CHIRAL METAL-COMPLEXES WITH LARGE OCTUPOLAR OPTICAL NONLINEARITIES

OPTICALLY nonlinear organic materials show considerable potential for applications in optical signal processing and telecommunications(1,2). Most materials are based on the p-nitroaniline template, in which the optical nonlinearities are intimately associated with quasi-one-dimensional charge transfer. But there are problems associated with this conventional approach, arising from the strongly dipolar nature of the molecules(2). It has recently been recognized(3-5) that two- and three-dimensional stereochemistry offers new possibilities for the design and synthesis of optically nonlinear molecules, in which charge transfer is multidirectional rather than dipolar in character; octupolar nonlinearities have now been demonstrated in several molecular systems(5-7). Tri-substituted ruthenium complexes(6) appear particularly attractive because intense, multidirectional metal-to-ligand charge transfer leads to a significant enhancement of the optical nonlinearity, as quantified by the quadratic hyperpolarizability, beta. Here we show that the choice of ligand can further increase beta to values in excess of 10(-27) e.s.u., comparable to the best dipolar optically nonlinear molecules.