Oligo(2,6-anthrylene)s: Acene-oligomer approach for organic field-effect transistors

Article abstract of DOI:10.1002/anie.200390305

Oligo(2,6-anthrylene)s 1 and their dihexyl derivatives have been synthesized by Suzuki coupling using palladium catalysts. Organic field-effect transistors (OFETs) of these anthracene oligomers exhibited FET activity, and high hole mobilities up to 0.18 c

Full text of DOI:10.1002/anie.200390305

Angewandte
Chemie
Organic Field-Effect Transistors
Oligo(2,6-anthrylene)s: Acene–Oligomer
Approach for Organic Field-Effect Transistors**
Kaname Ito, Toshiyasu Suzuki,* Youichi Sakamoto,
Daisuke Kubota, Youji Inoue, Fumio Sato, and
Shizuo Tokito
Anthracene has been widely studied as an organic photo-
[
1]
conductor during the past five decades. Hole mobilities in
anthracene single crystals were measured by the time-of-flight
photocurrent technique and were found to reach up to
2
À1 À1
[2]
3
cm V
s
at 300 K. Although anthracene may be a good
candidate for a p-type semiconductor for organic field-effect
[
3]
transistors (OFETs),
FET activity has not yet been
observed. Recently, OFETs with tetracene were realized
2
À1 À1
[4]
and showed a hole mobility of 0.01 cm V
s
on SiO /Si. Of
2
all the OFET materials reported so far, the highest field-effect
2
À1 À1
mobility has been recorded in pentacene (0.3–0.7 cm V
s
2
À1 À1
on SiO /Si and 1.5 cm V
s
on chemically modified SiO2/
2
[
5]
Si). The HOMO energy level in linear [n]acenes (n = 2:
naphthalene, 3: anthracene, 4: tetracene, 5: pentacene)
significantly increases with increasing n, which facilitates the
formation of radical cations (holes) at the interface between a
dielectric and a semiconducting layer. Furthermore, the
extended p system of a higher acene enhances the intermo-
lecular overlap of p–p systems in the solid state and leads to
high mobility. However, a problem of the linear acene
approach is the chemical instability of higher acenes. We
thought that the oligomerization of a small acene could also
[
6,7]
be an effective way to extend a p system.
Oligo(2,6-
anthrylene)s would be interesting because the anthracene
monomer itself has high time-of-flight mobility (Scheme 1),
and 2,6-substitution is expected to give the most extended
[
8]
[9]
p conjugation and the highest planarity. We report herein
the synthesis and characterization of 2,2’-bianthryl (2A), 2,6-
trianthrylene (3A), and their dihexyl derivatives (DH-2A
and DH-3A). OFETs with these oligomers have been
constructed, and their performances as p-type semiconduc-
tors are also presented.
Anthracene oligomers have been synthesized by the
[
10]
Suzuki coupling using palladium catalysts.
As shown in
Scheme 2, 2-bromoanthracene (1) was treated with bis(pina-
[
*] Prof. T. Suzuki, K. Ito, Dr. Y. Sakamoto
Institute for Molecular Science and
Department of Structural Molecular Science
The Graduate University for Advanced Studies
Myodaiji, Okazaki 444-8585 (Japan)
Fax: (+81)564-54-2254
E-mail: toshy@ims.ac.jp
D. Kubota, Dr. Y. Inoue, Dr. F. Sato, Dr. S. Tokito
NHK Science and Technical Research Laboratories
Kinuta, Setagaya-ku, Tokyo 157-8510 (Japan)
[**] This work was supported by the Japan Society for the Promotion of
Science (Grant-in-Aid for Scientific Research B 14340226).
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
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R
zene, 3A and DH-3A are almost insoluble in organic
solvents. The structures were determined by mass spectrom-
etry and elemental analyses. Differential scanning calorim-
etry (DSC) measurements on 2A and 3A showed sharp
R
[
10]
melting endotherms at 374 and 4908C, respectively. DH-
2A and DH-3A are thermally less stable than the parent
compounds and decompose before melting. The dimers (2A
and DH-2A) and the trimers (3A and DH-3A) exhibit strong
blue-green and green photoluminescence, respectively, in the
solid state. The emission maxima in chloroform shift to lower
energies in the order 2A > DH-2A > 3A > DH-3A (431, 436,
2
A (R = H)
DH-2A (R = C6H13)
R
[
12]
4
47, and 454 nm, respectively). The electrochemical meas-
R
3
A (R = H)
urement on DH-2A was performed in 1,2-dichlorobenzene.
The cyclic voltammogram (CV) showed a quasireversible
oxidation at 0.69 V, and the differential pulse voltammogram
DH-3A (R = C6H13)
Scheme 1. Structures of anthracene oligomers.
(DPV) exhibited two oxidation peaks at 0.69 and 0.99 Vand a
reduction peak at À2.40 V(versus the ferrocene/ferrocenium
+
couple (Fc/Fc )).
Br
O
O
O
O
[PdCl2(dppf)]
OFETs of anthracene oligomers were constructed on
+
B B
SiO /Si substrates by high-vacuum evaporation at different
2
KOAc
DMSO, 80°C
R
substrate temperatures using top-contact geometry. The
electrical measurements were performed at room temper-
1
4
(R = H)
(R = C6H13)
ature. Figure 1 shows the drain current (I ) versus drain
D
voltage (V ) characteristics for OFETs with 2A, 3A, DH-2A,
D
O
B
and DH-3A at various gate voltages (V ). FET activity was
G
O
1 or 4
Pd(PPh3)4]
Na2CO3, H2O
toluene, reflux
2
A (35%)
observed at the substrate temperatures (Tsub) between 50 and
708C in OFETs with 2A (Table 1). The hole mobilities
DH-2A (39%)
[
R
2
6
(R = H; 68%)
(R = C6H13; 67%)
Table 1: FET characteristics of anthracene oligomers fabricated at
different substrate temperatures.
Br
2
À1 À1
Compd
T [8C]
Mobility [cm V
s
]
On/off ratio
Br
3
4
4
4
2
3
A
A
50
0.0031
0.0088
0.013
0.064
0.069
0.072
0.031
0.11, 0.13
0.040
0.027
10 –10
3
3A (13%)
DH-3A (14%)
3
6
7
0
0
10 –10
3
10 –10
5
100
125
150
175
70
10
10
9
[
-hexyl-9-BBN
PdCl2(dppf)]
4
C6H13
4
5
3
4 (30%)
+
10 –10
K3PO4
THF, reflux
4
C6H13
10
10
10
10
10
10
4
5
DH-2A
DH-3A
4
90
Scheme 2. Synthesis of oligo(2,6-anthrylene)s by Suzuki coupling.
4
100
4
1
1
50
75
0.044
0.14, 0.18
4
colato)diboron in the presence of [PdCl (dppf)] (dppf = 1,1’-
2
bis(diphenylphosphanyl)ferrocene) to give boronic ester 2 in
6
8% yield. The Suzuki coupling of 1 with 2 in the presence of
calculated in the saturation regime ranged from 0.0031 to
0.013 cm V s , and the on/off ratios were 10 –10 . The
2
À1 À1
3
4 [13]
[
Pd(PPh ) ] afforded 2A in 35% yield. Similarly, the cross-
3
4
coupling of 2,6-dibromoanthracene (3) with two equivalents
of 2 provided 3A in 13% yield.[ An equivalent of 9-hexyl-9-
BBN (9-BBN = 9-borabicyclo[3.3.1]nonane), which was pre-
pared from 1-hexene and 9-BBN, was allowed to react with 3
oligomer 3A showed even higher mobil
11]
2
À1 À1
4
5
ities (0.031–0.072 cm V s ) and on/off ratios (10 –10 )
at Tsub = 100–1758C. The FET performances were dramati-
cally improved when 2A and 3A were modified with two
[
14]
in the presence of [PdCl (dppf)] to give a mixture of 2-bromo-
hexyl groups: OFETs with DH-2A have shown field-effect
2
2
À1 À1
6
-hexylanthracene (4, 30%), 2,6-dihexylanthracene (5), and
mobilities greater than 0.1 cm V
s
at Tsub = 708C.
3. This mixture was converted into boronic esters, and 6 was
Although mobilities of DH-3A OFETs were lower than
isolated in pure form (67%). The Suzuki coupling of 4 with 6
afforded DH-2A in 39% yield. The cross-coupling of 3 with
two equivalents of 6 yielded DH-3A in 14% yield.
Anthracene oligomers purified by train sublimation are
bright-yellow crystalline solids. Although 2A and DH-2A are
slightly soluble in aromatic solvents such as 1,2-dichloroben-
those of 3A OFETs at T = 100–1508C, the highest mo
sub
2
À1 À1
bilities (0.14–0.18 cm V s ) were observed at T
=
sub
1758C. These mobilities are still lower than that of pentacene
[
6]
but higher than those of oligothiophenes.
Films deposited on Si/SiO substrates were studied by X-
2
ray diffraction in reflection mode at room temperature. Sharp
1
160
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Angewandte
Chemie
Figure 1. Drain current (I ) versus drain voltage (V ) as a function of gate voltage (V ) for OFETs with anthracene oligomers. a) 2A (T =708C);
D
D
G
sub
b) 3A (Tsub =1508C); c) DH-2A (Tsub =708C); d) DH-3A (Tsub =1758C). Channel length L: 100 mm; channel width W: 1 mm (W/L=10).
and strong reflections up to the sixth order indicated a high
degree of lamellar ordering and crystallinity. In the cases of
soluble oligomers based on 9,10-dialkylanthracenes are
currently in progress and will be reported elsewhere.
2
A, 3A, and DH-2A, the layer spacings obtained from the
first reflection peaks (1.94, 2.84, and 3.20 nm, respectively)
correspond to the extended molecular lengths calculated by
PM3 (1.83, 2.71, and 3.16 nm, respectively).[ This result
suggests the molecules have a perpendicular orientation on
the substrates. Interestingly, the layer spacings of DH-3A
increase with increasing substrate temperatures during fab-
rication (Tsub = 1008C: 3.52; 1508C: 3.64; 1758C: 3.73 nm)
and are shorter than the calculated molecular length
Received: November 12, 2002 [Z50527]
15]
Keywords: biaryls · cross-coupling · oligomerization ·
.
semiconductors · thin films
[
[
1] P. M. Borsenberger, D. S. Weiss, Organic Photoreceptors for
Xerography, Marcel Dekker, New York, 1998, pp. 234 – 242.
2] a) M. Pope, C. E. Swenberg, Electronic Processes in Organic
Crystals and Polymers, Oxford University Press, New York,
1999; b) N. Karl, J. Marktanner, Mol. Cryst. Liq. Cryst. 2001, 355,
149 – 173, and references therein.
(
3.94 nm). This observation indicates that the molecules are
inclined relative to the substrate or there is interdigitation of
the hexyl chains.
The field-effect mobilities of anthracene oligomers
increased in the order 2A < 3A < DH-2A < DH-3A (0.01,
2
À1 À1
[3] For a recent review, see C. D. Dimitrakopoulos, P. R. L. Mal-
0
.07, 0.13, and 0.18 cm V s , respectively). The addition of
enfant, Adv. Mater. 2002, 14, 99 – 117.
alkyl groups (from 2A to DH-2A) is more effective than the
extension of p conjugation (from 2A to 3A).[ Although the
oxidation potential of DH-2A (0.69 V) is more positive than
that of tetracene (0.52 Vversus Fc/Fc in 1,2-dichloroben-
zene), the field-effect mobility of DH-2A (0.13 cm V s ) is
much higher than that of tetracene (0.01 cm V s ). These
results may indicate that the quality of a thin film is more
important than the ionization potential of a semiconductor.
In summary, we have shown that the acene–oligomer
approach is useful for producing stable p-type organic semi-
conductors with high field-effect mobilities. The fabrication of
OFETs from a solution of DH-2A and the synthesis of
[
4] D. J. Gundlach, J. A. Nichols, L. Zhou, T. N. Jackson, Appl. Phys.
Lett. 2002, 80, 2925 – 2927.
16]
[
5] a) D. J. Gundlach, Y.-Y. Lin, T. N. Jackson, S. F. Nelson, D. G.
Schlom, IEEE Electron Device Lett. 1997, 18, 87 – 89; b) Y.-Y.
Lin, D. J. Gundlach, S. F. Nelson, T. N. Jackson, IEEE Electron
Device Lett. 1997, 18, 606 – 608.
+
2
À À1
2
À1 À1 [4]
[
6] The oligomer approach for OFETs is the most successful in
oligothiophene semiconductors, see a) H. E. Katz, Z. Bao, S. L.
Gilat, Acc. Chem. Res. 2001, 34, 359 – 369; b) F. Garnier, A.
Yassar, R. Hajlaoui, G. Horowitz, F. Deloffre, B. Servet, S. Ries,
P. Alnot, J. Am. Chem. Soc. 1993, 115, 8716 – 8721.
[
7] Oligo(p-phenylene)s for OFETs: D. J. Gundlach, Y.-Y. Lin, T. N.
Jackson, D. G. Schlom, Appl. Phys. Lett. 1997, 71, 3853 – 3855.
Angew. Chem. Int. Ed. 2003, 42, No. 10
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Communications
[
8] Poly(2,6-anthrylene) as a conducting polymer and a potential
phene): a) J. G. Laquindanum, H. E. Katz, A. J. Lovinger, A.
Dodabalapur, Adv. Mater. 1997, 9, 36 – 39; b) X.-C. Li, H.
Sirringhaus, F. Garnier, A. B. Holmes, S. C. Moratti, N. Feeder,
W. Clegg, S. J. Teat, R. H. Friend, J. Am. Chem. Soc. 1998, 120,
2206 – 2207.
electroluminescent material: P. Hodge, G. A. Power, M. A.
Rabjohns, Chem. Commun. 1997, 73 – 74.
[
9] In crystalline oligo(9,10-anthrylene)s, the dihedral angles
between anthracene moieties were more than 758 as a conse-
quence of steric hindrance: a) U. Mꢀller, M. Adam, K. Mꢀllen,
Chem. Ber. 1994, 127, 437 – 444; b) H.-D. Becker, V. Langer, J.
Sieler, H.-C. Becker, J. Org. Chem. 1992, 57, 1883 – 1887.
[14] OFET materials with self-assembly properties by alkyl groups:
H. Meng, Z. Bao, A. J. Lovinger, B.-C. Wang, A. M. Mujsce, J.
Am. Chem. Soc. 2001, 123, 9214 – 9215. Also, see references [6a]
and [6b].
[15] Atomic force microscopy (AFM) images of 2A films prepared at
50–708C showed a series of terraces with the step height of
2.0 nm. See Supporting Information.
[
[
10] See Supporting Information for the experimental details.
11] Dehalogenation is a side reaction of the Suzuki coupling and
responsible for the low yields of the anthracene oligomers: N.
Miyaura, Top. Curr. Chem. 2002, 219, 11 – 59.
[
12] This is in agreement with the result of PM3 calculations: The
HOMO–LUMO energy gaps decrease in the order 2A
[16] A similar effect was observed in oligothiophenes: The field-
effect mobilities increased in the order 4T< 6T< DH-4T<
2
À1 À1
(
6.94 eV) > DH-2A
(6.91 eV) > 3A
(6.86 eV) > DH-3A
DH-6T (0.003, 0.02, 0.03, and 0.08 cm V s , respectively): F.
(
6.82 eV).
Garnier, R. Hajlaoui, A. E. Kassmi, G. Horowitz, L. Laigre, W.
Porzio, M. Armanini, F. Provasoli, Chem. Mater. 1998, 10, 3334 –
3339.
[
13] Interestingly, 2A is isoelectronic (14p ꢁ 2) with p-type OFET
materials such as bis(benzodithiophene) and bis(dithienothio-
1
162
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