Control of Chirality and Electrochromism in Copolymer-Type Chiral PEDOT Derivatives by Means of Electrochemical Oxidation and Reduction

Copolymer-type chiral poly(ethylenedioxythiophene) [PEDOT] derivatives were synthesized by two kinds of electrochemical polymerizations of (i) chiral EDOT-based monomers using a cyclic voltammetric method in acetonitrile and (ii) achiral EDOT-based monomers using a potentiostatic method in chiral nematic liquid crystal (N*-LC) employed as an asymmetric reaction field. The electrochromic and morphological changes of the chiral PEDOT derivatives upon electrochemical doping and dedoping were investigated. Drastic and reversible changes in not only electrochromism but also circular dichroism between neutral and oxidized states of the chiral PEDOT derivatives were observed. This indicates that the helicity of the present polymers can be controlled by the electrochemical doping and dedoping procedures. It is found that the helically twisted chain and/or helically π-stacked structure formed in the neutral PEDOT derivative are suppressed in the oxidized state, where the main chain becomes planar due to a formation of quinoid structure and the interchain distances are lengthened due to intercalation of dopants into the chains. Spiral morphologies with right- and left-handed screw directions were observed for the polymers synthesized in the N*-LC and well correlated with spiral textures of the N*-LCs.