Symmetric long alkyl chain end-capped anthracene derivatives for solution-processed organic thin-film transistors

Article abstract of DOI:10.1166/jnn.2012.5909

Three new anthracene derivatives, 2,6-bis(4-decylphenyl)anthracene (DDPAnt), 2-decyl-5-(2-(5-decylthiophen-2-yl)anthracen-6-yl)thiophene (DDTAnt), and 2,6-bis(4-decyloxy phenyl) anthracene (DDPXAnt) were synthesized by Suzuki cross-coupling reaction. The

Full text of DOI:10.1166/jnn.2012.5909

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Journal of
Nanoscience and Nanotechnology
Vol. 12, 4340–4343, 2012
Symmetric Long Alkyl Chain End-Capped
Anthracene Derivatives for Solution-Processed
Organic Thin-Film Transistors
Sang Hun Jang1, Dae Sung Chung3, Jin Young An2, Il Kang1, Hyunjin Kim2,
Chan Eon Park3, Yun-Hi Kim2, Soon-Ki Kwon1ꢀ∗, and Sang-Gyeong Lee2ꢀ∗
1School of Materials Science and Engineering and ERI, Gyeongsang National University, Jinju, 660-701, Korea
2Department of Chemistry, Research Institute of Natural Science, Gyeongsang National University, Jinju, 660-701, Korea
3Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 790-784, Korea
Three new anthracene derivatives, 2,6-bis(4-decylphenyl)anthracene (DDPAnt), 2-decyl-5-(2-(5-
decylthiophen-2-yl)anthracen-6-yl)thiophene (DDTAnt), and 2,6-bis(4-decyloxy phenyl) anthracene
(DDPXAnt) were synthesized by Suzuki cross-coupling reaction. The obtained oligomers were char-
acterized by 1H NMR, FT-IR, Mass, UV-visible spectroscopy, cyclovotammetry, differencial scanning
calorimetry, and thermogravimetric analysis. The thermal studies show that these oligomers are
stable up to 400 ꢀC. The solution processed OTFTs were fabricated using synthesized oligomers by
spin-coating and drop casting processes on Si/SiO2. OTFTs based on DDPAnt showed the mobility
of 7ꢀ6×10−3 cm2/Vs and on/off ratio of 105.
Keywords: Solution-Processing, Anthracene Derivatives, Suzuki Coupling, Organic Thin-Film
Transistors.
1. INTRODUCTION
thiophene-anthracene molecules, which show remarkably
high stability and very good electrical characteristics.
These anthracene derivatives introduced thiophene moiety
to improve the TFT performance (mobility of 0.5 cm2/Vs,
on/off ratio of 2ꢂ8×107ꢃ. Also introduction of hexyl side
chain in thiophene-anthracene has showed the greater sta-
bility due to large band gap and good molecular order-
ing of the alkyl side chain, especially at high substrate
temperatures.10–12
Thus we modified phenyl-, phenoxyl-as fused aromatic
unit instead thiophene unit to increase oxidation stabil-
ity and crystallinity. Also the anthracene derivatives with
long decyl end group increase solubility and fine molecu-
lar ordering due to improved self-assembly properties.12ꢀ13
In this paper, we report synthesis and characterization
of semiconductors based on anthracene-fused aromatic
hybride and their TFT characteristics.
Organic thin-film transistors (OTFTs) have attracted
intense interest in recent years because of their poten-
tial applications in active-matrix displays and integrated
circuits (ICs) for logic and memory chips.1ꢀ2 To realize
the full potential of these applications, it is necessary
to identify conjugated semiconductors with high mobil-
ity and robust environmental stability. Organic oligomers
investigated to date include p-type, n-type, and p/n-type
bipolar semiconductors.3ꢀ4 n-Linked benzene rings (n = 3:
anthracene; n = 4: tetracene; n = 5: pentacene) are promis-
ing candidates for organic semiconductors because their
planar shapes facilitate crystal packing and the extended
system over molecules enables the intermolecular overlap
of ꢁ systems.5 Especially, pentacene has been used as a
benchmark p-type semiconductor material with a charge
mobility over 1.0 cm−2/V · s, as reported by the several
groups.6 Yet the stability of these semiconductor types is
limited.7
2. EXPERIMENTAL DETAILS
Recent developments by several groups have resulted
in the improved stability, primarily through the judicious
choice of conjugated units and side chains.8ꢀ9 Meng’s
group reported two novel organic semiconductors based on
2.1. Device Fabrication
SiO2 (300 nm) as the dielectric layer. The hydrophobic
surface treatments of the dielectric surface such as with
hexamethyldisilazane (HMDS), octadecyltrichloro silane
∗Authors to whom correspondence should be addressed.
4340
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doi:10.1166/jnn.2012.5909

Jang et al.
Symmetric Long Alkyl Chain End-Capped Anthracene Derivatives for Solution-Processed OTFTs
(OTS-18), and polydimethylsiloxane (PDMS), were per-
formed via the well-known solution method. The water
contact angles for each case were measured to 25 2ꢀ
(untreated), 68 2ꢀ (HMDS), 99 2ꢀ (OTS-8), 108 1ꢀ
(OTS-18), 109 2ꢀ (PDMS). Semiconducting materials
were usually deposited onto modified dielectric surface via
spin-casting, drop-casting using chloroform, toluene, and
chlorobenzene and in some cases, substrates were annealed
to fabricate a more uniform layer. The Au source and drain
electrodes were thermally evaporated for 100 nm, and a
shadow mask was used to make the patterns and a chan-
nel region 1500 ꢄm long and 150 ꢄm wide. The field
effect mobility was extracted from the saturation regime
2.3. Synthesis of DDTAnt
DDTAnt. Following the procedure reported for DDPAnt.
DDTAnt was prepared using 2,6-dibromoanthracene (1 g,
2.98 mmol), 2-(5-decylthiophen-2-yl)-4,4,5,5-tetramethyl-
1,3,2-di-oxaborolane (1.9 g, 6.56 mmol), Pd(PPh3)4
(45 mg, 0.06 mmol), Aliquat® 336 (0.6 g, 1.49 mmol),
(2 M Na2CO3) sodium carbonate (1.48 g, 14 mmol),
toluene (48 mL) and water (7 mL), respectively. The crude
product was purified by soxhlet (silica gel, toluene) and
finally by recrystallization from toluene to give DꢀDTAnt
(0.80 g, 43%) as pale yellow powder. mp 233 C; IR
(KBr, cm−1ꢃ: 3050 (sp2 C–H), 2953–2847 (sp3 C–H), 1495
(C C); EI, MS m/z (%): 622 (100, M+).
from transfer characteristics, using the equation ꢄsat
=
ꢅ2IDSLꢃ/(WCꢅVg–Vthꢃ2ꢃ, where IDS is the saturation drain
current, C is the capacitance of the oxide dielectric, Vg is
the gate bias, and Vth is the threshold voltage.
2.4. Synthesis of DDPXAnt
DDPXAnt. Following the procedure reported for DDPAnt.
DDPXAnt was prepared using 2,6-dibromoanthracene
(0.97 g, 2.9 mmol), 2-(4-(decyloxy)phenyl)-4,4,5,5-
tetramethyl-1,3,2-dioxa -borolane (2.3 g, 6.38 mmol),
Pd(PPh3ꢃ4 (70 mg, 0.06 mmol), Aliquat® 336 (0.59 g,
1.45 mmol), (2 M Na2CO3) sodium carbonate (1.54 g,
14.5 mmol), toluene (48 mL) and water (8 mL), respec-
tively. The crude product was purified by soxhlet (sil-
ica gel, toluene) and finally by recrystallization from
toluene to give DDPXAnt ꢀ(0.92 g, 50%) as pale yellow-
ish green powder. mp 213 C; IR (KBr, cm−1ꢃ: 3080 (sp2
C–H), 2953–2850 (sp3 C–H), 1604–1517 (C C); EI, MS
m/z (%): 643 (100, M+).
2.2. Synthesis of DDPAnt
DDPAnt. To a solution of 2,6-dibromoanthracene (2.0 g,
5.95 mmol) and 2-(4-decyl-phenyl)-4,4,5,5-tetramethyl-
[1,3,2]dioxaborolane (4.51 g, 13.09 mmol) dissolved in
toluene (40 mL). The reaction mixture was added 6 mL of
(2 M Na2CO3ꢃ sodium carbonate (3.16 g, 29.8 mmol), fol-
lowed by the addition of the phase-transfer agent Aliquat®
336 (1.2 g, 2.98 mmol). The mixture was deoxygenated
with a stream of nitrogen. Then, Pd(PPh3ꢃ4 (0.14 g,
ꢀ
0.42 mmol) was added. The mixture was heated to 90 C
for three days under a nitrogen atmosphere. The reaction
mixture was cooled to room temperature and poured into
methanol (50 mL). The precipitate was filtered off, washed
with water, dilute acid (5% HCl), water, methanol and
then with acetone three times to remove the starting mate-
rial as well as the mono-substituted byproduct. The crude
product was purified by soxhlet (silica gel, toluene) and
finally by recrystallization from toluene to give DDPAnt
3. RESULTS AND DISCUSSION
The anthracene derivatives DDPAnt, DDTAnt and DDPX-
Ant with different aromatic unit were designed to
have each phenyl, thiophene and phenoxyl unit between
anthracene and decyl end group. The anthracene deriva-
tives were synthesized as depicted in Scheme 1. The mate-
rials DDPAnt, DDTAnt and DDPXAnt were synthesized
under the conditions of Suzuki coupling reaction in the
presence of palladium catalyst in water:toluene (1:6) to
give 80%, 43% and 50% yield, respectively. Their struc-
ꢀ
(2.9 g, 80%) as pale yellowish green powder. mp 227 C;
IR (KBr, cm−1ꢃ: 3036 (sp2 C–H), 2917–2848 (sp3 C–H),
1
1465 (C C); H-NMR (300 MHz, CDCl3ꢃ: ꢆ 8.49 (s, 2
1
tures were confirmed by FT-IR, H-NMR, 13C-NMR and
H), 8.21 (s, 2 H), 8.11–8.08 (d, 2 H, J = 8ꢂ3 Hz), 7.79–
7.77 (d, 2 H, J = 7ꢂ8 Hz), 7.74–7.71 (d, 4 H, J = 6ꢂ99
Hz), 7.36–7.33 (d, 4 H, J = 6ꢂ81 Hz), 2.70 (t, 4 H, J = 7ꢂ2
Hz), 1.7–1.65 (m, 4 H), 1.3 (m, 28 H), 0.91 (t, 6 H,
J = 6ꢂ37 Hz); EI, MS m/z (%): 610 (100, M+).
mass analysis. The synthesized materials have good solu-
bility in organic solvents under heating.
Figure 1 shows the UV-visible and photoluminescence
(PL) spectra in dilute CHCl3 solution and thin film and
X
C10 H21
Pd(PPh3) 4, 2M Na2CO3,
Aliquat 336
C10H21
Br
O
X
C10H21
X
B
+
O
toluene, 100 ºC
Br
O
S
X=
DDPAnt DDTAnt
DDPXAnt
Scheme 1. Synthesis of DDPAnt, DDTAnt, DDPXAnt.
J. Nanosci. Nanotechnol. 12, 4340–4343, 2012
4341

Symmetric Long Alkyl Chain End-Capped Anthracene Derivatives for Solution-Processed OTFTs
Jang et al.
DDPAnt UV(solution)
DDPAnt UV(film)
DDPXAnt UV(solution)
DDPXAnt UV(film)
DDTAnt UV(solution)
DDTAnt UV(film)
DDPAnt PL(solution)
DDPAnt PL(film)
DDPXAnt PL(solution)
DDPXAnt PL(film)
DDTAnt PL(solution)
DDTAnt PL(film)
shown in the range of −5ꢂ79 eV to −5ꢂ45 eV, which are
lower than that of pentacene (HOMO level of −5ꢂ0 eV).
These results indicate that the synthesized oligomers have
high oxidation stability. Moreover, these HOMO levels are
closed and therefore match well to the work function of
gold electrode (−5ꢂ4 eV) in OTFTs,17 which increases the
efficiency of the injection and transport of holes.
1.0
0.8
0.6
0.4
0.2
0.0
The thermal properties of oligomers were investigated
by thermal gravimetric analysis (TGA) and differential
scanning calorimetry (DSC) in a nitrogen atmosphere.
TGA curve reveals that the oligomers have high thermal
stability. Fiveꢀ percent weiꢀght loss (T5dꢃ is observed at
ꢀ
350
400
450
500
550
600
650
700
438 C, 333 C and 384 C for DDPAnt, DDTAnt and
Wavelength (nm)
DDPXAnt (Table I). From DSC, ꢀDDPAnt exhibits four
ꢀ
ꢀ
ꢀ
endothermic peaks at 131 C, 193 C, 220 C and 226 C
and four exothermic transition at at 83 ꢀC, 178 ꢀC, 215 ꢀC
Fig. 1. Optical absorption (UV) and emission (PL) of DDPAnt,
DDTAnt and DDPXAnt in dilute CHCl3 solution and in the solid state.
ꢀ
and 224 C. DSC of DDTAnt reveals two endothermic
ꢀ
ꢀ
data are summarized in Table I. Thin films of DDPAnt,
DDTAnt and DDPXAnt show a red shift about 40–60 nm
of the main absorption peak compared to that obtained
in dilute chloroform solution. These results can be origi-
nated from the formation of aggregation or excimer in thin
film due to ꢁ − ꢁ∗ stacking or intermolecular interaction
caused by their planar structure.
The electrochemical behaviors of oligomers were inves-
tigated by cyclic voltammetry (CV) in Bu4NClO4 (0.1
M) in CHCl3 at a scan rate of 50 mV/s under nitrogen.
A platinum electrode was used as working electrode. A Pt
wire was used as a counter electrode and an Ag/AgNO3
electrode was used as the reference electrode. All measure-
ments were calibrated using ferrocene value of −4ꢂ4 eV as
standard (Table I). HOMO energy level of oligomers were
peakꢀs at 213 C ꢀand 223 C and two exothermic peaks at
210 C and 218 C. DDTAnt also exhibited good thermal
feature under heating and cooling cycle. DSC of DDPX-
ꢀ
ꢀ
Ant reveals two endothermic peaks at 125 C aꢀnd 233 C
and an exothermic peaks were observed at 228 C respec-
tively. All revealed thermal features of DDPAnt, DDTAnt
and DDPXAnt showed that all of the three oligomers
are crystalline and it is expected that their thin films are
well ordered under heat treatment. DDPAnt, and DDPX-
Ant were used as active layer of OTFT device, and their
electrical characteristics were shown in Figure 2. In case
of DDPXEAnt, no semiconducting characteristics were
observed, and it may possibly be due to the poor film
structure. Both DDPAnt, and DDPXAnt showed semicon-
ducting performance after thermal annealing above 140 ꢀC.
Table I. Summary of the physical data of DDPAnt, DDTAnt and DDPXAnt.
ꢇabs/nm
ꢇem/nm
Compound
Solution
Film
Solution
Film
Eox/eV
T5d/ꢀC
Eg/eV
HOMO/eV
LUMO/eV
DDPAnt
DDTAnt
DDPXAnt
360, 385, 402
373, 436
393, 403, 425
380, 403, 428
386, 415, 444
417, 445
405, 429, 470
482, 515, 555
446, 471
478, 511
484, 519, 560
510, 533
1.19
1.35
1.01
438
333
384
2.87
2.59
2.70
−5ꢂ63
−5ꢂ79
−5ꢂ45
−2ꢂ76
−2ꢂ93
−2ꢂ98
10–5
0.0008
0.0012
(b)
(a)
10–6
10–6
10–7
10–7
0.0008
0.0004
0.0000
10–8
10–8
10–9
10–9
0.0004
0.0000
10–10
10–11
10–12
10–13
10–10
10–11
10–12
10–13
20
0
–20 –40 –60 –80
Vg (V)
20
0
–20 –40 –60 –80
Vg (V)
Fig. 2. Drain current (Idꢃ versus gate voltage (Vgꢃ characteristics of (a) DDPAnt (b) DDPXAnt.
J. Nanosci. Nanotechnol. 12, 4340–4343, 2012
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Jang et al.
Symmetric Long Alkyl Chain End-Capped Anthracene Derivatives for Solution-Processed OTFTs
(b) (c) (d)
(a)
Fig. 3. GIXD data of DDPAnt (a) as-spun film, (b) annealed at 140 ꢀC and DDPXAnt (c) as-spun film, (d) annealed at 140 ꢀC.
To study the crystalline structure of both films in more
detail, we have measured GIXD of DDPAnt and DDPX-
Ant (Fig. 3). In both cases, the intensity of (00l) diffraction
peaks increased as a result of annealing, originated from
re-ordering of semiconducting molecules. At the same
time, the number of deffraction spots along the qz (out-
of-plane) direction at a given qxy (in-plane) of DDPAnt
is larger than DDPXAnt, and their intensities also show
same trend. These results strongly suggested that DDPAnt
forms more densely packed three-dimensional (3D) multi-
layered structures rather than DDPXAnt, which may result
in higher charge carrier mobility. Maximum mobility of
DDPAnt was measured as 3ꢂ7×10−3 cm2/Vs, but around
half of this value (2ꢂ0×10−3 cm2/Vs) was exhibited in the
device based on DDPXAnt. This observation is followed
by general relationship between crystallinity of film and
device performance. In output curves, better output char-
Program in Strategic Technology, under Ministry of
Knowledge Economy of Korea, a grant (F0004010-2011-
34) from Information Display R&D Center, one of the
Knowledge Economy Frontier R&D Program funded by
the Ministry of Knowledge Economy of Korean govern-
ment, and Basic Science Research Program through the
National Research Foundation of Korea (NRF) funded by
the ministry of Education, Science and Technology (Grant
Number: 2010-0023775).
References and Notes
1. T. Hongkun, S. Jianwu, Y. Donghang, W. Lixiang, G. Yanhou, and
W. Fosong, Adv. Mater. 18, 2149 (2006).
2. X. Gao, C. Di, Y. Hu, X. Yang, H. Fan, F. Zhang, Y. Liu, H. Li, and
D. Zhu, J. Am. Chem. Soc. 132, 3697 (2010).
3. G. Horowitz, J. Mater. Res. 19, 1946 (2004).
4. B. A. Jones, M. J. Ahrens, M. Yoon, A. Facchetti, T. J. Marks, and
M. R. Wasielewski, Angew. Chem. Int. Ed. 43, 6363 (2004).
5. Y. Inoue, S. Tokito, K. Ito, and T. Suzuki, J. Appl. Phys. 95, 5795
(2004).
6. H. Klauk, M. Halik, U. Zschieschang, G. Schmid, W. Radlik, and
W. Weber, J. Appl. Phys. 92, 5259 (2002).
7. C. Pannemann, T. Diekmann, and U. Hilleringmann, J. Mater. Res.
19, 1999 (2004).
8. K. Ito, T. Suzuki, Y. Sakamoto, D. Kubota, Y. Inoue, F. Sato, and
S. Tokito, Angew. Chem. Int. Ed. 42, 1159 (2003).
9. H. Meng, J. Zheng, A. J. Lovinger, B. Wang, P. G. Van Patten, and
Z. Bao, Chem. Mater. 15, 1778 (2003).
ꢀ
acteristic was observed in 160 C annealed DDPAnt film,
ꢀ
compared to 180 C annealed DDPXAnt film. In output
curves, better output characteristic was observed in 160 ꢀC
annealed DDPAnt film, compared to 180 ꢀC annealed
DDPXAnt film. This observation is followed by general
relationship between crystallinity of film and device per-
formance. DDPXAnt is slightly tilted on the substrate
composed to DDPAnt because molecules inserted oxygens
are inclinded to have less ridigity.
10. H. Meng, F. Sun, M. B. Goldfinger, G. D. Jaycox, Z. Li, W. J.
Marshall, and G. S. Blackman, J. Am. Chem. Soc. 127, 2406
(2005).
11. F. Garnier, A. Yassar, R. Hajlaoui, G. Horowitz, F. Deloffre,
B. Servet, S. Ries, and P. Alnot, J. Am. Chem. Soc. 115, 8716
(1993).
12. J. A. Merlo, C. R. Newman, C. P. Gerlach, T. W. Kelley, D. V.
Muyres, S. E. Fritz, M. F. Toney, and C. D. Frisbie, J. Am. Chem.
Soc. 127, 3997 (2005).
13. S. A. Ponomarenko, S. Kirchmeyer, A. Elschner, N. M. Alpatova,
M. Halik, H. Klauk, U. Zschieschang, and G. Schmid, Chem. Mater.
18, 579 (2006).
14. H. Meng, F. Sun, M. B. Goldfinger, F. Gao, D. J. Londono, W. J.
Marshal, G. S. Blackman, K. D. Dobbs, and D. E. Keys, J. Am.
Chem. Soc. 128, 9304 (2006).
15. M. Wehmeier, M. Wagner, and K. Mullen, Chem. Eur. J. 7, 2197
(2001).
16. S. K. Lee, W. J. Yang, J. J. Choi, C. H. Kim, S. J. Jeon, and B. R.
Cho, Org. Lett. 7, 323 (2005).
17. S. Ando, J. Nishida, E. Fujiwara, H. Tada, Y. Inoue, S. Tokito, and
Y. Yamashita, Chem. Mater. 17, 1261 (2005).
4. CONCLUSION
We synthesized new 4-alkyl/alkoxybenzene end-capped
oligomers by Suzuki coupling reaction. Their thermal
properties revealed thatꢀ all oligomeꢀrs had good thermal
stability (between 333 C and 438 C). Investigation on
the optical and electrochemical properties showed that
the synthesized oligomers have higher oxidation poten-
tials due to their high HOMO energy levels (−5ꢂ63 eV
for DDPAnt, −5ꢂ79 eV for DDTAnt and −5ꢂ45 eV for
DDPXAnt). OTFTs showed the mobility of 3ꢂ3 × 10−3
ꢀ
cm2/Vs at 140 C for DDPAnt and 3ꢂ3 × 10−3 cm2/Vs at
ꢀ
180 C for DDPXAnt. In the case DDPAnt, only slightly
better mobility (7ꢂ6×10−3 cm2/Vs) was obtained by ther-
ꢀ
mal annealing at 160 C.
Acknowledgment: This research was supported and
MKE and KIAT through the Workforce Development
Received: 13 May 2010. Accepted: 4 July 2011.
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4343