Photoisomerization and [2 + 2] photocycloaddition in bichromophoric styrylbenzoquinoline dyads with o-xylylene bridge group

Abstract

Photochemical properties of bis(styrylbenzoquinoline) dyads in which two styrylbenzoquinoline (SBQ) moieties are bridged by an o-xylylene group linked to their styryl groups via oxy- and carboxy-functional groups have been studied. Two competitive reactions, photoisomerization of the SBQ moieties and stereoselective [2 + 2] photocycloaddition (PCA) to give tetrasubstituted cyclobutane, occur under irradiation. It is assumed that PCA occurs with participation of an intramolecular excimer, in which the photochemical process of dimerization to cyclobutane dominates over the photophysical process of fluorescence, because the emission band of the excimer is not observed in an explicit form in the fluorescence spectra of dyads.