TRANSIENT ABSORPTION AND TIME-RESOLVED RAMAN-STUDY OF THE PHOTOPHYSICS OF 4-PHENYLPYRIDINE IN SOLUTION

The transient absorption spectra and time-resolved resonance Raman spe ctra of 4-phenylpyridine (4PPY) in various organic solvents have been measured following pulsed photolysis at 266 nm using nanoseconaand pic osecond time resolution experiments. The T-1 and S-1 states are charac terized and attributed to pi pi and n pi* configurations, respectivel y, in aprotic solvents as well as in alcohols and water. In the presen ce of alcohols, both the S-1 and T-1 states are reduced to the same tr ansient product, the N-hydro radical 4PPYH(.). The overall photophysic al properties of 4PPY appear similar to those previously found for the diaza analogue, 4,4'-bipyridine. Vibrational analyses of the S-1 and T-1 states and of the radical 4PPYH(.) are proposed and compared with results reported in the literature for the neighboring compounds biphe nyl and 4,4'-bipyridine. The structure and electronic configuration of these transients are discussed on this basis.