5 - Chiral Polymers with Photoaffected Phase Behavior for Optical Data Storage

Abstract

It is noted that the chiral side chain polymers derived from asymmetric esters of terephthalic acid and hydroquinone can form an unusual mesophase (the isotropic smectic phase, IsoSm) characterized by high transparency and optical isotropy within the visible wavelength range, combined with a hidden layered smectic ordering and some elements of the helical superstructure at shorter dimensions of 10 to 250 nm. It is observed that if functionalized with an azobenzene chromophore, the resulting copolymers can also form the IsoSm phase in a broad range of compositions. They exhibit photochromism and photoinduced birefringence typical of azo dye LC copolymers, but they differ from the latter by their spontaneous formation of transparent, optically isotropic films, thus allowing for easy production of thick photoactive layers. Birefringence can be induced in optically isotropic photochromic IsoSm copolymers by UV illumination or by visible light within the blue–green wavelength range of 400 to 500 nm. The visible light is stable and shows no saturation up to several hours of illumination, whereas the birefringence induced by polarized UV light within the first few seconds disappears with further illumination.