A study of the thermally induced and photoinduced changes in the mechanical properties of thin azobenzene polymer layers utilizing electromechanical spectroscopy is presented. Upon illumination at room temperature, weak photoinduced plasticization is observed. This is well below the degree of softening induced by heating the layer above the glass transition temperature. At the same time, the polymer layer roughens, indicating light-induced diffusion of the macromolecules over micrometer distances. We propose an active photoinduced diffusion mechanism, in which free volume generated during the photoisomerization of one chromophore is reoccupied in the course of the photoinduced isomerization of an adjacent azobenzene molecule.

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Front Cover: Azobenzene undergoes E-Zisomerization upon irradiation. Polarized interfering light beams causing repeated isomerization cycles and a photoreorientation of the azobenzene groups result in a massive mass transport over mm distances. Employing polymers with different concentrations of photoactive groups it was investigated how many molecular motors are necessary to get polymer moving. Further details can be found in the Full Paper

Summary: Well defined azobenzene containing (co)polymers have been synthesized by atom transfer radical polymerization and subsequent polymeranalogeous reaction for introduction of the chromophores. Four different series were prepared varying only one of the following material parameters at a time, while keeping the others constant. Varied were the molecular weight, the azobenzene content, the glass transition temperature and the molecular architecture of the copolymers. With these four series of (co)polymers the influence of the molecular parameters on the photoinduced formation of surface relief gratings was investigated.

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