Chiral Liquid‐Crystalline Ionic Liquid Systems Useful for Electrochemical Polymerization that Affords Helical Conjugated Polymers

Abstract

AbstractIonic liquids bearing both liquid crystallinity and chirality are potentially applicable for chiral electrochemical syntheses and polymerizations. In this study, two types of chiral nematic liquid‐crystalline ionic liquids (N*‐LCILs) are developed to achieve asymmetric electrochemical polymerization without a supporting electrolyte and even a chiral dopant. N*‐LCILs are prepared i) by adding an axially chiral binaphthyl derivative as an external chiral dopant to imidazolium cation–based LCILs or ii) by incorporating a chiral binaphthyl phosphate as a counter anion in LCILs. Helical poly(3,4‐ethylenedioxythiophene) (H‐PEDOT) films are successfully synthesized through electrochemical polymerization of a dimer‐ or trimer‐type 3,4‐ethylenedioxythiophene (EDOT) monomer in an N*‐LCIL, where N*‐LCIL plays the role of both an asymmetric solvent and a supporting electrolyte. H‐PEDOT films have helically π‐stacked structures of conjugated chains and spiral morphologies consisting of one‐handed screwed fibril bundles. The plausible mechanism of the asymmetric electrochemical polymerization of EDOT in N*‐LCIL is proposed to elucidate the correlation of helical sense between the helically π‐stacked chains, screwed fibril bundles, and N*‐LCIL. The two present types of N*‐LCILs are the first to enable supporting electrolyte–free asymmetric electrochemical polymerization, and they have potential applications in various types of chiral electrochemical syntheses, expanding the potential utility of ionic liquids.