Two ruthenium complexes capable of storing multiple electrons on a single ligand – photophysical, photochemical and electrochemical properties of [Ru(phen)2(TAPHAT)]2+ and [Ru(phen)2(TAPHAT)Ru(phen)2]4+

Abstract

The photophysical, photochemical and electrochemical properties of two newly synthesized ruthenium complexes, [Ru(phen)₂(TAPHAT)]²⁺ and [Ru(phen)₂(TAPHAT)Ru(phen)₂]⁴⁺, are reported. We have developed a novel synthetic methodology that involves the metal-free oxidative coupling of diamino compounds to form a desired “pyrazine-type” core. This methodology is employed both on the free diamino ligand as well as on the different ruthenium complexes, therefore illustrating the applicability of this reaction. The TAPHAT ligand, which possesses 7 aromatic rings and 10 nitrogen atoms for 20 carbon atoms, gives rise to ruthenium complexes that can undergo up to three consecutive reductions centered on said ligand, a critical parameter for electron storage applications. A temperature-dependent study has confirmed the presence of a 4^th MLCT state. Excited-state quenching in the presence of guanine or hydroquinone allows to foresee biomedical applications.