Proton and charge transfer reactions dynamics of a hydroxyflavone derivative in a polar solvent and in a cyclodextrin nanocavity

In this work, we report on the observation of ultrafast intramolecular charge- and proton-transfer reactions of 4'-dimethylaminoflavonol (DMAF) in N,N-dimethyl formamide and in gamma-cyclodextrin (gamma-CD) solution. Upon femtosecond excitation an intramolecular charge transfer (ICT) reaction takes place to produce an ICT structure in similar to 200 fs. This structure may undergo a proton transfer reaction to generate a zwitterionic (Z) form in 2-3 ps, or relaxes in its potential energy well, to later equilibrate with that of Z in hundreds of ps. Addition of gamma-CD does not significantly affect the fast dynamics of the formed anion. The fs-emission signals of the parent molecule, 3-hydroxyflavone, indicate that the dimethyl amino group in DMAF enhances the rate constant of intermolecular proton-transfer and intramolecular charge-transfer reactions. (c) 2007 Elsevier B.V. All rights reserved.