Chiral BEDOT-based copolymers prepared by chemical and electrochemical polymerization

Optically active conjugated copolymers, poly[1,4-bis[2-(3,4-ethylenedioxy)thienyl]-2,5-benzoic acid-1-methylheptyl ester] [poly (BEDOT-B(OCT*)], were synthesized by chemical and electrochemical oxidative polymerizations. Poly[BEDOT-B(OCT*)] of both (R) and (S) configuration were synthesized by introducing chiral octyloxycarbonyl group in the side chain. The dibromo compounds, (R)-1 and (S)-1, were prepared by Mitsunobu reaction by an esterification of (R) or (S)-octanol and 2,5-dibromobenzoic acid with an aid of diethyl azodicarboxylate (DEAD) and triphenylphosphine (TPP) in tetrahydrofuran. The monomers were then prepared with Stille coupling technique using Pd(PPh3)4Cl2 as a catalyst to produce (R)-1 and (S)-1. The monomer was electropolymerized onto platinum button and ITO glass electrodes by repeated scanning from −1.0 V to +1.0 V versus Ag/Ag+ at 20 mV/s. The polymer was electrochromic and reversibly switching from purple green upon oxidation. The chemical polymerization was also carried out in dimethylformamide with a Ni(cod)2 catalyst. Optical absorption and circular dichroism (CD) measurements were examined. The polymers showed Cotton effects in CD spectra. This method therefore represents a new technique for the preparation of chiral polymer with helicity, which can disclose a possibility toward “chiralelectrochemistry”.