Hyper-Rayleigh scattering of trans-tetraammineruthenium(II) complexes

A novel series of tetraammineruthenium complex salts trans-[RuII (NH3)4(LD)(LA)] [PF6]3 has been investigated by using the hyper-Rayleigh scattering technique. These complexes exhibit very large and tunable static first hyper-polarizabilities in the range 10 × 10-30 to 410 × 10-30 esu. These high second-order non-linear optical responses are associated with intense, visible metal-to-ligand charge-transfer excitations. Further, changing the structure of the acceptor-substituted ligand going from a 4,4′-bipyridinium to a [trans-2-(4-pyridyl)ethenyl]pyridinium conjugated bridge leads to the notable conclusion that the extension of the conjugated bridge in these complexes neither significantly alters the metal-to-ligand charge-transfer energies nor leads to an increase in the static first hyperpolarizabilities. The non-linear optical responses of these dipolar complexes show a great sensitivity towards the oxidation state of the metal. It is proven that chemical oxidation of the ruthenium is an excellent tool to reversibly switch the molecular first hyper-polarizabilities. © 2001 Elsevier Science B.V. All rights reserved.