Effects of Solute-Solvent Interactions on Radiationless Decay of Thioketones Excited to Their S$\text{}_{2}$- and T$\text{}_{1}$-States

Spectral and photophysical properties of a few aromatic thioketones in their S$\text{}_{2}$- and T$\text{}_{1}$-states, in particular those determined by their interactions with solvents, are discussed. The reasons for a drastically different behaviour of thioketones in interactions with benzene as well as saturated hydrocarbons and perfluoroalkanes are analysed in more detail. Results of the time-resolved transient absorption measurements in the pico- and nanosecond time scale are given. An analysis of these results proves that a product of the decay of the S$\text{}_{2}$-state of xanthione in benzene is a new transient (τ $\text{}_{1}\text{}_{/}\text{}_{e}$ ≥ 60 ps) individuum which, regarding the system properties and the conditions of the experiment, has been identified as an exciplex in S$\text{}_{2}$-state formed as a result of an efficient interaction with benzene molecule. Also in xanthione//alkane systems the involvement of a transient individuum was proved. Most probably, this individuum was a thioketyl radical which could be formed by hydrogen abstraction from a hydrocarbon molecule by xanthione in the S$\text{}_{2}$-state. Such individua act as intermediates in passing excitation to the triplet states of thioketones and are effective channels of the S$\text{}_{2}$-state decay. The changes observed in the transient absorption spectra of xanthione in C$\text{}_{6}$H$\text{}_{6}$ in the time range of 10$\text{}^{-7}$-10$\text{}^{-6}$ s can be attributed to the formation of an excimer in the T$\text{}_{1}$-state as a result of the T$\text{}_{1}$-state selfquenching.