Substituent effects on fluorescent properties of imidazo[1,2- α]pyridine-based compounds

Article abstract of DOI:10.1246/bcsj.72.1327

In order to search for novel fluorescent organic compounds, 20 derivatives of imidazo[1,2-a]pyridine (1) were synthesized, and their fluorescent properties were studied. Though the parent compound I (λ(fl) = 370.5 nm, Φ = 0.57 in ethanol) was in the liquid state at ambient temperature, 2-phenylimidazo[1,2-a]pyridine (5), 2-(2-naphthyl)imidazo[1,2- a]pyridine (16), 7-methylimidazo[1,2-a]pyridine (3), 7-methyl-2- phenylimidazo[1,2-a]pyridine (12), and 7-methyl-2(2-naphthyl)imidazo[1,2- a]pyridine (17) were found to give thermally stable solid compounds (mp 55- 190 °C) without much affecting the fluorescent properties of the parent compound (λ(fl) = 374-381 nm, Φ = 0.50-0.78 in ethanol). Among the 4'- substituted 2-phenyl derivatives, it was found that the introduction of the strong electron-donating amino and dimethylamino groups (2-(4- aminophenyl)imidazo[1,2-a]pyridine (7) and 2-[4- (dimethylamino)phenyl]imidazo[1,2-a]pyridine (8), respectively) caused marked red shift of their fluorescence (λ(fl) = 445 and 446 nm, respectively, in ethanol), thus providing the way for tuning the fluorescence color of the IP derivatives. The observed red shift of the fluorescence of 7 and 8 was ascribed to the contribution of the excited intramolecular charge transfer state.