PHOTOCHEMISTRY OF ANTHRAQUINONE‐2,6‐DISODIUM SULPHONATE IN AQUEOUS SOLUTION

Abstract— Irradiation of anthraquinone‐2,6‐disodium sulphonate in aqueous solution leads to formation of hydroxyquinone and semiquinone, which undergoes disproportionation to form the fully reduced hydroquinone. The quantum yield for formation of the semiquinone depends upon pH, the results being attributed to the relative efficiency with which the various acid/base forms of the hydroquinone react with quinone. The photoreaction does not involve production of hydroxyl radicals and luminescence studies suggest that the quantum yield for formation of the triplet state is unity. Indeed, flash photolysis studies indicate the presence of a short‐lived triplet (τ < 1 μs) which reacts with water to form a photosolvolate (τ= 5 μs) which, in turn, decays to form the observed products. These findings are in agreement with a mechanism previously proposed by Stonehill.