Electron and energy transfer within dyads involving polypyridyl-ruthenium(II) and -osmium(II) centres separated by rigid alicyclic bridges

Rigid alicyclic frameworks (often referred to as molracs, relating to the molecular rack nature of the frame) have been used to vary the separation between organic electron-acceptor (quinone) moieties and chromophoric polypyridylruthenium(II) centres, and between metal centres in Ru-Ru and Ru-Os dinuclear complexes. Photophysical studies have allowed a preliminary insight into the effectiveness of such alicyclic structures in mediating intramolecular photoinduced energy and electron transfer. In the chromophore-spacer-quinone dyads, solvent-dependent quenching of the ruthenium(II) MLCT emission was observed and attributed to electron transfer processes. Distance and stereochemical dependencies of the quenching suggested that through-bond coupling was a factor in these systems. In the heterodinuclear systems, the photo-excited ruthenium(II) chromophore underwent intramolecular energy transfer to the osmium(II) component. A through-space Forster dipole-dipole mechanism could adequately account for the rate of the energy transfer process observed.