Surface modification of carbon and metal electrodes with bistable molecular redox switches by click and amide coupling

Abstract

Ruthenium complexes [Ru(R-Ph-tpy)(bpyMeOHpy)] (Ph-tpy = 4′-(4-R-phenyl)-2,2′:6′,2′′-terpyridine, R = NH₂, COOH, CCH, bpyMeOHpy = 1-[6-(2,2′-bipyridyl)]-1-(2-pyridyl)-ethanol) were covalently attached to carbon and metal electrodes by amide and click coupling reactions. Coupling agents were covalently grafted onto the electrodes by electrochemical reduction of p-functionalized diazonium tethers X-Ph-N₂⁺ (X = COOH, NO₂, N₃) followed by electrochemical reduction of the nitro tether. The modification of the electrode surfaces with the Ru complexes results in a hysteretic current–voltage response based on the redox-induced N₆/N₅O linkage isomerism of the ambidentate pyridyl/alkoxy unit in the bpyMeOHpy chelate ligand. The immobilized complexes can be exhaustively addressed electrochemically with scan rates ≤10 000 V s⁻¹ and can switch uniformly with kinetic and thermodynamic parameters similar to the properties of reference complexes in homogeneous solution.