Substituent Effects on the Electrochemistry and Electronic Coupling of Terphenyl-Bridged Cyclometalated Ruthenium–Amine Conjugated Complexes

[Image: see text] Six terphenyl-bridged cyclometalated ruthenium–amine conjugated complexes 4(PF(6))–9(PF(6)) were synthesized and studied. Three different substituents, methoxy, methyl, and chloro, were used to vary the electronic nature of the amine unit, and two terminal ligands 2,2′:6′,2″-terpyridine (tpy) and trimethyl-4,4′,4″-tricarboxylate-2,2′:6′,2″-terpyridine (Me(3)tctpy) were used to tune the electronic nature of the ruthenium component. All complexes, except 7(PF(6)) with the methoxy substituent and Me(3)tctpy ligand, display two well-separated redox waves in the potential range of +0.5 to +1.1 V versus Ag/AgCl. The regular electrochemical changes of these complexes help to establish the oxidation order of ruthenium and amine and hence of the direction of the electron transfer in odd-electron state. The degree of electronic coupling was estimated by analyzing the donor-to-acceptor charge transfer band in the near-infrared region obtained by oxidative spectroelectrochemical measurements. Electron paramagnetic resonance analyses and density functional theory calculations were performed on the one-electron oxidized forms to obtain information on the spin distribution of these complexes.