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

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.