LIFETIMES AND TRANSIENT PHENOMENA OF STILBENE RADICAL CATIONS IN THE 2ND EXCITED DOUBLET STATE

Radical cations of cis- and trans-stilbene (c-St(.+), t-Sr-.+) and of 1,2-diphenylcyclo-1-butene (CB.+) in the second excited doublet state (D-2) have been generated using sequential pulse radiolysis-laser flash photolysis, and their lifetimes have been measured using selective hole transfer quenching with anisole. In the deactivation of the D-2 State of c-St(.+), the internal conversion competes with the isomerization to t-Sr-.+ in a quantum yield of 0.49 +/- 0.12 and conversion to another product as a minor process, whereas the D-2 states of t-Sr-.+ and CB.+ are only deactivated via internal conversion. Lifetimes of the t-Sr-.+ and c-Sr-.+ D2 states are estimated to be approximately 240 and 120 ps, respectively, while that of the CB.+ D2 state is approximately 380 ps. The shorter lifetime of the c-Sr-.+ D-2 state is attributed to isomerization and conversion to another product via twisting about the central C=C double bond. The analogous process in CB is severely hindered by structural constraints. The transient phenomena of the D2 states of c-Sr-.+, t-Sr-.+, and CB.+ are compared in terms of thier lifetimes, structures, energies, and reaction processes.