Synthesis, Structure And Properties Of Tetraphenylpyrazine-Based Metal-Organic Frameworks

As a class of newly-developed crystalline porous materials,metal-organic framworks(MOFs)have attracted great research interest in the past few decades.The MOF morphologies and dimensions can be well controlled by judiciously selecting the metal clusters and organic bridging ligands,and the pore size,pore geometry,and surface chemistry can be eniginneered through reticular chemistry effectively.The functionalized MOFs have demonstrated a wide range of applications in gas adsorption and separation,chemical sensing,drug delivery,catalysis and many other fields.Luminescence materials with unique characteristics such as aggregation-induced emission(AIE)have drawn extensive attention.AIEgens(Aggregation-induced emission luminogens)with tunable colors and high quantum yields have been frequently reported and used in chemical sensing by means of immobilization on a variety of carriers.MOFs provide a good platform for the loading of AIEgens due to its controllable structure,large surface area,and good stability.The AIE-embedded crystalline porous materials have the advantages of high sensitivity,short response time,high specificity and recyclability,which provide new options for the rapid detection of various pollutant molecules.In this dissertation,we will discuss the design and synthesis,as well as the detection and removal performance of tetraphenylpyrazine-based MOFs.In the first part,we report the synthesis of three pairs of isostructural zirconium and hafnium-based homometallic MOFs with respective scu,sqc,and flu topologies by using the AIE ligand H₄BTTB.As expected,all of them show excellent luminescence properties,and their potential application in the detection of Cr₂O₇^2-has been extensively studied,which could be further correlated with the network topologies.Among them,Zr/Hf-MOF-2 exhibit high adsorption capacity for Cr₂O₇^2-(153 mg g^-1 and 149 mg g^-1,respectively),while Zr/Hf-MOF-3demonstrate exceptional sensitivity in the detection of Cr₂O₇^2-,and the limit of detections are calculated to be 0.013?M and 0.019?M,respectively.These values are comparable to the high-performance MOF materials reported so far.According to the U.S.EPA standard for drinking water(<100 ppb),Zr/Hf-MOF-2 appear to be very promising candidates in removing Cr₂O₇^2-from water.In conjunction with UV-Vis absorption and luminescence emission studies,the quenching mechanism was proposed to be a combined effect of competitive absorption and energy transfer.Overall,we have successfully demonstrated the detection by regulating the network topology.As versatile as MOF structures,the pursuit of suitable topology and matching pore size for targeted guests are of great significance to further improve the host-guest interaction.In the second part,we report a novel microporous MOF(JNU-200)with Co₁₀-cluster and shp topology,the highest-nuclearity Co-cluster in MOFs and the first example of shp topology in Co-based MOFs.The redox potential of Co²⁺/Co³⁺and the nitrogen-containing?-electron-rich BTTB render JNU-200 an ideal platform for iodine capture.Indeed,the adsorption capacity in iodine vapor can reach up to 1.08 g g^–1.Kinetic studies show that JNU-200 can capture most iodine from a hexane solution of 200 ppm within 48 h,corresponding to 99%removal efficiency,far exceeding many reported MOF materials.Single-crystal X-ray diffraction was studied to reveal the structural changes of JNU-200 upon iodine adsorption and the precise location of the trapped iodine.Raman spectra analysis was performed to shed light on the host-guest interactions and the iodine adsorption mechanism.Furthermore,JNU-200 exhibits a rapid and facile detection of histidine(His)with a luminescence turn-on response and a yellowish precipitate through a competitive coordination substitution mechanism.