Spectroscopic Investigation of a Ruthenium Tris-Diimine Complex Featuring a Bioinspired Alloxazine Ligand

Abstract

Molecular charge accumulating systems that act as both, photosensitizer and electron storage unit, are of interest in the context of multielectron redox processes, e. g. in solar fuel production. To this end, the photophysical properties of RuL1, a ruthenium tris-diimine complex with an alloxazine-based ligand as bioinspired structural motif, were investigated. The study includes absorption, emission, resonance Raman and transient absorption spectroscopy in combination with quantum chemical simulations to determine the light-driven reactivity of the complex. Moreover, spectroelectrochemistry was employed for an in-depth characterization of the optical properties of the reduced complex. Finally, a photolysis experiment using triethanolamine as electron source, in conjunction with redox titrations, demonstrated that visible light irradiation triggers the formation of the doubly-reduced singly-protonated derivative of RuL1, where both redox equivalents are stored on the alloxazine-based ligand.