ESIPT from S2 singlet state in 3-hydroxyflavone

Spectra of the dual fluorescence of 3-hydroxyflavone in ethyl acetate with picoseconds time resolution were obtained at excitation by tunable picoseconds pulses of the optical parametric generator within S1 and S2 bands of absorption. Spectra dynamics reveals time development of the internal proton transfer in the excited state of molecule from the hydroxyl to the carbonyl group. The relative contribution of the tautomer form to integral emission remains essentially higher during all interval of emission observation. The obtained data directly evidence an additional channel of the internal proton transfer from the S2 singlet state of 3-hydroxyflavone with the very high kinetic rate of 0.8 × 1012 s−1.