Ultrafast Relaxation Dynamics of Osmium鈥揚olypyridine Complexes in Solution

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• 作者：Olivier Br盲m ; Fabrizio Messina ; Etienne Baranoff ; Andrea Cannizzo ; Mohammad Khaja Nazeeruddin ; Majed Chergui
• 刊名：The Journal of Physical Chemistry C
• 出版年：2013
• 出版时间：August 8, 2013
• 年：2013
• 卷：117
• 期：31
• 页码：15958-15966
• 全文大小：466K
• 年卷期：v.117,no.31(August 8, 2013)
• ISSN：1932-7455

文摘

We present steady-state absorption and emission spectroscopy and femtosecond broadband photoluminescence up-conversion spectroscopy studies of the electronic relaxation of Os(dmbp)₃ (Os1) and Os(bpy)₂(dpp) (Os2) in ethanol, where dmbp is 4,4鈥?dimethyl-2,2鈥?biypridine, bpy is 2,2鈥?biypridine, and dpp is 2,3-dipyridyl pyrazine. In both cases, the steady-state phosphorescence is due to the lowest ³MLCT state, whose quantum yield we estimate to be 鈮?.0 脳 10^鈥?. For Os1, the steady-state phosphorescence lifetime is 25 ns. In both complexes, the photoluminescence excitation spectra map the absorption spectrum, pointing to an excitation wavelength-independent quantum yield. The ultrafast studies revealed a short-lived (鈮?00 fs) fluorescence, which stems from the lowest singlet metal-to-ligand-charge-transfer (¹MLCT) state and decays by intersystem crossing to the manifold of ³MLCT states. In addition, Os1 exhibits a 50 ps lived emission from an intermediate triplet state at an energy 2000 cm^鈥? above that of the long-lived (25 ns) phosphorescence. In Os2, the ¹MLCT鈥?sup>3MLCT intersystem crossing is faster than that in Os1, and no emission from triplet states is observed other than the lowest one. These observations are attributed to a higher density of states or a smaller energy spacing between them compared with Os1. They highlight the importance of the energetics on the rate of intersystem crossing.