Solvent effect on nonradiative process of pyronin B in protic and aprotic solvent systems

Absorption and emission spectra of pyronin B were taken in acetonitrile and acetonitrile-benzene solvent mixtures. Fluorescence lifetime (τf) and quantum yield (Φf) were determined as a function of temperature and nonradiative rate constant (knr) was calculated from τf and Φf. Activation energies of nonradiative process were obtained from Arrhenius plots of knr. Solvent effects on knr were discussed in terms of proposed models. The results were compared to those previously obtained for pyronin B in n-alcohols and alcohol–water mixtures. Solvent polarity and specific solute–solvent interactions were the main parameters controlling the internal conversion process for pyronin B in protic and aprotic solvent systems.