Photochemistry of methoxyanthraquinones

Abstract

The photochemical behaviour of 1- and 2-methoxyanthraquinones has been studied in a variety of solvents. No fluorescence or phosphorescence can be observed in deoxygenated fluid solutions, but phosphorescence is evident in rigid ethanol glasses at 77 K (ϕ_T(1-OMe)= 0·54; ϕ_T(2-OMe)= 0·28). Both derivatives can be photoreduced to the corresponding anthrahydroquinones in anaerobic benzene–propan-2-ol. In oxygenated, alkaline alcohol–water mixtures 1- and 2-hydroxyanthraquinones are formed. When oxygen is absent an intermediate is formed, which yields the same hydroxy-derivatives if oxygen is introduced after photolysis. The mechanisms of photolysis are discussed in terms of photosubstitution via the triplet states.