Iridescent Chiral Nematic Mesoporous Organosilicas with Alkylene Spacers

Abstract Mesoporous organosilica films with chiral nematic structures are prepared with a bridging urea group and with alkylene bridges, where the length of the alkylene bridge varies from C₁–C₆. To synthesize these materials, cellulose nanocrystals (CNCs) are used as liquid crystal templates, which coassemble with the organosilica precursor to give composite materials with a chiral nematic structure of CNCs embedded within. Removal of the CNCs by acid hydrolysis results in free‐standing, mesoporous organosilica films with long‐range chiral nematic ordering of the porous network. It is found that increasing the length of the organosilica bridging groups causes phase separation between the organosilica precursors and the aqueous CNC suspension. This problem is solved through two distinct methods: combining the long alkylene‐bridged precursors with shorter precursors or by using a mixed solvent system of water and dimethylformamide during self‐assembly. The new chiral nematic mesoporous organosilica films display photonic properties, good thermal stabilities, and interconnected pore structures.