Trinuclear and Tetranuclear Re(I) Rings Connected with Phenylene, Vinylene, and Ethynylene Chains: Synthesis, Photophysics, and Redox Properties

A series of highly luminescent trinuclear and tetranuclear ring-shaped Re(I) complexes wherein the Re units are linked with rigid bidentate phosphine ligands, namely, bis(diphenylphosphino)-p-phenylene, -trans-vinylene, and -ethynylene, were synthesized and fully characterized. Their strong emissive properties and the long lifetimes of their triplet metal-to-ligand charge transfer excited states originate primarily from enhanced, rigidity-induced interligand interactions between the 2,2'-bipyridine (bpy) ligand and the phenyl groups of the phosphine ligands. In addition, another type of interligand interaction was also observed between the bpy ligand and the phosphine-bridging group; this interaction also strongly affected the photophysical and redox properties of the Re-rings.