A FLASH PHOTOLYSIS STUDY OF 5-METHOXYINDOLE

Abstract— The microsecond flash photolysis of 5-methoxyindole in aqueous solutions has been studied at γ_exc≥ 290 nm. Transients identified in this time realm in neutral solutions are: e_aq^-, the 5-methoxyindole radical cation (γ_max≅ 440 nm), the neutral transient with γ_max≅ 530 nm) and an unidentified oxygen sensitive transient with γ_max≅ 435 nm. Radical cations and e^-_aq are shown to be produced in equal amounts consistent with a photoionization process as the only source of both transients. H⁺ quenching of fluorescence and radical cation production gives equivalent Stern-Volmer constants indicating that photoionization occurs from the fluorescent state. The unidentified oxygen sensitive transient exhibits a pK _a of2–2.5 and is quenched at lower pH values indicating that it also has a fluorescent state precursor.