Abstract
The alkynes HC CC6H2-2,6-Et-2-4-C CC6H4-4-NO2 (4) and HC CC6H4-4-C CC6H2-2,6-Et-2-4-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-Et-2-4-C CC6H4-4-NO2)(PPh3) (8), and Au(C CC6H4-4-C CC6H2-2,6-Et-2-4-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 pi-system lengthening and on introduction of electron-releasing substituents on the pi-bridge ring adjacent to the metal centre. The cubic non-linear optical properties of 1,4-{(PCy3)Au(C C)}(2)C6H4 (12) and {(PCy3)Au(C C-4-C6H4C C)}(6)C-6 (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.