Abstract
Abstract— Enzyme‐generated triplet species transfer energy very efficiently to thylakoid membrane fractions enriched in either photosystem‐I or photosystem‐II. Independent of the nature of the triplet donor, the emission is always more intense with photosystem‐I. Since the fluorescence quantum yield of chlorophyll in PS‐I is lower and the rate of energy transfer usually smaller than to chlorophyll in PS‐II, the yield of 1S chlorophylls in PS‐I is substantially higher. This is tentatively attributed to more favorable reverse intersystem crossing from an upper triplet state in PS‐I.