Synthesis Of Fluorescence Covalent Organic Polymers Film Via Interfacial Synthesis

Covalent organic polymers(COPs)are ordered porous organic materials which are connected by covalent bonds and polymerized reversibly by thermodynamics.COPs have large specific surface area,uniform pore size distribution,adjustable and precise customized functions.The two-dimensional or three-dimensional COPs film have broad application prospects in gas separation,chemical sensing,catalysis,drug delivery,etc.COPs are usually powder microcrystalline.In recent years,the preparation of high efficiency COPs films based on topological design and polycondensation has become a hotspot in this field.most single-layer or membrane COPs materials are prepared on metal substrate,and the substrate is difficult to remove.Therefore,the preparation of free-standing COPs membrane will effectively improve the application value of the materials.In this paper,two kinds of COPs films were prepared by surfactant assisted gas-liquid and liquid-liquid interface methods.The morphology,structure,crystallinity and fluorescence intensity of the film were characterized by scanning electron microscopy(SEM),atomic force microscopy(AFM),transmission electron microscopy(TEM),X-ray diffraction(XRD),fluorescence spectroscopy,Fourier transform infrared spectroscopy(FT-IR)and Raman spectroscopy.The effects of different reaction conditions on the morphology,crystallinity and fluorescence intensity of the films were investigated.In addition,the application of TFPT-DE in fluorescence sensing is preliminarily explored.The main contents of this paper are as follows:(1)Three 2D COPs films are synthesized via Schiff base reaction between4,4',4'',4'''-(pyrene-1,3,6,8-tetrayl)tetraaniline and linear aldehyde ligands with different side chain group(terephthalaldehyde,2,5-dimethoxybenzene-1,4-dialdehyde and 2,5-dihydroxybenzene-1,4-dialdehyde)by surfactant-monolayer-assisted interfacial synthesis(SMAIS).The SEM results show that surface morphologies of the three films are rod;the AFM results indicates thicknesses of Py-TA film,Py-DM film and Py-DH film are about 210 nm,95?130 nm and 70 nm,respectively.The thicknesses of the above three COPs films can be controlled by adjusting the concentration and volume of ligands in the system.The Py-TA thin film has a dual fluorescence emission effect and high crystallinity due to the introduction of intramolecular hydrogen bonds,which can be potentially used to detect the water content in organic solvents and the polarity of organic solvents.(2)Three fluorescent COPs films were prepared via Schiff base condensation reaction between aldehyde ligands(1,4,6-tris(p-formylphenyl)benzene and1,4,6-tris(4-aldehyde-phenyl)-1,3,5-triazine)and linear hydrazide ligands with different side chain lengths(2,5-dimethoxy-1,4-benzoylhydrazide and2,5-diethoxy-1,4-benzoylhydrazide)by liquid-liquid interface method.Fourier transform infrared spectroscopy(FTIR)and Raman spectroscopy(Raman)indicate that the Schiff base condensation reaction has been successfully carried out;the morphology of COPs films can be observed from the SEM images,TFPB-DH film is agglomerated irregular spheres,TFPB-DE film is intertwined filaments,and TFPT-DE film is coral clusters;TGA result indicates that three COPs films have good stability;fluorescence spectrum analysis indicates that three COPs films have good fluorescence intensity,the emission wavelengths of TFPB-DH,TFPB-DE and TFPT-DE film are 516 nm,489 nm and 478 nm,respectively.Among the three fluorescent COPs films prepared at liquid-liquid interface,the fluorescence of TFPT-DE film is quenched as well as the color of the film changes from light yellow to bright yellow after exposed to HCl gas.In addition,as the contact time between the film and HCl gas increases,the fluorescence intensity of the film gradually decreases.The discolored film will return to light yellow after in an NH₃ atmosphere,which realizes the reversible sensing.The fluorescence intensity of the film remains unchanged basically upon alternating treatment with HCl and NH₃ gases,indicating that the film has high stability and recyclability.