We present steady-state absorption and emission spectroscopy andfemtosecond broadband photoluminescence up-conversion spectroscopy studies of theelectronic relaxation of Os(dmbp)3 (Os1) and Os(bpy)2(dpp) (Os2) in ethanol,where dmbp is 4,4′-dimethyl-2,2′-biypridine, bpy is 2,2′-biypridine, and dpp is 2,3-dipyridyl pyrazine. In both cases, the steady-state phosphorescence is due to the lowest3MLCT state, whose quantum yield we estimate to be ≤5.0 × 10−3. For Os1, thesteady-state phosphorescence lifetime is 25 ns. In both complexes, the photoluminescenceexcitation spectra map the absorption spectrum, pointing to an excitationwavelength-independent quantum yield. The ultrafast studies revealed a short-lived(≤100 fs) fluorescence, which stems from the lowest singlet metal-to-ligand-charge-transfer (1MLCT) state and decays byintersystem crossing to the manifold of 3MLCT states. In addition, Os1 exhibits a 50 ps lived emission from an intermediatetriplet state at an energy ∼2000 cm−1 above that of the long-lived (25 ns) phosphorescence. In Os2, the 1MLCT−3MLCTintersystem crossing is faster than that in Os1, and no emission from triplet states is observed other than the lowest one. Theseobservations are attributed to a higher density of states or a smaller energy spacing between them compared with Os1. Theyhighlight the importance of the energetics on the rate of intersystem crossing.
|Numero di pagine||9|
|Rivista||JOURNAL OF PHYSICAL CHEMISTRY. C|
|Stato di pubblicazione||Published - 2013|
All Science Journal Classification (ASJC) codes