Photochemistry of aromatic olefins. III. Photochemical cis-trans isomerization of 1-phenyl-1-propene

The photochemical cis–trans isomerization of 1‐phenyl‐2‐butene has been studied. The isomerization takes place through both intermolecular and intramolecular energy transfer from the phenyl to the olefin groups. Both singlet–singlet and triplet–triplet energy transfer processes are operative in the system. The rates of intramolecular energy transfer are obtained as 1 × 106 sec−1 for singlet–singlet and 2 × 106 sec−1 for triplet–triplet. The intersystem crossover yield of the phenyl moiety is calculated to be 0.65 or less.