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Photochemical on-off switching of structural color of a multi-bilayered film consisting of azobenzene-polymer liquid crystal and polyvinylalcohol

Photo-responsive multi-bilayered film consisting of azobenzene polymer liquid crystals (PAzo) and polyvinylalcohol (PVA) was prepared on a glass substrate by spin coating of the polymer solutions alternately. The reflectivity of the multi-bilayered film disappeared by annealing at 80 °C. The disappearance of the reflection by the annealing was related to the thermal out-of-plane molecular orientation of PAzo even in the multi-bilayered film, leading to a very small difference in refractive indices between PAzo and PVA. The reflectance of the multi-bilayered film was increased again by UV irradiation because of the transformation from the out-of-plane orientation to the in-plane random orientation, resulting in the restoration of difference in the refractive indices. In this way, the on-off switching of the reflection was achieved by combination of the thermally spontaneous out-of-plane molecular orientation and following photoisomerization of PAzo comprising the multi-bilayered film.