Photodecomposition of Catecholamines. Photoproducts, Quantum Yields and Action Spectrum of Adrenaline

The photochemical decomposition of several catecholamines in aqueous solution was investigated. The respective aminochromes were found to be products of adrenaline and isoprenaline. Irradiation of adrenochrome and N‐isopropylnoradrenochrome produced their respective 5, 6‐dihydroxyindoles in addition to the ultimate formation of melanine. No trihydroxyindoles could be detected amongst the photoproducts of catecholamines. The action spectrum of adrenaline suggested that the catecholamine itself, in excited state, initiated the first step in the transformation process. The quantum yields for the decomposition were determined for several catecholamines: N‐alkyl compounds. decompose more rapidly under influence of light (λ 254 nm) than those with an unsubstituted amino group. In determining the quantum yields the use of corrections for the inner filter effect could be avoided.