A 3D electropolymerized thin film based on a thiophene-functionalized Ru(ii) complex: electrochemical and photoelectrochemical insights

Abstract

Electropolymerized organic films have been extensively investigated, and are usually one- or two-dimensional structures; three-dimensional (3D) electropolymerized thin films are rare. In this work, a new 3D thiophene-functionalized ruthenium complex of RuL₃(ClO₄)₂·5H₂O {L = 1-phenyl-2-(5-(thiophen-2-yl)thiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthrolin} was synthesized and electro-oxidized to form 3D polymerized poly-RuL₃, which was deposited onto an indium–tin oxide (ITO) electrode surface. The resulting films are studied by UV-Vis absorption spectroscopy, scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and cyclic voltammetry and photoelectrochemical measurements. It was found that the films exhibited surface-controlled Ru^III/II based redox behavior and cathodic photocurrent generation characteristics. Under irradiation of 100 mW cm⁻² white light, a poly(RuL₃)₂ modified ITO electrode biased at −0.4 V vs. SCE in 0.1 M Na₂SO₄ aqueous solution showed a photocurrent density of 1.52 μA cm⁻² in the absence of an added electron acceptor, which was increased to 2.30 μA cm⁻² when oxygen was bubbled into the electrolyte solution, indicating that the films acted as both excellent sensitizers and catalysts for oxygen reduction. This work would guide the construction of modified electrodes with more efficient photoelectric conversion and oxygen sensing and reduction.