A Flash Photolysis Study of 1‐methylindole

The conventional flash photolysis of 1‐methylindole in aqueous media was studied at Λexcitation≥290 nm. The transients observed 20 μs after excitation consisted mainly of the radical cation (R+). the hydrated electron (e‐aq) and the triplet state (T). Electron counting experiments indicate that photoionization is the only source of R+ with e‐aq/R+= 1.07±0.09 in neutral media. Quenching of the R+ yield with H+ indicates that the fluorescent state is the precursor to 80% of the photoionization events with the remainder probably arising from a prefluorescent state. The triplet decays with a lifetime of 29 μs in deaerated neutral media. This decay is unchanged by N2O saturation, but T reacts with acrylamide with k≥2.8 × 109M‐1. In 2 M Br‐, R+ and T yields are increased by factors of 2–3. Consideration of fluorescence quenching and T enhancement by Br‐permits an estimate of φIsc between 0.33 and 0.49. The increased R+yield at high Br‐concentrations cannot be accounted for by induced photoionization or triplet state reactions.