A Novel Mesogen: Generation of a Liquid Crystalline Phase from a Cylindrical Pi-Conjugated Helix

Abstract

We newly found that oligo(o-phenylene) (OOP), characterized by a cylindrical helical geometry, can serve as a novel mesogen. This finding is quite surprising since, in a general sense, such a three-dimensional bulky molecular unit that undergoes a dynamic conformational change cannot be used for mesogen. The liquid crystalline OOP derivative is an octamer of dimethoxy benzene, where each terminal benzene ring possesses a hexadecyloxy carbonyl group. In polarized optical microscopy, the OOP derivative displayed a clear birefringence upon both heating and cooling. X-ray diffraction analysis showed four broad peaks with d-spacings of 3.08, 1.08, 0.52, and 0.40 nm. These observations indicate that the OOP generates an enantiotropic nematic liquid crystalline mesophase. In this presentation, we will detail the phase behavior of the thermotropic liquid crystalline material.