A simple nickel bis(dithiolene) complex as an excellent n-type molecular semiconductor for field-effect transistors

Article abstract of DOI:10.1039/c2cc33445c

A simple nickel bis(dithiolene) complex has been developed as an excellent n-type molecular semiconductor for FETs, with an electron mobility of 0.11 cm² V^-1 s^-1 and an on/off ratio of 2 × 10⁶ despite its small π-conjugated system. Good FET stability in ambient conditions has also been observed. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2cc33445c

View Online / Journal Homepage
ChemComm
Accepted Manuscript
This is an Accepted Manuscript, which has been through the RSC Publishing peer
review process and has been accepted for publication.
Accepted Manuscripts are published online shortly after acceptance, which is prior
to technical editing, formatting and proof reading. This free service from RSC
Publishing allows authors to make their results available to the community, in
citable form, before publication of the edited article. This Accepted Manuscript will
be replaced by the edited and formatted Advance Article as soon as this is available.
Chemical Communications
www.rsc.org/chemcomm
Volume 46
| Number 32 | 28 August 2010 | Pages 5813–5976
To cite this manuscript please use its permanent Digital Object Identifier (DOI®),
which is identical for all formats of publication.
More information about Accepted Manuscripts can be found in the
Information for Authors.
Please note that technical editing may introduce minor changes to the text and/or
graphics contained in the manuscript submitted by the author(s) which may alter
content, and that the standard Terms & Conditions and the ethical guidelines
that apply to the journal are still applicable. In no event shall the RSC be held
responsible for any errors or omissions in these Accepted Manuscript manuscripts or
any consequences arising from the use of any information contained in them.
ISSN 1359-7345
COMMUNICATION
FEATURE ARTICLE
J. Fraser Stoddart et al.
Directed self-assembly of
ring-in-ring complex
Wenbin Lin et al.
a
Hybrid nanomaterials for biomedical
applications
1359-7345(2010)46:32;1-H
www.rsc.org/chemcomm
Registered Charity Number 207890

ChemComm
Page 1 of 4Journal Name
Dynamic Article Links ►
View Online
Cite this: DOI: 10.1039/c0xx00000x
www.rsc.org/xxxxxx
ARTICLE TYPE
A Simple Nickel Bis(Dithiolene) Complex as an Excellent n-Type
Molecular Semiconductor for Field-Effect Transistors
Li Qu,a Yunlong Guo,b Hao Luo,b Cheng Zhong,a Gui Yu,b Yunqi Liu,*b and Jingui Qin*a
Received (in XXX, XXX) Xth XXXXXXXXX 20XX, Accepted Xth XXXXXXXXX 20XX
5
DOI: 10.1039/b000000x
lower (1.3×10−3 cm2 V−1 s−1) than the SCLC values.5e Meanwhile,
Abstract: a simple nickel bis(dithiolene) complex has been
another square-planar nickel coordination compounds, bis(o-
40 diiminobenzosemiquinonate) nickel complexes were reported to
exhibit good p-type FET performance (with mobility of 3.8 ×
10−2 cm2 V−1 s−1) or ambipolar transport behavior (with mobility
of 4.3 × 10−3 cm2 V−1 s−1 for holes and 1.6 × 10−2 cm2 V−1 s−1 for
electrons) with different metal electrodes and dielectric layers.7
45 These facts suggest that much better FET performance of nickel
dithiolene complexes might be achieved through molecular
engineering and device optimizations.
developed as an excellent n-type molecular semiconductor for
FETs, with electron mobility of 0.11 cm2V-1s-1 and on/off ratio
of 2×106 despite its small π-conjugated system. Good FET
10 stability in ambient condition has been also observed.
In the past decades, molecular semiconductors have received
great attentions and undergone tremendous progress for
fabrication of field effect transistors (FET) and complementary
1
logic circuits. Although some robust and efficient n-type
In most cases, the nickel dithiolene complexes that have been
studied for FET are bis(1,2-di-aryl-1,2-ethenedithiolato) nickel
50 complexes (Figure 1a), there is no report on FET property of
bis(1-aryl-1,2-ethenedithiolato) nickel analogues (Figure 1b).
Based on the above information, we have recently designed and
studied a bis(1-(4’-trifluoromethylphenyl)-1,2-ethenedithiolato)
nickel complex 1 (Figure 1c) as a new n-type semiconductor.
55 There are two considerations for this molecular design: 1) In 1,2-
di-aryl substituted complex, the presence of the four outer
aromatic groups is disadvantageous to the molecular packing due
to the bulkiness of four substituents,5d,8 while in a 1-aryl
substituted complex, the steric effect is much less by removing
60 two outer rings.9 2) Trifluoromethylphenyl ring has been one of
the most widely used end-capped groups for n-type
semiconducting materials, since trifluoromethyl group (-CF3) can
further lower the LUMO and is favorable for molecular packing
and the film morphology.10 It was found that the complex 1
65 exhibited high electron mobility over 0.1 cm2 V−1 s−1 with on/off
ratio up to 2 × 106. To the best of our knowledge, this is the best
FET performance among square-planar nickel complexes.
15 materials have been realized, their development has still lagged
behind that of p-type semiconductors by contrast.2,3 The research
on n-type molecular semiconductors are mainly focused on
electro-negative substituted small molecules and polymers with
π-conjugated structures, and relatively low air-stability and
20 tedious synthetic procedures have restricted their development.3
Nickel bis(dithiolene) complexes has become one type of
molecular semiconductors since the first nickel dithiolene charge
transfer complex showing n-type behavior in 1994.4 However,
the FET performance of nickel dithiolenes were low, with
25 mobilities ranging from 10−3 to 10−5 cm2 V−1 s−1,5 far behind
organic conjugated molecules. To date, only a small number of
nickel dithiolene semiconductors have been reported, and the
research on their molecular design and structure-property
relationship remain deficient.
30 Nickel dithiolene complexes usually possess square-planar
configurations, and they can easily form an electron delocalized
system with low LUMO energy level. Their properties and mode
of the conjugations can be modulated by changing substitutions
on the dithiolene part.6 High electron mobility (2.8 cm2 V−1s−1)
35 determined by space-charge limited current (SCLC) technique
was observed for one nickel dithiolene complex, but its field-
effect mobilities were found to be over two orders of magnitude
As depicted in Figure 1c, complex 1 was conveniently
synthesized with good yields and purified by recrystallization
70 from chloroform. It was characterized by 1H NMR spectroscopy,
a Department of Chemistry and Hubei Key Lab on Organic and Polymeric
Optoelectronic Materials , Wuhan University, Wuhan 430072, P. R.
China, E-mail: jgqin@whu.edu.cn
b
Beijing National Laboratory for Molecular Sciences and CAS Key
Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of
Sciences, Beijing 100190, P. R. China, E-mail: liuyq@iccas.ac.cn
† Electronic Supplementary Information (ESI) available: details of
synthesis and characterization data, DFT calculation, crystallographic
data, device fabrication, stability test and mophlogy studies. CCDC
836362 (1) and 836363 ([Bu4N]+[1]-). See DOI: 10.1039/b000000x/
Figure 1. a) 1,2-di-aryl substituted nickel dithiolene complexes. b) 1-aryl
substituted nickel dithiolene complexes. c) Synthesis of the complex 1.
This journal is © The Royal Society of Chemistry [year]
[journal], [year], [vol], 00–00 | 1

ChemComm
Page 2 of 4
View Online
complex 1 lies about an inversion centre, with the Ni atom on an
inversion centre. As shown in Figures 2a and 2b, the complex 1
45 has a herring bone packing motif with staggered layers. S-S
contacts of 3.67Å and S-π contacts of 3.63 Å can be found in
different directions (Figure 2c), thus substantial carrier transport
path ways among neighboring molecules can be constructed.
Different from many nickel dithiolene complexes with paired
50 crystal structures and triclinic crystal system,5d,8,9a the crystal of
complex
1 exhibits monoclinic crystal system, and no
dimerization was found in it. Since monoclinic crystal system
usually exhibit better symmetry and more densely crystal packing
than triclinic crystal system, and dimerized structures of these
55 compounds may not be good for charge transport,5d,14 better FET
performance of complex 1 than some reported nickel dithiolene
semiconductors has been expected.
In the crystal structure of [Bu4N]+[1]- (Figure S4 in Supporting
Information), the ions lie in general positions in the asymmetric
60 unit and there is no crystallographically-imposed inversion
symmetry as was found in the structure of complex 1. Selected
bond lengths and angles as well as dihedral angles in the complex
Figure 2. Crystal structure of the complex 1: a) b-axis projection, b)
herring bone packing motif, c) short contacts.
mass spectrometry, elemental analysis and single crystal structure
(see Supporting Information for details, and its mono-anionic
form [Bu4N]+[1]- was also synthesized for comparison). The basic
physical properties of 1 were characterized by thermo gravimetric
analysis, UV-Vis-NIR absorption spectra and cyclic
voltammograms (CV). Related figures and data are shown in
1
and [Bu4N]+[1]- are listed in Table S4 in Supporting
5
Information. It can be seen that geometry changes between
65 neutral (1) and mono-anionic ([Bu4N]+[1]-) forms are really
small, implying small electron-transport reorganization energy, in
agreement with the DFT results.
Semiconductive property of the complex 1 was investigated by
FETs. Thin films were vacuum deposited on octadecyl-
70 trichlorosilane-treated SiO2/Si (OTS-SiO2/Si) substrates and
polystyrene-treated SiO2/Si (PS-SiO2/Si) substrates, respectively,
at substrate temperatures (Tsub) of 20, 30, 70 or 100 °C. The Au
source/drain contacts were deposited on the semiconducting layer
10 Supporting Information (Table S1).
From the CV data, its HOMO and LUMO levels as well as
band-gap can be estimated.11 The complex 1 has very low LUMO
levels (−4.51 eV) and narrow band-gaps (−1.08 eV), which are
indicative of the electron-deficiency and electron delocalization.
15 These results imply that the complex 1 may be an air-stable n-
type semiconducting material.5b In addition, perfectly reversible
and reproducible reduction process of 1 have been observed,
which are favorable for electron transport.
Density Functional Theory (DFT) calculations were performed
20 using the Gaussian 09 program at B3LYP level (with Lanl2dz
pseudo potential basis set for Ni and 6-31+g(d) for all other
atoms) to estimate the electron-density-distribution of frontier
molecular orbitals as well as reorganization energy for the
complex 1 (see Supporting Information for details). The HOMO
25 is mainly located on the dithiolene ligands, and does not have any
coefficient of nickel atom; while the LUMO incorporates both
nickel atom and dithiolene part, demonstrating efficient LUMO
delocalization. The reorganization energies of electron- and hole-
transport of the complex 1 are calculated (Table S2). Its electron-
30 transport reorganization energy is 0.20 eV, which is a quite small
value compared to that of some electron-transport materials
calculated at the same level.12 According to Marcus theory, high
electron mobility of the complex 1 may be achieved.13
through
a shadow mask, affording a top-contact device
75 configuration (see Supporting Information for more details). The
devices were first tested in vacuum conditions. Inspiringly, high
electron mobilities have been obtained, which are in the range of
0.01−0.18 cm2 V−1 s−1 on both substrates. On OTS−SiO2/Si
substrates, the highest mobility is up to 0.18 cm2 V−1s−1, but the
80
Figure 3. I–V characteristics of the complex 1 based FET prepared on
PS-SiO2/Si substrate deposited at Tsub = 70 °C, under nitrogen atmosphere:
a) Plot of IDS vs. VGS for VDS = 60 V. b) Plot of IDS vs. VDS
.
Table 1. FET performances of the complex 1
Single crystals of the complex 1 as well as its mono-anionic
35 form [Bu4N]+[1]- were grown by slow evaporation from solutions
in chloroform or THF, and their crystal structures were
determined by X-ray crystallographic analysis.14 In the crystal
structure of the complex 1, two dithiolene rings in the same
molecule are strictly coplanar (the dihedral angle of two
40 dithiolene rings in the complex 1 is 0°), while the dihedral angle
between external 4’-trifluoromethylphenyl ring and the square-
planar nickel dithiolene moiety is 34.5°. It should be noted
ꢀ/cm2 V−1s−1
0.040
0.18
Substrates
OTS-SiO2
Tsub /°C
20
30
70
100
20
30
70
100
Ion/Ioff
276
363
0.093
0.081
0.018
0.063
0.11
1200
2600
4400
105
PS-SiO2
2×106
8×104
0.045
85
2
| Journal Name, [year], [vol], 00–00
This journal is © The Royal Society of Chemistry [year]

Page 3 of 4
ChemComm
View Online
on/off current ratios are relatively low (<104). On PS−SiO2/Si
Notes and references
substrates, better switching characteristics of FETs can be
achieved. When Tsub= 70 °C (Figure 3), thin film of the complex
1 exhibits excellent n-type FET performance with a mobility of
0.11 cm2 V−1 s−1 and on/off ratio of 2 × 106. The device
performances of the complex 1 are summarized in Table 1.
Except for the high charge carrier mobility, good stability in air
is also a key parameter for the potential application of FETs. The
on/off current cycle test was performed on one representative
10 device (on PS-SiO2/Si substrate) and a good stability was shown
over 1000 test cycles (Figure S7a). Furthermore, FET
performances of the complex 1 in ambient conditions have been
examined. On PS-SiO2/Si substrate at Tsub = 70 °C, the mobility
(0.089 cm2 V−1 s−1) and on/off current ratio (4 × 104) remain in a
15 high level; and after the devices were stored in ambient
conditions for about 30 days, the mobility showed little changing
(ꢀ/ꢀ0 > 0.82) and the current on/off ratio was still kept between
104 and 105 (Figure S7b). These results indicated good air
stability of complex 1, which implies its practical application
20 value.
Atomic force microscopy (AFM) was taken to study the vacuum
deposited films of the complex 1 (Figures S8a and S8b).
Complex 1 forms interconnected films. The grain size increases
and the grain boundaries become more obscure when increasing
25 substrate temperatures. However, the device performance is not
further enhanced at the highest Tsub, probably because the carrier
trap size also becomes larger.15
To gain insight into the film structures, XRD were carried out
for thin films of the complex 1 (Figures S8c and S8d).On PS-
30 SiO2/Si substrates, a series of sharp peaks are observed, and
strongest diffractions appears at Tsub = 70 °C, consistent with the
Tsub at which the best FET performance appeared; on OTS-
SiO2/Si substrates the intensities of diffractions are relatively
weak. The first diffraction peak (5.28 °) is corresponding to layer
35 spacing of 16.8 Å, close to the length of the molecule observed in
the X-ray single crystal structure of the complex 1 (17.4 Å). The
results reveal good crystallinity and ordering of the thin film of
the complex 1, and may imply that the molecules take edge-on
molecular orientation in the film.
60
65
1
(a) H. Klauk, U. Zschieschang, J. Pflaum and M. Halik, Nature,
2007, 445, 745; (b) G. Gelinck, P. Heremans, K. Nomoto and T.
Anthopoulos, Adv. Mater., 2010, 22, 3778.
For recent reviews on molecular semiconductors and OFETs, see:
(a) H. Dong, C. Wang and W. Hu, Chem. Commun., 2010, 46, 5211;
(b) S. Allard, M. Forster, B. Souharce, H. Thiem and U. Scherf,
Angew. Chem. Int. Ed., 2008, 47, 4070; (c) M. Mas-Torrent and C.
Rovira, Chem. Soc. Rev., 2008, 37, 827; (d) A. R. Murphy and J. M.
Fréchet, Chem. Rev., 2007, 107, 1066.
For recent reviews on n-type molecular semiconductors, see: (a) J. E.
Anthony, A. Facchetti, M. Heeney, S. R. Marder and X. Zhan, Adv.
Mater., 2010, 22, 3876; (b) Y. Wen and Y. Liu, Adv. Mater., 2010,
22, 1331; (c) J. Zaumseil and H. Sirringhau, Chem. Rev., 2007, 107,
1296.
2
5
3
70
4
5
C. Pearson, A.J. Moore, J. E. Gibson, M. R. Bryce and M. C. Petty,
Thin Solid Films, 1994, 244, 932.
75
(a) T. D. Anthopoulos, S. Setayesh, E. Smits, M. Cölle, E. Cantatore,
B. Boer, P. W. M. Blom and D. M. Leeuw, Adv. Mater., 2006, 18,
1900; (b) T. D. Anthopoulos, G. C. Anyfantis, G. C. Papavassiliou
and D. M. Leeuw, Appl. Phys. Lett., 2007, 90, 122105; (c) T.
Taguchi, H. Wada, T. Kambayashi, B. Noda, M. Goto, T. Mori, K.
Ishikawa and H. Takezoe, Chem. Phys. Lett., 2006, 421, 395; (d) H.
Wada, T. Taguchi, B. Noda, T. Kambayashi, T. Mori, K. Ishikawa
and H. Takezoe, Organic Electronics, 2007, 8, 759; (e) J. Y. Cho, B.
Domercq, S. C. Jones, J. Yu, X. Zhang, Z. An, M. Bishop, S. Barlow,
S. R. Marder and B. Kippelen, J. Mater. Chem., 2007, 17, 2642.
For recent reviews on metal dithiolene complexes, see: (a) B. G.
Bonneval, K. I. M. C. Ching, F. Alaryc, T. T. Bui and L. Valade,
Coord. Chem. Rev., 2010, 254, 1457; (b) R. Kato, Chem. Rev., 2004,
104, 5319; (c) N. Robertson and L. Cronin, Coord. Chem. Rev.,
2002, 227, 93.
(a) S. Noro, H. C. Chang, T. Takenobu, Y. Murayama, T. Kanbara,
T. Aoyama, T. Sassa, T. Wada, D. Tanaka, S. Kitagawa, Y. Iwasa, T.
Akutagawa and T. Nakamura, J. Am. Chem. Soc., 2005, 127, 10012;
(b) S. Noro, T. Takenobu, Y. Iwasa, H. C. Chang, S. Kitagawa, T.
Akutagawa and T. Nakamura, Adv. Mater., 2008, 20, 3399.
(a) M. M. Belombev and B. Nuber, Bull. Chem. Soc. Jpn., 1989, 62,
4092; (b) D. Sartain and M. R. Truter, J. Chem. Soc., 1967, 1264.
(a) A. Sugimori, N. Tachiya, M. Kajitaniv and T. Akiyama,
Organometallics, 1996, 15, 5664; (b) V. Madhu and S. K. Das, Inorg.
Chem., 2008, 47, 5055.
80
85
6
7
90
95
8
9
100
105
10 (a) S. Ando, R. Murakami, J. Nishida, H. Tada, Y. Inoue, S. Tokito
and Y. Yamashita, J. Am. Chem. Soc., 2005, 127, 14996; (b) M.
Mamada, J. Nishida, D. Kumaki, S. Tokito and Y. Yamashita, Chem.
Mater., 2007, 19, 5404; (c) M. Akhtaruzzaman, N. Kamata, J.
Nishida, S. Ando, H. Tada, M. Tomura and Y. Yamashita, Chem.
Commun., 2005, 3183; (d) T. Kono, D. Kumaki, J. Nishida, S.
Tokitoa and Y. Yamashita, Chem. Commun., 2010, 46, 3265.
11 D. W. De Leeuw, M. M. J. Simenon, A. R. Brown and R. E. F.
Einerhand, Synthetic Metals, 1997, 87, 53.
40 It is worth noticing that the complex 1 has a simple structure
with less extended π-conjugation compared to most of organic
semiconductors, such n-type FET performance is unprecedented.
In addition, the ease of synthesis and high ambient stability of
these materials will be ideal for low-cost production and practical
45 application. Therefore, these may open up a new window for the
development of high-performance n-type semiconductors.
In summary, a simple nickel bis(dithiolene) complex 1, bis(1-
(4’-trifluoromethylphenyl)-1,2-ethenedithiolato) nickel, has been
designed and synthesized. Despite its small π-conjugated system,
50 thin film of 1 has shown excellent n-type field-effect transistor
response, with electron mobility of 0.11 cm2 V−1 s−1 and on/off
110 12 (a) B. C. Lin, C. P. Cheng, Z. Q. You and C. P. Hsu, J. Am. Chem.
Soc., 2005, 127, 66; (b) H. Wang, Y. Wen, X. Yang, Y. Wang, W.
Zhou, S. Zhang, X. Zhan, Y. Liu, Z. Shuai and D. Zhu, ACS App.
Mater. Int., 2009, 1, 1122; (c) H. Usta, C. Risko, Z. Wang, H. Huang,
M. K. Deliomeroglu, A. Zhukhovitskiy, A. Facchetti and T. J. Marks,
115
J. Am. Chem. Soc., 2009, 131, 5586.
13 (a) R. A. Marcus, Rev. Mod. Phys., 1993, 65, 599; (b) L. Wang, G.
Nan, X. Yang, Q. Peng, Q. Li and Z. Shuai, Chem. Soc. Rev., 2010,
39, 423; (c) V. Coropceanu, J. Cornil, D. A. da Silva Filho, Y.
Olivier, R. Silbey and J. L. Brédas, Chem. Rev., 2007, 107, 926.
ratio of 2 × 106. Good FET stability in ambient condition has 120 14 B. Noda, H. Wada, M. Katsuhara, I. Aoyagi, T. Mori, T.
been also observed. These results suggest the new design
strategy and bright future of square-planar nickel complexes for
55 molecular electronics. Further work is in progress to investigate
Kambayashi, K. Ishikawa and H. Takezoe, Multifunctional
Conducting Molecular Materials, eds. G. Saito, F. Wudl, R.C.
Haddon, K. Tanigaki, T. Eoki, H.E. Katz and M. Maesato, RSC
Publishing, Cambridge, 2007, 286.
the structure-property relationships.
125 15 C. Di, G. Yu, Y. Liu, and D. Zhu, J. Phys. Chem. B, 2007, 111,
14083.
This work was financially supported by the National Natural
Science Foundation of China (No. 20772094).
This journal is © The Royal Society of Chemistry [year]
Journal Name, [year], [vol], 00–00 | 3

ChemComm
Page 4 of 4
View Online
The table of contents entry
exploratory research on
A
a
nickel bis(dithiolene) complex
—
bis(1-(4’-trifluoromethyl- phenyl)-1,2-ethane -dithiolato) nickel as n-type molecular
semiconductor is presented. Despite its simple structure and small π-conjugated
system, thin film of it has shown excellent n-type field-effect transistor response, with
electron mobility of 0.11 cm2V-1s-1 and on/off ratio of 2×106. Good FET stability in
air has been also observed.
TOC figure