Investigations On Third-order Nonlinear Optical And Magnetic Properties Of1,3-Dithiol-2-Thioxo-4,5-Dithiolate Complexes

Organometallics are a series of compounds that possess good application value and prospects in asymmetric catalysis, porous gas adsorption, optics, electronics and magnetism because of their structural diversities and uniqueness. It is one of the most popular topics in current coordination chemistry, material science and bioscience. Among many organic ligands,1,3-dithiol-2-thioxo-4,5-dithiolate (DMIT) possesses a good π-conjugated structure, which greatly facilitates the charge-transferring, electron-conducting and spin-exchanging. Since it is first synthesized in1975, more than300papers have been reported concerning the physical properties of DMIT complexes. Meanwhile, the research fields these reports involve are very extensive, including superconductor, semiconductor, organic molecule magnets and nonlinear optical (NLO) materials. The dissertation aims at synthesizing novel coordination compounds, discovering new physical properties and investigating structure-property relationships, and makes use of DMIT ligand, transition metals and various counter-cations to assembly a series of complexes. The obtained complexes are characterized by spectroscopic analyses, elementary physicochemical tests and X-ray crystallographic studies, with their NLO and magnetic properties particularly and deeply investigated. The main research contents are summarized as follows:1. Design and synthesis of complexes for all-optical switching applications and investigations of third-order NLO propertiesFor realization of all-optical switching devices, the following material requirements have to be met:large third order nonlinear refractive coefficient, fast response time, low absorption and optical transmission loss, high physicochemical stability and thermal stability and processability to form original all-optical switching waveguide device. This dissertation is devoted to the exploration and investigation of third-order NLO materials with high third-order NLO effects and ultra-fast response time. According to material requirements of all-optical switchings, multiple factors influencing the third-order NLO properties of materials were probed and discussed from the molecular structures of the material. A series of complexes based on Hg(dmit)2, Mn(dmit)2and Cd(dmit)2were successfully synthesized by changing counter-cations and central metal ions and using highly delocalized π-electron system. Elementary physicochemical characterizations and third-order NLO studies are performed on these complexes.Z-scan technique was selected for the NLO property studies using a532nm,20ps laser pulse irradiation. A complex of (TBA)2[Cd(dmit)2](TBA=tetrabutylammonium) which could be of potential interests in all-optical switching applications at blue-green light band has been discovered. Micro-crystallization morphology was used to study crystallization tendency in different solvents. A small bulk single-crystal was obtained through solvent evaporation and spontaneous nucleation. Closed-aperture shows a typical central-symmetric profile, which indicates no nonlinear absorption. The magnitude of third-order nonlinear refraction index n2and the second order molecular hyperpolarizability γ are9.409×10-18m2/W and2.774×10-30esu, respectively, both of which are much larger than analogous compounds. The high nonlinear refraction coefficient and extremely low nonlinear absorption coefficient, combined with the fast response time, suggests that this material could be a potential candidate for application as all-optical switching devices.2. Magnetic studies of DMIT complexesTwo Ni-DMIT complexes:(ethyl-triphenylphosphate)[Ni(dmit)2] and (propyl-triphenylphosphate)[Ni(dmit)2] were designed and synthesized using large cations alkyl-triphenylphosphates. Elementary physicochemical characterizations and single crystal X-ray diffractions have been performed on these two salts. Structural analyses indicate strong magnetic interactions within polymers. To investigate the magnetic properties, variable-temperature magnetic measurements and electron paramagnetic resonance were carried out. Both salts exhibit unusual susceptibility-temperature curves, which suggest magnetic-orders in the compounds. Since these curves have no typical shapes of atom-based magnets, molecular magnetism strategies are needed to explain the phenomenon. Based on the crystal structures, spin models were established and the magnetic properties were analyzed. It turns out that a magnetic tetramer is observed in (propyl-triphenylphosphate)[Ni(dmit)2], which is quite rarely seen in DMIT complexes. This is also the first example of Ni(dmit)2tetramers obtained by regular metathetical reactions.In summary, in this dissertation a series of DMIT materials have been prepared through molecular designing and crystal engineering, and their third-order NLO and magnetic properties have also been selectively studied. One compound as a potential candidate in all-optical switching and an anti-ferromagnetic tetramer based on DMIT have been discovered.