First excited state properties and static hyperpolarizability of ruthenium(II) ammine complexes

First principles calculations were used to study the electronic excitation energies (E), transition dipole moments (u), and difference of dipole moments between ground and excited states (Δμ) for low-lying singlets of the series of ruthenium(II) ammine complexes. Both cases of the gas phase and the acetonitrile solution were investigated in order to explain the discrepancy between the recent experimental and theoretical results and to develop the optimal way of estimation for the first static hyperpolarizability in the framework of a two-state model introduced by Oudar and Chemla. The present calculations reveal that the effect of solvent on the electronic properties of investigated compounds is not only the change of the excitation energy but also the increasing of ground-state molecular polarization and intensification of metal-to-ligand intramolecular charge transfer for electronic excitations. These effects lead to increasing of the values of Δμ and ground-state dipole moment μ_g in solution as compared with the gas-phase ones. The proposed theoretical approach gives good agreement with experiment and allows one to apply it for designing a new perspective nonlinear optical active organometallics.