Photoinduced Deformations in Azobenzene Polymer Films

This review is devoted to the microscopic mechanism behind photoinduced deformations in side-chain azobenzene polymers. We present the analysis of selected experiments that allows us to propose main criteria for a proper choice of the light induced force. Particularly, we provide convincing evidence that, contrary to a well-spread belief, light induced softening is a very weak accompanying effect rather than a necessary condition for the formation of surface relief gratings. Hence, the theories which need a concept of photo-induced softening are not able to describe the phenomenon correctly. Using molecular dynamics simulations, we show that chromophore reorientation alone is capable of the film deformation under homogeneous illumination. Finally, we discuss a recent microscopic theory that satisfies all main criteria for a proper choice of the light induced force. The theory is based on the orientation mechanism of azobenzene chromophores and takes the internal structure of side-chain azobenzene polymers explicitly into account.