Photoswitching properties of photonic crystals infiltrated with polymer liquid crystals having azobenzene side chain groups with different methylene spacers

Photo-tunable photonic crystals were prepared by infiltrating a photoresponsive material into SiO2 inverse opal films. Azobenzene-containing polymer liquid crystals, including poly(X-(4-methoxy-4′-oxy-azobenzene) alkyl acrylate), or PMAzXAc, where X is the number of methylene groups in the side chains (3, 6 and 11), were used as the photoresponsive material. PMAzXAc polymers were infiltrated in a spherical void of SiO2 inverse opal films to give photo-tunable photonic crystals that showed a photonic band gap. The photonic band gap of the photonic crystals could be controlled by irradiation with linearly and circularly polarized lights, leading to a reversible change in reflection from the photonic crystals. The change in the reflection band was found to be dependent on the methylene spacer length of the PMAzXAc. PMAz6Ac showed the largest shift of the reflection band (25 nm), while very little shift was observed for PMAz11Ac.