Angular-shaped naphthalene tetracarboxylic diimides for n-channel organic transistor semiconductors

Article abstract of DOI:10.1039/c2cc15733k

A series of compounds based on the angular-shaped naphthalene tetracarboxylic diimide core have been synthesized, characterized and used as active layers of organic field-effect transistors (OFETs). The fabricated OFET devices exhibit n-type semiconducting characteristics, demonstrating the first examples of semiconductors based on angular-shaped naphthalene tetracarboxylic diimides. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2cc15733k

View Article Online / Journal Homepage / Table of Contents for this issue
Dynamic Article Links
ChemComm
Cite this: Chem. Commun., 2012, 48, 1254–1256
www.rsc.org/chemcomm
COMMUNICATION
Angular-shaped naphthalene tetracarboxylic diimides for n-channel
organic transistor semiconductorsw
Shan-ci Chen, Qikai Zhang, Qingdong Zheng,* Changquan Tang and Can-Zhong Lu*
Received 16th September 2011, Accepted 29th November 2011
DOI: 10.1039/c2cc15733k
A series of compounds based on the angular-shaped naphthalene
tetracarboxylic diimide core have been synthesized, characterized
and used as active layers of organic field-effect transistors
(OFETs). The fabricated OFET devices exhibit n-type semi-
conducting characteristics, demonstrating the first examples of
semiconductors based on angular-shaped naphthalene tetra-
carboxylic diimides.
In the past decade, organic field-effect transistors (OFETs) have
attracted tremendous interest due to their unique advantages,
such as light weight, mechanical flexibility, and low-cost produc-
tion, compared to their traditional inorganic counterparts.1–11
Scheme 1 Chemical structures of some diimide molecules.
A tremendous amount of conjugated polymers and small
made to fabricate transistors from the isomeric NTDI with
molecular compounds were synthetized as semiconducting
angular-shaped structures. Importantly, the 3,7 positions of the
materials, wherein small molecular compounds were exten-
angular-shaped NTDI core can be further functionalized via a
sively studied due to their advantages in convenient purifica-
bromination reaction as a good alternating unit for new n-channel
tion, uniform molecular weight and strong intermolecular
NTDI polymers with a possible more ordered packing.
interactions.12 n-channel and p-channel semiconductors play
Herein, we report the synthesis, characterizations and pro-
equally important roles in electronic applications, especially
perties of five compounds based on the angular-shaped NTDI
for organic complementary metal oxide semiconductor
core. The transistor behaviors of devices fabricated from these
(CMOS) circuits. A large number of p-channel organic semi-
compounds are also investigated.
conductors with ambient mobilities comparable to that of
Scheme 2 outlines the synthetic route for compounds 5a–e.
amorphous silicon have been developed in the past decade.
These angular-shaped NTDIs were synthesized according to
the procedure reported previously23 by reacting angular-shaped
In contrast, the development of n-channel OFETs materials
has lagged far behind that of p-channel OFETs since there
naphthalene tetracarboxylic dianhydride (NTDA) with the
are only a limited number of organic materials that can be
used for n-channel OFETs.3,4,7,13–19 Recently, rylenes and
related aromatic cores3,13–16,20–28 such as benzene, naphthalene,
perylene, and anthracene diimide derivatives (Scheme 1) have
received increasing attention since the report of naphthalene
tetracarboxylic diimides (NTDIs) as air stable n-channel materials
with mobility up to 0.1 cm2 (V s)À1 29
.
Among the investigated NTDI cored semiconductor materials,
the two dicarboxylic imides are flanked on the naphthalene core
in a linear-shaped structure. Surprisingly, no attempt has been
State Key Laboratory of Structural Chemistry, Fujian Institute of
Research on the Structure of Matter, Chinese Academy of Science,
155 Yangqiao West Road, Fuzhou, Fujian, P. R. China.
E-mail: qingdongzheng@fjirsm.ac.cn, czlu@fjirsm.ac.cn;
Fax: +86-591-83721625
w Electronic supplementary information (ESI) available: Experimental
details, synthesis and characterization of compounds 5a–f, XRD
patterns of 5a, 5d–5e, and current–voltage characteristics of 5c and
5f. See DOI: 10.1039/c2cc15733k
Scheme 2 Synthesis of compounds 5a–e.
c
1254 Chem. Commun., 2012, 48, 1254–1256
This journal is The Royal Society of Chemistry 2012

View Article Online
corresponding amines (Scheme 2). This angular-shaped NTDA
(4) was synthesized from 2,6-dimethylnaphthalene following
the literature procedure.30 Compound 5a was obtained in
83% yield by reacting 4 with 4-(trifluoromethyl)benzylamine
in quinoline in the presence of zinc acetate. The other four
compounds (5b–e) were synthesized using the similar method
with the yields of 54%, 51%, 62%, and 68%, in that order. The
corresponding amines of 5b and 5c were synthesized from
[p-(trifluoromethyl)phenyl] acetonitrile and (pentafluorophenyl)-
acetonitrile, respectively, according to literature procedures.31,32
The corresponding amines for 5d and 5e were synthesized from
(perfluoroalkyl)alkan-1-ol.28 Details of the synthesis and charac-
terizations are provided in ESI.w For comparison, a linear-
shaped NTDI analogue 5f with the same substituent as 5b
was also synthesized. All the products were purified by vacuum
sublimation before property testing and device fabrication. And
elemental analysis was carried out to ensure the purity of the
sublimed products. The thermal behavior of these compounds
was determined by a second heating–cooling cycle using differ-
ential scanning calorimetry (DSC) (Fig. S1, ESIw).
compared to the five-membered dicarboxylic imides on the
angular-shaped NTDI. In the potential scale of À1.5–0 V,
another electron reduction peak at BÀ1.30 V was observed
for 5f. However, we did not find the second electron reduction
peaks for 5a–b since they locate at the scale more negative than
À1.5 V, which is similar to other five-membered dicarboxylic
imides such as pyromellitic diimides.22 It should be noted that
we could not obtain the CV data of 5c–5e due to their low
solubility in solvents.
Top-contact bottom-gate transistors were fabricated by subli-
mation of the semiconductors on a SiO2/Si substrate treated
with octadecyltrichlorosilane (OTS). Then gold top contact
source and drain electrodes were deposited on the top of
semiconducting films of 45 nm thickness. The channel width
and length were approximately 6.0 mm and 300 mm, respec-
tively. X-Ray diffraction (XRD) spectra (Fig. 2) of the sublimed
thin films for 5b–c show that these materials afford crystalline
thin films with the lamella-like layered structure on the substrate.
The layer spacings of the films for 5b and 5c are 17.5 A and
21.4 A, respectively, which suggest that these molecules orient
perpendicular to the substrate with some degree of tilting (The
calculated lengths of 5b and 5c are 24.27 A and 22.95 A,
respectively). Under the same deposition conditions, the films
of 5a, 5d, and 5e were found to form less ordered structures
according to the XRD patterns (Fig. S2, ESIw) Therefore, no
transistor behaviors were found for FET devices based on
compounds 5a, 5d, and 5e. The measured current–voltage
characteristics for all the devices based on 5b and 5c exhibit
n-type semiconducting behavior since the drain current increases
as the gate voltage becomes more positive (Fig. 3 and Fig. S3
(ESIw)). As an example, Fig. 3 depicts the current–voltage
characteristics of 5b, where Id, Vd, Vg represent the source–drain
current, source–drain voltage and gate voltage, respectively. The
saturation region mobilities were calculated from the transfer
characteristics of the FETs using the slope derived from the
square root of the absolute value of the current as a function of
gate voltage between 90 V and 50 V. The threshold voltages of
the FETs were derived from the onsets of the transfer curves.
Device performance data of 5b and 5c are listed in Table 1.
The maximum mobilities for 5b and 5c in a N2 atmosphere
were found to be 0.011 and 0.024 cm2 (V s)À1, respectively.
The on/off current ratios for both compounds are around 104
and 105, respectively, which will minimize leakage currents.
The electrochemical properties of 5a and 5b were examined
by cyclic voltammetry (Fig. 1). Cyclic voltammograms (CV)
were carried out in a three-electrode cell using platinum
electrodes at a scan rate of 100 mV sÀ1, a Ag/Ag+ (0.1 M
AgNO3 in acetonitrile) as the reference electrode in dichloro-
methane solutions (0.5–1 mg mLÀ1) and 0.1 M tetrabutyl-
ammonium tetrafluoroborate as the supporting electrolyte.
Under these conditions, the onset oxidation potential (E1/2 ox
)
of ferrocene was 0.07 eV versus Ag/Ag+. It is assumed that the
redox potential of Fc/Fc+ has an absolute energy level of
À4.80 eV to vacuum.33 The LUMO energy levels were calcu-
lated according to the following equation: ELUMO = À(Fred
+ 4.73) (eV) where Fred is the onset reduction potential vs.
Ag/Ag+. The LUMO levels of 5a and 5b are calculated to be
BÀ3.62 eV and BÀ3.55 eV. The relatively low-lying LUMO
levels for these compounds indicate their possibility for electron
conduction. For comparison, the LUMO level of compound 5f
is measured to be BÀ3.88 eV (Fig. 1). Thus LUMO energy of
5f is 0.33 eV more negative than that of 5b, though these two
compounds have the same side chains. This can be attributed
to the fact that the six-membered dicarboxylic imides on the
linear-shaped NTDI have better electron accepting ability
Fig. 2 X-Ray diffraction patterns of compounds 5b–c deposited at
25 1C on an OTS-SAM treated substrate.
Fig. 1 Cyclic voltammograms (CV) of 5a–b and 5f.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 1254–1256 1255

View Article Online
more ordered packing. The results on the angular-shaped NTDI
based polymeric semiconductors for the FET application are in
progress and will be published elsewhere.
This work was in part supported by 100 Talents Programme
of The Chinese Academy of Sciences in part supported by the
National Basic Research 973 Program (2011CB935900).
Notes and references
1 C. A. Di, Y. Q. Liu, G. Yu and D. B. Zhu, Acc. Chem. Res., 2009,
42, 1573–1583.
2 W. Jiang, Y. Zhou, H. Geng, S. D. Jiang, S. K. Yan, W. P. Hu,
Z. H. Wang, Z. G. Shuai and J. Pei, J. Am. Chem. Soc., 2011, 133, 1–3.
3 Y. Li, L. Tan, Z. H. Wang, H. L. Qian, Y. B. Shi and W. P. Hu,
Org. Lett., 2008, 10, 529–532.
4 Y. Wen and Y. Liu, Adv. Mater., 2010, 22, 1331–1345.
5 H. E. Katz, Z. Bao and S. L. Gilat, Acc. Chem. Res., 2001, 34, 359–369.
6 J. E. Anthony, Chem. Rev., 2006, 106, 5028–5048.
Fig. 3 Current–voltage characteristics of 5b: plot of Id versus Vd
(left); plot of Id-sat versus Vg (right).
7 C. R. Newman, C. D. Frisbie, D. A. da Silva Filho, J.-L. Bredas, P. C.
´
Table 1 Mobilities, on–off current ratios and threshold voltages of
angular-shaped NTDI based OFETs prepared by vapor deposition
Ewbank and K. R. Mann, Chem. Mater., 2004, 16, 4436–4451.
8 J. Sun, B. Zhang and H. E. Katz, Adv. Funct. Mater., 2011, 21, 29–45.
9 S. Allard, M. Forster, B. Souharce, H. Thiem and U. Scherf,
Angew. Chem., Int. Ed., 2008, 47, 4070–4098.
10 H. Klauk, Chem. Soc. Rev., 2010, 39, 2643–2666.
11 Y. Zhou, T. Lei, L. Wang, J. Pei, Y. Cao and J. Wang, Adv. Mater.,
2010, 22, 1484–1487.
Compounds ma/cm2 (V s)À1 Threshold/V On/off No. devices tested
5b
5c
0.011 (0.0074) 12–45
0.024 (0.015) 9–40
104
105
11
12
a
Maximum values of electron mobility, values in parentheses are
average values.
12 Q. Meng, H. L. Dong, W. P. Hu and D. B. Zhu, J. Mater. Chem.,
2011, 21, 11708–11721.
13 J. H. Oh, S. L. Suraru, W.-Y. Lee, M. Konemann, H. W. Hoffken,
¨
¨
C. Roger, R. Schmidt, Y. Chung, W.-C. Chen, F. Wurthner and
¨
¨
Z. Bao, Adv. Funct. Mater., 2010, 20, 2148–2156.
14 M. Gsanger, J. H. Oh, M. Konemann, H. W. Hoffken, A.-M. Krause,
¨
¨
Z. Bao and F. Wurthner, Angew. Chem., Int. Ed., 2010, 49, 740–743.
¨
¨
15 (a) Y. B. Hu, X. K. Gao, C. A. Di, X. D. Yang, F. Zhang,
Y. Q. Liu, H. X. Li and D. B. Zhu, Chem. Mater., 2011, 23,
1204–1215; (b) Z. X. Liang, Q. Tang, J. Liu, J. H. Li, F. Yan and
Q. A. Miao, Chem. Mater., 2010, 22, 6438–6443.
16 X. Gao, C.-A. Di, Y. Hu, X. Yang, H. Fan, F. Zhang, Y. Liu,
H. Li and D. Zhu, J. Am. Chem. Soc., 2010, 132, 3697–3699.
17 Q. X. Tang, H. X. Li, Y. L. Liu and W. P. Hu, J. Am. Chem. Soc.,
2006, 128, 14634–14639.
18 D. Shukla, S. F. Nelson, D. C. Freeman, M. Rajeswaran, W. G.
Ahearn, D. M. Meyer and J. T. Carey, Chem. Mater., 2008, 20,
7486–7491.
19 H. F. Wang, Y. G. Wen, X. D. Yang, Y. Wang, W. Y. Zhou,
S. M. Zhang, X. W. Zhan, Y. Q. Liu, Z. G. Shuai and D. B. Zhu,
ACS Appl. Mater. Interfaces, 2009, 1, 1122–1129.
Fig. 4 AFM image of 5b deposited at 25 1C on an OTS-SAM treated
substrate.
20 X. Zhan, A. Facchetti, S. Barlow, T. J. Marks, M. A. Ratner,
M. R. Wasielewski and S. R. Marder, Adv. Mater., 2011, 23, 268–284.
21 F. Wurthner and M. Stolte, Chem. Commun., 2011, 47, 5109–5115.
22 Q. Zheng, J. Huang, A. Sarjeant and H. E. Katz, J. Am. Chem.
Soc., 2008, 130, 14410–14411.
23 H. E. Katz, J. Johnson, A. J. Lovinger and W. Li, J. Am. Chem.
Soc., 2000, 122, 7787–7792.
24 H. Yan, Z. Chen, Y. Zheng, C. Newman, J. R. Quinn, F. Dotz,
M. Kastler and A. Facchetti, Nature, 2009, 457, 679–686.
For comparison, the transistor behaviour of the linear-shaped
NTDI analogue 5f was also investigated (Fig. S4, ESIw). The
maximum mobility for 5f was found to be 0.035 cm2 (V s)À1, and
the on/off current ratio is around 105. The mobilities and on/off
ratios of 5b and 5c are comparable with those of 5f. An AFM
image of a thin film of 5b was recorded and is depicted in Fig. 4.
As shown in the figure, the AFM image shows that the deposited
film has relatively small interconnected grains, a mean roughness
of 4.5 nm. It should be noted that the mobilities of 5b and 5c can
be further optimized by varying the substrate temperature during
the film deposition.22,28 At the same time, fabrication of FET
devices based on 5a and 5d–e, with elevated substrate tempera-
tures, is in progress which will be published in due course.
In summary, a family of n-channel materials based on the
angular-shaped NTDI core have been synthesized, characterized
and fabricated for organic field effect transistors. Two compounds
exhibit n-type semiconducting behaviors, which represent the first
examples of semiconductors based on angular-shaped NTDIs.
The results also suggest that angular-shaped NTDIs can be used
as building blocks for n-channel polymeric semiconductors with a
25 (a) Y. Avlasevich, S. Muller, P. Erk and K. Mullen, Chem.–Eur. J.,
¨
¨
2007, 13, 6555–6561; (b) A. R. Mohebbi, C. Munoz and F. Wudl,
Org. Lett., 2011, 13, 2560–2563.
26 J. H. Oh, W.-Y. Lee, T. Noe, W.-C. Chen, M. Konemann and
¨
Z. Bao, J. Am. Chem. Soc., 2011, 133, 4204–4207.
27 N. Sakai, J. Mareda, E. Vauthey and S. Matile, Chem. Commun.,
2010, 46, 4225–4237.
28 B. J. Jung, K. Lee, J. Sun, A. G. Andreou and H. E. Katz, Adv.
Funct. Mater., 2010, 20, 2930–2944.
29 H. E. Katz, A. J. Lovinger, J. Johnson, C. Kloc, T. Siegrist, W. Li,
Y. Y. Lin and A. Dodabalapur, Nature, 2000, 404, 478–481.
30 T. Sato, H. Niino and A. Yabe, Chem. Commun., 2000, 1205–1206.
31 D. J. Miller and W. H. Saunders, J. Org. Chem., 1981, 46, 4247–4252.
32 R. Filler, W. Chen and S. M. Woods, J. Fluorine Chem., 1995, 73,
95–100.
33 J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt, H. Bassler,
¨
M. Porsch and J. Daub, Adv. Mater., 1995, 7, 551–554.
c
1256 Chem. Commun., 2012, 48, 1254–1256
This journal is The Royal Society of Chemistry 2012