Identification and characterization of redox sites in supramolecular systems and their relevance for the design of photoactive devices. Ru(II)/C-60-based donor-acceptor dyads

Two dyads consisting of a mononuclear or a dinuclear ruthenium complex covalently linked to a fullerenopyrrolidine through a rigid androstane spacer, have been prepared through azomethine ylide cycloaddition to C-60. Electrochemical and photophysical studies revealed that ground-state electronic interactions between the dinuclear ruthenium chromophore and the fullerenopyrrolidine moiety are small. The redox series observed for the dyads correspond to the superimposition of the reduction patterns of the fullerene core and of the Ru(II)-bipyridine moieties. The results of the electrochemical investigation allow us to rationalize the photophysical behaviour of the two species by identifying the thermodynamically allowed and forbidden routes for the deactivation of the Ru-based metal-to-ligand charge transfer (MLCT) excited state.