U-shaped oligomers with a molecular biaxiality stabilizing blue phases

Abstract

After preparing catechol or biphenyl derivatives possessing two 2,3-difluoro-1,4-diphenylbenzene units, we investigated the phase transition behaviour of their mixture with a chiral additive with a high twisting power. Their transition behaviour was dependent on the methylene number in the spacer. Both derivatives possessing a hexamethylene unit in the spacer were found to exhibit wide-temperature blue phases in the chiral mixture. The appearance of the blue phases was discussed in terms of helical twisting power, elasticity, and molecular biaxiality. It was independent of the helical twisting power. A large molecular biaxiality or small bend elastic constant might stabilize the blue phases. The results provide important information related to molecular design for optically isotropic blue phases with frustrated molecular organization.