The Effect of Substitution of 3-Perylenyl Group, an Aromatic Nucleus with a Very Low Triplet Energy, on Photochemical Isomerization of the Unsaturated Bond. Direct Observation of Triplet State Isomerization of a Styrene Derivative

3-Styrylperylene undergoes one-way cis → trans photoisomerization in the triplet state through a quantum chain process. The conversion of cis to trans triplet state was directly observed by laser spectroscopy to proceed with an activation energy of 6.6 kcal mol−1. This finding clearly demonstrates that in the series of styrylarenes, ArCH=CHPh, lowering of the triplet excitation energy of Ar group alters the mode of isomerization from two-way to one-way.