with amine donor and nitrile acceptor moieties and examined
their optical properties. In this letter, we report a new series
of thermally stable donor-acceptor nonplanar quateraryls
and their potential use in preparing multilayer blue OLED
devices.
Benzene rings functionalized with polyaryl groups have
been synthesized either by the coupling of biaryltriflate
compounds with Grignard reagents in the presence of a
palladium catalyst in moderate to good yields10 or by the
iterative coupling of aryl boronic acid with aromatic halides11
separately. However, it has been observed that iterative
coupling on functionally crowded aryl trihalides to prepare
triarylated-benzene compounds places constraints on the
choice of reagents/catalysts.12 Our aim to prepare blue light
emitting compounds with donor-acceptor groups was
achieved by preparing a key intermediate R-oxo-ketene-S,S-
acetal13 1 from easily accessible precursors methyl cyanoac-
etate, carbon disulfide, and methyl iodide, following the
Tominagaprotocol.14Substrate1,onMichaeladdition-cyclization
reaction with various substituted acetophenones 2a-e under
alkaline conditions, furnished 6-aryl-2H-pyran-2-ones 3a-e
in excellent yields (Scheme 1). In order to prepare com-
pounds with N,N-dialkylamino functionality, a good leaving
methylsulfanyl group of lactones 3a-e was replaced with
an amine (piperidine) to furnish 6-aryl-2-oxo-4-piperidin-1-
yl-2H-pyran-3-carbonitriles (4a-e) in good yields. These
compounds 4a-e were reacted with functionalized deoxy-
benzoins 5 to yield 5′-(piperidin-1-yl)-[1,1′;2′,1′′;3′,1′′′]quater-
phenyl-4′-carbonitriles (6a-e) in excellent yields (Scheme
1).
Figure 1. Various π-conjugated frameworks for blue light emitting
materials (I-III), small molecule polyphenylphenyl dendron (IV),
and new donor-acceptor quateraryl (V). F, fluorenyl; P, phenalenyl;
Ar, aryl; D, donor; A, acceptor.
green-emission defect)6 resulting in an additional undesirable
low-energy broadband in the EL spectrum, which not only
reduces emission efficiency but also destroys the blue color
purity.6 The blue light emitting materials generally have a
low affinity for the electrons from the cathode in OLEDs
due to the large band gap energy. Recently Komatsu and
co-workers7 elucidated electronic properties of fluorene
having a radical cation and dication through computational
and experimental studies, which provided insights for low
electrical conductivity observed for poly(2,7-fluorene)s.
Therefore, new chemical entities that may overcome the
drawbacks of existing blue light emitters are urgently
required for preparing B-OLEDs.
Recently, a great deal of attention has been focused on
synthesizing small molecule polyphenylphenyl dendrons (IV)
for preparing B-OLEDs.8 Studies have also shown that the
presence of strong electron-donating N,N-dialkylamine func-
tionalities in π-conjugated materials enhances the device
efficiency by elevating the HOMO energy levels of the
molecules for ease of hole injection/transporting in the film,8
and the presence of the cyano group influences photophysical
and electroluminescent properties by lowering the energy of
the LUMO, thus exhibiting a relatively low threshold voltage
and high quantum efficiency in LED devices.9 Considering
these aspects, we designed quateraryls (V) functionalized
A plausible mechanism, depicted in Scheme 2, suggests
that the reaction is initiated by the Michael addition of an
anion, generated from a molecule of deoxybenzoin 5, to the
2H-pyran-2-one 4 followed by intramolecular cyclization to
form a bicyclic intermediate. This bicyclic intermediate on
decarboxylation, protonation, and dehydration furnished
quateraryl 6 in excellent yield.
To examine the solid state molecular organization, the
crystallizations of these quateraryls in various solvent systems
were attempted. All the quateraryls except 6c were amor-
phous substances. The X-ray structural analysis of compound
6c (Figure 2) revealed that the aryl rings are arranged
(5) (a) Kottas, G. S.; Clarke, L. I.; Horinek, D.; Michl, J. Chem. ReV.
2005, 105, 1281. (b) Setayesh, S.; Grimsdale, A. C.; Weil, T.; Enkelmann,
V.; Mullen, K.; Meghdadi, F.; List, E. J. W.; Leising, G. J. Am. Chem.
Soc. 2001, 123, 946. (c) Sun, D.; Rosokha, S. V.; Kochi, J. K. Angew.
Chem., Int. Ed. 2005, 44, 5133. (d) Chen, C.-T.; Chiang, C.-L.; Lin, Y.-C.;
Chan, L.-H.; Huang, C.-H.; Tsai, Z.-W.; Chen, C.-T. Org. Lett. 2003, 5,
1261. (e) Wakamiya, A.; Ide, T.; Yamaguchi, S. J. Am. Chem. Soc. 2005,
127, 14859.
Hamer, P. J. Synth. Met. 1995, 71, 2117. (c) Wu, C.-J. J.; Xue, C.; Kuo,
Y.-M.; Luo, F.-T. Tetrahedron 2005, 61, 4735. (d) Hwu, J. R.; Chuang,
K.-S.; Chuang, S. H.; Tsay, S.-C. Org. Lett. 2005, 7, 1545.
(10) (a) Satoh, T.; Kawamura, Y.; Miura, M.; Nomura, M. Angew.
Chem., Int. Ed. Engl. 1997, 36, 1740. (b) Kamikawa, T.; Hayashi, T. Synlett
1997, 163.
(11) (a) Blake, A. J.; Cooke, P. A.; Doyle, K. J.; air, S.; Simpkins, N. S.
Tetrahedron Lett. 1998, 39, 9093. (b) Bahl, A.; Grahn, W.; Stadler, S.;
Feiner, F.; Bourhill, G.; Bra¨uchle, A. R.; Jones, P. G. Angew. Chem., Int.
Ed. Engl. 1995, 34, 1485.
(6) (a) Li, J. Y.; Ziegler, A.; Wegner, G. Chem. Eur. J. 2005, 11, 4450.
(b) Scherf, U.; List, E. J. W. AdV. Mater. 2002, 14, 477. (c) Romaner, L.;
Pogantsch, A.; de Freitas, P. S.; Scherf, U.; Gaal, M.; Zojer, E.; List, E. J. W.
AdV. Funct. Mater. 2003, 13, 597. (d) Kulkarni, A. P.; Kong, X.; Jenekhe,
S. A. J. Phys. Chem. B 2004, 108, 8689. (e) List, E. J. W.; Guentner, R.;
de Freitas, P. S.; Scherf, U. AdV. Mater. 2002, 14, 374.
(12) (a) Hassan, J.; Se´vignon, M.; Gozzi, C.; Schulz, E.; Lemaire, M.
Chem. ReV. 2002, 102, 1359. (b) Goel, A.; Singh, F. V.; Kumar, V.; Reichert,
M.; Gulder, T. A. M.; Bringmann, G. J. Org. Chem. 2007, 72, 7765. (c)
Goel, A.; Singh, F. V.; Dixit, M.; Verma, D.; Raghunandan, R.; Maulik,
P. R. Chem. Asian J. 2007, 2, 239.
(7) (a) Nishinaga, T.; Inoue, R.; Matsuura, A.; Komatsu, K. Org. Lett.
2002, 4, 4117. (b) Yamazaki, D.; Nishinaga, T.; Komatsu, K. Org. Lett.
2004, 6, 4179.
(13) (a) Dieter, R. K. Tetrahedron 1986, 42, 3029. (b) Junjappa, H.;
Ila, H.; Asokan, C. V. Tetrahedron 1990, 46, 5423. (c) Tominaga, Y. Trends
Heterocycl. Chem. 1991, 2, 43.
(8) Huang, C.; Zhen, C.-G.; Su, S. P.; Loh, K. P.; Chen, Z.-K. Org.
Lett. 2005, 7, 391.
(9) (a) Greenham, N. C.; Moratti, S. C.; Bradley, D. D. C.; Friend, R. H.;
Holmes, A. B. Nature 1993, 365, 628. (b) Moratti, S. C.; Cervini, R.;
Holmes, A. B.; Baigent, D. R.; Friend, R. H.; Greenham, N. C.; Gru¨ner, J.;
(14) (a) Tominaga, Y.; Ushirogouchi, A.; Matsuda, Y. J. Heterocycl.
Chem. 1987, 24, 1557. (b) Tominaga, Y.; Ushirogouchi, A.; Matsuda, Y.;
Kobayashi, G. Chem. Pharm. Bull. 1984, 32, 3384.
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