CONDUCTING POLYMERS FROM ANODIC COUPLING OF SOME REGIOCHEMICALLY DEFINED DIALKOXY-SUBSTITUTED THIOPHENE OLIGOMERS

Electrochemical polymerization of thiophene oligomers (n = 2-4) bearin g pentoxy groups in regiochemically defined positions (3 or 4 of the t erminal thiophene rings) was performed in acetonitrile. Cyclic voltamm etry and UV-Vis spectroscopy showed that the degree of polymerization decreases as the monomer length increases and this result is accounted for by the corresponding decrease of the coupling rate constant, meas ured by cyclic voltammetry for the less reactive 3-substituted series. Compared with alkyl substitution, alkoxy substitution induces a small er bandgap and lowers the oxidation potential, therefore giving the po lymer a higher stability of the doped state. However, no variation in the effective conjugation length was found when alkoxy groups were pre sent in head-to-head or tail-to-tail linkages. It is suggested that th e presence of the oxygen atom not only minimizes the steric hindrance but also plays a role in planarizing the polymer chain.