It is accepted that the transferred electron in the lowest-excited 3 MLCT states of [Ru(bpy) 2 (bpz)] 2+ is localized on the bpz ligand. We have investigated the luminescence spectrum of the complexes [Ru(bpy) 2 (bpz)] 2+ and [Ru(bpy-d 8 ) 2 (bpz)] 2+ in the [Zn(bpy) 3 ](ClO 4 ) 2 host with great precision, and we are able to unambiguously identify sidelines associated with the spectator bpy/bpy-d 8 ligands over the entire vibrational frequency range. Thus, the mere presence or absence of high-frequency vibrational sidelines in 3 MLCT emission cannot be used to argue for delocalization or localization of the transferred electron. Dominant sidelines reported previously by another group for [Ru(bpy) 2 (bpz)] 2+ in [Zn(bpy) 3 ](ClO 4 ) 2 are due to a contamination of the sample with the chromophore [Os(bpy) 2 (bpy-d 8 )] 2+ .

Luminescence and excitation spectra in the region of the lowest-energy 3 MLCT electronic origins of the specifically deuterated complexes [Ru(bpy) 3-x (bpy-6,6′-d 2 ) x ] 2+ (x ) 0-3) in [Zn(bpy) 3 ](ClO 4 ) 2 and in the neat [Ru(bpy) 3-x (bpy-6,6′-d 2 ) x ](PF 6 ) 2 (x ) 0-3) crystals are reported. The deuteration of the 6,6′ positions represents a minimal variation of the bpy ligand. The x ) 1, 2 systems show independent 3 MLCT transitions to the bpy-6,6′-d 2 and the bpy ligand. Intensity ratios of luminescence involving the bpy-6,6′-d 2 ligand or the bpy ligand in the x ) 1, 2 systems vary as a function of temperature in accord with expectations. Measurements are made providing an estimate of ∼(2.1 ( 0.8) × 10 9 s -1 for the intramolecular 3 MLCT excitation transfer from bpy-6,6′-d 2 to bpy. We also report a simple high-yield method to deuterate the 6,6′ positions of the bpy ligand.