Synthesis And Optical Properties Of Titanium Cage Based Porous Materials

Metal organic cages（MOCs）synthesized by metal ligand coordination and self-assembly have attracted extensive attention of researchers and become one of the hotspots in the field of supramolecular chemistry because of their special internal cavities and potential applications in catalysis,molecular recognition and other fields.In recent decades,a lot of research work has been devoted to the structural design and functional modification of MOCs,while there are few further assembly studies based on MOCs.In the previous work,a soluble,stable titanium organic cage（Ti₄L₆;L=embonate）with coordination assembly function was combined,and a series of interesting titanium cage based functional materials were synthesized by using Ti₄L₆as precursor,self-assembly with transition metals(Co²⁺,Zn²⁺and Mn²⁺)or rare earth metal(Ln³⁺)ions and mixed organic auxiliary ligands.Based on the previous work,my research contents will further focus on the multi-level assembly of Ti₄L₆ cage with alkaline earth metal ions or polynuclear metal clusters,and study the third-order nonlinear optical（NLO）properties of the materials.The main research contents are divided into the following three parts:（1）Materials based on titanium organic cages and alkaline earth metal ions:Under solvothermal conditions,Ti₄L₆ cages were used to react with Mg²⁺,Ca²⁺,Ba²⁺ions respectively.By adjusting the type and molar ratio of solvents,four Ti₄L₆ caged compounds with different dimensional structures were successfully constructed.The third-order NLO performance research results show that the 3D Ti₄L₆ cage based frame material with abundantπ···πweak force in the structure has obvious optical limiting effect.（2）Molecular sieve like materials based on titanium organic cages and polynuclear barium units:Based on the previous synthesis,the assembly behavior of Ti₄L₆ cage and Ba²⁺ions with high coordination number was further explored.Similarly,under solvothermal conditions,Ti₄L₆ cage was used to coordinate and assemble with mononuclear or polynuclear Ba units,and three Ti₄L₆ cage based compounds with 3D structure were obtained.Among them,Ti₄L₆ cage based frame material with zeolite like BCT topological network has obvious optical limiting effect.We speculate that the existence of Ba₃ cluster base unit in this structure has a positive contribution to its third-order NLO response.（3）Materials based on titanium organic cages and metal clusters:While introducing organic auxiliary ligands,continue to explore the effect of the combination of Ti₄L₆ cage and other metal clusters on the properties of third-order NLO.In the presence of dicarboxylic acid or tridentate imidazole ligand,Ti₄L₆ cage was used to react with Pb²⁺,Ba²⁺,Zn²⁺ions respectively,and three cage-cluster based3D frame materials were successfully constructed.They have rare cluster units,including twisted cubane type[Pb₄（μ₃-OH）₄]⁴⁺,spherical[Ba₆（μ₂-OH）₈]⁴⁺clusters and[Zn₁₂（μ₃-OH）₄（μ₂-OH）₁₂]⁸⁺clusters withα-Keggin hollow configuration synthesized for the first time.The third-order NLO performance study found that Ti₄L₆ cage has different third-order NLO response behaviors（saturated absorption and reverse saturated absorption）under the synergistic action of different cluster units and organic auxiliary ligands.