Bicycle-Pedal Isomerization in a Rhodopsin Chromophore Model

Probing the isomerization of a retinal chromophore model we have found the first ab initio realization of the so-called bicycle-pedal mechanism. In an ensemble of 47 starting geometries generated by ground-state zero-point-energy sampling one single. trajectory followed the aforementioned reaction mode which was proposed by Warshel in 1976. Furthermore restrained optimization of synchronous rotation mode shows that two-double-bond isomerization is barrierless for the conrotatory and disrotatory pathway.