A comparative spectroelectrochemistry of homo- and copolymerization of pyrrole and N-methylpyrrole with indole on a gold electrode

Electrochemical formation and properties of intrinsically conducting homo- and copolymers of polypyrrole (PPy), poly-N-methylpyrrole (PNMPy), polyindole (PIn), poly(pyrrole-indole) [P(Py-In)], poly(N-methylpyrrole-indole) [P(NMPy-In)] on gold electrode were studied comparatively. Characterization of the samples was performed by cyclic voltammetry, in situ UV-Vis and FTIR spectroscopy methods, in situ resistance measurements and scanning electron microscopy (SEM) techniques. The voltammograms exhibited different behavior for various concentration ratios of the monomer in the feed with redox peaks observed at different positions. Positive shifts of the oxidation peaks were observed for copolymers synthesized using higher concentrations of monomer during the electropolymerization. In situ UV-Vis and FTIR spectroscopy results showed a spectroscopic behavior of the copolymers intermediate between those of the homopolymers. The resistance of copolymers generally grew with increasing (In)/(Py) and (In)/(NMPy) concentration ratio. This was most likely due to a smaller amount of pyrrole units in the copolymer backbone yielding a less extended pi-conjugation system along the copolymer backbone. In comparison, the resistance of P(NMPy-In) was higher than that of P(Py-In) copolymers. The morphology of polymers and copolymers was studied and compared using SEM. The SEM micrographs showed similarities between homo- and copolymers. A mechanism was suggested for the formation of copolymers proceeding via radical cations of indole, pyrrole and that of the possibly formed copolymer.