Optical deformations of azobenzene polymers: Orientation approach vs. photofluidization concept

Recently in literature appeared quite a number of claims that cyclic isomerization of azobenzene (azo) chromophores may cause an athermal transition of the glassy azo-polymers or, more generally, glassy azo-materials into a fluid state. In this study, we provide a critical overview of recently published findings and show that observations presented not only fail to support this photofluidization concept but rather show the contrary. The glassy azo-materials remain in the solid state under light illumination. Thus, the sound claims made in the titles of recent studies contradict the experimental observations presented in their texts. Further, we discuss a number of rigorous studies, which present strong evidence against the photofluidization concept, including our own theoretical predictions made in the frame of orientation approach. This approach provides values of anisotropic light-induced stress large enough to deform glassy azo-polymers with diverse chemical structures. The values of the stress are in a perfect accord with recent experimental findings, which show deformation of the bonds in metal and graphene multilayers adsorbed on the top of illuminated azo-polymers.