Electron transfer mediated geometrical photoisomerization of α,β-unsaturated ketones in the presence of electron donors in solution

The phototransformation of α,β-unsaturated ketones (I–IV) in the presence of electron donor triphenylamine in polar media has been investigated by using the chemically induced dynamic nuclear polarization (CIDNP) technique. For these compounds, it was demonstrated, that the electron transfer mechanism of isomerization results only in cis-isomers formation. Isomerization occurs in the triplet excited states of I–IV arising from back electron transfer in the triplet radical ion pairs of radical ions of ketone and triphenylamine. The set of isomers formed via this mechanism differs from phototransformation products observed after direct photolysis of these ketones in homogeneous and organized media.