Mid-infrared spectrum of [Ru(bpy)(3)](2+)

The first time-resolved infrared difference spectra for metal-to-ligand charge transfer (MLCT) excited states in the fingerprint region from 1400 to 1625 cm(-1) are reported for [Ru(bpy)(3)](2+)* and [Re(bpy)(CO)(3)(4-Etpy)](+)* in CD3CN at 298 K (bpy is 2,2'-bipyridine; 4-Etpy is 4-ethylpyridine). The spectra are assigned by comparison to ground-state spectra and electrochemically generated [RuIII(bpy)(3)](3+) and [Ru-II(bpy(.-))(bpy)(2)](+). The data provide clear evidence for the localized description [Ru-III(bpy(.-))(bpy)(2)](2+)* on the similar to 100 ns time scale. They also give insight into electronic distribution in the excited state based on the magnitudes and directions of the infrared shifts.