A fluorescence study of the solute–solvent interactions of aminochalcones in a room-temperature ionic liquid

Unlike most other electron donor–acceptor (EDA) molecules, aminochalcones exhibit unusual solvent polarity-dependent fluorescence behavior. The photophysical behavior of two aminochalcones, namely, 4-aminochalcone (AC) and 4-dimethylaminochalcone (DMAC), has been studied in a viscous room-temperature ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF ], by steady-state and time-resolved fluorescence techniques. The observation of a single emission band in viscous IL, which is similar to the one observed in less viscous polar conventional solvents, suggests no twisting is necessary for the formation of the charge-transfer state from which the emission of aminochalcones originates. The fluorescence decay profiles, solvation dynamics, and excitation-wavelength-dependent emission behavior of AC are found to be quite different from those of DMAC in the IL. The observed difference is attributed to specific H-bonding interaction between AC and [bmim][PF ].