文摘
The variations in band shape with excited state energy found for the triplet metal to ligand charge transfer (3MLCT) 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 (kRAD) for these emissions. Experimental values for kRAD were determined relative to known literature references for Ru-bpy complexes. When the lowest energy excited states are metal centered, kRAD 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 3MLCT energy-dependent contribution to kRAD in addition to the expected classical energy cubed factor for complexes with excited state energies greater than 10鈥?00 cm鈥?. This correlates with the DFT calculations which show significant excited state electronic delocalization between a 蟺(bpy-orbital) and a half-filled d蟺*-(RuIII-orbital) for Ru-bpy complexes with 3MLCT excited state energies greater than about 16鈥?00 cm鈥?. 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.