Organometallic complexes for nonlinear optics: Part 20. Syntheses and molecular quadratic hyperpolarizabilities of alkynyl complexes derived from ( E)-4,4′-HCCC 6H 4NNC 6H 4NO 2

Abstract

The syntheses of the alkyne ( E)-4,4′-HCCC 6H 4NNC 6H 4NO 2 ( 1) and alkynyl complexes L n M{( E)-4,4′-CCC 6H 4NNC 6H 4NO 2} [L n M= trans-[RuCl(dppm) 2] ( 2), Ru(PPh 3) 2(η-C 5H 5) ( 3), Au(PPh 3) ( 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CC 6H 4XCHC 6H 4NO 2}( PPh 3 ) (X=CH, N) reveals that complex 4 has a significantly larger quadratic nonlinearity than its ene- or imino-linked analogues.