Construction Of Fluorescence Covalent Organic Frameworks And Its Selective Detection Of Amine Compounds

Fluorescence sensing has been widely studied in the field of chemical and biological analysis because of its high sensitivity,simple operation,and real-time response.The development of new functionalized fluorescent porous framework materials has been one of the focuses of fluorescence sensing research.Covalent organic frameworks(COFs),as one of them,are unique in that the functionalized luminescent segments can be spatially preorganized into the material framework.Owing to reproducing multiple identical binding sites within the extended framework,this ability indicates that when the analyte interacts with identical binding sites,the fluorescence signal can be efficiently transmitted and amplified by the framework to achieve the highest sensitivity response.It is these unique advantages that make COFs have a highly sensitive fluorescence response to various analytes and have become a promising fluorescent sensing material.In this thesis,we synthesized three fluorescent COFs for the detection of amine compounds.The specific work of this thesis is as follows:(1)Cyano-functionalized COF-Py-AN for efficient and selective detection of aromatic aminesIn this chapter,1,3,6,8-tetrakis(4-formyl-phenyl)pyrene and 1,4-phenylenediacetonitrile were synthesized into an alkenyl fluorescent COF(named COFPy-AN)with electron-deficient groups through Knoevenagel condensation reaction,which provides a functional platform for sensing electron-rich aromatic amines.The fluorescence quenching of COF-Py-AN occurs in the presence of aromatic amines such as aniline,which has good selectivity for a variety of aromatic amine molecules,and its detection limit for aniline was only 1.29 μM.Furthermore,COF-Py-AN can distinguish between aromatic and aliphatic amines on a broad spectrum.(2)Rapid and selective detection of p-phenylenediamine by β-ketoamine functionalized TD-COFBuilding on the previous chapter,instead of limiting ourselves to the broad-spectrum detection of aromatic amines using fluorescent COFs,it is now envisioned that a fluorescent COF can be synthesized to achieve specific recognition of a certain class of aromatic amines.In this chapter,1,3,5-triformylphloroglucinol and 2,6-diaminoanthraquinone were synthesized to the fluorescent TD-COF with β-ketoenamine bond through Schiff base condensation,and the electron-deficient anthraquinone in the skeleton structure was used as an electron acceptor to recognize electron-rich aromatic amines.After adding a series of amine compounds into the system,the fluorescence TDCOF only performed specific fluorescence quenching recognition on aromatic amine and p-phenylenediamine,and its detection limit was 0.35 μM.(3)Ligand-driven porphyrins NiP-COF exfoliation and fluorescence sensingFurthermore,most of the current fluorescent COFs exhibit more recognition for the quenching of analytes and less for fluorescence enhancement.Therefore,the construction of functionalized materials with fluorescence-on recognition of analytes is worth being investigated.In this chapter,5,10,15,20-tetrakis(4-aminophenyl)-21 H,23H-porphine(containing Nicoordination),and 2,5-dihydroxy-terephthaladehyde were synthesized to a COF without luminance through Schiff base condensation reaction.The metalloporphyrin in the framework structure was utilized as a site for the recognition of amine compounds.When various amine compounds were added to the system,NiP-COF only showed specific fluorescence enhancement to aniline.When the porphyrin metal active site interacts with the ligand aniline,the π-π stacking between the NiP-COF layers is broken and the aggregation-induced quenching(ACQ)effect between the layers is reduced so that the NiP-COF loses its intrinsic planarity and covalent organic nanosheets(CONs)are obtained,which can achieve efficient luminescence of the material.In addition,these exfoliated CONs can self-assemble into crystalline COF films through layer-by-layer interactions between non-covalent bonds.This work not only lays the foundation for achieving efficient fluorescence sensing of COF on aniline but also provides a new strategy for obtaining thin-layer nanosheets.