Lifetimes and Transient Phenomena of Stilbene Radical Cations in the Second Excited Doublet State

Article abstract of DOI:10.1021/j100027a021

Radical cations of cis- and trans-stilbene (c-St^.+, t-St^.+) and of 1,2-diphenylcyclo-1-butene (CB^.+) in the second excited doublet state (D₂) have been generated using sequential pulse radiolysis-laser flash photolysis, and their lifetime have been measured using selective hole transfer quenching with anisole.In the deactivation of the D₂ state of c-St^.+, the internal conversion competes with the isomerization to t-St^.+ in a quantum yield of 0.49 +/- 0.12 and conversion to another product as a minor process, whereas the D₂ state of t-St^.+ and CB^.+ are only deactivated via internal conversion.Lifetimes of the t-St^.+ and c-St^.+ 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-St^.+ D₂ state is attributed to isomrization 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-St^.+, t-St^.+, and CB^.+ are compared in terms of their lifetimes, structures, energies, and reaction processes.