Photosensitized Z-E isomerization of cinnamate by covalently linked 2-(3′,4′-dimethoxybenzoyl)benzyl moiety via triplet-triplet energy transfer

(Z)- and (E)-2-(3′,4′-Dimethoxybenzoyl)benzyl cinnamate (3Z and 3E) and (E)-N-(2-(3′,4′-dimethoxybenzoyl)benzoxycarbonymethyl) cinnamide (4E) have been prepared. The photosensitized isomerization of cinnamates via intramolecular triplet-triplet (T-T) energy transfer from the triplet 2-dimethoxybenzophenone (DMBP) moiety was observed. The phosphorescence of the DMBP moiety is quenched by the attached cinnamate, indicating efficient T-T energy transfer from triplet DMBP to the cinnamate. On the basis of the intramolecular phosphorescence quenching and the intermolecular quenching experiments, it can conclude that T-T energy transfer to the E isomer is more efficient than to the Z isomer, and faster than the overall decay rate of the sensitizer triplets, and the non-isomerization radiationless decays of triplet 2, or triplet cinnamate moiety in 3 and 4 are faster than the isomerization. The latter be an important reason for low quantum yields of isomerization.