Effect of electronic structure of energy transfer in bimetallic Ru(ii)/Os(ii) complexes

Novel monometallic (mu-LL ')Ru, Ru(mu-LL '), homobimetallic Ru(mu-LL ')Ru, and heterodimetallic Ru(mu-LL ')Os and Os(mu-LL ')Ru complexes based on two asymmetrical ligands LL ' (where LL ' = (LL1 ')-L-1, (LL2 ')-L-2) have been synthesized and characterized. Spectroscopic analysis indicates that all complexes exhibit intense spin-allowed ligand-centered (LC) transitions at 288 nm and Ru-based moderate spin-allowed MLCT absorption between 440-450 nm. The Ru(mu-LL ')Os and Os(mu-LL ')Ru dinuclear complexes show Os-based unit absorption in the range of 565-583 nm. The Ru-based units of the complexes present different emission intensities due to differing steric hindrance at the coordination sites of the two bridging ligands. The Os(mu-LL ')Ru dinuclear complexes present weaker emission intensity than their parent monometallic complexes (mu-LL ')Ru. These results indicate that the emission of Os(mu-LL ')Ru dinuclear complexes is quenched by the Os(ii)-based units.