Generation of microstructures in novel supramolecular ionic materials based on azobenzene

Light-induced mass transport in azobenzene functionalized polymers has been used for generation of surface relief gratings (SRG) for different optical applications. The effect of grating formation has been ascribed to the light-induced motion of the azobenzene chromophores involving the covalently bound polymer chains. We propose a concept of supramolecular materials for the effective all-optical generation of surface relief structures and optical anisotropy. The materials are based on the non-covalent interactions between charged photochromic azobenzene units and oppositely charged polymer matrix, for example polyelectrolytes including charged alkoxysilanes. This new supramolecular approach opens a new way for the simple, cost effective and environment friendly preparation from building blocks of a variety of materials for the effective formation of SRG. Up to 1.65 μm deep relief gratings were inscribed onto a few micrometers thick films of these materials. The high thermal stability of the induced structures has been explained in terms of the network of oppositely charged ions inherent to the materials. Also 2D-structures, for example square and hexagonal gratings, were inscribed by the successive recordings. The latter possibility was also used to generate gratings with non-sinusoidal profiles by Fourier transform technique. A new technique to control the grating profile has been developed based on the real-time process of grating formation in these materials. The gratings with sow-tooth like profiles were induced by this method. The diffraction efficiencies up to 60 % in one diffraction order were achieved.