The complex [Ru(bpy)(AN)(4)](2+) (bpy = 2,2'-bipyridyl, AN = acetonitrile) has a Ru(II) -> pi*(bpy) MLCT band at 388 nm. Upon irradiation on this absorption band, the compound undergoes total regioselective photocleavage yielding complexes fac-[Ru(bpy)(AN)(3)(H2O)](2+) and trans-[Ru(bpy)(AN)(2)(H2O)(2)](2+) in two consecutive steps with quantum yields of 0.43 and 0.09, respectively. This behavior is a consequence of the stronger sigma-donor ability of the bpy nitrogens that determines the orbital ordering and therefore the nature of the lowest lying (3)d-d state responsible for the photochemistry. The two-step photoreaction, which can be followed by UV-vis and NMR spectra, provides a quantitative path to the preparation of trans-polypyridine species with potentially interesting photochemical properties.