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 m olecular rack nature of the frame) have been used to vary the separation be tween organic electron-acceptor (quinone) moieties and chromophoric polypyr idylruthenium(II) centres, and between metal centres in Ru-Ru and Ru-Os din uclear complexes. Photophysical studies have allowed a preliminary insight into the effectiveness of such alicyclic structures in mediating intramolec ular photoinduced energy and electron transfer. In the chromophore-spacer-q uinone dyads, solvent-dependent quenching of the ruthenium(II) MLCT emissio n was observed and attributed to electron transfer processes. Distance and stereochemical dependencies of the quenching suggested that through-bond co upling was a factor in these systems. In the heterodinuclear systems, the p hoto-excited ruthenium(II) chromophore underwent intramolecular energy tran sfer to the osmium(II) component. A through-space Forster dipole-dipole mec hanism could adequately account for the rate of the energy transfer process observed.