Molecular dynamics study of the solid state photoreactivity of 3-and 4-cyano-trans-cinnamic acids

Molecular dynamics (MD) simulation studies show the importance of molecular motion and optimal pi-pi overlap of incipient reactive double bonds in the topochemical photodimerisation reactions of 3- and 4-cyanocinnamic acids. These simulations have been carried out in minicrystals consisting of 180 m olecules and confirm earlier conclusions arising from packing calculations of static structures. A two-step diradical pathway for the dimerisation is possible. A stepwise MD study has also been performed in which two molecule s at the centres of the minicrystals have been dimerised and these calculat ions reveal the importance of thermal motion in these solid state photochem ical reactions.