Supramolecular functions related to the redox activity of transition metals

The combination of the properties of different subunits in a multicomponent system may give rise to a function which is defined supramolecular. The presence of transition metals in one or more subunits may induce inter-component processes related to their redox and electron transfer (eT) properties, which trigger the supramolecular function (SF). The following examples are considered: (I) a receptor for transition metals is covalently linked to a fluorescent fragment; following recognition, a metal-to-fluorophore eT process quenches the fluorescence. SF: fluorosensing. (2) an azacyclam macrocycle, hosting the Ni-II/Ni-III redox couple, is covalently linked to a photoactive fragment: the Ni-III state quenches the neighboring fluorophore through an eT mechanism, the Ni-II state does not. SF: redox switching of a fluorescent signal. (3) a Cull ion is coordinated by two 2,2`-bipyridine molecules, each bearing a cyclam subunit containing a nickel centre; when nickel is in the divalent state, an inorganic anion X- (N-3(-),NCO-, NCS-) is bound to Cu-II on oxidation, X- moves to the Ni-III centre. SF: electrochemically triggered translocation of X- from copper to nickel and vice versa