Heteroleptic ruthenium(II) chromophores based on tunable polytopic 4′-(benzamidinato)-2,2′:6′,2′′-terpyridines

A modulable and simple approach towards heteroleptic ruthenium(II) complexes of amidine-based polypyridine ligands is presented. New complexes 1 and 2 ([(terpyridine)Ru(terpyridine-C6H4-C(NR)(NHR))]2+ with R = propyl and R = phenyl derivatives, respectively) were characterized by NMR spectroscopy in solution and by X-ray diffraction, which confirmed the obtention of the (E) stereoisomer alone. Depending on the bulkiness of the R-substituents introduced on the amidine moiety, rotational isomerism around the C–N bond could be observed at r.t. Spectroscopic and electrochemical studies showed that the nature of the R-substituents introduced on the amidine moiety can significantly influence the redox and ground-state acido-basic properties of the complexes, while maintaining their electronic features. This particular tunability of polytopic 4′-(amidinato)-terpyridines offers an interesting perspective for photoactive units in larger multi-functional arrays.