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.