Expanded bite angles in tridentate ligands. Improving the photophysical properties in bistridentate RuII polypyridine complexes

Bistridentate metal complexes as photosensitizers are ideal building blocks in the construction of rod-like isomer-free assemblies for intramolecular photoinduced charge separation. Approaches to obtain long-lived luminescent metal-to-ligand charge transfer excited states in bistridentate Ru^II polypyridine complexes via the manipulation of metal-centered state energies are discussed. Following an introduction to general strategies to prolong the excited state lifetimes, more recent work is explored in detail where tridentate ligands with expanded 2,2′:6′,2″-terpyridine cores are utilized. The synthesis of these tridentate ligands and their corresponding Ru^II complexes is covered. Bistridentate Ru^II complexes with microsecond metal-to-ligand charge transfer excited state lifetimes are described, and are used in electron donor–photosensitizer–electron acceptor assemblies for efficient vectorial photoinduced charge separation.