Cyclophanes and [2]catenanes as ligands for transition metal complexes: Synthesis, structure, absorption spectra, and excited state and electrochemical properties

Cyclophane and catenanes that incorporate a 2,2'-bpy group are very good ligands toward Re(I), Ru(II), Ag(I), or Cu(I). Resulting complexes show a combined redox and spectroscopic behavior of their individual active molecular components: PQ²⁺, bpy, M(bpy) and, for the catenanes, the PQ²⁺... dioxonaphthyl unit. Interaction between these components was found to be rather limited, not influencing each other's behavior. However, the electronic coupling with the PQ²⁺ groups is still sufficient to allow for a bpy→PQ²⁺ intramolecular electron transfer, altering thus the dynamics of the M→bpy MLCT excited state (M = Ru, Re). Location of the polyether crown ring in the complexes of the catenane ligands is affected by the coordination to the metal and it also depends on the oxidation state of the PQ(n+) units. These supramolecular species may find use as components of photo- or electro- driven molecular devices.