Synthesis and properties of mono- and oligo-nuclear Ru(II) complexes of tridentate ligands: The quest for long-lived excited states at room temperature

Manipulation of metal-to-ligand charge-transfer states of Ru(II) complexes incorporating tridentate ligands has been made possible through careful synthetic designs and has led to enhancement of the photophysical properties of various complexes. Light-harvesting mono- and oligo-nuclear complexes possessing these optimised photophysical properties are excellent candidates for applications in artificial photosynthetic devices. In this review, we summarise the synthetic methods used to improve the photophysical properties of Ru(II) complexes based on tridentate ligands and explore the application of these strategies to oligonuclear complexes incorporating Ru(II) metal centres. Current methods of improving the photophysical properties of Ru(tpy)22+-type complexes (tpy = 2,2′:6′,2″-terpyridine) concentrate on changing the coordination sphere of the metal ion by incorporating different heterocycles into the ligand or by expanding the tpy core.