Light-induced modification of kinetic molecular properties: Enhancement of optical Kerr effect in absorbing liquids, photoinduced torque and molecular motors in dye-doped nematics

In this paper we review some experimental and theoretical results on the enhancement of orientational optical nonlinearities observed in dye-doped liquids and liquid crystals. We argue that this enhancement is derived from a photoinduced modification of kinetic molecular properties. Moreover we highlight an analogy between the mechanism of this effect in nematic liquid crystals and the working principles of "molecular motors". This analogy helps us to refine the understanding of this effect and to identify the molecular parameters which play the main role. Finally we review some recent experimental results about the dependence of the optical nonlinearity enhancement on the detailed dye and host molecular structures. These results provide some insight into the light-induced phenomena taking place inside a dye molecule.