Organometallic complexes for nonlinear optics: Part 20. Syntheses and molecular quadratic hyperpolarizabilities of alkynyl complexes derived from (E)-4,4′-HCCC6H4NNC6H4NO2

The syntheses of the alkyne (E)-4,4′-HCCC6H4NNC6H4NO2 (1) and alkynyl complexes LnM{(E)-4,4′-CCC6H4NNC6H4NO2} [LnM=trans-[RuCl(dppm)2] (2), Ru(PPh3)2(η-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CC6H4XCHC6H4NO2}(PPh3) (X=CH, N) reveals that complex 4 has a significantly larger quadratic nonlinearity than its ene- or imino-linked analogues.