Solution-processable n-type semiconductors based on unsymmetrical naphthalene imides: Synthesis, characterization, and applications in field-effect transistors

Article abstract of DOI:10.1002/asia.201300895

A series of unsymmetrical naphthalene imide derivatives (1-5) with high electron affinity was synthesized and used in n-channel organic field-effect transistors (OFETs). They have very good solubility in common organic solvents and good thermal stability up to 320 °C. Their photophysical, electrochemical, and thermal properties were investigated in detail. They showed low-lying LUMO energy levels from -3.90 to -4.15 eV owing to a strong electron-withdrawing character. Solution-processed thin-film OFETs based on 1-4 were measured in both N₂ and air. They all showed n-type FET behavior. The liquid-crystalline compounds 1 a, 1 b, and 3 showed good performance owing to the self-healing properties of the film in the liquid-crystal phase. Compound 3 has an electron mobility of up to 0.016 cm ² V^-1 s^-1 and current on/off ratios of 10 ⁴-10⁵.Copyright

Full text of DOI:10.1002/asia.201300895

FULL PAPER
DOI: 10.1002/asia.201300895
Solution-Processable n-Type Semiconductors Based on Unsymmetrical
Naphthalene Imides: Synthesis, Characterization, and Applications in Field-
Effect Transistors
[
a]
Jinjun Shao, Jingjing Chang, and Chunyan Chi*
Abstract: A series of unsymmetrical
naphthalene imide derivatives (1–5)
with high electron affinity was synthe-
sized and used in n-channel organic
field-effect transistors (OFETs). They
have very good solubility in common
organic solvents and good thermal sta-
bility up to 3208C. Their photophysical,
electrochemical, and thermal proper-
ties were investigated in detail. They
showed low-lying LUMO energy levels
from ꢀ3.90 to ꢀ4.15 eV owing to
a strong electron-withdrawing charac-
both N2 and air. They all showed n-
type FET behavior. The liquid-crystal-
line compounds 1a, 1b, and 3 showed
good performance owing to the self-
healing properties of the film in the
liquid-crystal phase. Compound 3 has
an electron mobility of up to
ter.
Solution-processed
thin-film
OFETs based on 1–4 were measured in
Keywords: electrochemistry · naph-
2
ꢀ1 ꢀ1
0.016 cm V
s
and current on/off
thalene imides
· photophysics ·
4
5
ratios of 10 –10 .
semiconductors · thin films
Introduction
et al. reported a series of unsymmetrical naphthalene imide
derivative, naphthaleneamidinemonoimide-fused oligothio-
phenes, which showed electron mobility up to
Organic semiconductors are of great importance and inter-
est from the viewpoints of their fundamental optoelectronic
properties and potential applications, such as for organic
2
ꢀ1 ꢀ1
0.35 cm V
s
based on vapor-deposited thin films. Howev-
er, the solution-processed films gave electron mobility of
[1–9]
ꢀ5
ꢀ3
2
ꢀ1 ꢀ1
[30]
field-effect transistors (OFETs).
hole-transporting (p-type) organic semiconductors,
After large success with
only 4ꢀ10 to 3ꢀ10 cm V
s
under vacuum.
When
[10–13]
re-
the length of the electron-donating oligothiophene fragment
increases, the majority-carrier charge transport can be
cently there has been increasing attention on the develop-
ment of high-performance electron-transporting (n-type)
semiconductors, which are desirable for the fabrication of
p–n junction diodes, bipolar transistors, and complementary
[29]
switched from n-type to ambipolar behavior.
For large-scale fabrication of low-cost devices, solution-
based film-deposition processes with high charge-carrier mo-
[
14–19]
[31–33]
integrated circuits.
Naphthalene diimide (NDI) is
bility are highly desirable.
Herein, we report the synthe-
a promising building block, which has been widely employed
to construct n-type semiconductors with high performance
and good air stability. Based on core-expansion or core-sub-
sis of a family of unsymmetrical naphthalene imide deriva-
tives 1a, 1b, and 2–5 with high electron affinity, and their
applications in solution-processed n-channel OFETs. The
unsymmetrical naphthalene imide derivatives were prepared
here owing to the following reasons: 1) Based on previous
[20–27]
stitution strategies,
considerable NDI derivatives with
symmetrical structures have been designed and synthesized
for n-channel OFETs. Some of them showed high electron
mobility. Nevertheless, unsymmetrical naphthalene diimide
derivatives have rarely been synthesized and used for n-
[34,35]
reports,
some unsymmetrical molecules showed higher
or comparable charge mobilities compared to the corre-
sponding symmetric analogues. 2) Easier synthesis proce-
dures compared with the symmetrical NDI derivatives. Only
reflux in acetic acid (HOAc) is required in the last step; the
palladium-catalyzed reaction is not necessary. 3) The formed
structure has an electron-deficient imine (ꢀN=) moiety,
[28–30]
channel OFETs.
A series of n-type semiconductors, 1,8-
naphthoylene(trifluoromethylbenzimidazole)-4,5-dicarboxyl-
ic acid imide (NTFBII) derivatives, were reported by Zhang
et al., and they exhibited electron mobility up to
2
ꢀ1 ꢀ1
[28]
0
.08 cm V
s
by means of vacuum deposition.
Marks
which will result in a lower LUMO energy level. 4) Com-
[28–30]
pared to previous work,
one imide group in these un-
[
a] J. Shao, J. Chang, Prof. C. Chi
Department of Chemistry
National University of Singapore
symmetric naphthalene imides was annulated with benzoi-
midazole or an imidazole unit carrying various electron-
withdrawing substituents (e.g., imide, cyano, and nitro
groups). Thus these new molecules are expected to show ex-
tended p conjugation and high electron affinity with tunable
LUMO energy levels, which are essential for air-stable n-
channel OFETs. Their electronic, photophysical properties,
3
Science Drive 3, 117543 (Singapore)
Fax : (+65)6779-1691
E-mail: chmcc@nus.edu.sg
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201300895.
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Chunyan Chi et al.
1
thermal behavior, molecular packing, and OFET device per-
formance are studied in this paper.
devices by convenient solution-processing techniques.
H
1
3
and C NMR spectroscopy, mass spectrometry (HRMS (EI)
and MALDI-TOF MS), and elemental analysis were used to
identify the chemical structure and purity of all the new
compounds (see the Experimental Section).
Photophysical Properties
The UV-visible absorption and photoluminescence (PL)
spectra of compounds 1a,b and 2–5 were recorded in chloro-
form and as solid films (Figure 1, Table 1, and the Support-
Results and Discussion
Synthesis
The synthesis of these electron-deficient organic semicon-
ductors is shown in Scheme 1. The key reaction is the con-
densation between the naphthalene monoanhydride 6 and
different diamines (7a, 7b, 9, 11–13). Naphthalene monoan-
ꢀ5
Figure 1. a) Absorption spectra (c=1ꢀ10 m) and b) normalized emis-
ꢀ6
3
sion spectra (c=1ꢀ10 m) of solutions of 1a, 1b, and 2–5 in CHCl . The
emission spectra of 1a, 1b, and 2–5 were recorded under the excitation
wavelength of 432, 432, 416, 416, 416, and 416 nm, respectively.
Table 1. Absorption and PL data for compounds 1a, 1b, and 2–5.
[
a]
[b]
ꢀ1
ꢀ1
[c]
[d]
l
abs [nm]
e
max [m cm
]
l
em [nm]
QY [%]
Scheme 1. Synthetic route to 1a, 1b, and 2–5.
1
1
2
3
4
5
a
b
432
432
416
416
416
416
42300
42000
41000
40500
41600
41900
528
528
500
500
498
498
65
66
81
45
42
41
hydride 6 and diamines 7a, 7b, and 13 were prepared ac-
cording to reported literature procedures.
[31–33]
To synthesize
4
,5-diaminophthalonitrile (9), NaBH was first employed to
4
[32]
reduce benzothiadiazole-4,7-dicarbonitrile (8),
however,
[a] UV-visible absorption maximum. [b] Molar extinction coefficient at
the absorption maximum. [c] Photoluminescence maximum. [d] Fluores-
cence quantum yields by using fluorescein (QY=90%,
the yield was only 12%. Later Fe powder was applied to
[37]
[32]
pHꢁ11,
reduce 8 in acetic acid at reflux, and 9 was obtained in
0% yield. Similarly, 2,3-diaminoterephthalonitrile (11) was
prepared from 10 under the same conditions in 85%
NaOH aqueous solution) as a standard.
8
[36]
yield. The naphthalene imide derivatives 1a, 1b, and 2–5
were then prepared by condensation between 6 and dia-
mines 7a, 7b, 9, and 11–13, respectively, in 81–88% yields.
Compounds 1a, 1b, and 2–5 showed good solubility in
normal organic solvents such as dichloromethane (CH Cl )
ing Information). In solution, for 1a and 1b, the alkyl chains
had no effect on the spectra profiles, and both showed an
absorption maximum (l ) at 432 nm and an emission maxi-
mum (lem ) at 528 nm. For 2 and 3, the position of the two
cyano groups has little effect on the absorption profiles, with
the same labs at 416 nm and lem at 500 nm. For 4, although
with one benzene ring less than 2, it exhibited similar labs at
max
abs
max
2
2
max
max
and THF, which allows us to perform various characteriza-
tions in solution, and makes it possible to fabricate OFET
max
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Chunyan Chi et al.
max
onset
4
16 nm and lem at 498 nm. For 5, in which two cyano
potential (Ered ) is ꢀ3.90 and ꢀ3.92 eV for 1a and 1b, re-
groups were replaced by two nitro groups relative to 2, the
absorption and emission maxima are almost the same as
those of 2. It is worth noting that all of these compounds
show moderate-to-high photoluminescence quantum yields
ranging from 41 to 81% in chloroform (Table 1). In the
thin-film state, the absorption spectra of these compounds
became much broader, and emission spectra are redshifted
compared to that in solution. For compound 5 with two
nitro groups, no emission was observed. These phenomena
are due to the aggregation in the solid state.
spectively. Accordingly, the respective HOMO energy levels
are deduced as ꢀ6.43 and ꢀ6.46 eV for 1a and 1b, respec-
opt
tively, based on the equation HOMO=LUMOꢀE , in
g
opt
which E is the optical energy gap determined from the
g
lowest-energy absorption onset. For 2, 3, and 4, two quasi-
1=2
reversible reduction waves were observed with E at ꢀ0.88
red
and ꢀ1.28 V for 2, ꢀ0.95 and ꢀ1.35 V for 3, and ꢀ0.75 and
onset
red
ꢀ1.19 V for 4. The LUMO energy level derived from E
was ꢀ4.00, ꢀ3.90, and ꢀ4.15 eV, respectively, and the
HOMO energy level was calculated to be ꢀ6.68, ꢀ6.58, and
ꢀ
6.73 eV, respectively. By changing the position of the two
cyano groups, the LUMO energy level was shifted by
.10 eV (2 versus 3), and by removal of one benzene moiety
Electrochemical Properties
0
The electrochemical properties of solutions of 1a, 1b, and
from 2 to 4, the LUMO energy level was lowered by around
0.15 eV. For compound 5, four quasi-reversible reduction
2
–5 in CH Cl were investigated by cyclic voltammetry and
2 2
1=2
differential pulse voltammetry (Figure 2, Table 2). Three
waves were observed with E at ꢀ0.86, ꢀ1.24, ꢀ1.71, and
red
quasi-reversible reduction waves were observed for 1a and
ꢀ1.99 V. Hence the LUMO and HOMO were calculated to
be ꢀ4.02 and ꢀ6.70 eV, respectively. For all compounds, no
clear redox waves were observed upon oxidation up to
1.80 V. Because strong electron-withdrawing groups are
fused to the naphthalene imide, the LUMO energy levels of
these compounds between ꢀ3.90 and ꢀ4.15 eV are lower
than those of reported naphthaleneamidinemonoimide-
1
red
=2
1
ꢀ
b, with the half-wave potential (E ) at ꢀ0.95, ꢀ1.35, and
+
2.41 V for 1a (versus Fc /Fc), and the different alkyl
chains showed less effect on the redox behaviors. The
LUMO energy level derived from the onset of the reduction
[29,30]
fused oligothiophenes,
than those of trifluoromethylbenzene-fused derivatives.
Some of them are even lower
[28]
The low-lying LUMO energy level (i.e., large electron affin-
ity) of these compounds indicates that they can serve as
promising candidates for n-channel OFETs with good air
[40]
stability.
Thermal Behavior
The thermal behavior and self-assembly of 1a,b and 2–5 in
the solid state were investigated by a combination of ther-
mogravimetric analysis (TGA), differential scanning calo-
rimetry (DSC), polarizing optical microscopy (POM), and
powder X-ray diffraction (XRD) techniques (Figures 3 and
4
, Table 3, and the Supporting Information). TGA measure-
ments revealed that all compounds were thermally stable
over 3208C with 5% weight loss (Figure 3, Table 3). Com-
pounds 1a, 1b, and 3 show a crystalline-phase-to-liquid-crys-
talline-phase transition at 31, ꢀ0.5, and 648C, respectively,
which can be confirmed by DSC (Figure 4) and POM (in
the Supporting Information)
Figure 2. Cyclic voltammograms of 1a, 1b, and 2–5 in dry CH
2 2
Cl with
0
.1m Bu NPF as supporting electrolyte, a gold disk electrode, a Pt wire,
4
6
and an Ag/AgCl electrode were used as the working electrode, the coun-
ter electrode, and the reference electrode, respectively, with a scan rate
ꢀ1
at 50 mVs
.
studies. The powder XRD
Table 2. Cyclic voltammogram data for compounds 1a, 1b, and 2–5.
measurements of 1a and 1b
1
red
=2
onset
red
[a]
[b]
[c]
showed only one major reflec-
tion peak (in the Supporting In-
formation), so their packing
structures cannot be obtained.
A clear XRD peak at 3.31 ꢂ
correlated to intermolecular p–
p stacking was observed for 3,
which indicates the existence of
Compound
E
[V]
E
[V]
LUMO [eV]
HOMO [eV]
E
g
[eV]
1
1
2
3
4
5
a
b
ꢀ0.95
ꢀ0.96
ꢀ0.88
ꢀ0.95
ꢀ0.75
ꢀ0.86
ꢀ1.35
ꢀ1.33
ꢀ1.28
ꢀ1.35
ꢀ1.19
ꢀ1.24
ꢀ2.41
–
–
–
–
–
ꢀ0.90
ꢀ0.88
ꢀ0.80
ꢀ0.90
ꢀ0.65
ꢀ0.78
ꢀ3.90
ꢀ3.92
ꢀ4.00
ꢀ3.90
ꢀ4.15
ꢀ4.02
ꢀ6.43
ꢀ6.46
ꢀ6.68
ꢀ6.58
ꢀ6.73
ꢀ6.70
onset
2.53
2.54
2.68
2.68
2.68
2.68
ꢀ2.51
–
–
–
ꢀ1.71
ꢀ1.99
onset
red
[
a] The LUMO was calculated according to the equation, LUMO=ꢀ
A
H
U
G
R
N
U
(4.80+E ), in which E
is the onset
red
+
potential of the first reduction wave, 4.8 eV is the energy level of ferrocene/ferrocenium (Fc /Fc) below the
vacuum level.
mated from the absorption edge in solution.
[
38,39]
ordered
p
stacking. Com-
[b] HOMO was estimated according to the equation, HOMO=LUMOꢀE
g g
. [c] E was esti-
pounds 2 and 4 are both crystal-
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Chunyan Chi et al.
OFET Characterization
The charge-transport properties of 1a, 1b, and 2–5 were
characterized by using OFETs. Bottom-gate top-contact
+
OFETs were fabricated on p -Si/SiO substrates by spin-
2
casting a 0.8–1.0 wt% chloroform solution onto octadecyltri-
methoxysilane
(OTMS)-
or
octadecyltrichlorosilane
(
ODTS)-treated substrates. The thin films were then an-
nealed at selective temperatures for 30 min. Au source/drain
electrodes (80 nm) were patterned on the organic layer
through a shadow mask. All devices were characterized
Figure 3. TGA curves for compounds 1a, 1b, and 2–5 with a heating rate
of 108Cmin under nitrogen.
ꢀ
1
under both N and ambient conditions. The typical transfer
2
and output curves are shown in Figure 5 and in the Support-
Table 3. Thermal properties of 1a, 1b, and 2–5.
[
a]
Compound
T
d
[8C]
Phase transition during heating process
1
1
2
3
4
5
a
b
430
(Cr)!318C (LC)!3628C (I)
(Cr)!ꢀ0.58C (LC)!2528C (I)
(Cr)!2458C (I)
458
392
395
359
329
(Cr)!648C (LC)!3208C (I)
(Cr)!2008C (I)
2178C (I)
[
a] Cr: crystal phase; LC: liquid-crystal phase; I: isotropic phase.
line materials at room temperature with a melting point at
45 and 2008C, respectively. The crystals can be observed
D
Figure 5. a) Representative output and b) transfer (V =70 V) character-
istics of OFET devices fabricated by solution-casting of 3 on OTMS-
2
under POM and many reflection peaks appeared in the
XRD curves. Compound 5 turned out to be an amorphous
solid at room temperature with a melting point at 1978C.
The liquid-crystalline properties of 1a, 1b, and 3 may facili-
tate the formation of self-healed, ordered thin films in
OFET devices.
treated substrates.
ing Information. The thin film of 5 did not show any field-
effect behavior in this study, presumably owing to its amor-
phous character in the solid state (in the Supporting Infor-
mation). The devices of 1a, 1b, and 2–4 all operate in the n-
ꢀ
1
Figure 4. DSC curves for compounds a) 1a, b) 1b, c) 2, d) 3, e) 4, f) 5 with a heating/cooling scan rate of 108Cmin under nitrogen (Cr=crystalline
phase, LC=liquid crystal phase, I=isotropic phase).
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Chunyan Chi et al.
Table 4. The optimized OFET characteristic data for 1a, 1b, and 2–4.
Surface
treatment
Annealing
temperature [8C]
In N
2
In air
2
ꢀ1 ꢀ1
2
ꢀ1 ꢀ1
m
e
[cm V
s
]
V
T
[V]
I
on/off
5
m
e
[cm V
s
]
V
T
[V]
I
on/off
4
ꢀ3
ꢀ2
ꢀ3
ꢀ2
ꢀ3
ꢀ3
ꢀ3
ꢀ2
ꢀ5
ꢀ4
ꢀ4
1
1
2
3
4
a
ODTS
OTMS
ODTS
OTMS
ODTS
OTMS
ODTS
OTMS
ODTS
OTMS
as-spun
as-spun
as-spun
as-spun
150
150
150
150
100
6.3ꢀ10
1.2ꢀ10
6.4ꢀ10
1.0ꢀ10
1.1ꢀ10
2.8ꢀ10
4.8ꢀ10
1.6ꢀ10
3.2ꢀ10
4.5ꢀ10
15
15
20
15
10
10
10
18
5
10
10
10
10
10
10
10
10
10
10
5.6ꢀ10
2.1ꢀ10
5.7ꢀ10
2.4ꢀ10
3.6ꢀ10
1.6ꢀ10
1.6ꢀ10
6.1ꢀ10
5.4ꢀ10
1.0ꢀ10
45
25
26
36
8
12
20
16
20
20
10
10
10
10
10
10
10
10
10
10
5
5
5
4
4
4
5
3
4
ꢀ3
ꢀ5
ꢀ3
ꢀ4
ꢀ3
ꢀ3
ꢀ4
ꢀ6
ꢀ4
4
4
4
3
4
5
5
3
3
b
100
5
channel region, and their characteristic data are summarized
in Table 4 and in the Supporting Information. Various an-
nealing temperatures were employed to optimize the device
performance. Under an N2 atmosphere, the as-spun thin-
film devices based on 1a and 1b on OTMS-treated sub-
strates showed high electron mobilities of about 0.01–
2
ꢀ1 ꢀ1
0
.012 cm V s , which renders them attractive for low-tem-
perature processes and facilitates device fabrication for or-
ganic electronics. However, upon thermal annealing, the
device performance slightly decreases. In contrast, for thin
films of 2 and 3, when annealing at 1508C, the devices ex-
hibited relatively higher average electron mobilities
2
ꢀ1 ꢀ1
2
ꢀ1 ꢀ1
(
0.0028 cm V
s
for 2 and 0.016 cm V
s
for 3 on an
OTMS-treated substrate) compared to the as-deposited de-
vices under N . These results are comparable to those previ-
2
ously reported owing to coplanarity of these series of deriva-
[29]
tives. Nonetheless, upon annealing at 1008C, thin films of
Figure 6. X-ray diffraction patterns for the thin films of 1a,b (as-spun); 2
and 3 (annealed at 1508C); and 4 (annealed at 1008C).
4
showed much lower electron mobility (about 4ꢀ
ꢀ
4
2
ꢀ1 ꢀ1
10
cm V s ). The current on/off ratio for all the devices
4
5
is about 10 –10 , and the threshold voltage is around 10–
0 V. When the devices operated in air, a slight decrease of
2
electron mobility and on/off ratio were observed (Table 4).
As can be seen, the cyano-substituted compounds 2–4
showed less degradation compared to the alkyl-chain-substi-
tuted compounds (1a and 1b). The slightly better device sta-
bility of 2–4 relative to the alkyl-chain-substituted com-
pounds (1a and 1b) might be ascribed to the low-lying
LUMO energy levels and dense solid-state packing of these
derivatives owing to cyano substitution.
Thin-film morphology and solid-state microstructure were
characterized by tapping-mode atomic force microscopy
(
AFM) and XRD. The thin films of 1a, 1b, and 2–4 exhibit-
ed intense and sharp Bragg reflections in XRD patterns
Figure 6), which are correlated to a lamellar packing struc-
ture with interlayer distance of 3.15, 3.45, 2.28, 1.94, and
.11 nm, respectively. AFM images of the thin films revealed
(
2
polycrystalline or liquid-crystalline grains with different
shapes (Figure 7 and the Supporting Information). Thin
films of 2 and 4 exhibited a relatively larger grain boundary,
and thus poor FET performance. However, the liquid-crys-
talline 1a, 1b, and 3 showed more continuous thin films and
higher charge-carrier mobilities.
Figure 7. AFM height images (2 mmꢀ2 mm) of the thin films of a) 1a (as-
spun), b) 1b (as-spun), c) 2 (annealed at 1508C), d) 3 (annealed at
1
508C), and e) 4 (annealed at 1008C).
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Chunyan Chi et al.
Conclusion
2 4
with a solution of NaOH and water, dried over anhydrous Na SO , and
the solvent was removed to afford a yellow residue, which was purified
by column chromatography (silica gel, hexanes (Hex)/THF=1:1) to give
In summary, a series of unsymmetric naphthalene imide de-
rivatives 1a, 1b, and 2–5 were synthesized. They have very
good solubility in common organic solvents, and good ther-
mal stability up to 3208C. Owing to their strong electron-
withdrawing character, they have a low-lying LUMO energy
level from 3.90 to 4.15 eV. These compounds can be easily
processed from solution at low temperature. All of the
1
pure 9 as a white solid (0.632 g, 80%). H NMR (500 MHz, [D
6
]DMSO):
]DMSO):
13
d=6.87 (s, 2H) 5.87 ppm (br, 4H); C NMR (125 MHz, [D
6
d=139.06, 117.82, 115.52, 101.39 ppm; EIMS: m/z calcd for C
58.0592; found: 158.1.
8 6 4
H N :
1
Synthesis of 2,3-Diaminoterephthalonitrile (11)
A mixture of benzo[c][1,2,5]thiadiazole-4,7-dicarbonitrile (10; 0.930 g,
AHCTUNGTRENNUNG
5
.0 mmol), iron powder (3.360 g, 60 mmol, 12 equiv), and glacial acetic
OFETs showed n-type behavior under both N and air con-
ditions. It was found that liquid-crystalline compounds 1a,
acid (20 mL) was heated under reflux for around 30 min. The mixture
was then cooled to room temperature, basified with a solution of NaOH,
and extracted with diethyl ether. The combined ether extract was washed
with a solution of NaOH and water, dried over anhydrous Na SO , and
2 4
the solvent was removed to afford a yellow residue, which was purified
2
1
b, and 3 showed good performance owing to the self-heal-
ing properties of the film in the liquid-crystal phase. Com-
2
ꢀ1 ꢀ1
pound 3 has electron mobility up to 0.016 cm V
s
and
by column chromatography (silica gel, Hex/THF=1:1) to give pure 11 as
4
5
1
current on/off ratios of 10 –10 . Therefore, these materials
have promising applications in solution-processed organic
electronics.
a white solid (0.672 g, 85%). H NMR (500 MHz, [D
(
1
6
]DMSO): d=6.71
]DMSO): d=139.62,
18.48, 117.66, 95.05 ppm; HR EIMS: m/z calcd for C : 158.0592;
found: 158.0586 (error=ꢀ0.4 ppm); elemental analysis calcd (%) for
: C 60.75, H 3.82, N 35.42; found: C 60.47, H 3.89, N 35.19.
1
3
s, 2H), 6.06 ppm (br, 4H); C NMR (125 MHz, [D
6
8 6 4
H N
64 76 6 4
C H N O
General procedure to synthesize 1–5 through condensation reaction
between anhydride and diamine
Experimental Section
General Information
A mixture of 6 (1.0 equiv) and diamine (1.0 equiv) was heated to reflux
in acetic acid under a nitrogen atmosphere overnight. Upon cooling, the
All NMR spectra were recorded on a Bruker AMX500 500 MHz spec-
1
13
suspension was dissolved with CH
CH Cl . The combined organic phase was washed with saturated NaCl
aq), dried over Na SO , and concentrated under reduced pressure to
2 2
Cl and water, and extracted with
trometer.
H
and C NMR spectra were recorded in CDCl
3
,
2
2
CDCl CDCl
2
2
, and [D ]DMSO. All chemical shifts are quoted in ppm,
6
(
2
4
using the residual solvent peak as a reference standard. MS was recorded
in EI mode and high-resolution mass spectrometry was recorded with an
EI source. Matrix-assisted laser desorption ionization time-of-flight
give a residue that was purified by column chromatography to give the
pure product.
(
MALDI-TOF) analysis was performed on a Bruker Autoflex IIIMAL-
Synthesis of 10-(3,7-Dimethyloctyl)-2-octyl-1H-
DI-TOF instrument by using 1,8,9-trihydroxyanthracene as matrix and
Pepmix as internal standard or external standard. UV-visible absorption
and fluorescence spectra were recorded on Shimadzu UV-1700 and RF-
benzo
A
T
N
T
E
N
N
ACTHUNGTRENNGNU[ 2,1-b] ACHTUGNTRENNUNG[ 3,8]phenanthroline-
1
,3,6,9,11ACTHUNGTRENNUNG
Compound 6 (152 mg, 0.4 mmol), diamine 7a (127 mg, 0.4 mmol); 1a was
obtained as a golden yellow solid (230 mg, 87%). H NMR (500 MHz,
5
301 spectrometers in HPLC pure solvents. Cyclic voltammetry was per-
1
formed on a CHI 620C electrochemical analyzer with a three-electrode
CDCl
2 2
CDCl , 373 K): d=9.07 (d, J=8.0 Hz, 2H), 9.01–8.98 (m, 2H),
cell in a solution of 0.1m tetrabutylammonium hexafluorophosphate
ꢀ
1
8.88–8.83 (m, 2H), 8.34 (s, 1H), 4.26 (t, J=7.0 Hz, 2H), 3.81 (d, J=
(
4 6 2 2
Bu NPF ) dissolved in dry CH Cl at a scan rate of 50 mVs . A gold
7
.5 Hz, 2H), 1.87–1.81 (m, 2H), 1.64–1.23 (m, 20H), 1.05 (d, J=6.5 Hz,
disc electrode with a diameter of 2 mm, a Pt wire, and an Ag/AgCl elec-
trode were used as the working electrode, the counter electrode, and the
reference electrode, respectively. The potential was calibrated against the
ferrocene/ferrocenium couple. Thermogravimetric analysis (TGA) was
1
3
3
2 2
H), 0.96–0.92 ppm (m, 9H); C NMR (125 MHz, CDCl CDCl , 373 K):
d=167.10, 162.22, 162.05, 158.72, 150.44, 147.80, 135.25, 131.70, 131.19,
30.56, 130.26, 129.96, 128.28, 127.61, 127.24, 126.36, 125.79, 125.63,
124.35, 120.13, 116.02, 111.42, 40.88, 39.04, 36.84, 36.66, 35.28, 31.43,
0.76, 28.91, 28.77, 27.88, 27.59, 26.82, 24.23, 22.27, 22.22 ppm; MALDI-
1
ꢀ
1
carried out on a TA instrument 2960 at a heating rate of 108Cmin
under N flow. Differential scanning calorimetry (DSC) was performed
on a TA instrument 2920 at a heating/cooling rate of 108Cmin under
flow. The initial phase transitions and corresponding temperatures for
3
2
+
ꢀ1
40 44 4 5
TOF-MS: m/z calcd for C H N O : 660.3312; found: 661.3343 [M+H] ;
elemental analysis calcd (%) for C64
found: C 72.57, H 6.61, N 8.61.
76 6 4
H N O : C 72.70, H 6.71, N 8.48;
N
2
these compounds were determined by the OLYMPUS BX51 polarizing
optical microscope equipped with the Linkam TP94 programmable hot
stage. XRD measurements were performed on a Bruker-AXS D8 DIS-
COVER with GADDS powder X-ray diffractometer, both with CuKa ra-
diation.
Synthesis of 10-(2-Decyltetradecyl)-2-octyl-1H-
benzo[lmn]isoindolo[5’,6’:4,5]imidazo[2,1-b][3,8]phenanthroline-
,3,6,9,11(2H,10H)-pentaone (1b)
A
H
U
T
E
N
N
A
H
U
G
R
N
U
G
ACHTUNGTRENNUNG
1
ACHTUNGTRENNUNG
Compound 6 (143 mg, 0.375 mmol), diamine7b (192 mg, 0.375 mmol); 1b
Synthesis
1
was obtained as
a
golden yellow solid (282 mg, 88%). H NMR
, 323 K): d=8.94–8.91 (m, 2H), 8.84 (s, 1H), 8.81–8.76
m, 2H), 8.17 (s, 1H), 4.21 (t, J=8.0 Hz, 2H), 3.63 (d, J=7.0 Hz, 2H),
(
(
500 MHz, CDCl
3
7
5
2
-Octyl-1H-isochromeno[6,5,4-def]isoquinoline-1,3,6,8
,6-diamino-2-(3,7-dimethyloctyl)isoindoline-1,3-dione (7a), 5,6-diamino-
-(2-decyltetradecyl)isoindoline-1,3-dione (7b), benzo[c]-
[1,2,5]thiadiazole-4,7-di-
carbonitrile (10), and 4,5-dinitrobenzene-1,2-diamine (13) were prepared
ACHTUNGTRENNUN(G 7H)-tetraone (6),
1
9
1
.93 (br, 1H), 1.81–1.75 (m, 2H), 1.49–1.24 (m, 50H), 0.90–0.85 ppm (m,
1
3
H); C NMR (125 MHz, CDCl
3
, 323 K): d=167.75, 167.73, 162.50,
ACHTUNGTRENNUNG[ 1,2,5]thiadiazole-5,6-dicarbonitrile (8), benzo[c] ACHTGNUTRENNUNG
62.34, 158.84, 150.52, 147.84, 135.33, 132.07, 131.52, 130.88, 130.31,
[
31–33,36]
130.02, 128.45, 127.82, 127.42, 126.46, 125.91, 125.83, 124.43, 116.18,
11.73, 42.88, 41.15, 37.22, 31.92, 31.82, 29.98, 29.68, 29.65, 29.63, 29.59,
29.32, 29.28, 29.18, 28.16, 27.15, 26.45, 22.64, 22.61, 13.99 ppm; HR
EIMS: m/z calcd for C54 : 856.5503; found 856.5536 (error=
.9 ppm); elemental analysis calcd (%) for C64 : C 75.66, H 8.47,
N 6.54; found: C 75.37, H 8.29, N 6.38.
according to a literature procedure.
1
Synthesis of 4,5-Diaminophthalonitrile (9)
mixture of benzo[c][1,2,5]thiadiazole-5,6-dicarbonitrile (8; 0.930 g,
72 4 5
H N O
A
ACHTUNGTRENNUNG
3
76 6 4
H N O
5
.0 mmol), iron powder (3.360 g, 60 mmol, 12 equiv), and glacial acetic
acid (20 mL) was heated under reflux for around 30 min. The mixture
was then cooled to room temperature, basified with a solution of NaOH,
and extracted with diethyl ether. The combined ether extract was washed
Chem. Asian J. 2014, 9, 253 – 260
258
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Chunyan Chi et al.
[
41]
Synthesis of 2-Octyl-1,3,6-trioxo-1,2,3,6-
tetrahydrobenzo[lmn]benzo[4,5]imidazo
dicarbonitrile (2)
the literature : the clean substrates were spin-casted with 10 mm OTMS
solution in trichloroethylene and placed in an environment saturated
with ammonia vapor for 7 h at room temperature, then washed with de-
ionized water and toluene. The octadecyltrichlorosilane (ODTS) treat-
ment was conducted by immersing the sample in a 3 mm solution of
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
H
U
G
R
N
U
G
ACTHUNGTRENNU[GN 2,1-b] ACHTUNGERTNNUNG[ 3,8]phenanthroline-9,10-
Compound 6 (190 mg, 0. 50 mmol), diamine 9 (79 mg, 0.50 mmol); 2 was
obtained as a yellow solid (202 mg, 81%). H NMR (500 MHz, CDCl ,
3
1
2
ODTS in hexadecane at RT for 16 h in N . It was then rinsed with tolu-
2
2
73 K): d=9.08 (d, J=7.5 Hz, 1H), 9.04–9.02 (m, 2H), 8.91–8.88 (m,
H), 8.35 (s, 1H), 4.22 (t, J=7.5 Hz, 2H), 1.79–1.73 (br, 2H), 1.56–1.28
ene and isopropyl alcohol (IPA). The semiconductor layer was deposited
on top of the OTMS- or ODTS-modified dielectric surface by spin-coat-
ing or -casting from the solution of active component in chloroform (0.8–
1
3
(
(
1
1
2
m, 10H), 1.49–1.24 (m, 50H), 0.88 ppm (t, J=6.5 Hz, 3H); C NMR
125 MHz, CDCl , 323 K): d=162.40, 162.25, 159.04, 152.45, 146.20,
34.06, 132.66, 131.65, 131.12, 128.97, 128.82, 127.58, 126.70, 126.64,
26.28, 126.05, 123.80, 121.82, 115.49, 115.33, 113.42, 112.58, 41.25, 31.80,
9.26, 29.16, 28.16, 27.12, 22.60, 13.96 ppm; HR EIMS: m/z calcd for
3
1
wt%). For ODTS-treated substrates, the solutions were deposited from
spin-coating. However, for OTMS-treated substrates, owing to the poor
wetting problem, only compounds 1a, 1b, and 3 have good thin-film for-
mation; whereas, compounds 2 and 4 were processed from drop-casting.
Subsequently, gold source/drain electrodes were deposited by thermal
evaporation through a metal shadow mask to create a series of FETs
channel width (W)=1 mm; channel length (L)=50–100 um). The FET
devices were then characterized by using a Keithley SCS-4200 semicon-
ductor parameter analyzer in the N glovebox or in air. The FET mobility
C
30
H
23
N
5
O
3
: 501.1801; found 501.1814 (error=2.6 ppm); elemental analy-
sis calcd (%) for C64 : C 71.84, H 4.62, N 13.96; found: C 71.99, H
.89, N 13.68.
76 6 4
H N O
4
(
Synthesis of 2-Octyl-1,3,6-trioxo-1,2,3,6-
tetrahydrobenzo[lmn]benzo[4,5]imidazo
dicarbonitrile (3)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
H
U
G
R
N
U
G
ACTHUNGTRENNU[GN 2,1-b] ACHTUNGERTNNUNG[ 3,8]phenanthroline-8,11-
2
was extracted by using the following equation in the saturation regime
from the gate sweep [Eq. (1)]:
Compound 6 (190 mg, 0. 5 mmol), diamine 11 (79 mg, 0.5 mmol); 3 was
1
obtained as a yellow solid (210 mg, 84%). H NMR (500 MHz, CDCl
73 K): d=9.17 (d, J=8.0 Hz, 1H), 9.05 (d, J=7.5 Hz, 1H), 8.89–8.86
m, 2H), 7.98 (d, J=8.0 Hz, 1H) 7.92 (d, J=8.0 HZ, 1H), 4.21 (t, J=
.5 Hz, 2H), 1.79–1.73 (br, 2H), 1.46–1.25 (m, 10H), 0.88 ppm (t, J=
3
,
2
(
W
L
2
I
D
¼ 2
C
i
mðV
G
ꢀ V Þ
T
7
7
1
1
1
1
3
3
.5 Hz, 3H); C NMR (125 MHz, CDCl , 273 K): d=162.42, 162.25,
58.73, 151.30, 146.49, 133.02, 132.59, 131.70, 131.18, 130.99, 130.05,
29.13, 128.64, 127.24, 126.36, 125.93, 125.76, 123.59, 115.83, 114.52,
09.13, 104.88, 41.15, 31.79, 29.27, 29.16, 28.09, 27.06, 22.62, 14.07 ppm;
in which I
D
is the drain current, m is the field-effect mobility, C
, 200 nm, C
are the gate voltage and threshold voltage,
i
is the ca-
pacitance per unit area of the gate dielectric layer (SiO
2
i
=
ꢀ
2
HR EIMS: m/z calcd for C30
.6 ppm); elemental analysis calcd (%) for C64
N 13.96; found: C 71.77, H 4.91, N 13.77.
H
23
N
5
O
3
: 501.1801; found 501.1814 (error=
1
7 nFcm ), and V
G T
and V
2
76 6 4
H N O
: C 71.84, H 4.62,
respectively.
Synthesis of 2-Octyl-1,3,6-trioxo-1,2,3,6-tetrahydrobenzo ACTHUNGERTNNUNG[ lmn]imidazo ACHTUNGRTENNUNG[ 2,1-
b][3,8]phenanthroline-8,9-dicarbonitrile (4)
ACHTUNGTRENNUNG
Acknowledgements
Compound 6 (190 mg, 0. 5 mmol), diamine 12 (54 mg, 0.5 mmol); 4 was
obtained as a yellow solid (210 mg, 84%). H NMR (500 MHz, CDCl ,
3
1
We acknowledge the financial support from MOE AcRF FRC (grant R-
43-000-510-112) and NUS Start Up (grant R-143-000-486-133).
2
8
73 K): d=9.04 (d, J=7.5 Hz, 1H), 8.92 (d, J=7.5 Hz, 1H), 8.90 (d, J=
.0 Hz, 1H), 8.05 (d, J=7.5 Hz, 1H), 4.20 (t, J=7.5 Hz, 2H), 1.78–1.71
1
1
3
(
(
1
1
2
5
m, 2H), 1.46–1.25 (m, 10H), 0.87 ppm (t, J=7.0 Hz, 3H); C NMR
125 MHz, CDCl , 273 K): d=162.12, 161.96, 156.68, 147.44, 134.29,
31.84, 131.10, 129.64, 128.75, 127.31, 127.14, 126.44, 125.09, 124.31,
22.37, 110.50, 109.38, 107.20, 41.23, 31.76, 29.22, 29.14, 28.05, 27.04,
2.60, 14.06 ppm; HR EIMS: m/z calcd for C30 : 501.1801; found
01.1814 (error=2.6 ppm); elemental analysis calcd (%) for C64
3
[
[
[
[
[
[
1] M. Bendikov, F. Wudl, D. F. Perepichka, Chem. Rev. 2004, 104, 4891.
2] J. Wu, Curr. Org. Chem. 2007, 11, 1220.
3] J. Wu, W. Pisula, K. Mꢃllen, Chem. Rev. 2007, 107, 718.
4] A. R. Murphy, J. M. J. Frꢄchet, Chem. Rev. 2007, 107, 1066.
5] J. Zaumseil, H. Sirringhaus, Chem. Rev. 2007, 107, 1296.
6] M. Mas-Torrent, C. Rovira, Chem. Soc. Rev. 2008, 37, 827.
23 5 3
H N O
H
76
N
6
O
4
:
C 69.17, H 4.69, N 15.51; found: C 69.36, H 4.92, N 15.53.
Synthesis of 9,10-dinitro-2-octylbenzo[lmn]benzo[4,5]imidazo
A
T
N
T
E
N
N
A
H
U
G
R
N
U
G
A
H
U
G
R
N
U
G
[7] X. Zhan, A. Facchetti, S. Barlow, T. J. Marks, M. A. Ratner, M. R.
b][3,8]phenanthroline-1,3,6(2H)-trione (5)
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
A
H
U
G
R
N
U
G
Wasielewski, S. R. Marder, Adv. Mater. 2011, 23, 268.
[
[
8] F. Wꢃrthner, M. Stolte, Chem. Commun. 2011, 47, 5109.
9] Z. Sun, Q. Ye, C. Chi, J. Wu, Chem. Soc. Rev. 2012, 41, 7857.
Compound 6 (228 mg, 0. 6 mmol), diamine 13 (118 mg, 0.6 mmol); 5 was
1
3
obtained as a yellow solid (270 mg, 83%). H NMR (500 MHz, CDCl ,
[
[
[
[
10] H. E. Katz, Z. Bao, S. L. Gilat, Acc. Chem. Res. 2001, 34, 359.
11] R. A. Pascal, Jr., Chem. Rev. 2006, 106, 4809.
12] J. E. Anthony, Chem. Rev. 2006, 106, 5028.
2
8
2
73 K): d=9.13 (s, 1H), 9.09 (d, J=8.0 Hz, 1H), 9.04 (d, J=8.0 Hz, 1H),
.91–8.88 (m, 2H), 8.43 (s, 1H), 4.23 (t, J=8.0 Hz, 2H), 1.80–1.74 (br,
H), 1.32–1.29 (m, 10H), 0.88 ppm (t, J=7.0 Hz, 3H); C NMR
273 K): d=162.36, 162.20, 158.90,153.41, 145.47,
13] J. E. Anthony, Angew. Chem. 2008, 120, 460; Angew. Chem. Int. Ed.
(
125 MHz, CDCl
3
,
2
008, 47, 452.
1
1
2
5
42.02, 141.13, 132.94, 132.78, 131.64, 131.11, 129.02, 128.86, 127.55,
26.75, 126.21, 125.84, 123.66, 117.57, 113.32, 41.25, 31.80, 29.26, 29.16,
[
14] M.-H. Yoon, S. A. Dibeneddetto, A. Facchetti, T. J. Marks, J. Am.
Chem. Soc. 2005, 127, 1348.
8.15, 27.11, 22.60, 13.97 ppm; HR EIMS: m/z calcd for C28
41.1597; found 541.1617 (error=3.7 ppm); elemental analysis calcd (%)
: C 62.10, H 4.28, N 12.93; found: C 62.28, H 4.28, N
[
[
[
[
[
15] Y. Sun, Y. Liu, D. Zhu, J. Mater. Chem. 2005, 15, 53.
16] C. Di, G. Yu, Y. Liu, D. Zhu, J. Phys. Chem. B 2007, 111, 14083.
17] H. Qu, W. Cui, J. Li, J. Shao, C. Chi, Org. Lett. 2011, 13, 924.
18] Q. Ye, J. Chang, K.-W. Huang, C. Chi, Org. Lett. 2011, 13, 5960.
19] a) J. Chang, H. Qu, Z.-E. OOI, J. Zhang, Z. Chen, J. Wu, C. Chi, J.
Mater. Chem. C 2013, 1, 456; b) X. Shi, J. Chang, C. Chi, Chem.
Commun. 2013, 49, 7135; c) Q. Ye, J. Chang, K.-W. Huang, X. Shi, J.
Wu, C. Chi, Org. Lett. 2013, 15, 1194.
for C64
2.83.
76 6 4
H N O
1
Device Fabrication
Top-contact, bottom-gate OFET devices were prepared on the p silicon
+
wafer and a 200 nm thermally grown SiO layer served as the gate dielec-
tric. The SiO /Si substrate was cleaned with acetone and isopropanol,
then immersed in a piranha solution (H SO /H ) for 8 min, and
2
2
[20] Y. Hu, X. Gao, C.-A. Di, X. Yang, F. Zhang, Y. Liu, H. Li, D. Zhu,
Chem. Mater. 2011, 23, 1204.
2
4
2 2
O
washed with deionized water. The octadecyltrimethoxysilane (OTMS)
treatment was performed according to a modified procedure reported in
[21] J. Chang, Q. Ye, K.-W. Huang, J. Zhang, Z.-K. Chen, J. Wu, C. Chi,
Org. Lett. 2012, 14, 2964.
Chem. Asian J. 2014, 9, 253 – 260
259
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

www.chemasianj.org
Chunyan Chi et al.
[
22] W. Yue, A. Lv, J. Gao, W. Jiang, L. Hao, C. Li, Y. Li, L. E. Polander,
S. Barlow, W. Hu, S. Di Motta, F. Negri, S. R. Marder, Z. Wang, J.
Am. Chem. Soc. 2012, 134, 5770.
[31] S. R. Greenfield, W. A. Svec, D. Gosztola, M. R. Wasielewisky, J.
Am. Chem. Soc. 1996, 118, 6767.
[32] J. Shao, J. Chang, C. Chi, Org. Biomol. Chem. 2012, 10, 7045.
[33] G. W. H. Cheeseman, J. Chem. Soc. 1962, 1170.
[34] C. Wang, H. Dong, W. Hu, Y. Liu, D. Zhu, Chem. Rev. 2012, 112,
2208.
[35] M. L. Tang, M. E. Roberts, J. J. Locklin, M. M. Ling, H. Meng, Z.
Bao, Chem. Mater. 2006, 18, 6250.
[36] K. Pilgram, R. D. Skiles, J. Heterocycl. Chem. 1974, 11, 777.
[37] J. N. Demas, G. A. Crosby, J. Phys. Chem. 1971, 75, 991.
[38] A. J. Bard, L. R. Faulkner, Electrochemical Methods: Fundamentals
and Applications, Wiley, New York, 1984.
[39] J. Pommerehne, H. Vestweber, W. Guss, R. F. Mahrt, H. Bassler, M.
Porsch, J. Daub, Adv. Mater. 1995, 7, 551.
[40] C. P. Constantinides, P. A. Koutentis, J. Schatz, J. Am. Chem. Soc.
2004, 126, 16232.
[41] Y. Ito, A. A. Virkar, S. Mannsfeld, J. H. Oh, M. Toney, J. Locklin, Z.
Bao, J. Am. Chem. Soc. 2009, 131, 9396.
[
[
[
23] Y. Zhao, C. Di, X. Gao, Y. Hu, Y. Guo, L. Zhang, Y. Liu, J. Wang,
W. Hu, D. Zhu, Adv. Mater. 2011, 23, 2448.
24] D. Shukla, S. F. Nelson, D. C. Freeman, M. Rajeswaran, W. G.
Ahearn, D. M. Meyer, J. T. Carey, Chem. Mater. 2008, 20, 7486.
25] L. E. Polander, S. P. Tiwari, L. Pandey, B. M. Seifried, Q. Zhang, S.
Barlow, C. Risko, J.-L. Brꢄdas, B. Kippelen, S. R. Marder, Chem.
Mater. 2011, 23, 3408.
[
26] F. Zhang, Y. Hu, T. Schuettfort, C. Di, X. Gao, C. R. McNeill, L.
Thomsen, S. C. B. Mannsfeld, W. Yuan, H. Sirringhaus, D. Zhu, J.
Am. Chem. Soc. 2013, 135, 2338.
[
[
[
[
27] X. Gao, C.-A. Di, Y. Hu, X. Yang, H. Fan, F. Zhang, Y. Liu, H. Li,
D. Zhu, J. Am. Chem. Soc. 2010, 132, 3697.
28] P. Deng, Y. Yan, S.-D. Wang, Q. Zhang, Chem. Commun. 2012, 48,
2
591.
29] R. P. Ortiz, H. Herrera, C. Seoane, J. L. Segura, A. Facchetti, T. J.
Marks, Chem. Eur. J. 2012, 18, 532.
30] R. O. P. Ortiz, H. Herrera, R. L. Blanco, H. Huang, A. Facchetti,
T. J. Marks, Y. Zheng, J. L. J. Segura, J. Am. Chem. Soc. 2010, 132,
Received: July 7, 2013
Revised: August 13, 2013
8
440.
Published online: October 17, 2013
Chem. Asian J. 2014, 9, 253 – 260
260
ꢁ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim