Role of adiabatic pathways in the photoisomerization of aromatic olefins

An account is given of the research work carried out in the authors’ laboratory on the excited state behaviour of diarylalkenes with the particular aim of investigating which are the structural factors responsible for the change of mechanism from the diabatic to the less common adiabatic pathway. The effects of the configurational and conformational structure and of the medium polarity on the shape of the potential energy surfaces of the lowest singlet and triplet excited states allow a general interpretation of the adiabatic mechanism to be proposed. The results of combined fluorimetric and photochemical measurements (dependence of spectra, quantum yields and lifetimes on λexc and temperature) and of the statistical “principal component analysis”, are described with emphasis on some representative cases.