The photochemistry of 1-phenylpropenes

Abstract

An examination of the photochemical and photophysical processes resulting from excitation in the α and A bands of cis- and trans-1-phenylpropene in the gas phase has been carried out. Measurement of quantum yields of fluorescence, fluorescence lifetimes, and quantum yields of isomerization on excitation in the α bands has revealed that the value for the sum of the non-radiative processes in this first excited singlet state (ΣK_NR) is the same for both isomers. A consideration of the potential energy diagrams for the ground state and first two excited singlet and triplet states strongly suggests that geometric isomerization is solely a triplet process for excitation in the α bands. This in turn implies that the major contribution to ΣK_NR for each isomer is the intersystem crossing rate constant. In contrast to observations made on solutions of monophenylalkenes, excitation in the A bands of the phenylpropenes does not lead to efficient geometric isomerization. Polymerization is the major detectable process.