Fluorescence Sensors Constructed Based On COFs Porous Materials And Their Applications In Detection

The environmental and food safety are both closely related to human life and health,and they have become common concerns worldwide.Food quality problems caused by spoilage of meat and environmental safety hazards caused by pesticides seriously affect people’s lives,so their effective detection has attracted a great deal of attention from researchers.Fluorescence sensing has triggered great interest as a simple and convenient method due to its fast response,high sensitivity and good selectivity.Compared with conventional fluorescent sensing materials,covalent organic frameworks(COFs)are characterized by high crystallinity,low density,large specific surface area,adjustable pores and devisable structures.Their ordered framework structures effectively avoid fluorophore aggregation-induced fluorescence quenching,and their porous structures have good adsorption properties,providing a large number of active sites,which in turn increases the recognition probability and detection sensitivity of COFs for target analytes,thus COFs show unique advantages in fluorescent sensing and gas detection.Usually,the introduction of luminescent functions and recognition sites in COFs requires ligand design or the modification of chemical groups on the backbone by employing post-modification methods,which demands complex synthetic designs and harsh reaction conditions,hence their widespread applications are limited.With this in mind,this thesis focuses on the development of sensitive,portable and fastresponding fluorescent sensors with applications in food safety and environmental safety related to the detection of gas phase.Using an emulsion-confined assembly strategy,highly emissive fluorescent molecules were selected to react with the COFs monomers(1,3,5-tris(4aminophenyl)benzene(TAPB)and 2,5-dimethoxyterephthaldehyde(DMTP))to prepare fluorescent sensing materials based on COFs,and subsequently fluorescence sensing was achieved using a constructed device for gas detection.The thesis mainly consists of the following three parts.Chapter 1 describes the necessity of meat freshness assessment in food safety and pesticide detection in environmental safety,and introduces relevant background knowledge on porous materials,preparation methods and applications of COFs materials,fluorescent sensing materials,etc.It also highlights the current status of research on the development and application of fluorescence sensing materials of COFs at home and overseas in recent years.On this basis,the research ideas for this dissertation are put forward.In Chapter 2,PDI(?)TAPB-DMTP-COFs fluorescent sensing materials were successfully fabricated by combining the fluorescent molecule perylene diimide(PDI),which has a high quantum yield and can act as an electron acceptor,with COFs monomers(TAPB and DMTP).The morphology,structure and properties of the materials were characterized by TEM,SEM,FTIR,XRD,N2 adsorption-desorption,CLSM,fluorescence spectroscopy,fluorescence lifetime and quantum yield,respectively.The materials gradually changed from solid spheres to hollow spheres as the crystallization time increased.The addition of PDI did not significantly reduce its crystallinity,and the PDI(?)TAPB-DMTP-COFs composites still maintained the high specific surface area and original pore structures of the TAPB-DMTP-COFs materials.The highly sensitive and selective detection of amine vapors such as trimethylamine(TMA)(with a detection limit as low as 1.2 ppb)was achieved using PDI(?)TAPB-DMTP-COF,and the mechanism of TMA detection has been investigated by theoretical calculations and UV diffuse reflection.In addition,the fluorescence sensing materials was applied to real samples and successfully detected gases such as amines released during spoilage of white shrimps.The constructed PDI(?)TAPB-DMTP-COFs fluorescence sensor has potential applications in monitoring the freshness of seafood and other meat products.In Chapter 3,highly luminescent poly(9,9-dioctyfluorene-alt-benzothiadiazole(F8BT)with a sulfur-bonded donor group was combined with COFs monomers(TAPB and DMTP)to construct F8BT(?)TAPB-DMTP-COFs fluorescence sensing materials to enhance the specific recognition of organophosphorus pesticide molecules.It was observed that the as-prepared F8BT(?)TAPB-DMTP-COFs exhibited a unique morphology similar to "tripes",which provided a large number of sites for the detection of analytes.Based on the results of theoretical calculations,it is known that the phosphate ester group of omethoate readily forms a sulfur bond with the benzothiadiazole fluorophore of F8BT,and electrostatic interaction exists between its electronegative amide bond and the electropositive methoxy in F8BT(?)TAPBDMTP-COFs.The resulting binary arrays composed of F8BT aggregates and F8BT(?)TABPDMTP-COFs materials produce opposite fluorescence response signals to omethoate vapor:the fluorescence of the F8BT aggregates was enhanced by omethoate,while an irreversible fluorescence quenching was caused for the F8BT(?)TAPB-DMTP-COFs materials.thereby enabling selective detection of omethoate in organophosphorus pesticides in the gas phase.Meanwhile,upon exposure to vapors of six organophosphorus pesticides(omethoate,dichlorvos,trichlorphon,malathion,phoxim,parathion)and interfering compounds(including water and multiple VOCs)with different concentrations,the binary arrays could differentiate them by the different fluorescence responses.The constructed F8BT(?)TAPB-DMTP-COFs fluorescence sensor materials has meaningful applications in monitoring the safety of organophosphorus pesticides in volatile environments.