Energy Dependence of the Ruthenium(II)-Bipyridine Metal-to-Ligand-Charge-Transfer Excited State Radiative Lifetimes: Effects of 蟺蟺*(bipyridine) Mixing

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• 作者：Ryan A. Thomas ; Chia Nung Tsai ; Shivnath Mazumder ; I Chen Lu ; Richard L. Lord ; H. Bernhard Schlegel ; Yuan Jang Chen ; John F. Endicott
• 刊名：Journal of Physical Chemistry B
• 出版年：2015
• 出版时间：June 18, 2015
• 年：2015
• 卷：119
• 期：24
• 页码：7393-7406
• 全文大小：639K
• ISSN：1520-5207

文摘

The variations in band shape with excited state energy found for the triplet metal to ligand charge transfer (<sup>3sup>MLCT) emission spectra of ruthenium-bipyridine (Ru-bpy) chromophores at 77 K have been postulated to arise from excited state/excited state configurational mixing. This issue is more critically examined through the determination of the excited state energy dependence of the radiative rate constants (k<sub>RADsub>) for these emissions. Experimental values for k<sub>RADsub> were determined relative to known literature references for Ru-bpy complexes. When the lowest energy excited states are metal centered, k<sub>RADsub> can be anomalously small and such complexes have been identified using density functional theory (DFT) modeling. When such complexes are removed from the energy correlation, there is a strong <sup>3sup>MLCT energy-dependent contribution to k<sub>RADsub> in addition to the expected classical energy cubed factor for complexes with excited state energies greater than 10鈥?00 cm<sup>鈥?sup>. This correlates with the DFT calculations which show significant excited state electronic delocalization between a 蟺(bpy-orbital) and a half-filled d蟺*-(Ru<sup>IIIsup>-orbital) for Ru-bpy complexes with <sup>3sup>MLCT excited state energies greater than about 16鈥?00 cm<sup>鈥?sup>. Overall, this work implicates the 鈥渟tealing鈥?of emission bandshapes as well as intensity from the higher energy, strongly allowed bpy-centered singlet 蟺蟺* excited state.