Organometallic Complexes for Non-Linear Optics. 51. Second- and Third-Order Non-Linear Optical Properties of Alkynylgold Complexes*

The alkynes HC=CC6H2-2,6-Et2-4-C=CC6H4-4-NO2 (4) and HC=CC6H4-4-C=CC6H2-2,6-Et2-4-C=CC6H4-4-NO2 (6) and gold alkynyl complexes Au{C=CC6H2-2,5-(OEt)2-4-C=CC6H4-4-NO2}(PPh3) (7), Au(C=CC6H2-2,6-Et2-4-C=CC6H4-4-NO2)(PPh3) (8), and Au(C=CC6H4-4-C=CC6H2-2,6-Et2-4-C=CC6H4-4-NO2)(PPh3) (9) have been synthesized. The linear optical properties and quadratic optical non-linearities of 7–9 have been measured, the latter by hyper-Rayleigh scattering at 1064 nm, and compared with data for the previously reported complexes Au(C=CC6H4-4-NO2)(PPh3) (10) and Au(C=CC6H4-4-C=CC6H4-4-NO2)(PPh3) (11). The optical absorption maximum red-shifts and the first hyperpolarizabilities increase on p-system lengthening and on introduction of electron-releasing substituents on the p-bridge ring adjacent to the metal centre. The cubic non-linear optical properties of 1,4-{(PCy3)Au(C=C)}2C6H4 (12) and {(PCy3)Au(C=C-4-C6H4C=C)}6C6 (13) have been assessed by wide spectroscopic range femtosecond Z-scan studies; the maximal values of the imaginary component and the effective two-photon absorption cross-section increase markedly on proceeding from linear complex 12 to 6-fold-symmetric complex 13, an increase that is maintained when data are scaled by relative molecular weight.