Multi-center redox-active system: Amine-amine electronic coupling through a cyclometalated bisruthenium segment

A multicenter redox-active system with a linear N-Ru-Ru-N array, where two distal triarylamine sites are bridged by a cyclometalated bisruthenium segment, has been synthesized and characterized with single-crystal X-ray analysis. This system displays four consecutive and separate anodic redox waves at low potentials, indicating the presence of amine-amine electronic coupling with a distance of 19.16 Å through the cyclometalated bisruthenium segment. In contrast, when a noncyclometalated bisruthenium bridge is used, no amine-amine coupling is present. Upon stepwise oxidation by chemical or electrochemical methods, four-step absorption spectral changes occur in the visible to near-infrared region. In addition, the EPR studies and DFT and TDDFT calculations of the singly oxidized state are presented.