Cholesteric Liquid Crystal Inductive Asymmetric Polymerization: Synthesis of Chiral Polythiophene Derivatives from Achiral Monomers in a Cholesteric Liquid Crystal

Abstract

Inductive asymmetric polymerization from achiral monomers is achieved through the use of cholesteric liquid crystal as an asymmetric reaction solvent. The chirality of the polymers, which have no chiral substituent, is considered to derive from the asymmetry produced by the chiral liquid crystal media during polymerization. No chiral molecules reacted chemically with the monomer during polymerization, and the cholesteric liquid crystal acted solely as a physical reaction environment. Polymers without chiral centers exhibit exciton couple-type circular dichroism and circular polarized luminescence. The chirality of the polymer is due to chiral aggregation, which occurs during the propagation process in the cholesteric liquid crystal medium and which is locked by interchain interaction in the π-conjugated system. Heat treatment of the polymer causes disaggregation and loss of chirality. The present results demonstrate cholesteric liquid crystal inductive asymmetric reaction can be performed by polycondensation in π-conjugated systems.