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

alpha- and beta-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(III)Pc(2-)/Mn(IV)Pc(2-), Mn(III)Pc(2-)/Mn(II)Pc(2-), Mn(II)Pc(2-)/Mn(I)Pc(2-), and Mn(I)Pc(2-)/MnIPc(3-) couples respectively. The existence of oxygen in solution significantly affects the in situ spectroelectrochemical behavior of the complexes due to the formation of mu-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 potentio-statically, show considerable high electrocatalytic activity to hydrogen evolution reactions in aqueous solution. (C) 2009 Elsevier Ltd. All rights reserved.