Effect of substituent structure on formation and properties of poly-hydroxyphenyl porphyrin films obtained by superoxide-assisted method

Abstract

In this work, we have studied electrochemical formation of poly-2H-5,10,15,20-tetrakis (meta-hydroxyphenyl)porphyrin (H2T (3-OHPh)P) and poly-2H-5,10,15,20-tetrakis (para-hydroxyphenyl)porphyrin (H2T (4-OHPh)P) films from solutions in dimethyl sulfoxide in potentiostatic and potentiodynamic conditions. We have found the potential regions and determined the stages of poly-porphyrin film formation. It has been shown that the interaction of hydroxyporphyrin with superoxide anion radical (O2•–) makes a significant contribution to the electrochemical deposition of the films. For the first time, it has been proved that it is possible to form poly-H2T (3-OHPh)P and poly-H2T (4-OHPh)P films in potentiostatic conditions in the region of oxygen reduction potentials. We have also studied precursor structure effects on the formation kinetics of such films, their thickness, surface morphology and physico-chemical characteristics. It has been determined that poly-H2T (3-OHPh)P films whose formation is assisted by O2•– have more pronounced passivating properties than poly-H2T (4-OHPh)P ones formed in the same conditions. It has been shown that applying the discussed deposition method leads to the formation of a polymeric structure in which the C–O–C bridges are the main binding motif of the hydroxyphenylporphyrins in the poly-porphyrin film. In this work, we also discuss the mechanism of polyporphyrin film formation. For the poly-H2T (4-OHPh)P film, we have evaluated the specific resistance (1500 Ohm∗cm) and found the quasi-reversible electrochromic effect opening up a lot of opportunities for practical applications of such films.