Excitation wavelength dependence of photo-induced intramolecular excited state proton transfer reaction of 4'-N,N-diethylamino-3-hydroxyflavone in various liquids has been investigated by steady-state and time-resolved fluorescence measurements. It was found that the relative fluorescence intensity of the tautomer excited state to that of the normal excited state significantly decreases in ionic liquids with changing the excitation wavelength from 380 to 470 nm. The initial proton transfer rate excited at 470 nm was different from that obtained at 400 nm excitation. The excitation wavelength dependence was discussed in relation with the inhomogeneous distribution of the solute in the ionic liquids. (C) 2012 Elsevier B.V. All rights reserved.