Organometallic complexes for nonlinear optics .8. Syntheses and molecular quadratic hyperpolarizabilities of systematically varied (triphenylphosphine)gold sigma-arylacetylides: X-ray crystal structures of Au(C CR)(PPh(3)) (R=4-C6H4NO2, 4,4'-C6H4C6H4NO2)

The series of complexes Au(C=CR)(PPh(3)) (R=Ph (2), 4-C6H4NO2 (3), 4,4'-C6H4C6H4NO2 (4), (E)-4,4'-C6H4CH=CHC6H4O2 (5), (Z)-4,4'-C6H4CH=CHC6H4NO2 (6), 4,4'-C6H4C=CC6H4NO2 (7), 4,4'-C6H4N=CHC6H4NO2 (8)) have been synthesized by reaction of AuCl(PPh(3)) with the corresponding acetylene and methoxide, and complexes 3-8 have been structurally characterized. The molecular first hyperpolarizabilities for the complexes have been determined by hyper-Rayleigh scattering at 1064 nm. Introduction of the nitro substituent (in proceeding from 2 to 3) leads to a significant increase in nonlinearity. Experimental beta values increase as 3 < 4 < 6 approximate to 7 < 8 < 5 consistent with nonlinearity increasing with (i) chain lengthening, (ii) replacing biphenyl (4) or yne linkage (7) by ene linkage (5), (iii) replacing (Z)-ene stereochemistry (6) with (E)-ene stereochemistry (5), and (iv) ene linkage (5) being more efficient than imino linkage (8). The same trend is observed with two-level-corrected data. A linear correlation of both experimentally-determined and two-level-corrected nonlinearities of the acetylides with precursor acetylenes is observed.