Effect of the nature of the aromatic groups on the lowest excited states of trans-1,2-diarylethenes

Abstract

The photophysical and photochemical behaviour of a series of diarylethenes has been investigated experimentally. For the same compounds the potential-energy curves of trans→cis photoisomerisations and the ethenic bond orders in the S₁ and T₁ states have been calculated. The purpose of the study is to assess which properties of the aryls govern the photophysical behaviour of the diarylethenes. It is found that the relative energies of the L_a and L_b states of the larger aryl with respect to the ethene B_u state determine to a large extent the photophysical and photochemical properties of the diarylethenes.