Synthesis, in situ spectroelectrochemical, in situ electrocolorimetric and electrocatalytic investigation of brown-manganese phthalocyanines

Abstract

α- and β-substituted tetrakis(6-hydroxyhexylthiol) phthalocyaninato manganese (III) chloride complexes have been prepared via cyclotetramerization. Both complexes have been characterized by elemental analysis, FTIR, MS and UV–Vis spectral data. The voltammetric and in situ spectroelectrochemical studies reveal that both complexes exhibit an oxidation and three reduction processes having reversible, one-electron, and diffusion controlled mass transfer characteristics, which are assigned to Mn IIIPc 2−/Mn IVPc 2−, Mn IIIPc 2−/Mn IIPc 2−, Mn IIPc 2−/Mn IPc 2−, and Mn IPc 2−/Mn IPc 3− couples respectively. The existence of oxygen in solution significantly affects the in situ spectroelectrochemical behavior of the complexes due to the formation of μ-oxo MnPc species. An in situ electrocolorimetric method has been applied to investigate the colors of the electro-generated anionic and cationic forms of the complexes for the first time in this study. The complexes, coated on a glassy carbon electrode potentiostatically, show considerable high electrocatalytic activity to hydrogen evolution reactions in aqueous solution.