The metal-to-ligand charge-transfer (MLCT) excited states of Ru(bpy)(2)(deeb)(PF6)(2), where bpy is 2,2-bipyridine and deeb is 4,4'-(CO2CH2CH3)(2)-2,2'-bipyridine, in dichloromethane were found to be efficiently quenched by iodide at room temperature. The ionic strength dependence of the UV-visible absorption spectra gave evidence for ion pairing. Iodide was found to quench the excited states by static and dynamic mechanisms. Stern-Volmer and Benesi-Hildebrand analysis of the spectral data provided a self-consistent estimate of the iodide-Ru(bpy)(2)(deeb)(2+) adduct in dichloromethane, K = 59700 M-1. Transient absorption studies clearly demonstrated an electron-transfer quenching mechanism with transient formation of I-2(center dot-) in high yield, phi = 0.25 for 355 or 532 nm excitation. For Ru(bpy)(2)(deeb)(PF6)(2) in acetonitrile, similar behavior could be observed at higher iodide concentrations than that required in dichloromethane. The parent Ru(bpy)(3)(2+) compound also ion pairs with iodide in CH2Cl2, and light excitation gave a higher I-2(center dot-) yield, phi = 0.50. X-ray crystallographic, IR, and Raman data gave evidence for interactions between iodide and the coordinated deeb ligand in the solid state.