Organometallic complexes for nonlinear optics Part 20.: Syntheses and molecular quadratic hyperpolarizabilities of alkynyl complexes derived from (E)-4,4′-HCCC6H4N=NC6H4NO2

The syntheses of the alkyne (E)-4,4'-HC drop CC6H4N=NC6H4NO2 (1) and alkynyl complexes LnM{(E)-4,4'-C drop CC6H4N=NC6H4NO2} [LnM: = trans-[RuCl(dppm)(2)] (2), Ru(PPh3)(2)(eta-C5H5) (3), Au(PPh3) (4)] are reported. A structural study of 2 reveals E stereochemistry about the azo- linkage. Electrochemical data for the ruthenium complexes reveal that the azo-linkage in complexes 2 and 3 perturbs the metal-centred oxidation potential compared to all other alkynyl complexes of similar composition. Quadratic optical nonlinearities by hyper-Rayleigh scattering (HRS) at 1064 nm are very large for 2 and 3, but resonance-enhanced. Comparison of HRS data for 4 with those of Au{(E)-4,4'-C drop CC6H4X=CHC6H4NO2}(PPh3) (X = CH, N) reveals that complex 4 has a significantly larger quadratic nonlinearity than its ene- or imino-linked analogues. (C) 2000 Elsevier Science S.A. All rights reserved.