Supramolecular Functions Related to the Redox Activity of Transition Metals

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Abstract
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: (1) 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 NiII/NiIII redox couple, is covalently linked to a photoactive fragment: the NiIII state quenches the neighboring fluorophore through an eT mechanism, the NiII state does not. SF: redox switching of a fluorescent signal. (3) a CuII 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− (N3 −,NCO−,NCS−) is bound to CuII; on oxidation, X− moves to the NiIII centre. SF: electrochemically triggered translocation of X− from copper to nickel and vice versa.