Photochemical switching behavior of azo-functionalized mesoporous silica photonic crystals

We report a photochemically tunable photonic crystals (PCs) system, based on azobenzene derivatives covalently grafted onto mesoporous silica photonic crystals (azo-MS-PCs), of which the reflectance at the stopband position can be modulated by alternating UV/Visible (UV/Vis) light irradiation. The stop-band position of azo-MS-PCs was found to be dependent on the photoisomerization of azo ligands. The decreased effective refractive index of azo-MS-PCs at the cis-state under UV light irradiation led to a blue-shift of stopband position. Upon irradiation with Vis light, the stopband position was recovered after photoisomerization from the cis-state to the trans-state. The introduction of mesoporous silica matrix could not only enhance the grafting content, mechanical, chemical, and thermal stability of the responsive moieties, but also meet the steric demands of azo photoisomerization process. This work may open a new way to fabricate multi-functional PCs materials with the tunable band gap.