Matrix isolation FTIR studies of non-planar trans-stilbene

When cis-stilbene was trapped in inert gas matrixes (N2, Ar, Kr) and then photoirradiated, evidence was obtained for the presence of the non-planar trans isomer of stilbene, in the matrix, which was identified using infrared spectroscopy. On annealing the matrix after photoirradiation, the intensity of the non-planar trans features decreased in intensity, while those of the planar trans isomer concomitantly increased. This observation indicates a conversion of the non-planar trans isomer to the planar trans structure, indicating that the planar form is the more stable of these two structures, separated by only a small barrier. The assignment of experimental spectral features to the non-planar isomer were corroborated by computations at the B3LYP/6-31++G** level.