In situ spectroscopic study of the electropolymerization and properties of polyterthiophene

Abstract

The electrochemical polymerization of terthiophene has been studied using time resolvedin situ UV-visible transmission spectroscopy. The similarity of monomer and polymer oxidation potentials allows one to deposit partially or fully doped polymer. Both coulometric and spectroscopic data show that the level of doping increases with polymerization potential up to about 1.1 V, at which point it attains its maximum value of one positive charge per four rings, as for the parent thiophene. At the relatively low polymerization potentials employed, incompletely polymerized material is trapped within the polymer film. Direct evidence for the presence of trapped monomer is the disappearance of a peak at 355 nm upon the application of positive potentials to a film transferred to monomer-free background electrolyte. Spectroscopic and coulometric assay of these species shows that they constitute an appreciable fraction (ca. 20%) of the immobilized material at low polymerization potentials. The ability of these species to remain unpolymerized decreases with increasing polymerization potential. In all cases, they are polymerized during subsequent potential cycling in the range 0.0–1.15V. The redox composition of the polymer, estimated using optical data, shows non-Nernstian behaviour.