Synthesis and third-order nonlinear optical properties of square planar complexes with donor-metal-acceptor structure

A new series of mixed-ligand (imine and dithiolate) metal complexes with square planar donor-metal-acceptor structure were designed and synthesized for the study of third-order nonlinear optical property. It was found that complexes containing 4,5-dimercapto-1,3-dithiole-2-thionate (dmit) ligand exhibit large third-order optical nonlinearity at 1064 nm. Their second molecular hyperpolarizability (gamma) 1111 is in the order of 10-31 approximately 10-30 esu. The excited-state enhancement of the third-order nonlinear optical susceptibility of complex (Py)2Pt(mnt) (Py equals pyridine; mnt equals maleonitriledithiolate) was observed when the sample was optically pumped by either a picosecond or a nanosecond pump beam at the wavelength of 355 nm. For the picosecond case, the temporal behavior of the enhancement is characterized by a fast and a slow component, which is attributed to population of the first excited state S1 and the second excited state S2, respectively. For the nanosecond case, the enhancement of the nonlinearity is attributed predominantly to the first excited state S1. The molecular hyperpolarizabilities of the first excited state S1 and the second excited state S2, i.e., (gamma) S1 and (gamma) S2, were determined to be 1.9 X 10-31 and 1.0 X 10-30 esu, respectively, which are much larger than that of the ground state ((gamma) g less than 5.6 X 10-33 esu).