In this Letter, we report on steady-state and time-resolved emission studies of 4'-dimethylaminoflavonol (DAMF) in two families of solvents where we observed a reversible or an irreversible proton motion in the ultrafast formed charge-transfer (CT) state of DMAF. The slower (picosecond) proton-transfer time constant of DMAF compared to the femtosecond one observed in non-substituted 3-hydroxyflavones is due the involvement of an intramolecular CT. For the reversible situation, increasing the polarity of the medium increases the rate of proton motion. (C) 2003 Elsevier B.V. All rights reserved.