Photoinduced Trans -> Cis Isomerization and Intermolecular-Charge-Transfer Interaction. Photochemistry and Picosecond Laser Spectroscopy of 4-Substituted β-(1-Pyrenyl)styrenes

Article abstract of DOI:10.1021/j150657a009

The effect of intramolecular-charge-transfer interaction upon trans -> cis photoisomerization has been examined in the case of 4-substituted β-(1-pyrenyl)styrenes with methyl, methoxy, and dimethylamino groups as the substituent, where the pyrenyl group acts as an electron acceptor and the 4-substituted phenyl group as an electron donor.The reaction yield measurements, picosecond and nanosecond laser photolysis and transient absorption, as well as fluorescence measurements in various solvents of different polarity show clearly that the isomerization occurs exclusively from the singlet excited state and the trans -> cis photoisomerization yield and the rate constant of isomerization increase with increase of the substituent electron-donating ability and the solvent polarity, in general.This result has been explained as due to the fact that the lowering of the energy of the intermediate perpendicular configuration with complete-charge-transfer structure increases with increase of the substituent electron-donating power and also with increase of the solvent polarity, and this lowering of the energy of the perpendicular configuration makes the barrier between the fluorescent state and the perpendicular state lower.