SOLVENT AND TEMPERATURE EFFECTS ON THE FLUORESCENCE AND COMPETITIVE PHOTOREACTIONS OF CIS-9-STYRYLANTHRACENE

A fluorimetric and photochemical study of cis-9-styrylanthracene as a function of temperature has been carried out in different solvents with the aim of answering some open questions about the behavior of its first excited singlet state, S-1. In non-polar solvents, a parallel photoreactive pathway, leading to a cyclization adduct, was found to compete with fluorescence and isomerization already at 200 K, its contribution increasing markedly with temperature. The cis --> trans photoisomerization occurs prevalently by a triplet mechanism, a detectable contribution of diabatic and adiabatic isomerization in S-1 being operative in these solvents from room temperature upwards. In polar solvents, the main deactivation pathway competitive with fluorescence is isomerization to Irans, which occurs prevalently through a mixed singlet mechanism with a major diabatic and a minor adiabatic components.