Synthesis and characterization of anthracene derivative for organic field-effect transistor fabrication

Article abstract of DOI:10.1166/jnn.2012.5941

Here we report on the synthesis and characterization of anthracene derivative for solution processable organic field-effect transistors. The transistor devices with bottom-contact geometry provided a maximum field-effect mobility of 3.74×10^-4 cm² V^-1 s ^-1 as well as current on/off ratio of 5.05×10⁴ and low threshold voltage. Structural information in the solid state is obtained by thermal analysis and two-dimensional wide angle X-ray scattering (2D-WAXS). From the 2D-WAXS, it is clear that the planes of anthracene rings and benzene ring of the molecule are different in solid state. We assume similar arrangement in the thin-film which limit the effective hopping and thus charge mobility. Copyright

Full text of DOI:10.1166/jnn.2012.5941

Copyright © 2012 American Scientific Publishers
All rights reserved
Printed in the United States of America
Journal of
Nanoscience and Nanotechnology
Vol. 12, 4269–4273, 2012
Synthesis and Characterization of Anthracene Derivative
for Organic Field-Effect Transistor Fabrication
1
1
1
2
2
Pramod Kandoth Madathil , Jae-Geon Lim , Tae-Dong Kim , Dirk Beckmann , Alexey Mavrinskiy ,
2
2
2
1ꢀ∗
Wojciech Pisula , Martin Baumgarten , Klaus Müllen , and Kwang-Sup Lee
1Department of Advanced Materials, Hannam University, Daejeon, 305-701, Korea
2
Max-Planck-Institute for Polymer Research, Ackermannweg 10, Mainz, 55128, Germany
Here we report on the synthesis and characterization of anthracene derivative for solution process-
able organic field-effect transistors. The transistor devices with bottom-contact geometry provided a
−
4
2
−1 −1
4
maximum field-effect mobility of 3.74×10 cm V
s
as well as current on/off ratio of 5.05×10
and low threshold voltage. Structural information in the solid state is obtained by thermal analy-
sis and two-dimensional wide angle X-ray scattering (2D-WAXS). From the 2D-WAXS, it is clear
that the planes of anthracene rings and benzene ring of the molecule are different in solid state.
We assume similar arrangement in the thin-film which limit the effective hopping and thus charge
mobility.
Keywords: Organic Field-Effect Transistors, Anthracene Derivative, Supramolecular
Organization.
Delivered by Publishing Technology to: University of Waterloo
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Copyright: American Scientific Pub
16
lishers
1
. INTRODUCTION
and stability compared to the most studied pentacene
1
7
derivatives. Here we report the synthesis and OFET per-
formance of an anthracene-based semiconducting material
bearing two anthracene units connected to a dialkoxy-
lated diethynyl benzene core. The alkoxy chains increase
the solubility and the rigid acetylene bonds extend
the ꢀ-conjugation of the molecule. Wide angle X-ray
diffraction was used to understand the structural ordering
of the molecule in solid state.
Organic field-effect transistors (OFETs) have attracted
great attention over the past decades to replace vacuum-
deposited amorphous silicon-based thin-film transistors
because of their potential for low cost, light weight and
1
–6
large-area processability. They have proved to be highly
suitable for applications in flexible displays, electronic
papers, radio frequency identification (RF-ID) tags, and
sensors.7 The most important aspect of OFET is flexi-
18
–10
1
1
bility realized by fabrication on polymer substrates. High
mobility and on-off current ratio are the most impor-
tant requirements for wider application of an organic
2. EXPERIMENTAL DETAILS
2.1. Reagents and Solvents
1
2
semiconductor. In metals and inorganic semiconductors,
charge transport occurs in delocalized states where as in
organic semiconductors, the charge delocalization can only
occur between the ꢀ-orbitals of adjacent molecules. There-
2
-Aminoanthraquinone (technical grade) and other rea-
gents were purchased from Sigma Aldrich and were
used as received. Solvents were dried according to con-
ventional methods prior to the reactions. 1,4-Diiodo-
2,5-didodecyloxybenzene 4 was synthesized according to
fore, charge transport in organic materials is believed to
occur through charge hopping mechanism.13 For effec-
1
9
reported literature procedures.
tive hopping the molecule should possess structural order-
1
4
ing through strong ꢀ–ꢀ stacking. It has been proved
2
.2. Instrumentation
that the charge carrier mobility strongly depends on the
1
5
supramolecular organization of the molecules. For our
studies, we have considered anthracene-based molecules
because of their easy derivatization, higher solubility
Proton nuclear magnetic resonance ( H NMR) and 13C
1
NMR spectra were obtained at 300 MHz on a Varian
Oxford-300 NMR spectrometer. Mass spectra were recor-
ded on a JMS-AX505WA mass spectrometer. Differen-
tial scanning calorimetry (DSC) analysis was performed
∗
Author to whom correspondence should be addressed.
J. Nanosci. Nanotechnol. 2012, Vol. 12, No. 5
1533-4880/2012/12/4269/005
doi:10.1166/jnn.2012.5941
4269

Synthesis and Characterization of Anthracene Derivative for Organic Field-Effect Transistor Fabrication
Madathil et al.
ꢀ
in nitrogen atmosphere with a heating rate of 10 C/min
using a TA Instrument 2100 equipped with differential
scanning calorimetry cell. The thermograms were obtained
heated at reflux for 12 h. Aqueous 3 M HCl was added
until bubbling ceased and the mixture was filtered and
residue was washed with dichloromethane. The filtrate
was concentrated and purified by column chromatogra-
ꢀ
on powder sample after it had been heated to 200 C and
air-cooled to room temperature. Thermogravimetric anal-
ysis (TGA) was performed in nitrogen atmosphere with
a heating rate of 10 C/min using a TA Hi-Res TGA
phy using dichloromethane/hexane (1:9) as eluent to afford
1
2-bromoanthracene 3 (9.8 g, 55%). H NMR (CDCl ꢄ: ꢅ
3
ꢀ
8.44 (s, 1 H), 8.34 (s, 1 H), 8.19 (d, J = 1ꢃ0, 1 H), 8.01
1
3
2
950 thermogravimetric analyzer. UV-vis absorption spec-
(m, 2 H), 7.89 (d, J = 9ꢃ2 Hz, 1 H), 7.51 (m, 3 H).
C
tra and photoluminescence (PL) spectra were measured
by a Shimadzu UV-2401 and LS-50B luminescence spec-
trophotometer, respectively. The two-dimensional wide-
angle X-ray diffraction experiments were performed by
means of a rotating anode (Rigaku 18 kW) X-ray beam
with a pinhole collimation and a 2D Siemens detector with
a beam diameter of 1 mm. A double graphite monochro-
NMR (CDCl ꢄ: 132.50, 132.40, 131.91, 129.90, 129.70,
3
129.60, 128.42, 128.11, 128.20, 125.60, 125.40, 119.11.
EI-Mass specta m/z, calcd for C H Br: 257.13. Found:
1
4
9
257.0.
2.3.3. Synthesis of 1,4-Bis(dodecyloxy)-2,
5-Diethynyl-Benzene (4)
mator for the CrK radiation (ꢂ = 0ꢃ154 nm) was used.
ꢁ
This compound was prepared by using previously
reported two-step procedure from 1,4-bis(dodecyloxy)-2,5-
The sample was prepared by filament extrusion at elevated
temperatures.
1
9
diiodobenzene.
1
H NMR (CDCl ꢄ: ꢅ 6.95 (s, 2 H), 3.97 (t, 4 H), 3.33
s, 2 H), 1.8–0.9 (m, 46 H). C NMR (CDCl ꢄ: 151.40,
3
2
.3. Synthetic Procedures
1
3
(
3
2
.3.1. Synthesis of Bromoanthraquinone (2)
118.30, 113.0, 82.30, 81.41, 31.90, 29.60, 29.30, 25.90,
2
4
2.70, 14.11. EI-Mass specta m/z, calcd for C H O :
94.79. Found: 494.7.
34 54 2
Into a 1 L, two-necked round-bottom flask, were placed
cupric bromide (46 g, 206 mmol) and acetonitrile
(
2
300 mL). To the reaction mixture, tert-butyl nitrite (25 mL,
2
.3.4. Synthesis of 1,4-Bis(anthracen-2-ylethynyl)-2,
10.4 mmol) was added with vigorous stirring. A solution
5-Bis(dodecyloxy) Benzene (P2)
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of 2-aminoanthraquinone 1 (20 g, 89.6 mmol) in dry THF
(
IP: 192.81.0.87 On: Wed, 14 Oct 2015 18:26:28
350 mL) was added drop wise at room temperature. After
Into a 100 mL two-necked round-bottom flask equipped
with a reflux condenser were placed compound 4 (0.5 g,
1.0 mmol), diisopropylamine (24 mL), compound 3
(0.52 g, 2.0 mmol), Pd(PPh ꢄ Cl (0.16 g, 0.2 mmol), CuI
(0.04 g, 0.2 mmol) and dry THF (40 mL). After overnight
reflux, the reaction mixture was cooled to room tempera-
ture, filtered, and extracted with CH Cl . The organic layer
Copyright: American Scientific Publishers
stirring for 20 h, the reaction mixture was concentrated and
the solid residue was triturated with water. This slurry was
filtered, washed with dichloromethane and the filtrate was
concentrated. The crude product was purified by column
chromatography using ethyl acetate/hexane (1:4) as eluent
3
2
2
1
to afford 20 g of 2-bromoanthraquinone 2 (80%). H NMR
2
2
(
(
(
CDCl ꢄ: ꢅ 8.5 (d, J = 2ꢃ0 Hz, 1 H), 8.3 (m, 2 H), 8.1
was dried over MgSO and the solvent was evaporated.
The crude product was purified by column chromatogra-
3
4
d, J = 8ꢃ3 Hz, 1 H), 7.9 (dd, J = 8ꢃ3, 2.0 Hz, 1 H), 7.8
m, 2 H). 13C NMR (CDCl ꢄ: 182.10, 135.10, 134, 133.61,
3
phy using hexane/chloroform (3:1) as eluent to yield 0.5 g
1
1
32.60, 132.10, 128.20, 128.30, 126.81, 126.50. EI-Mass
of P2 (56%). H NMR (CDCl ꢄ: ꢅ 8.40 (s, 4 H), 8.22
3
specta m/z, calcd for C H BrO : 287.11. Found: 286.90.
(s, 2 H), 8.0 (m, 6 H), 7.60–7.45 (m, 6 H), 7.10 (s, 2 H),
1
4
7
2
4
.10 (t, 4 H), 1.90 (m, 4 H), 1.70 (m, 4 H), 1.50–1.10
1
3
(m, 32 H), 0.98 (t, 6 H). C NMR (CDCl ꢄ: 151.3, 131.7,
2
.3.2. Synthesis of 2-Bromoanthracene (3)
3
1
1
2
8
31.3, 128.9, 128.10, 127.70, 126.50, 125.60, 119.10,
18.31, 112.31, 93.30, 84.20, 68.10, 64.0, 31.9, 29.6,
9.3, 22.7, 14.1. EI-Mass specta m/z, calcd for C H O :
Into a 500 mL two-necked round-bottom flask were placed
2
propanol (300 mL). After the mixture was stirred at room
temperature for 30 min, sodium borohydride (11.4 g,
-bromoanthraquinone 2 (20 g, 69.7 mmol) and iso-
6
2
70
2
47.22. Found: 847.0.
3
01 mmol) was added. After stirring for 12 h, the sus-
2.4. Fabrication of the OFET Devices
pension was poured into 1 L of cold water and a solid
obtained by filtration. The solid was treated with aqueous
Bottom-contact and top-contact FET devices were fabri-
cated on a common gate of highly n-doped silicon with a
ꢀ
3
M HCl (500 mL), and heated at 75 C for 6 h. The
suspension was cooled and filtered to give a brownish–
yellow solid that was placed in a 500 mL round-bottom
flask and dissolved in isopropanol (300 mL). The reac-
tion mixture was treated with sodium borohydride (15.9 g,
200 nm thermally grown SiO dielectric layer. For some
2
of the devices, octyltrichlorosilane (OTS) and hexamethyl-
disilazane (HMDS) were used to produce hydrophobic
dielectric surface. For bottom-contact devices, gold was
evaporated through a shadow mask to form source and
4
20.3 mmol) at room temperature and the mixture was
4
270
J. Nanosci. Nanotechnol. 12, 4269–4273, 2012

Madathil et al.
Synthesis and Characterization of Anthracene Derivative for Organic Field-Effect Transistor Fabrication
ꢀ
ꢀ
Scheme 1. Reagents and conditions: (I) t-BuONO, acetonitrile, CuBr , THF, 60 C; (II) NaBH , isopropanol, 25 C; (III) Pd(PPh ꢄ Cl , CuI,
diisopropylamine, THF, 80 C.
2
4
3
2
2
ꢀ
ꢀ
drain electrodes. The channel length and channel width
of the devices were 20 ꢆm and 1400 ꢆm respectively.
Thin layers of P2 were spin-coated at 2000 rpm for 60
seconds from a 2 wt% chloroform solution, with a thick-
ness of 50 nm. For top-contact devices, gold source and
drain electrodes were evaporated on the organic semicon-
ducting layer through a shadow mask. The channel width
and length were the same as mentioned above. All the
preparations and electrical measurements using a Keithley
weight loss was observed at 390 C. The DSC scan dur-
ing heating revealed multiple peaks for P2, whereby the
material entered the isotropic melt at 161 C. During this
scan also two other endothermic phase transitions appeared
at 116 C and 152 C which were attributed to transi-
tions between crystalline states (see X-ray analysis below).
Additionally, one exothermic peak was observed at 83 C,
which could be correlated to the solid state rearrangement.
Interestingly, only one exothermic peak at 128 C during
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
4
200 semiconductor parameter analyzer were performed
cooling arose probably due to a quick cooling rate. This is
the reason why any birefringence through cross-polarized
under nitrogen atmosphere at room temperature. The satu-
rated field-effect mobilities Dw ee lri ev ee rx et rda cb t ye dPi un bt hl i se hs ian t gu r Ta t ei oc nh nol oo gp yt i ct oa l: Um ni ci vr oe sr cs oi tpy eo cf o Wu l ad t eb re lo do iscerned since the material
regime from the slopes of the source–drain currents using
the classical equations describing field-effect transistors.
IP: 192.81.0.87 On: Wed, 14 Oct 2015 18:26:28
remained in an amorphous and/or disordered state after
fast cooling from the isotropic state.
Copyright: American Scientific Publishers
3. RESULTS AND DISCUSSION
3.3. Structural Studies
3
.1. Synthesis
Solid state order was investigated by two-dimensional
wide-angle X-ray diffraction (2D-WAXS) from mechani-
cally aligned fibers of P2. The fiber samples were mounted
perpendicular to the incident X-ray beam, and diffracted
X-rays were collected with an area detector. The pattern
A novel anthracene derivative P2 was synthesized using
the procedure shown in Scheme 1. Compound 2 was pre-
pared by bromo substitution of compound 1 with 80%
yield. Reduction of compound 2 with sodium borohydride
yielded compound 3. Sonogashira cross-coupling reaction
of compound 3 and compound 4 provided target molecule
P2 with 56% yield.
ꢀ
recorded at 30 C is presented in Figure 3(a) and is char-
acteristic for a crystalline state of matter.
3
.2. Optical and Thermal Properties
The optical properties of P2 were investigated using UV-
vis and photoluminescence spectroscopies. Solution of
P2 in chloroform exhibited absorption between 300 and
4
4
50 nm with absorption maxima at 312, 325, 366, 390 and
11 nm and emission maximum at 441 nm. The UV-vis
and PL spectra are shown in Figure 1 which are compa-
2
0
rable to previously reported anthracene derivatives. The
thermal properties of P2 were evaluated by thermogravi-
metric analysis (TGA) and differential scanning calorime-
try (DSC) in nitrogen atmosphere (Fig. 2). TGA revealed
good thermal stability of the compound. Three percent
Fig. 1. Absorption and emission spectra of P2 in chloroform solution.
J. Nanosci. Nanotechnol. 12, 4269–4273, 2012
4271

Synthesis and Characterization of Anthracene Derivative for Organic Field-Effect Transistor Fabrication
(a)
Madathil et al.
ꢀ
Fig. 3. (a) 2D-WAXS pattern of P2 at 30 C, and (b) schematic illus-
tration of the organization.
3.4. OFET Properties
To investigate the charge transport properties of P2, top-
contact and bottom-contact FETs were fabricated and
annealed at different temperatures. Various devices were
made with and without surface treatments using HMDS or
OTS. The best device performances were obtained from
the bottom-contact device which was fabricated without
(
b)
−4
2
surface treatment with a hole mobility of 3.74×10 cm
−
1
−1
4
V
s , current on/off ratio of 5.05 × 10 and threshold
voltage of −3.5 V. This particular device was made by
spin-coating 2 wt% solution of P2 in chloroform on sili-
con substrate at a speed of 2000 rpm for 60 seconds and
OFET characteristics were measured at room temperature
(
a)
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ꢀ
Fig. 2. (a) TGA thermogram obtained a tI Pa :h 1e a9t i2n g. 8r 1a t. e0 o. 8f 71 0O Cn /: m Wi ned, 14 Oct 2015 18:26:28
(
1
b) DSC thermograms obtained at a heati nCg o pa nyd ri gc oh otl :i n Ag mr aet er i co af n Scientific Publishers
ꢀ
0 C/min.
The equatorial reflections indicated that the molecules
are arranged in stacks which were oriented along the fiber
axis in the extrusion direction. A distance between the
stacks of 1.51 nm was derived and is in accordance to the
molecular structure. The meridional reflection (I) corre-
sponded to an intermolecular distance of 0.51 nm along the
stacks, while the wide-angle equatorial scattering intensi-
ties (II) were related to the ꢀ-stacking distance of 0.37 nm
of the anthracene units. As depicted in the schematic illus-
tration of the supramolecular organization in Figure 3(b),
the molecules are stacked on top of each other due to
(
b)
ꢀ
-stacking interactions. Furthermore, the anthracene units
are out-of-plane tilted towards the molecular plane by an
ꢀ
angle of ca 90 leading to the wide-angle equatorial reflec-
tions. For this molecular arrangement, the benzenes are
most probably slightly shifted laterally towards each other.
This is the reason for the larger distance of 0.51 nm
between the packed benzene building blocks. Interestingly,
this crystalline organization is maintained above the phase
ꢀ
ꢀ
transitions at 116 C and 152 C. An identical observa-
tion has been made for other reported crystalline small
molecules.1 At elevated temperatures only the ꢀ-stacking
8
Fig. 4. (a) Drain current (I ꢄ versus drain–source voltage (V ꢄ charac-
D
D
ꢀ
distance increases slightly to 0.38 nm (above 116 C) and
.39 nm (above 152 C).
teristics of P2 at different gate voltages (V ꢄ. (b) Drain current (I ꢄ ver-
G
D
ꢀ
0
sus gate voltages (V ꢄ characteristics of P2 at a drain voltage of −40 V.
G
4
272
J. Nanosci. Nanotechnol. 12, 4269–4273, 2012

Madathil et al.
Synthesis and Characterization of Anthracene Derivative for Organic Field-Effect Transistor Fabrication
under nitrogen atmosphere. The output and transfer char-
acteristics of the bottom-contact OFET device are shown
in Figure 4.
Economy. K.-S. Lee acknowledges partial support from the
National Research Foundation of Korea (No. R11-2007-
050-00000-0) and the 2011 University Research Program
in Hannam University.
Among top-contact OTFTs, the device made by spin-
coating 2 wt% solution of P2 in chloroform on OTS
ꢀ
treated silicon substrate and annealed at 80 C showed a
References and Notes
−
5
2
best performance with a hole mobility of 5 × 10 cm
s .
The molecular organization in the solid state evidenced
−
1
−1
V
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4
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Received: 9 May 2010. Accepted: 21 July 2011.
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4273