Thermally Invertible Helical PEDOTs Synthesized by Asymmetric Electrochemical Polymerization in Temperature-Responsive Chiral Liquid Crystals.

Abstract

A thermal stimulus-responsive chiral nematic liquid crystal (N*-LC) is prepared by adding a chiral dopant with a thermally switchable helical sense into a host nematic liquid crystal. The helical sense of the N*-LC is reversibly controlled with a temperature difference of just 20 °C. Helical poly(3,4-ethylenedioxythiophene)s (H-PEDOTs) are synthesized through the asymmetric electrochemical polymerization of ter-ethylenedioxythiophene (EDOT) in N*-LCs containing an electrolyte. The helical senses of the H-PEDOTs are rigorously controlled by modulating the polymerization temperature. Changes in the chiroptical and electrochemical properties of H-PEDOTs upon electrochemical doping and dedoping were investigated. The circular dichroism (CD) spectra measured from the visible to near-infrared regions indicate that the helically π-stacked structure formed in neutral H-PEDOT is preserved even in oxidized H-PEDOT after electrochemical doping. This is the first example revealing that a helically π-stacked structure exists in the polaron and bipolaron states of conjugated polymers. The relationships between the helical sense of the N*-LC and those of the helically π-stacked structure, screwed fibril bundles and spiral morphology of the H-PEDOT were elucidated using a newly proposed mechanism for electrochemical polymerization in the N*-LC.