Preparation And Third-order Nonlinear Optical Properties Of Azoaniline Complexes

In recent years,organic materials with large nonlinear optical（NLO）characteristics and ultra-fast response have been widely used in the fields of optical switches,optical communication,optical limiters and optical sensors.Among these organic materials,azo Schiff base complexes have become a research hotspot because of their unique optical properties.In this paper,three azo Schiff base ligands were designed and synthesized,and nine Schiff base complexes were formed by coordination reaction with transition metal salts of Co（Ⅱ）,Ni（Ⅱ）,Cu（Ⅱ）and Zn（Ⅱ）respectively.Their molecular structures were characterized,and their thermal stability and nonlinear optical properties were also studied.The research content includes the following three parts:（1）The Schiff base ligand 2-methoxy-6-（（E）-（4-（（E）-phenyldiazenyl）phenyl）imino）methyl)phenol（mpdp）was synthesized using4-aminoazobenzene and 2-hydroxy-3-methoxybenzaldehyde as raw materials,and was combined with transition metal salts coordination reaction to synthesize complexes 1-4.The data of ligands and complexes were characterized and analyzed by ¹H-NMR,MS,IR,UV and fluorescence spectra.Single crystal tests show that complexes 1,3 and 4have similar crystal structures,while complex 2 has a special trinuclear structure.The thermogravimetric analysis showed that complexes 1-4began to decomposed at about 280°C,and had certain thermal stability.Z-scan data also showed that ligand and complex had strong saturation absorption effect,and ligand mpdp and complex 3 had self-defocusing effect.（2）On the basis of ligand mpdp,the influence of electron-donating groups on ligands and complexes was explored.Schiff base ligand2-methoxy-6-（（E）-（2-methyl-4-（（E）-o-tolyldiazenyl）phenyl）imino）methyl)phenol（mtap）was synthesized by introducing two methyl groups on4-aminoazobenzene,and was combined with transition metal salts coordination reaction to synthesize complexes 5-7.The crystal structures of complexes 5 and 6 are similar to those of complex 3,both of which are typical Schiff base coordination modes,while complex 7 is a typical Co₄O₄ configuration.Thermogravimetric analysis shows that complexes5-6 have good thermal stability.The introduction of methyl group on azobenzene has little effect on the nonlinear absorption coefficient of ligand and complex.（3）On the basis of ligand mtap,the influence of electron withdrawing groups was explored.Schiff base ligand2-（（E）-（2-methyl-4-（（E）-o-tolyldiazenyl）phenyl）imino）methyl)-4-nitrophe nol（motp）was synthesized by introducing a nitro group at the para position of salicylaldehyde,and was combined with transition metal salts coordination reaction to synthesize complexes 8-9.Single-crystal tests show that the crystal structure of complex 8 is a tetrahedral configuration,while that of complex 9 is a typical Ni₄O₄ configuration;Z-scan test shows that ligand motp has a larger nonlinear absorption coefficient than ligands mpdp and mtap due to the existence of electron-withdrawing nitro group,and its complex 8 also has the largest nonlinear absorption coefficient among all complexes.Therefore,the introduction of electron-donating and electron-withdrawing groups on the molecular structure will affect the nonlinear optical properties.