Tuning the mechanism of proton-transfer in a hydroxyflavone derivative

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.