Tuning And Nitrofuran Antibiotics Fluorescence Sensing Analysis Based On Luminescent Sp~2c-covalent Organic Framework Materials

Luminescent covalent organic framework（LCOF）is a class of emissive crystalline porous polymer,which has attracted extensive attention due to their structural tunability at the molecular level and excellent photoelectric properties.The excellent and tunable photoelectric properties of LCOFs make them widely used in sensing,information encryption and light-emitting diodes.In this thesis,the emission of LCOFs was tuned by carefully selecting monomers and used for the detection of nitrofuran antibiotics（furazolidone（FZD）,nitrofurantoin（NFT）and nitrofurazone（NF））.The main works in this thesis are as follows:（1）Benzotrithiophene-based sp²c-covalent organic framework for FZD sensing.COF_PDAN-BTTwas synthesized by Cannizzaro reaction of benzo[1,2-b:3,4-b’:5,6-b’’]trithiophene-2,5,8-tricarbaldehyde（BTT）and 1,4-phenyl-enediacetonitrile（PDAN）.The benzotrithiophene unit in the BTT monomer is a typical aggregation-induced quenching（ACQ）fluorophore,and the cyanostilbene unit has certain aggregation-induced emission（AIE）properties.The connection of ACQ fluorophore and AIE fluorophore can fully improve the ACQ degree of LCOFs.Under the excitation of 370 nm,COF_PDAN-BTT exhibits emission at 500 nm.Based on the internal filtering effect between COF_PDAN-BTT and FZD,COF_PDAN-BTTwas used for FZD detection.The I₀/I showed a good linear relationship with the concentration of FZD in the range of 0.034-20μg m L^-1（0.149-88.9μM）,and the detection limit was as low as 0.011μg m L^-1（0.049μM）.Based on the AIE property of COF_PDAN-BTT,a fluorescent test strip was prepared for visual detection of FZD.This work provides a reference for improving the emission of COFs.（2）Multiemissive sp²c-COFs based on side chains tuning for NFT sensing.A series of sp²c-COFs（CPTDD-TPA-CH=CH₂,CPTDD-TPA and CPTDD-TPA-OCH₃）were obtained by the reaction of 2,2’-（5’-（4-（cyanomethyl）-phenyl）-[1,1’:3’,1’’-terphenyl]-4,4’’-diyl）diacetonitrile（CPTDD）with2,5-divinylterephthalaldehyde（TPA-CH=CH₂）,terephthalaldehyde（TPA）and2,5-dimethoxyterephthalaldehyde（TPA-OCH₃）,respectively.The D-π-A structure was formed by using the-CN in the sp²c-COF connection unit as the electron-deficient unit,the benzene ring as the electron-rich unit,and the vinyl group as theπbridge,which usually has the intramolecular charge transfer（ICT）.Through the selection of the side chain on the benzene ring,the regulation of the electron-donating properties of the benzene ring was realized,and the ICT degree of COF was further changed.According to the degree of ICT from weak to strong,the emission color changes from green（CPTDD-TPA-CH=CH₂:511 nm）to orange（CPTDD-TPA:534 nm）to orange-red（CPTDD-TPA-OCH₃:589 nm）.These sp²c-COFs were eventually used to construct an NFT detection array and anti-counterfeiting code applications.This work provides a feasible idea for tuning the emission wavelength of LCOFs.（3）Design and application of three-component sp²c-COFs.Three-component sp²c-COFs(COF-BTDD₁₀,COF-BTDD₃₃ and COF-BTDD₆₇)were synthesized from CPTDD with different ratios of 4,4’-（benzo[c][1,2,5]thiadiazole-4,7-diyl）dibenzaldehyde（BTDD）and[1,1’:4’,1’’-terphenyl]-4,4’’-dicarbaldehyde（TD）.The three-component sp²c-COFs have the fluorescence properties of COF-BTDD₀and COF-BTDD₁₀₀,and have dual emission at 370 nm（blue）and 545 nm（yellow）.Based on its flexible fluorescence properties,COF-BTDD₃₃ can be used in a variety of applications.COF-BTDD₃₃ emits white light under the excitation of 310 nm,which has the potential of white light emitter.Based on the special response of the fluorescence of COF-BTDD₃₃ to NF,a ratiometric fluorescent sensor for NF detection was constructed.Based on the excitation-dependent behavior of COF-BTDD₃₃,a two-dimension code with anti-counterfeiting and information encryption is designed by combining it with COF-BTDD₁₀₀.This work adopts a three-component strategy to design dual-emission LCOFs,which broaden the design ideas of dual-emission LCOFs.