Hydrogen-bonded 4H-1-benzopyrane-4-thione–water complexes properties in the S2 excited state: the mechanism and dynamics of deactivation

Abstract

Unexpected results of spectral emission and photophysical study of S₂-excited 4H-1-benzopyrane-4-thione (BPT) in water solution were explained by intermolecular hydrogen bonding. There are at least two types of BPT–water complexes that participate in the S₂-fluorescence similarly as in S₀ → S₂ absorption. They both deactivate with high efficiency in internal conversion S₂ → S₁ and in intersystem crossing S₁ → T₁ processes.