ESIPT reaction starting from S2 and S3 singlet states in 3-hydroxyflavone

Spectra fluorescence at excitation of emission within spectral intervals of S3, S2 and S1 bands of absorption, and excitation at registration of fluorescence at maxima of blue and green bands of emission have been studied in 3-hydroxyflavone solution. A possibility of ESIPT reaction starting from S3 and S2 states of parent 3HF molecule was shown for the first time follows from observations of differences in excitation spectra of normal and tautomer forms of 3HF, and from different ratios of these forms intensities upon excitation in different ranges of UV spectra of absorption.