Methylthiophenyl- and Methylthiobiphenyl-Substituted A2B CoIIIcorroles: Modulating Electrocatalyzed Hydrogen Evolution Reactions on Surface-Modified Gold Electrodes

Four A2B-type CoIIIcorroles (2a???2d) with electrondonating/withdrawing substituents at the A2 meso-aryl substituents and a 4-(methylthio)phenyl ring at the B position have been synthesized and characterized, along with a series of meso-extended CoIIIcorroles (4a???4c) with 4???-(methylthio)biphenyl moieties. The electronic structures and structure???property relationships of the dyes have been analyzed by comparing their redox and optical properties to trends predicted in density functional theory calculations. Au electrodes surface-modified with 2a???2d and 4a??? 4c are highly efficient catalysts for electrocatalyzed hydrogen evolution reactions, and the electrocatalytic properties can be readily modulated by fine-tuning the electronic structure of the CoIIIcorrole and the distance between the ???Au???S??? bond and CoIII center.