Synthesis, photophysical evaluation, and computational study of 2-methoxy- and 2-morpholino pyridine compounds as highly emissive fluorophores in solution and the solid state. (December 2019)

• Record Type: Journal Article
• Authors: Hagimori, Masayori; Nishimura, Yasuhisa; Mizuyama, Naoko; Shigemitsu, Yasuhiro
• Is Part Of: Dyes and pigments. Volume 171(2019)
• Publication Date: 2019-12
• Subjects: Keto–enol tautomerism of 2-pyridone -- Pyridine -- Fluorescence -- TDDFT -- CASSCF -- Conical intersection; Dyes and dyeing -- Periodicals; Pigments -- Periodicals; 667.2
• DOI: 10.1016/j.dyepig.2019.107705
• Languages: English
• ISSNs: 0143-7208

Abstract

Abstract: Two 2-pyridone tautomeric analogs, methoxypyridine4 and N -methylpyridone5, were synthesized, and their spectroscopic properties were investigated both experimentally and computationally. A detailed photophysical study reveals that4 shows high fluorescence quantum yields not only in chloroform but also in ethanol, and the strong fluorescence in solution might be attributed to the enol form (pyridine) of the 2-pyridone. Furthermore, we designed and synthesized novel 2-substitued pyridines to achieve more intense emissions in both solution and the solid state. Substituent modification with phenylsulfonyl, morpholino, and 4-diethylamino groups greatly affected the fluorescence properties, and methoxypyridine7 and morpholinopyridine compound8 showed fluorescence in various solvents (Ф = 0.59–0.95) and the solid state (Ф = 0.12–0.15). A hypsochromic shift in the emission maximum wavelength and strong fluorescence in the solid state (Ф = 0.39) were observed for dimorpholinopyridine9 . Morpholinopyridine11 showed intense fluorescence in all nonpolar and polar solvents. Systematic time-dependent density functional theory calculations were performed for the compounds whose electronic and fluorescent maxima were computationally reproduced with good agreement to those from experiment. In detail, the drastic difference in the emission intensity between4 and5 in solution was successfully explained using CASSCF calculations, which revealed the presence of conical intersections between the ground and the excited states. Highlights: Joint experimental and computational studies of new 2-pyridone tautomeric compounds were performed. Strong fluorescence in solution is attributed to the enol form of the 2-pyridone. Methoxypyridine and morpholinopyridines exhibited solid-state fluorescence and a high fluorescence quantum yield in solution. Fluorescence solvatochromic effects depend on the chemical structure and arrangement of the substituents were observed.