As has been already indicated, the most straightforward comparison of the new motor's predicted operation mechanism can be made to that of the second-generation motors. Namely, for a given rotation chirality set by the orientation of the switch, the system starts with an optical S 0 → S 1 excitation of its stable isomer, S, initiating so-called 'optical' step of the rotation cycle. From that moment, PFCN structure begins to evolve at the first excited-state potential energy surface (PES), which can be followed with the reaction path profile shown in Figure . Thanks to the maintained overcrowded-alkene character, PFCN is expected to adiabatically relax on the S 1 PES from the S Franck-Condon region towards the area of small S 1 /S 0 energy-gap values, where the central C=C bond between the rotor and the stator adopts close-to-perpendicular orientations.