Regulation Of Structure,Morphology And Fluorescence Properties And Analytical Applications Of Covalent Organic Framework Materials

Covalent organic framework materials（COFs）,an emerging class of porous crystalline polymers,are composed of light elements（such as B,C,Si,N,and O）connected to organic units through strong covalent bonds（such as B-O,C-N,C=N and C=C-N）,which are constructed by dynamic reversible covalent chemistry and can precisely integrate organic units into periodic columnarπarrays and ordered channels.Compared with traditional materials,COFs have some unique properties,such as large surface area,pre-designable pore geometry,excellent crystallinity,inherent adaptability,and high flexibility in structural and functional design,which make COFs show great potential in various applications.Especially,their large surface area and tunable porosity combined with unique optoelectronic properties will make COFs a good platform for analytical applications such as pollutant adsorption and fluorescence sensing.However,according to the current reports,there are still many problems to be solved in the research of COFs materials.This research mainly focuses on the current problems of covalent organic frameworks（COFs）in the fields of morphology,topology control and synthesis of fluorescent COFs.The specific work is as follows:1.TTA-TFP-COF was synthesized by both solvothermal and room temperature solvent methods,with 2,4,6-Tris（4-aminophenyl）-1,3,5-triazine（TTA）and 1,3,5-tris（4-formylphenyl）-benzene（TFP）were used as the raw material.Using different synthesis conditions and adding aniline and benzaldehyde as regulators in the synthesis process can slow down the reaction speed,increase the exchange and metathesis reactions of dynamic reversible reactions,improve the reversibility of the reaction system,and controlled synthesis of TTA-TFP-COFs with different morphologies,such as random particles,regular hollow tubes with controllable diameters and flower shapes.Using the principle that Fe（Ⅲ）and Cr（Ⅲ）ions can coordinate with N,O in TTA-TFP-COF,the structure of TTA-TFP-COF is partially destroyed,and the particles become smaller,resulting in the weakening of its scattering intensity,within a certain concentration range,rapid and highly selective analytical detection of Fe（Ⅲ）and Cr（Ⅲ）ions is achieved.2.Two structurally isomeric BATD-Dma-COF materials were synthesized by using D₂h-symmetric tetraphenylaminobenzene（BATD）and C₂-symmetric 2,5-dimethoxybenzene-1,4-dicarbaldehyde（Dma）for organic monomers.And by using solvothermal and room temperature solvent synthesis methods,controlling different synthesis conditions and introducing regulators to increase the energy difference between different products,the only product with the lowest energy can be synthesized under specific conditions.This method can realize the precise synthesis of structurally heterogeneous and morphologically controllable COFs by changing the experimental conditions.Using the principle that Pb（Ⅱ）ion can coordinate with N,O on the surface of COF materials,the scattering of BATD-Dma-COF K and BATD-Dma-COF R is enhanced,and in a certain concentration range,the degree of scattering enhancement is proportional to the concentration of Pb（Ⅱ）ion.Based on this,a COF nano-scattering probe was established to realize the analysis and detection of metal Pb（Ⅱ）ion in environmental water samples.3.An ETBA-ODA-COF with good crystallinity,solvent stability and yellow-green fluorescence was synthesized by using 4,4’,4’’,4’’’-（ethene-1,1,2,2-tetrayl）tetrabenzaldehyde（ETBA）and flexible 4,4’-diaminodiphenyl ether（ODA）with a chelating site as raw material to modulateπ-πinteractions in the COF structure.It was found experimentally that the fluorescence of ETBA-ODA-COF suspensions dispersed in ethanol could be quenched by Fe（Ⅲ）,Hg（Ⅱ）ions and folic acid small molecules.And it has a good linear relationship with the concentrations of Fe（Ⅲ）,Hg（Ⅱ）ions and folic acid small molecules in a wide concentration range.It is found that the good metal ion selectivity of this COF material is attributed to the unique pore structure and the synergistic effect with the N and O chelation sites on the wall of ETBA-ODA-COF.However,the folic acid small molecules quenched the fluorescence of ETBA-DOA-COF due to their electrostatic interaction.Based on this phenomenon,a fluorescent nanoprobe was established to realize the analysis and detection of metal Fe（Ⅲ）,Hg（Ⅱ）ions and folic acid small molecules.4.TAPB-DMTP-COF was rapidly synthesized by grinding method,which greatly shortened the synthesis time.And by controlling the pH value of the suspension,part of the structure of the COF material is destroyed to reduce theπ-πaccumulation.The problem of fluorescence quenching of COFs caused by ACQ effect is solved,so that the original non-luminescent TAPB-DMTP-COFs emit blue-violet fluorescence.The experiment also found that in the presence of H₂O,the fluorescence maximum emission of TAPB-DMTP-COF was red-shifted,and the degree of red-shift was proportional to the content of H₂O.Within a certain content range,there is a good linear relationship between the degree of red shift and water content.Based on this,a method for the analysis and detection of H₂O content in solvent was established.