Electrochemistry of new derivatives of phenothiazine: Electrode kinetics and electropolymerization conditions

Electrochemical properties of two new derivatives of phenothiazine, i.e., 3,7-bis(4-aminophenylamino)phenothiazin-5-ium chloride (PhTz-(NH2)2) and 3,7-bis(4-carboxyphenylamino)phenothiazin-5-ium chloride (PhTz-(COOH)2), has been investigated on glassy carbon electrode. The pH influence on their electrode reactions was specified. The compounds studied showed complex kinetics of electrode reactions. Heterogeneous constants of the electron transfer at pH = 7.0 calculated from the Tafel plot were equal to 8.3 × 10−4 and 7.4 × 10−4 cm s−1 and transfer coefficients to 0.52 and 0.36 for PhTz-(NH2)2 and PhTz-(COOH)2, respectively. For carboxylate derivative, significant influence of the pH of working solution on the transfer coefficient was mentioned. Based on cyclic voltammetry, quartz crystal microbalance and spectroscopy of electrochemical impedance, deposition of oxidation products was found for PhTz-(NH2)2 and PhTz-(COOH)2 in multiple potential cycling. The carboxylic groups critically influenced electropolymerization of appropriate compound. The formation of bonds typical for electropolymerization was also confirmed by diffusion reflectance IR spectra. The electropolymerization product exerted high electrochemical activity within a broad pH range. Heterogeneous rate constant of the electropolymerized product was found to be 4.5 × 10−1 s−1.