Y. Shigemitsu et al. / Dyes and Pigments 99 (2013) 940e949
941
derivatives. The computational analysis is focused on the
condensed phase effects exerting on the spectroscopic properties,
by means of ONIOM and FMO methods to evaluate the electronic
structures in solution as well as in the crystalline phase. From
physicochemical viewpoints, 2(1H)-pyridone, the simplest com-
pound, has attracted much attention on its ketoeenol tautomerism
associated with inter- and intra-molecular hydrogen atom transfer,
and been examined in detail on the rotational Duschinsky effect
[18], cluster structures in solvents [19], phase transition in solid
state [20]. Borst et al. reported that the complex of the two tauto-
mers showed stronger fluorescence than solely respective species
[21]. The compounds possess medical properties found in anti-
bacterial antifungal as potential drug candidates for various dis-
eases [22,23].
This article is organized as follows. The synthesis and spectro-
scopic properties are concisely described and followed by the
computational details. The calculation results are presented and
discussed on the UVevis and fluorescence of the compounds both
in solution and in the solid state, then brief conclusions are
presented.
2. Syntheses, UVevis and fluorescence spectra
A
convenient synthesis of poly functionalized-2(1H)-pyr-
idones through the reaction of various methyl ketones with
ketene dithioacetals has been reported previously [24]. It has
been found that ketene dithioacetals are useful and convenient
reagents for the synthesis of a variety of heterocycles [25]. Fig. 1
illustrates the synthetic scheme of the present study, whereby
the reactions occurred smoothly in the presence of sodium hy-
droxide in dimethylsulfoxide to give 6-aryl-4-methylsulfanyl-
2(1H)-pyridone-3-carbonitriles 3, which were further converted
into 6-aryl-4-pyrrolidino-2(1H)-pyridones 5, 2-methoxypyridine
6
and 1-methyl-2(1H)-pyridone 7. One-pot synthesis was
attempted instead of the selective methylation [26] to obtain
both 6 and 7, which were separated easily upon eluting silica-gel
column. 1-Methyl-4-pyrrolidono-2(1H)-pyridones 8 were ob-
tained from 7 via the reactions with pyrrolidine, as illustrated in
Figs. 1e3.
Fig. 1. Synthetic scheme of (3, 5, 6, 7, 8).
The measurement of absorption and fluorescence spectra was
carried out at room temperature in ethanol and in the solid state,
respectively. Absorption maxima, molar absorption, fluorescence
maxima, and relative fluorescence intensities in the solid state are
listed in Tables 1e3. In ethanol, 3f, some 2-methoxypyridines 6 and
7f were found to be slightly fluorescent with their quantum yields
less than 0.03. Remaining 2(1H)-pyridones 3 and 1-methyl-2(1H)-
pyridones 7 were non-fluorescent. In general, sulfur atoms in fluo-
rescent compounds generally weaken emission intensities due to
spin orbit couplings [17] [27]. In the solid state, the fluorescence
properties of 2(1H)-pyridone are expected to be influenced by both
the electronic and the steric effect of substituents, as shown in a
previous study of 2(1H)-pyrones [16]. Compound 3b with an
electron-donating group at position 4 on the phenyl ring showed
enhanced emissionwith Relative Intensity (R.I.) of 1.28, significantly
larger than that of 3a (0.99). The fluorescent intensity of 6-
(3,4-dimethoxyphenyl)-2(1H)-pyridone 3c and 3,4,5-trimethoxy-2
(1H)-pyridone 3e remain unchanged qualitatively. 6-styryl-2(1H)-
pyridone 3k and 6-(4-dimethylaminophenyl)vinyl-2(1H)-pyridone
3l showed their emission maxima at 560 nm and 564 nm, respec-
tively, with a significant bathochromic shift from other 3 series,
owing to an analogous chromophore with 4-(dicyanomethylene)-2-
methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM). 2-methoxypy
introduction of a methoxy group to the phenyl ring (7b) enhances
the fluorescence in comparison with 7a and a significant bath-
ochromic shift was observed via the introduction of styryl group 7k.
The details of synthesis and spectroscopic measurements are
described in Experimental Section.
3. Computational details
Ground state geometry optimizations of the single molecules at
DFT level were carried out using B3LYP [28,29] functional with 6-
311G(2d,2p) and S1 state geometries were optimized using
TDDFT(B3LYP)/6-31 þ G(d), respectively, with the default conver-
gence criterion on force and displacement. The optimized geome-
tries were validated with vibrational frequency analysis for the
compounds. Our TDDFT study has proved that TDDFT(B3LYP)/6-
31 þ G(d) serves as well-balanced level of theory between
computational burden and accuracy in the prediction of the ab-
sorption lmax of maleimide-derived heterocycles [30]. The single
point TDDFT calculations employed PBE0 [31] and CAM-B3LYP [32]
functional as well as B3LYP to obtain the vertical S0eS1 excitation
energies and their associated oscillator strengths. Solvent effects of
ethanol were considered using two PCM methods, non-equilibrium
linear response formulation (LR-PCM) [33] and its state-specific
variant (SS-PCM) [34]. Complete Active Space Self Consistent
Field CASSCF(10e,10o)/ANO-L and Multi-State second order
ridines
6 and the corresponding 1-Methyl-2(1H)-pyridones
7, derived from the respective 2-pyridine proton tautomers,
have almost the same fluorescence characteristics, in that the
Shigemitsu, Yasuhiro
