Step-scan Fourier transform infrared absorption difference time-resolved spectroscopy ((SFT)-F-2-IR Delta A TRS) was used to study electronic structure in MLCT excited states of [Ru(bpy)(2)(4-COOEt-4’-CH(3)bpy)](2+) and [Ru(bpy)(2)(4,4’-(COOEt)(2)bpy)](2+). Detailed insight on the excited state electronic structure was obtained by comparing the transient AA spectra of the MLCT states in the region of <(nu)over bar>(C=O) of the ester group to those of the one-electron-oxidized and -reduced forms of the complexes. Delta A data were collected with 10 ns time resolution.