Redox hysteresis on carbon electrodes covalently modified with a bistable ruthenium complex

Abstract

A ruthenium complex bearing an ambidentate ligand was covalently attached to glassy carbon and carbon fiber electrodes by reduction of an aryldiazonium anchoring group placed on the terpyridine spectator ligand. The diazonium grafting method results in robust attachment and yields high surface concentrations of 2.4 × 10⁻¹⁰ mol cm⁻². The attached complexes can be addressed electrochemically and the electrodes were characterized with scan rates of up to 2000 V s⁻¹. The redox-induced N/O linkage isomerism of the pyridyl/alkoxy ambidentate ligand results in a hysteretic current–voltage response () of the modified electrodes. The immobilization has no deleterious effects on the isomerization reactions of the molecular material that proceed with thermodynamic (2.4 < pK₁ < 3.7 (Ru(III) O → N), −6.0 < pK₂ < −4.8 (Ru(II) O → N)) and kinetic parameters (k_b1 = 2.5 × 10² s⁻¹ (Ru(III) N → O), k_f2 = 2.5 × 10² s⁻¹ (Ru(II) O → N)) comparable to analogous complexes in homogeneous solution.