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Chemistry Letters Vol.36, No.8 (2007)
Synthesis and Spectroscopic Properties
of New Fluorescent 3,6-Diaryl-4-phenyl-2-pyridone Derivatives
Satoshi Minakata,Ã1 Shouta Moriwaki,1 Hiroshi Inada,1 Mitsuo Komatsu,Ã1 Hirotake Kajii,2
Yutaka Ohmori,2 Manabu Tsumura,3 and Kiyoyuki Namura3
1Department of Applied Chemistry, Graduate School of Engineering, Osaka University,
2-1 Yamadaoka, Suita, Osaka 565-0871
2Center for Advanced Science and Innovation, Osaka University,
2-1 Yamadaoka, Suita, Osaka 565-0871
3Kaneka Corporation, 3-2-4 Nakanoshima, Kita-ku, Osaka 530-8288
(Received May 2, 2007; CL-070484; E-mail: minakata@chem.eng.osaka-u.ac.jp)
Novel fluorescent 3,6-diaryl-4-phenyl-2-pyridone deriva-
promising material as blue emitters. Relative fluorescent intensi-
ties of the pyridones were evaluated by comparing them with
that of pyrene, which is a well-known, representative blue-
fluorescent pigment. The intensities of the pyridones, with the
exception of 1a and 1g, were stronger than that of pyrene; 1e
and 1c emitted a considerably stronger fluorescence (Figure 1).
Because pyridone 1e exhibited the strongest blue fluorescent
intensity, the influence of substituents of the phenyl ring at
the 3- and 6-positions on fluorescent properties of pyridones
tives were synthesized and their fluorescent properties were
investigated. These compounds emit intense brilliant blue
fluorescence only in the solid state, not in solution. An elec-
tron-donating substituent on the 6-phenyl group caused a
red-shift in fluorescence maxima.
Fluorescent organic molecules have garnered much interest
for a variety of applications including their use as fluorescent
probes and in optoelectronics due to their spectroscopic proper-
ties.1–3 Thus, a new series of fluorophores have been devel-
oped.4–6 Fluorophores that show fluorescence in the solid state
are particularly useful in photofunctional applications, such as
fluorescent pigments used in electroluminescent devices.7 We
previously reported on 6-aryl-3,4-diphenyl-ꢀ-pyrone derivatives
that are potential candidates for these applications, because they
show intense blue to orange (ꢁflu: 470–570 nm) fluorescence
only in the solid state.8 To intensify the brilliance and color pu-
rity of blue-emitters the present study focused on the pyridone
framework,9 aza-analogs of pyrones, for the synthesis of the
novel fluorophores. The replacement, in the ring, of oxygen with
nitrogen changes the contribution of the resonance structures,
causing blue-shift. This paper describes synthesis of pyridone
derivatives and their unique fluorescent properties. Since the
desired pyridones are expected to emit in the solid state in a
similar manner with pyrones,8 the present study would be basic
research directly connecting with practical fluorophores.
Table 1. Synthesis of pyridones and their spectroscopic
properties
Ph
Ph
Ph
.
RNH2 HCl (50 equiv.)
Ph
O
Ph
O
R
Et3N (50 equiv.)
O
N
EtOH, 150 °C, 24 h
in an autoclave
Ph
α
-pyrone
Entry
R
Pyridone Yield/%
ꢁ
abs/nma
ꢁflu/nm
1
2
3
4
5
6
7
Me
Et
n-Pr
i-Pr
n-Bu
i-Bu
sec-Bu
1a
1b
1c
1d
1e
1f
89
82
74
67
79
71
60
340
337
339
342
339
340
340
441
437
432
440
439
425
441
1g
aIn a solution of CH2Cl2 (1:0 Â 10À4 M).
The desired N-alkylated 3,4,6-triphenyl-2-pyridones were
readily synthesized, with good yields, by reacting the corre-
sponding pyrones with amines (Table 1). The absorption spectra
of the pyridones were measured in dichloromethane. The absorp-
tion maxima of all compounds occurred at nearly the same
wavelength approximately 340 nm. In solution, the pyridone
derivatives did not emit fluorescence, which was consistent
with previously published results for ꢀ-pyrones.8 As discussed
in our previous work,8 the phenomenon would be explained by
rotational freedom of the 6-phenyl group. Although X-ray struc-
ture analysis should be performed, the phenyl ring would be
fixed in the solid state by molecular packing and the path of
fluorescence was thus increased. On the other hand, the free
rotation of the phenyl group would be allowed in solution.
However, the pyridones emitted an intense blue fluorescence
in the solid state, and, as expected, the fluorescent maxima were
remarkably blue-shifted compared with the maxima of pyrones.
The emission of the shorter wavelength makes pyridones
400
1a : R = Me
1b : R = Et
1b
Ph
Ph
1e
1c
Ph
O
R
1f
1c : R = n-Pr
1d : R = i-Pr
1e : R = n-Bu
1f : R = i-Bu
300
N
pyrene
1d
1g : R = sec-Bu
200
100
α
-pyrone
1g
1a
0
400
450
500
wavelength/nm
550
600
Figure 1. Comparison of fluorescence intensity of pyridones 1
with that of pyrene and ꢀ-pyrone at the powdered form.
Copyright Ó 2007 The Chemical Society of Japan