Liquid crystalline PEDOT derivatives exhibiting reversible anisotropic electrochromism and linearly and circularly polarized dichroism

Abstract

The multifunctional poly(3,4-ethylenedioxythiophene) [PEDOT] derivatives that exhibit liquid crystallinity, reversible anisotropic electrochromism, and linearly and circularly polarized dichroism are developed. A series of copolymer-type liquid-crystalline PEDOT (LC PEDOT) derivatives are synthesized and evaluated in terms of optical and electrochromic properties. Two of the polymers are monosubstituted LC PEDOT derivatives with phenylcyclohexyl (PCH) or cyanobiphenyl (CB) mesogenic side chain moieties linked to the main chain via an ester bond. Four are disubstituted polymers bearing PCH or CB side chain moieties linked to the main chain via an ester or an ether bond. All of the polymers showed thermotropically nematic LC (N-LC) phases of an enantiotropic nature. Macroscopically aligned LC PEDOT derivatives were prepared by rubbing the polymer films in their N-LC phases, yielding linearly polarized fluorescence and anisotropic electrochromism. The morphologies of the polymer films reversibly changed between the neutral and oxidized states through electrochemical dedoping and doping procedures. The electrochromism between the neutral and oxidized states occurred in the parallel and perpendicular directions of the aligned polymer film, affording a novel anisotropic electrochromism. The chiral nematic LC (N*-LC) phases were also induced in the polymers by adding chiral binaphthyl derivatives as chiral inducer into the LC PEDOT derivatives. The polymer films with the induced N*-LC phase exhibited circular dichroism, implying the formation of an interchain helically π-stacked structure or intrachain helically twisted structure.