Synthesis and properties of BF2 complexes to dihydroxydiones of tetracene and perylene: Novel electron acceptors showing n-type semiconducting behavior

Article abstract of DOI:10.1021/ol802470k

BF₂ complexes containing tetracene and perylene moieties were synthesized as new types of electron-deficient arene compounds. These compounds exhibit long wavelength absorption and high electron affinities, as revealed through spectral and electrochemical studies, due to their quadrupolar structures represented by resonance contributors. The BF₂ complex containing tetracene exhibits an n-type semiconducting behavior. These compounds are new types of electron acceptors functionalized by BF₂ chelation.

Full text of DOI:10.1021/ol802470k

ORGANIC
LETTERS
2009
Vol. 11, No. 1
149-152
Synthesis and Properties of BF2
Complexes to Dihydroxydiones of
Tetracene and Perylene: Novel Electron
Acceptors Showing n-Type
Semiconducting Behavior
Katsuhiko Ono,*,† Hiroyuki Yamaguchi,† Keijiro Taga,† Katsuhiro Saito,†
Jun-ichi Nishida,‡ and Yoshiro Yamashita‡
Department of Materials Science and Engineering, Nagoya Institute of Technology,
Gokiso, Showa-ku, Nagoya 466-8555, Japan, and Department of Electronic Chemistry,
Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of
Technology, Nagatsuta, Midori-ku, Yokohama 226-8502, Japan
ono.katsuhiko@nitech.ac.jp
Received October 31, 2008
ABSTRACT
BF2 complexes containing tetracene and perylene moieties were synthesized as new types of electron-deficient arene compounds. These
compounds exhibit long wavelength absorption and high electron affinities, as revealed through spectral and electrochemical studies, due to
their quadrupolar structures represented by resonance contributors. The BF2 complex containing tetracene exhibits an n-type semiconducting
behavior. These compounds are new types of electron acceptors functionalized by BF2 chelation.
Currently, research on organic field-effect transistors
(OFETs)1 based on π-extended aromatic compounds is being
actively pursued because of their potential applications in
organoelectronic devices such as flexible displays, low-cost
memories, and photovoltaic cells. A synthetic study of n-type
semiconductors is crucial for the development of p-n
junctions because the number of electron-transporting ma-
terials is still limited compared to that of p-type semiconduc-
tors.2 Among these semiconductors, polycyclic aromatic
compounds have been extensively studied. These compounds
have extended π-conjugation and rigid planarity, thereby
resulting in suitable intermolecular π-π overlap and face-
to-edge interactions in the solid state.3 For the synthesis of
n-type semiconductors with high electron affinities, introduc-
tion of fluorine and trifluoromethyl groups into arene moieties
† Nagoya Institute of Technology.
‡ Tokyo Institute of Technology.
(1) (a) Murphy, A. R.; Fre´chet, J. M. J. Chem. ReV. 2007, 107, 1066.
(b) Zaumseil, J.; Sirringhaus, H. Chem. ReV. 2007, 107, 1296. (c) Anthony,
J. E. Chem. ReV. 2006, 106, 5028. (d) Muccini, M. Nat. Mater. 2006, 5,
605. (e) Newman, C. R.; Frisbie, C. D.; da Silva Filho, D. A.; Bre´das,
J.-L.; Ewbank, P. C.; Mann, K. R. Chem. Mater. 2004, 16, 4436. (f) Sun,
Y.; Liu, Y.; Zhu, D. J. Mater. Chem. 2005, 15, 53. (g) Dimitrakopoulos,
C. D.; Malenfant, P. R. L. AdV. Mater. 2002, 14, 99. (h) Katz, H. E.; Bao,
Z.; Gilat, S. L. Acc. Chem. Res. 2001, 34, 359.
10.1021/ol802470k CCC: $40.75
Published on Web 12/03/2008
2009 American Chemical Society

is effective, for example, perfluoropentacene,2c hexafluoro-
hexa-peri-hexabenzocoronene,4 and 2,6-bis(4-trifluorometh-
ylphenyl)anthracene.5 Furthermore, electron-withdrawing
imide substituents yield naphthalene-, anthracene-, and
perylene-based materials.6 Electron-deficient heterocyclic
compounds such as pyrazinoquinoxaline7 and anthrazoline8
are investigated as building blocks for electron-transporting
materials. On the other hand, BF2 complexes have been
studied as potential electron-transporting materials.9 In these
compounds, the BF2-chelating moieties behave as electron-
accepting units.9c An OFET device that uses a BF2 complex
with 1,6-diphenyl-1,3,4,6-hexanetetrone exhibits an n-type
semiconducting behavior.9a We synthesize BF2 complexes
containing tetracene (1) and perylene (2) as new types of
electron-deficient arene compounds (Scheme 1). The BF2
chelation contributes toward electron withdrawal and π-elec-
tron delocalization of the tetracene and perylene moieties,
as represented by the resonance contributors 1A and 2A.10
The quadrupolar structures yield small HOMO-LUMO
energy gaps.11 These molecules have rigid, planar structures
leading to effective intermolecular π-π overlap in the solid
state. In this paper, we report the synthesis and properties
of BF2 complexes 1 and 2 and the application of 1 to OFET
devices.
Scheme 1. Structures of BF2 Complexes 1 and 2
The synthesis of BF2 complexes 1 and 2 was performed
by chelation of 6,11-dihydroxy-5,12-naphthacenedione
(DHND)12 and 4,9-dihydroxy-3,10-perylenedione (DHPD)13
with boron trifluoride-diethyl etherate (BF3·OEt2). Com-
pound 1 was obtained in the form of red crystals with a yield
of 61% after sublimation at 400 °C under 10-3 Torr.
Compound 2 was prepared as a dark red solid with a crude
yield of 88%, but it could not be sublimed. Compound 1
was slightly soluble in common organic solvents such as
chloroform, dichloromethane, DMF, toluene, and acetonitrile,
whereas compound 2 was insoluble in common solvents and
very slightly soluble in DMF and acetonitrile. The structure
of 1 was determined by 1H NMR, IR, and EI mass
spectrometry and elemental analysis. The structure of 2 was
determined by IR and MALDI-TOF mass spectrometry. The
molecular ion peak of 2 was observed by using the negative
mode (see Supporting Information) instead of the positive
mode. This suggests that compound 2 had high electron
affinity. Both compounds were stable in air in the solid state.
The stability of 1 to moisture considerably increased as
compared to that of the BF2 complex of 1,4-dihydroxyan-
thraquinone (quinizarin), which decomposed in air in the
solid state within 5 h. The BF2-chelating moieties of 1 and
2 were thermally stable in the solid state under nitrogen. The
differential scanning calorimetry (DSC) of 1 revealed a
melting point of 368.6 °C. The thermogravimetric analysis
(TGA) of 2 exhibited the decomposition of a BF2 moiety
between 350 and 450 °C. The melting point of 1 was
comparable to those of DHND (mp 351 °C) and tetracene
(mp 357 °C), suggesting the strong intermolecular π-π
interactions.
(2) (a) Ando, S.; Murakami, R.; Nishida, J.; Tada, H.; Inoue, Y.; Tokito,
S.; Yamashita, Y. J. Am. Chem. Soc. 2005, 127, 14996. (b) Ando, S.;
Nishida, J.; Tada, H.; Inoue, Y.; Tokito, S.; Yamashita, Y. J. Am. Chem.
Soc. 2005, 127, 5336. (c) Sakamoto, Y.; Suzuki, T.; Kobayashi, M.; Gao,
Y.; Fukai, Y.; Inoue, Y.; Sato, F.; Tokito, S. J. Am. Chem. Soc. 2004, 126,
8138. (d) Naraso; Nishida, J.; Kumaki, D.; Tokito, S.; Yamashita, Y. J. Am.
Chem. Soc. 2006, 128, 9598. (e) Yoon, M.-H.; DiBenedetto, S. A.; Facchetti,
A.; Marks, T. J. J. Am. Chem. Soc. 2005, 127, 1348. (f) Handa, S.; Miyazaki,
E.; Takimiya, K.; Kunugi, Y. J. Am. Chem. Soc. 2007, 129, 11684. (g)
Facchetti, A.; Deng, Y.; Wang, A.; Koide, Y.; Sirringhaus, H.; Marks, T. J.;
Friend, R. H. Angew. Chem., Int. Ed. 2000, 39, 4547. (h) Ie, Y.; Nitani,
M.; Ishikawa, M.; Nakayama, K.; Tada, H.; Kaneda, T.; Aso, Y. Org. Lett.
2007, 9, 2115.
(3) Bendikov, M.; Wudl, F.; Perepichka, D. F. Chem. ReV. 2004, 104,
4891.
(4) Kikuzawa, Y.; Mori, T.; Takeuchi, H. Org. Lett. 2007, 9, 4817.
(5) Ando, S.; Nishida, J.; Fujiwara, E.; Tada, H.; Inoue, Y.; Tokito, S.;
Yamashita, Y. Chem. Mater. 2005, 17, 1261.
(6) (a) Tatemichi, S.; Ichikawa, M.; Koyama, T.; Taniguchi, Y. Appl.
Phys. Lett. 2006, 89, 112108. (b) Jones, B. A.; Facchetti, A.; Wasielewski,
M. R.; Marks, T. J. J. Am. Chem. Soc. 2007, 129, 15259. (c) Chen, H. Z.;
Ling, M. M.; Mo, X.; Shi, M. M.; Wang, M.; Bao, Z. Chem. Mater. 2007,
19, 816. (d) Wang, Z.; Kim, C.; Facchetti, A.; Marks, T. J. J. Am. Chem.
Soc. 2007, 129, 13362. (e) Jones, B. A.; Facchetti, A.; Marks, T. J.;
Wasielewski, M. R. Chem. Mater. 2007, 19, 2703. (f) Jones, B. A.; Ahrens,
M. J.; Yoon, M.-H.; Facchetti, A.; Marks, T. J.; Wasielewski, M. R. Angew.
Chem., Int. Ed. 2004, 43, 6363.
(7) Nishida, J.; Naraso; Murai, S.; Fujiwara, E.; Tada, H.; Tomura, M.;
Yamashita, Y. Org. Lett. 2004, 6, 2007.
(8) Tonzola, C. J.; Alam, M. M.; Kaminsky, W.; Jenekhe, S. A. J. Am.
Chem. Soc. 2003, 125, 13548.
(9) (a) Sun, Y.; Rohde, D.; Liu, Y.; Wan, L.; Wang, Y.; Wu, W.; Di,
C.; Yu, G.; Zhu, D. J. Mater. Chem. 2006, 16, 4499. (b) Domercq, B.;
Grasso, C.; Maldonado, J.-L.; Halik, M.; Barlow, S.; Marder, S. R.;
Kippelen, B. J. Phys. Chem. B 2004, 108, 8647. (c) Ono, K.; Yoshikawa,
K.; Tsuji, Y.; Yamaguchi, H.; Uozumi, R.; Tomura, M.; Taga, K.; Saito,
K. Tetrahedron 2007, 63, 9354.
(10) (a) Haddon, R. C.; Chichester, S. V.; Marshall, J. H. Tetrahedron
1986, 42, 6293. (b) Mandal, S. K.; Samanta, S.; Itkis, M. E.; Jensen, D. W.;
Reed, R. W.; Oakley, R. T.; Tham, F. S.; Donnadieu, B.; Haddon, R. C.
J. Am. Chem. Soc. 2006, 128, 1982.
(12) Tomura, M.; Yamaguchi, H.; Ono, K.; Saito, K. Acta Crystallogr.
2008, E64, o172.
(11) Briseno, A. L.; Miao, Q.; Ling, M.-M.; Reese, C.; Meng, H.; Bao,
Z.; Wudl, F. J. Am. Chem. Soc. 2006, 128, 15576.
(13) Cameron, D. W.; Chan, H. W.-S. J. Chem. Soc. C 1966, 1825.
150
Org. Lett., Vol. 11, No. 1, 2009

Table 2. CV Data for 1 and 2a
ox
compound
Ered1 (V)
Ered2 (V)
Ep (V)
1
2
-0.36
-0.18
-1.20
-2.06
-0.90
-0.50
-1.77
DHND
tetracene
+0.52
a 0.1 M n-Bu4NClO4 in DMF, Pt electrode, scanning rate 100 mV s-1
,
V versus Fc/Fc+.
dichloromethane (Table 1). Furthermore, the broadening of
the PL bands is observed, and the PL maximum is red-shifted
by 66 nm as compared to that of the shortest wavelength
emission in dichloromethane. This phenomenon can be
rationalized on the basis of an exciplex formation between
compound 1 and electron-donating toluene. DHND exhibits
a similar behavior in toluene, whereas tetracene does not
show such a red-shift and broadening of PL bands.
To investigate the electron affinity of compounds 1 and
2, cyclic voltammetry (CV) is performed. The voltammo-
grams of the compounds display two reversible reduction
waves; the half-wave potentials are listed in Table 2. The
reduction potentials of 1 and 2 are more positive than those
of DHND and tetracene, indicating that compounds 1 and 2
have higher electron affinities. The electron-accepting ability
of 2 is larger than that of 1. These electron affinities are
attributed to contribution by quadrupolar structures based on
1A and 2A (Scheme 1). The difference between the first and
second reduction potentials for 1 (0.54 V) is similar to that
for DHND (0.57 V), indicating that the on-site Coulomb
repulsion is not affected by BF2 chelation. The on-site
Coulomb repulsion in compound 2 (0.32 V) is smaller than
that observed in compound 1 owing to expansion of the arene
skeleton. The reduction potentials of 1 and 2 are more
positive than that of perfluoropentacene (-1.13 V versus Fc/
Fc+).2c Compounds 1 and 2 do not exhibit oxidation waves,
whereas the oxidation potential of perfluoropentacene is
reported to be +0.79 V. This indicates that both the HOMO
and LUMO energies of 1 and 2 are lower than those of
perfluoropentacene.
Figure 1. Absorption and PL spectra of 1 in (a) CH2Cl2 and (b)
toluene.
The absorption and photoluminescence (PL) spectra of
compound 1 in dichloromethane are shown in Figure 1a, and
the optical properties of the compounds are listed in Table
1. The absorption bands between 420-550 nm and the PL
bands between 500-650 nm are attributed to the tetracene
moiety. These maxima are similar to those of DHND and
are red-shifted relative to those of tetracene. The absorption
and PL spectra of compound 2 in 1,1,2,2-tetrachloroethane
are analogous to those of 1 in dichloromethane, and the
maxima of 2 are red-shifted as compared to those of 1 (Table
1). According to the absorption edges, the energy gaps
between the HOMO and LUMO levels for compounds 1 and
2 are found to be 2.15 and 2.04 eV, respectively. These
values are smaller than that of tetracene and larger than that
of perfluoropentacene (1.95 eV).2c The Stokes shifts are
found to be 6 and 3 nm for compounds 1 and 2, respectively.
These results confirm that the BF2-chelated complexes 1 and
2 have a rigid geometry such as those of tetracene (4 nm)
and DHND (10 nm). Figure 1b shows the absorption and
PL spectra of compound 1 in toluene. The absorption bands
are slightly red-shifted as compared to those measured in
Table 3. B3LYP/6-31G(d) Calculations for 1 and 2
compound
HOMO (eV)
LUMO (eV)
energy gap (eV)
1
2
-6.59
-6.88
-5.61
-4.84
-3.86
-4.35
-2.88
-2.07
2.73
2.53
2.73
2.77
DHND
tetracene
Table 1. Optical Properties of 1 and 2
compound
λabs (nm)
λPL (nm)
λedge (eV)
1a
523, 487, 455
532, 495, 464
575, 533, 468, 440 578, 624
529, 567, 615
595
2.15
The molecular orbital (MO) calculations14 of compounds
1 and 2 were performed using B3LYP/6-31G(d) in order to
estimate the π-electronic states, which are summarized in
Table 3. The HOMO and LUMO energies of 1 are lower
1b
2c
2.04
2.16
2.45
DHNDa
518, 484, 457
528, 566, 604 sh
tetracenea 473, 444, 418, 395 477, 511, 549
a In CH2Cl2. b In toluene. c In CHCl2CHCl2.
(14) See Supporting Information for the MO calculations.
Org. Lett., Vol. 11, No. 1, 2009
151

Figure 2. HOMO and LUMO of 1.
than those of DHND and tetracene. This result demonstrates
that the BF2 chelation decreases the HOMO and LUMO
energies of the arene π-electron systems. Furthermore, the
HOMO and LUMO energies of 1 and 2 are lower than those
of perfluoropentacene (HOMO, -5.39 eV; LUMO, -3.35
eV). The HOMO-LUMO energy gap of 2 is smaller than
those of 1 and DHND (Table 3), although the energy gaps
of 1 and 2 are larger than that of perfluoropentacene (2.04
eV).15 These calculations support the high electron affinities
and long wavelength absorption of 1 and 2. The HOMO and
LUMO energies of 1 are delocalized on the entire moiety of
tetracene, as shown in Figure 2. The delocalization of
molecular orbitals on the tetracene skeleton is favorable for
the intermolecular π-π overlap, which provides effective
carrier transport.
The OFET device developed using compound 1 was
fabricated on an SiO2/Si substrate by a high-vacuum (ca.
10-6 Pa) evaporation method with bottom contact geometry
at room temperature. Gold electrodes were prepared with
L/W of 5 µm/38 mm. The OFET measurement was carried
out under vacuum conditions. Figure 3 shows the output
characteristics for the OFET device. The drain current
increases as the gate voltage (Vg) becomes more positive;
this means that the film of compound 1 exhibits n-type
semiconducting behavior. The electron mobility and on/off
ratio are calculated to be 1.5 × 10-5 cm2 V-1 s-1 and 4000,
respectively. This result is the first example of BF2-chelated
polycyclic aromatic compounds showing n-type semicon-
ducting behavior.
Figure 3. OFET characteristics for the film of 1 deposited at room
temperature. Gate voltage (Vg) was applied in the range between 0
and 100 V.
In conclusion, we synthesized BF2 complexes containing
tetracene and perylene moieties as new types of electron-
accepting compounds. These compounds exhibited small
HOMO-LUMO gaps and high electron affinities, as ob-
served from spectral and electrochemical studies. The
properties of these compounds were attributed to the qua-
drupolar structures represented by resonance contributors.
The BF2 complex containing tetracene showed an n-type
semiconducting behavior. This indicates that BF2 chelation
to arene moieties is a useful method for developing n-type
semiconductors. Further investigation on the OFET applica-
tions of the BF2 complexes is in progress.
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research (No. 19550034) from the
Ministry of Education, Culture, Sports, Science and Technol-
ogy, Japan. We thank M. Suto and K. Eguchi (Dow Corning
Toray Co., Ltd.) for the DSC and TGA.
Supporting Information Available: Synthetic procedures
and additional characterization data. This material is available
free of charge via the Internet at http://pubs.acs.org.
(15) Sakamoto, Y.; Suzuki, T.; Kobayashi, M.; Gao, Y.; Inoue, Y.;
Tokito, S. Mol. Cryst. Liq. Cryst. 2006, 444, 225.
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