Photoswitching properties of photonic band gap materials containing azo-polymer liquid crystal

Photochemically tunable photonic band gap materials were prepared by infiltration of liquid crystal polymers having azobenzene groups into voids of SiO₂ inverse opal films. Linearly polarized light irradiation resulted in transformation from a random to an anisotropic molecular orientation of azobenzene side chains in the voids of the SiO₂ inverse opal film, leading to the reversible and stable shift of the reflection band to longer wavelength more than 15 nm. In order to improve switching properties, we used copolymers with azobenzene monomer and tolane monomer, which indicate higher birefringence, as infiltration materials into the voids. The azo-tolane copolymers were found to show the higher birefringence than azobenzene homopolymers by the linearly polarized light irradiation. Thus, the reflection band of the SiO₂ inverse opal film infiltrated with the azo-tolane copolymers was shifted to long wavelength region more than 55 nm by the irradiation of linearly polarized light.