Ring-Shaped Re(I) Multinuclear Complexes with Unique Photofunctional Properties

We synthesized for the first time a series of emissive ring-shaped Re­(I) complexes (Re-rings) with various numbers of Re­(I) units and various lengths of bridge ligands. The photophysical properties of the Re-rings could be varied widely through changes in the size of the central cavity. A smaller central cavity of the Re-rings induced intramolecular π–π interactions between the ligands and consequently caused a stronger emission and a longer lifetime of the excited state. The Re-rings can function as efficient and durable photosensitizers. The combination of a trinuclear Re-ring photosensitizer with fac-[Re­(bpy)­(CO)3(MeCN)]+ (bpy = 2,2′-bipyridine) as a catalyst photocatalyzed CO2 reduction with the highest quantum yield of 82%.