Electrochemical quartz crystal microbalance study of magnesium porphine electropolymerization process

Material and charge balances in the course of the electropolymerization process of the non-substituted Mg(II) porphine (MgP) at a low oxidation potential from its acetonitrile solutions of various concentrations have been studied via the in situ electrochemical quartz crystal microbalance method (EQCM). Thus, registered electrode mass increase due to the MgP oxidation at its surface has been used, in combination with in situ spectroelectrochemical data, for determination of the key parameters of the polymerization process and of the magnesium polyporphine films deposited on the electrode surface: current efficiency of the film deposition process, average charge spent for transformation of a monomer molecule into monomer unit inside the film, number of monomer units inside the deposited film, average number of valence bonds per one monomer unit inside the film. Besides, the EQCM method applied to the discharge process of the electropolymerized film has allowed us to estimate the average charging (oxidation) degree of the monomer unit inside the film at the polymerization potential and the degree of the solvent participation in the course of the polymer’s redox transitions. It has been established that the number of bonds between porphine units is within the range of 2.2 to 2.4, with its slight increase for films deposited at higher monomer concentrations. Conclusions on the structure of polyporphine chains have been made.