Quenching of the Excited States of 2‐phenylbenzoxazole by Azide Anion. Fluorescence and Esr Study

Electron spin resonance, spin‐trapping and fluorescence techniques demonstrate that 2‐phenylbenzoxazole (P) participates in photo‐induced reactions with alcohols and electron donors like the azide ion. Irradiation of Pat 300 nm in deaerated ethanol produces ethoxyl and hydroxyethyl radicals which can be detected with the spin trap, 5,5‐dimethyl‐l‐pyrroline‐l‐oxide (DMPO). However, irradiation of P in the presence of N‐3 leads to the appearance of the azide radical, N‐3, which also reacts with DMPO. Studies with the nitroxyl radical, 2,2,6,6‐tetramethylpiperidine‐l‐oxyl (TEMPO), suggest that electron transfer from the azide anion to an excited state of P yields the semi‐reduced sensitizer, P‐, which in turn reacts with TEMPO. The effect of sodium azide upon the fluorescence intensity and lifetime of P in aqueous ethanol has also been studied.