Transient absorption and time-resolved Raman study of the photophysics of 4-phenylpyridine in solution

The transient absorption spectra and time-resolved resonance Raman spectra of 4-phenylpyridine (4PPY) in various organic solvents have been measured following pulsed photolysis at 266 nm using nanoseconaand picosecond time resolution experiments. The T-1 and S-1 states are characterized and attributed to pi pi* and n pi* configurations, respectively, in aprotic solvents as well as in alcohols and water. In the presence of alcohols, both the S-1 and T-1 states are reduced to the same transient product, the N-hydro radical 4PPYH(.). The overall photophysical 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 biphenyl and 4,4'-bipyridine. The structure and electronic configuration of these transients are discussed on this basis.