The effect of a 4-carboxyphenyl or a 4-nitrophenyl thin film at the surface of a glassy carbon electrode on their electrochemical responses in the presence of various electroactive probes has been investigated. The grafting of a substituted phenyl group to a glassy carbon electrode was achieved by electrochemical reduction of the corresponding substituted phenyldiazonium derivative in acetonitrile. The blocking properties of the film depend primarily on electrostatic and electrolyte/solvent effects. Permselectivity for the 4-carboxyphenyl film can be achieved by controlling the dissociation of the carboxy group. The substituted phenyl layer is much more compact and less permeable in contact with a nonaqueous solvent than with an aqueous solvent presumably because the layer is poorly solvated. Electrochemical impedance measurements indicate that the kinetics of electron transfer are slowed down when the time used to modify the glassy carbon electrode is increased. Cyclic voltammetry and X-ray photoelectron spectroscopy measurements for 4-nitrophenyl- or 4-carboxyphenyl-modified glassy carbon electrode have indicated close to monolayer coverage for the substituted phenyl groups. The presence of a peak at 400 eV on the nitrogen 1s core level spectra was tentatively attributed to the reaction of phenol groups present at the glassy carbon electrode surface with the diazonium salt since this peak is not observed for the unmodified glassy carbon electrode.

No abstract

Spectroscopic and electrochemical properties of cobalt phthalocyanine (CoPc) polymers, which are believed to have two-and three-dimensional structures, have been studied and the results are reported. The spectral bands are shifted and a significant band broadening is observed as expected. The cyclic voltammetric results suggest that there are two energetically different Co ions in the three-dimensional polymer. The spectroscopic and electrochemical results indicate that the Co ion on the polymers appears to be in a partially reduced state in solution phases, as evidenced by the presence of the metal-ligand charge-transfer band. When adsorbed onto the carbon surface, this band becomes more prominent even in the formally unreduced state, perhaps due to the coordination of u-electron clouds of carbon into the coaxial axis of the complex, resulting in the partially reduced Co ion. As a result of this partial reduction, the electron transfer from CoPc polymers appears to be enhanced, which becomes the basis for the catalytic activities observed for this class of compounds.