Three 1,3-dithiole-2-thioxo-4,5-dithiolato compounds, ethyltriphenylphosphonium bis(2-thioxo-1.3-dithiole-4,5-dithiolato)aurate(III) (TPEPADT), benzyltriethylamine bis(2-thioxo-1.3-dithiole-4,5-dithiolato)aurate(III) (BTEAADT) and benzyltriethylamine bis(2-thioxo-1.3-dithiole-4,5-dithiolato)nickel(III) (BTEANDT), were synthesized and the BTEAADT-doped PMMA thin film (BD film) and TPEPADT-doped PMMA thin film (TD film) with mass fraction of 1% were prepared by spin-coating method. The third-order nonlinear optical properties of thin films and three compounds in acetonitrile solutions were investigated by using the laser [Formula: see text]-scan technique with 20 ps pulses at 1064 nm. The [Formula: see text]-scan spectra revealed that TPEPADT and BTEAADT exhibited self-defocusing effect and negligible nonlinear absorption, but BTEANDT exhibited self-focusing effect and stronger saturable absorption. The reason for this difference was analyzed. The magnitudes of third-order nonlinear refractive indices and third-order nonlinear susceptibility were [Formula: see text], 10[Formula: see text] esu for the solution samples and [Formula: see text], [Formula: see text] esu for thin films. All these results suggest that these materials are promising candidates for application in the nonlinear optical area at infrared band.
