Reduction of isoviolanthrone by reaction with photogenerated radicals

Abstract

The properties of isoviolanthrone (V₁) and its corresponding dihydro form (V₁–H₂) in argon-saturated 1-phenylethanol in the presence of acetophenone were examined by photophysical and photochemical methods. Upon photolysis of the sensitizer, a radical-induced reduction of V₁ to V₁–H₂ occurs. The quantum yield of this reduction is close to unity. The fluorescence of V₁ has a quantum yield of 0.08, for V₁–H₂Φ_f is strongly enhanced and the emission maximum is blue-shifted. The ketyl radical, the semiquinone radical and V₁–H₂ were observed in this sequence by flash photolysis. V₁–H₂ is unstable and undergoes oxidation to V₁ on admission of oxygen.