The synthesis of tetrahedral bipyridyl metallo-octupoles with large second- and third-order nonlinear optical properties

Two new 4,4'-bis(donor)-6,6'-diphenyl- 2,2'-bipyridine ligands and their corresponding D-2d (Cu-1, Ag-1, Zn-II) octupolar metal complexes were synthesized, and their linear and nonlinear optical properties were investigated. A single crystal X-ray structure was also determined for the bis[4,4'-bis(diethylaminostyryl)-6,6'-diphenyl-bipyridine]copper(1) complex, which revealed a distorded pseudo-tetrahedral geometry. Molecular second-order nonlinear optical properties were determined for the complexes using the Harmonic Light Scatterring technique at 1.91 mu m. These metallo-chromophores display large first hyperpolarizabilities beta(1.91) in the range of 211-340 x 10(-30) esu, which increase with the Lewis acidity of the metal ion. The two-photon absorption properties of the bipyridyl ligands and related complexes were determined using either the two-photon emission method for fluorescent compounds or the open aperture Z-scan technique for non emissive ones. The complexes display red-shifted two-photon absorption bands compared to their metal-ion free chromophores, as well as a large increase of the maximum two-photon absorption cross-sections. (C) 2011 Elsevier Ltd. All rights reserved.