Relationship between formation yield of radical cation and laser intensity during resonant two-photon ionization of stilbene and methoxyl-substituted stilbenes using a 25-ns XeCl excimer laser

Radical cations of trans-stilbene (1), trans-4-methoxystilbene (2), and 2,4-(3), 3,4-(4), 3,5-(5), and 4,4′-dimethoxystilbene (6) were generated from the resonant two-photon ionization (RTPI) in acetonitrile using a excimer laser (308 nm, 25 ns). The photostationary state of the S1 and Sn is attained within the laser flash duration of 25 ns in the RTPI of 1–6. Based on the photostationary state analysis, the relationship of Φion∝I2 was obtained for the RTPI of 1–4 with shorter singlet lifetimes (<100 ps), while Φion∝I was obtained for the RTPI of 5 and 6 with longer singlet lifetimes (>300 ps).