Chiral liquid crystal polymers. 6. Preparation and properties in solution and in bulk of optically active thermotropic copolyesters

Abstract

Optically active cobipolyesters based on (S)-1,2-propanediol and mixtures of linear, mesogenic bis(4-carboxyphenyl) terephthalate and nonlinear, nonmesogenic isomeric bis(4-carboxyphenyl) phthalate or bis(4-carboxyphenyl) isophthalate were prepared by polycondensation in solution and analyzed for their properties in solution and in bulk. Chemical composition data and solubility properties of the bipolyesters prepared are indicative of a random distribution of structurally different hard segments. Optical rotation, UV absorption, and induced circular dichroism measured in dilute solution are consistent with the existence of specific electronic interactions among the aromatic moieties embedded in a chirally homogeneous conformational environment. Thermotropic properties of the bipolyesters studied by coupled thermal analysis and optical microscopy observation allowed highlighting of the direct dependence of the onset, stability, and breadth of the temperature range of the polymer mesophase upon chemical composition. Liquid crystal behavior was observed up to as high as 70% incorporation of "nonmesogenic" aromatic units. Cholesteric mesophases with temperature-sensitive selective reflection of visible light were established at certain copolymer compositions and could be irreversibly frozen to room temperature. The great value of the copolymerization process to provide a variety of mesomorphic polyesters with modulated thermotropic behavior is stressed.

Enhanced optical asymmetry in supramolecular chiroplasmonic assemblies with long-range order

“…High g-factors between 0.02 and 0.2 have been obtained for single plasmonic and magnetic NPs (11)(12)(13) with complex molecular and nanoscale structures, but their origins are fundamentally different from those of LCs. The high optical asymmetry of LC media originates from the long-range order of chiral molecules, whereas the g-factors of individual LC molecules are very small-typically below 0.001 (14,15). Thus, the question emerges: Is it possible to increase the optical asymmetry of plasmonic assemblies by creating the longrange organization of nanoscale constituents that, by themselves, have low g-factors?…”