ELECTROCHEMICAL INVESTIGATION OF NOVEL POLYMERIZABLE THIOPHENE FERROCENE CONJUGATES

A series of 3-alkyl-substituted thiophenes has been synthesized, where the 3-position is substituted by -(CH2)2-O-(CH2)n-OC(O)Fc(n = 6,8,10,12,16; Fc = ferrocene). The electrochemical properties of both the ferrocene and the thiophene moieties have been investigated in detail. The ferrocene/ferricenium couple is quasi-reversible at Pt, and oxidation of the thiophene at almost-equal-to +2 V leads to the deposition of a monolayer of a poly(thiophene) species. Pulsed potential, fixed potential, and cycled potential techniques all yield polymer surface films whose ferrocene pendant group exhibits quasi-ideal surface wave behavior. Monolayer and not multilayer films were uniquely accessible with these materials. Electrochemical deposition of these 3-alkylthiophene derivatives onto a Pt electrode precoated with a conducting 3-methylthiophene film was successful and was also limited to monolayer equivalent coverage. Copolymerization of the thiophene/ferrocene conjugates with 3-methylthiophene results in a film with a greater than monolayer equivalent coverage of ferrocene derivative. A comparison of the electropolymerization conditions provides insight into the deposition mechanism of these poly(thiophene) conjugates onto an electrode surface and establishes a methodology for deliberately producing monolayer coverages of conducting polymers.