Design,Synthesis And Performance Of Metal-organic Frameworks Based On AIE Ligands

Metal-organic frameworks（MOFs）are hybrid inorganic-organic crystalline materials composed of metal ions/clusters and organic linkers.MOFs have been widely studied in practical applications such as gas storage and separation,heterogeneous catalysis,chemical sensors,biomedical application due to their controllable structure,regular channels,and large specific surface area.Of the large variety of such materials candidates,luminescent metalorganic frameworks（MOFs）stand out from peers owing to their highly tunable luminescence and structural diversity,but these materials do not effectively regulate fluorescence efficiency or improve quantum yield.Therefore,the selection of appropriate functionalized organic ligands is the key to the realization of multi-functional MOFs.In recent years,researchers have demonstrated that it is a very effective strategy for the tunable of fluorescence energy and enhancement of the quantum yield to restrict intramolecular rotation（RIR）by building the aggregation-induced emission（AIE）fluorophore within the metal-organic frameworks.AIE is a very interesting luminescence phenomenon.Fluorogens with AIE properties（AIEgens）exhibit weak fluorescence in their molecular state while become strongly emissive in the aggregate state because of the restriction of intramolecular motions.This thesis selects an AIEgen fluorophore of high symmetry and a rigid skeleton,tetraphenylpyrazine-based carboxylic acid as functional organic ligands.On the one hand,pyrazine core with two N atoms is propitious to enhance the adsorption ability for CO₂ and the sensing selectivity of analytes,so as to realize the functional material research.On the other hand,the AIE effect of H₄TCPP will probably endow MOFs with interesting luminescent properties.We designed to construct AIEgen fluorophore in metal-organic frameworks to regulate fluorescence energy.Studies have shown that rigidifying AIEgen fluorophores on metal ions in the rigid skeleton of MOFs is an alternative mechanism to restrict the rotation of benzene rings.Through tailoring outer shell electron configurations of cations and the designing of the crystal structure,the fluorescence intensity of the MOFs will be adjusted to complete non-emission,and the purpose of the research on the functionalization of the materials can be realized.This thesis has studied four MOFs based on nitrogen-containing AIEgens fluorophore,and preliminarily explored their fluorescence sensing and photocatalytic reduction CO₂,and the potential value of metal-organic frameworks with such functionalized organic ligands is proposed.The main contents are as follows:1.Two new three-dimensional MOFs,Mg-TCPP and Cd-TCPP based on tetraphenylpyrazine derivatives show a strong blue fluorescence.And their fluorescence and sensing properties were researched.Studies have shown that fluorescence intensity and quantum efficiency of Mg-TCPP and Cd-TCPP are much higher than those of the H₄TCPP ligand itself.We also studied the sensing properties of Mg-TCPP and Cd-TCPP and found that they can be used as sensor materials for the detection of nitro explosives with fluorescent quenching efficiency around 94%,exhibiting good selectivity and sensitivity.At the same time,we have found that arginine has fluorescence enhancement phenomena to Mg-TCPP,which can be used as a potential amino acid sensor.2.Based on the N-ligand derivative and a reasonable change of metal cations,two MOFs of Co-TCPP and Mn-TCPP,are successfully constructed.And their photocatalytic properties for CO₂ reduction were studied.These two crystals are particularly characterized by a connection between the Co/Mn and ligands,which exhibits a better catalytic effect inthe photocatalytic CO₂ reduction.We made a deep research on the catalytic properties of MOFs materials in the photocatalytic CO₂ reduction,and we also speculate on the catalytic mechanism.After 1 h of visible light irradiation,Co-TCPP had a CO yield of 12.76 mmol/g and an H₂ yield of 16.96 mmol/g,while a CO yield of 7.03 mmol/g and an H₂ yield of 3.12mmol/g for Mn-TCPP.And studies found that CO production of Co-TCPP is higher than Mn-TCPP,while the selectivity of Mn-TCPP is superior to Co-TCPP.