Electrochemical properties and electrocatalytic activity of novel iron and manganese tribenzopyrazinoporphyrazine complexes

Two novel tribenzopyrazinoporphyrazines with peripheral 4-methoxyphenyl substituents were synthesized to evaluate the effect of the centrally coordinated transition metal cation (4 – Mn3+ or 5 – Fe3+) on their electrochemical properties. The obtained complexes were characterized by UV–vis spectrophotometry, mass spectrometry, and NMR techniques. The electrochemical measurements, involving the CV and DPV voltammetry, were performed and revealed four or six redox processes in researched compounds with one related to the reduction of the central metal cation. The HOMO-LUMO electrochemical band gaps of the synthesized porphyrazines were estimated, and the obtained values were in a good agreement with the optical band gaps calculated from UV–vis. The empirical studies were accompanied by the theoretical ones including linear response time-dependent density function theory (LR TD-DFT) calculations. In both porphyrazines, the HOMOs presented similar shapes. The electrochemical sensing properties of porphyrazines were studied after their deposition on the surface of multi-walled carbon nanotubes (MWCNT). The obtained hybrid materials were embedded on glassy carbon electrodes (GC) using the drop and dry technique. The functionalized electrodes were studied for electrocatalytic reduction of diclofenac sodium salt revealing the superior performance of the GC/MWCNT/5 electrode.