Role of the Triplet State in the Photoreduction of Chlorophyll

Abstract

IN 1948, Krasnovsky reported¹ that chlorophyll can be photochemically reduced, in dry pyridine, by ascorbic acid. The product is a pink pigment. The quantum yield of the reaction was not measured; but indirect evidence² indicates that it was of the order of magnitude of 10⁻². The reaction is reversible; the green colour of the solution returns slowly on standing, or more rapidly if a suitable oxidant is added. The regeneration of chlorophyll is never complete; part of it being converted into phæophytin. This and analogous photochemical reactions were studied extensively, in subsequent years³, by Krasnovsky and Evstigneev et al. They have adopted the view that the reversible photoreduction of chlorophyll plays an essential part in photosynthesis and in chlorophyll-sensitized reactions in vitro.