Photoinduced [2 + 2] cycloreversion reactions of 1-vinylpyrene–4-dimethylaminostyrene cycloadducts

Abstract

The reaction quantum yields of the photoinduced [2 + 2] cycloreversion of the cycloadducts trans- and cis-1-(4-dimethylaminophenyl)-2-pyren-1-ylcyclobutane (3t and c) were determined and the transient absorption spectra were analysed with a nanosecond laser photolysis. In the non-polar solvent benzene, photocycloreversion of cycloadducts occurred efficiently, whereas in polar acetonitrile the quantum yield of the photocleavage reaction decreased remarkably. Transient spectroscopy revealed the photocleavage route of the cyclobutane ring via an intramolecular exciplex state in a non-polar solvent. In the polar solvent, this exciplex state was stabilized as an ion-pair which was largely deactivated by intramolecular charge recombination.