrometer. Elemental analysis was performed on a Carlo
Erba model 1160 elemental analyzer. TGA (SHIMADZU DTG-60)
measurements were performed under nitrogen atmosphere at a
heating rate of 10 1C minÀ1. Solution and thin films absorption
spectra were measured with a JASCO V-570 UV-Vis spectro-
photometer. Cyclic voltammetric measurements were carried
out in a standard three-electrode cell using a Pt working
electrode, a Pt counter electrode and a Ag/AgCl (saturated
KCl) reference electrode on a computer-controlled CHI660C
instrument. The scan rate was 100 mV sÀ1, and n-Bu4NPF6
(0.1 M) was used as the supporting electrolyte.
Fig. 6 AFM images of thin films of 1 (A) and 3 (B) after annealing at 120, 160
and 180 1C, respectively.
c
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X-Ray diffraction (XRD) measurements were carried out in 4.28 (d, 4H), 2.09 (br, 2H), 1.34–1.22 (m, 64H), 0.85 (br, 12H). 13
C
the reflection mode at room temperature, using a 2 kW Rigaku NMR (100 MHz, CDCl3) d 180.36, 161.80, 161.13, 160.71, 160.13,
X-ray diffraction system. The thin film surfaces were examined 155.15, 142.30, 135.36, 134.95, 133.59, 132.35, 129.45, 129.03,
by tapping-mode AFM using a Digital Instruments Nanoscope V 126.80, 126.51, 124.67, 124.05, 117.85, 116.33, 46.00, 45.89, 36.52,
atomic force microscope in ambient air conditions in the dark. 36.41, 31.92, 31.66, 31.60, 30.11, 29.65, 29.36, 26.43, 26.33, 22.68,
AFM samples and microscopic images were identical to those 14.11. MALDI-TOF: 1115.7 (M+); elemental analysis: calcd for
used in organic filed effect transistors. The molecular structures C61H87Br2N3O4S: C, 65.52; H, 7.84; N, 3.76; S, 2.87; found: C,
of the compounds were calculated with the DFT method at 65.83; H, 7.80; N, 3.74; S, 2.82.
B3LYP/6-31G (d, p) level. All calculations were performed with
the Gaussian 09 program.
Synthesis of 1. To the solution of compound 5 (112 mg,
0.10 mmol) in 50 mL of THF was added (n-Bu4N)2Zn(dmit)2
(104 mg, 0.11 mmol). The reaction mixture was stirred at room
temperature for 1.0 h and then concentrated by rotary evapora-
Fabrication of OFET devices
Bottom gate bottom contact OFETs were fabricated with con- tion. The residue was subjected to column chromatography
ventional techniques. Briefly, a heavily doped n-type Si wafer with petroleum ether (60–90 1C)/CH2Cl2 (1 : 1, v/v) as eluent to
and a layer of dry oxidized SiO2 (300 nm, with roughness lower give 1 as a dark green solid (109 mg) in 94% yield. M.p. 240.0–
than 0.1 nm and capacitance of 11 nF cmÀ2) were used as a gate 241.2 1C. 1H NMR (400 MHz, CD2Cl2) d 7.90 (br, 1H), 7.75
electrode and gate dielectric layer, respectively. The drain-source (d, 1H), 7.22 (br, 1H), 4.23–4.20 (m, 4H), 2.05 (br,2H), 1.36–1.24
(D-S) gold contacts were fabricated by photo-lithography. The (m, 64H), 0.85–0.84 (m, 12H). 13C NMR (100 MHz, CDCl3) d
channel length and width are 50 and 1440 mm, respectively. The 210.30, 172.69, 162.68, 162.52, 161.77, 159.83, 154.81, 142.74,
substrates were cleaned in water, deionized water, alcohol, 142.44, 141.94, 136.38, 134.29, 132.61, 130.45, 129.74, 129.18,
and rinsed in acetone. Then, the surface was modified with 125.39, 123.80, 122.56, 121.96, 116.96, 114.74, 45.77, 45.61,
n-octadecyltrichlorosilane (OTS). The Au electrodes were modified 36.61, 36.37, 31.93, 31.56, 30.19, 29.69, 29.39, 26.35, 26.28,
by immersing the OFETs in 0.1% (volume fraction) ethanol 22.70, 14.13. MALDI-TOF: 1159.8 (M+); elemental analysis: calcd
solution of pentafluorothiophenol. Compounds 1–4 were dissolved for C62H85N3O4S7: C, 64.15; H, 7.38; N, 3.62; S, 19.34; found: C,
in CHCl3 (about 10 mg mLÀ1) and spin-coated on the above 64.12; H, 7.39; N, 3.68; S, 19.31.
substrates at 2000 rpm. The annealing processes were carried in
vacuum conditions for 1.0 h at each temperature.
Synthesis of 2. Compound 2 was prepared similarly with
compound 6 and (n-Bu4N)2Zn(dmit)2. A solid was obtained after
Field-effect characteristics of the devices were determined in purification in 96% yield. M.p. 211.4–212.3 1C. 1H NMR
air by using a Keithley 4200 SCS semiconductor parameter (400 MHz, CDCl3) d 8.34 (d, 2H), 7.62–7.57 (m, 3H), 4.27 (m,
analyzer. The field-effect mobility of electrons (me) was calcu- 4H), 2.12–2.09 (br, 2H), 1.40–1.23 (m, 64H), 0.86–0.84 (m, 12H).
lated by fitting a straight line to the plot of the square root of 13C NMR (100 MHz, CDCl3) d 210.24, 179.93, 162.69, 162.55,
IDS vs. VG (saturation region), according to the expression IDS
(W/2L)meCi(VG À VTH)2.
=
161.73, 159.98, 154.85, 143.08, 142.55, 141.82, 133.61, 132.06,
130.35, 129.71, 129.41, 128.95, 125.27, 123.81, 122.62, 121.99,
117.31, 115.35, 45.75, 45.68, 36.62, 36.43, 31.93, 31.60, 30.20,
29.68, 29.38, 26.37, 26.29, 22.69, 14.12. MALDI-TOF: 1154.0
Synthesis and characterization
Synthesis of 5. Under N2 atmosphere, a mixture of 4BrNDI (M+); elemental analysis: calcd for C64H87N3O4S6: C, 66.57; H,
(457 mg, 0.4 mmol) and thiophene-2-carbothioamide (57 mg, 7.59; N, 3.64; S, 16.66; found: C, 66.42; H, 7.66; N, 3.61; S, 16.43.
0.4 mmol) in EtOH (50 mL) was refluxed for 8 h. Then the
Synthesis of 3. To the solution of compound 5 (112 mg,
mixture was filtrated after cooling to room temperature. The 0.10 mmol) in 50 mL of THF was added sodium 2,2-dicyano-
residue was subjected to column chromatography with petro- ethene-1,1-bis(thiolate) (20.5 mg, 0.11 mmol). The reaction
leum ether (60 1C–90 1C)/CH2Cl2 (1 : 1, v/v) as eluent to give 5 as mixture was stirred at room temperature for 1.0 h and then
a red solid (342 mg) in 76% yield (based on 4BrNDI). M.p. concentrated by rotary evaporation. The residue was subjected
161.2–162.4 1C. 1H NMR (400 MHz, CD2Cl2) d 8.00 (br, 1H), 7.81 to column chromatography with petroleum ether (60–90 1C)/
(d, 1H), 7.29 (br, 1H), 4.22 (d, 4H), 2.04 (br, 2H), 1.36–1.23 (m, CH2Cl2 (2 : 3, v/v) as eluent to give 3 as a dark red solid (78 mg)
64H), 0.86-0.84 (m, 12H). 13C NMR (100 MHz, CDCl3) d 173.09, in 71% yield. M.p. 271.6–272.4 1C. 1H NMR (400 MHz, CD2Cl2) d
161.83, 161.11, 160.67, 159.96, 155.07, 142.39, 136.52, 135.03, 7.90–7.88 (m, 2H), 7.33 (br, 1H), 4.28–4.23 (m,4H), 2.09 (br, 2H),
134.80, 134.16, 132.61, 129.17, 126.72, 126.63, 124.56, 124.00, 1.41–1.23 (m, 64H), 0.85–0.84 (m, 12H). 13C NMR (100 MHz,
117.50, 115.67, 46.02, 45.84, 36.52, 36.35, 31.92, 31.65, 31.58, CDCl3) d 183.85, 172.08, 162.63, 162.55, 161.73, 159.19, 154.71,
30.16, 29.66, 29.36, 26.42, 26.33, 22.69, 14.12. MALDI-TOF: 144.18, 143.82, 141.70, 136.24, 135.39, 133.08, 129.67, 125.09,
1121.6 (M+); elemental analysis: calcd for C59H85Br2N3O4S2: C, 122.54, 118.68, 117.52, 117.11, 114.19, 111.95, 111.89, 69.74,
63.03; H, 7.62; N, 3.74; S, 5.70; found: C, 63.13; H, 7.64; N, 3.76; 46.23, 45.83, 36.71, 36.32, 31.92, 31.60, 31.54, 30.19, 29.68,
S, 5.68.
29.38, 26.41, 22.69, 14.11. MALDI-TOF: 1103.2 (M+); elemental
Synthesis of 6. Compound 6 was prepared similarly with analysis: calcd for C63H85N5O4S4: C, 68.50; H, 7.76; N, 6.34; S,
4BrNDI and benzothioamide. A yellow solid was obtained after 11.61; found: C, 68.43; H, 7.81; N, 6.35; S, 11.56.
purification in 83% yield (based on 4BrNDI). M.p. 154.4–155.8 1C.
Synthesis of 4. Compound 4 was prepared similarly with
1H NMR (400 MHz, CDCl3) d 8.36 (d, 2H), 7.64-7.58 (m, 3H), compound 6 and sodium 2,2-dicyanoethene-1,1-bis(thiolate).
c
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Paper
6 M. Um, J. Jang, J. Hong, J. Kang, D. Y. Yoon, S. H. Lee, J. Kim
and J. Hong, New J. Chem., 2008, 32, 2006; J. Kwon, J. Hong,
S. Noh, T. Kim, J. Kim, C. Lee, S. Lee and J. Hong, New J.
Chem., 2012, 36, 1813; A. Wurl, S. Goossen, D. Canevet,
A red solid was obtained after purification in 82% yield. M.p.
267.3–268.1 1C. 1H NMR (400 MHz, CDCl3) d 8.27 (d, 2H), 7.74–
7.72 (m, 1H), 7.66–7.64 (m, 2H), 4.29 (br, 4H), 2.10 (br, 2H),
1.38–1.22 (m, 64H), 0.85 (br, 12H). 13C NMR (100 MHz, CDCl3) d
183.56, 179.15, 162.66, 162.55, 161.65, 159.32, 154.51, 144.31,
144.16, 141.18, 134.23, 131.45, 130.02, 128.84, 124.86, 122.55,
118.70, 117.51, 117.38, 114.73, 111.81, 69.98, 46.21, 45.86,
36.73, 36.37, 31.92, 31.64, 31.57, 30.20, 29.67, 29.38, 26.41,
22.68, 14.11. MALDI-TOF: 1097.3 (M+); elemental analysis: calcd
for C65H87N5O4S3: C, 71.06; H, 7.98; N, 6.37; S, 8.76; found: C,
70.45; H, 7.93; N, 6.24; S, 8.49.
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Acknowledgements
The present research was financially supported by NSFC, the
State Basic Program and Chinese Academy of Sciences.
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c
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New J. Chem., 2013, 37, 1720--1727 1727