EFFECTS OF SOLUTE-SOLVENT INTERACTIONS ON RADIATIONLESS DECAY OF THIOKETONES EXCITED TO THEIR S-2-STATES AND T-1-STATES

Spectral and photophysical properties of a few aromatic thioketones in their S-2- and T-1-states, in particular those determined by their in teractions with solvents, are discussed. The reasons for a drastically different behaviour of thioketones in interactions with benzene as we ll as saturated hydrocarbons and perfluoroalkanes are analysed in more detail. Results of the time-resolved transient absorption measurement s in the pico- and nanosecond time scale are given. An analysis of the se results proves that a product of the decay of the S-2-state of xant hione in benzene is a new transient (tau(1/e) greater than or equal to 60 ps) individuum which, regarding the system properties and the cond itions of the experiment, has been identified as an exciplex in S-2-st ate formed as a result of an efficient interaction with benzene molecu le. Also in xanthione/alkane systems the involvement of a transient in dividuum was proved. Most probably, this individuum was a thioketyl ra dical which could be formed by hydrogen abstraction from a hydrocarbon molecule by xanthione in the S-2-state. Such individua act as interme diates in passing excitation to the triplet states of thioketones and are effective channels of the S-2-state decay. The changes observed in the transient absorption spectra of xanthione in C6H6 in the time ran ge of 10(-7)-10(-6) s can be attributed to the formation of an excimer in the T-1-state as a result of the T-1-state selfquenching.