Excitation wavelength dependence of photo-induced intramolecular proton transfer reaction of 4′-N,N-diethylamino-3-hydroxyflavone in various liquids

► Excited state intramolecular proton transfer (ESIPT) was measured by fluorescence. ► The reactant was 4′-N,N-diethylamino-3-hydroxyflavone. ► The ESIPT was investigated at different excitation wavelength. ► The yield of ESIPT in ionic liquids was significantly modified. ► The PT rate was also revealed to be dependent on the excitation wavelength.