The first hyperpolarizability (beta) of [Ru-II-(NH3)(5)(4-AcPhQ)](3+) and of its oxidized form [Ru-III-(NH3)(5)(4-AcPhQ)](4+), previously synthesized and characterized by Coe and co-workers by means of hyper-Rayleigh scattering measurements, has been calculated using time-dependent density functional theory and analyzed resorting to the summation-over-states scheme. Besides confirming a beta contrast of at least one order of magnitude, calculations point out the key role of the metal-to-ligand charge transfer state, which is responsible for the larger beta response of the reduced Ru(II) form. Results also evidence the small contribution to beta of the higher-energy intra-ligand charge transfer excited states, as well as the small changes of the depolarization ratio upon oxidation. (C) 2013 Elsevier B.V. All rights reserved.