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

A novel series of tetraammineruthenium complex salts trans-[Ru-II (NH3)(4)( L-D)(L-A)][PF6](3) has been investigated by using the hyper-Rayleigh scatte ring technique. These complexes exhibit very large and tunable static first hyper-polarizabilities in the range 10 x 10(-30) to 410 x 10(-30) esu. The se high second-order non-linear optical responses are associated with inten se, visible metal-to-ligand charge-transfer excitations. Further, changing the structure of the acceptor-substituted ligand going from a 4,4 ' -bipyri dinium to a [trans-2-(4-pyridyl)ethenyl]pyridinium conjugated bridge leads to the notable conclusion that the extension of the conjugated bridge in th ese complexes neither significantly alters the metal-to-ligand charge-trans fer energies nor leads to an increase in the static first hyperpolarizabili ties. The non-linear optical responses of these dipolar complexes show a great se nsitivity towards the oxidation state of the metal. It is proven that chemi cal oxidation of the ruthenium is an excellent tool to reversibly switch th e molecular first hyper-polarizabilities. (C) 2001 Elsevier Science B.V. Al l rights reserved.