Excited-State Electronic Structure in Polypyridyl Complexes Containing Unsymmetrical Ligands
- 12 February 1999
- journal article
- research article
- Published by American Chemical Society (ACS) in Inorganic Chemistry
- Vol. 38 (5) , 951-956
- https://doi.org/10.1021/ic981338l
Abstract
Step-scan Fourier transform infrared absorption difference time-resolved (S2FTIR ΔA TRS) and time-resolved resonance Raman (TR3) spectroscopies have been applied to a series of questions related to excited-state structure in the metal-to-ligand charge transfer (MLCT) excited states of [Ru(bpy)2(4,4‘-(CO2Et)2bpy)]2+, [Ru(bpy)2(4-CO2Et-4‘-CH3bpy)]2+, [Ru(bpy)(4,4‘-(CO2Et)2bpy)2]2+, [Ru(4,4‘-(CO2Et)2bpy)3]2+, [Ru(bpy)2(4,4‘-(CONEt2)2bpy)]2+, [Ru(bpy)2(4-CONEt2-4‘-CH3bpy)]2+, and [Ru(4-CONEt2-4‘-CH3bpy)3]2+ (bpy is 2,2‘-bipyridine). These complexes contain bpy ligands which are either symmetrically or unsymmetrically derivatized with electron-withdrawing ester or amide substituents. Analysis of the vibrational data, largely based on the magnitudes of the ν̄(CO) shifts of the amide and ester substituents (Δν̄(CO)), reveals that the ester- or amide-derivatized ligands are the ultimate acceptors and that the excited electron is localized on one acceptor ligand on the nanosecond time scale. In the unsymmetrically substituted acceptor ligands, the excited electron is largely polarized toward the ester- or amide-derivatized pyridine rings. In the MLCT excited states of [Ru(bpy)2(4,4‘-(CO2Et)2bpy)]2+ and [Ru(bpy)2(4,4‘-(CONEt2)2bpy)]2+, Δν̄(CO) is only 60−70% of that observed upon complete ligand reduction due to a strong polarization interaction in the excited state between the dπ5 RuIII core and the excited electron.Keywords
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