Ultrafast Relaxation Dynamics of Osmium−Polypyridine Complexesin Solution

Fabrizio Messina, Olivier Bräm, Mohammad Khaja Nazeeruddin, Majed Chergui, Andrea Cannizzo, Etienne Baranoff, Fabrizio Messina

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27 Citations (Scopus)


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.
Original languageEnglish
Pages (from-to)15958-15966
Number of pages9
Publication statusPublished - 2013

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • General Energy
  • Physical and Theoretical Chemistry
  • Surfaces, Coatings and Films


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