Reduction of isoviolanthrone by reaction with photogenerated radicals.

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 V1to V1–H2occurs. The quantum yield of this reduction is close to unity. The fluorescence of V1has a quantum yield of 0.08, for V1–H2Φfis strongly enhanced and the emission maximum is blue-shifted. The ketyl radical, the semiquinone radical and V1–H2were observed in this sequence by flash photolysis. V1–H2is unstable and undergoes oxidation to V1on admission of oxygen. [ABSTRACT FROM AUTHOR]