Electrochemical polymerization and characterization of new copolymers of 3-substituted thiophenes

This work presents the electrochemical synthesis and characterization of 3-substituted thiophene conducting copolymers suitable for applications in electrochromic displays. The 3-methoxythiophene (MOT), 3-thiophenemethanol (TM), 3-thiopheneethanol (TE) and 3-thiophenecarboxylic acid (TCA) monomers showed oxidation potentials at 1.1, 1.5, 1.5 and 1.8 V/SCE, respectively. Copolymers containing MOT (PMOT-co-TE, PMOT-co-TM and PMOT-co-TCA) were synthesized by oxidative electropolymerization and characterized by GPC, FTIR, UV–vis and cyclic voltammetry. The copolymers were found to be soluble in acetonitrile, N,N-dimethylformamide and N,N-dimethylsulfoxide. PMOT, PMOT-co-TE and PMOT-co-TCA showed a dependence of the anodic potential on the scan rate and a quasi-reversible profile. PMOT-co-TM showed an irreversible electrochemical profile. PMOT and PMOT-co-TE were the most electroactive polymers. The oxidation potentials vs. SCE of PMOT, PMOT-co-TE, PMOT-co-TM and PMOT-co-TCA were 0.22, 0.30, 1.16 and 0.20 V/SCE at 50 mV s−1, respectively. The copolymers deposited on ITO showed reversible color variation between blue in the oxidized state to orange when reduced, demonstrating their potential for electrochromic applications.