Thermal and Photochemical Control of Molecular Orientation of Azo-Functionalized Polymer Liquid Crystals and Application for Photo-Rewritable Paper.

A photo-responsive multi-bilayered film consisting of azobenzene polymer liquid crystals (PA6Az1) and poly(vinyl alcohol) (PVA) has been prepared on a glass substrate by alternate spin coating of the polymer solutions. The reflectivity of the multi-bilayered film disappears by annealing at 80 °C. The disappearance of the reflection by the annealing is related to the thermal out-of-plane molecular orientation of PA6Az1 even in the multi-bilayered film, which leads to a very small difference in refractive indices between PA6Az1 and PVA. The reflectance of the multi-bilayered film is increased again by UV irradiation because of the transformation from the out-of-plane orientation to an in-plane random orientation. In this way, on-off switching of the reflection is achieved by combination of the thermally spontaneous out-of-plane molecular orientation and following photoisomerization of PA6Az1 comprising the multi-bilayered film.