Synthesis And Properties Of Two-dimensional Covalent Organic Frameworks Based On P-hydroxybiphenyl Tetraldehyde

Covalent organic frameworks（COFs）with high specific surface area,adjustable pore size,modifiable backbone structure,and good stability have shown promising applications in the fields of adsorption and separation,fluorescence sensing,and photoelectric catalysis.The incorporation of functional monomers and easily modifiable functional groups into the frameworks is expected to broaden the scope of applications and enhance the materials’performance.This topic focuses on the synthesis of two-dimensional covalent organic framework materials and the investigation of their optoelectronic properties.The main contents are as follows:（1）Synthesis and multiple fluorescence recognition performance of two-dimensional heteroporous covalent organic framework（TFBD-Py-COF）:The tetra-connected building block 3,3’,5,5’-tetraformyl-4,4’-dihydroxybiphenyl（TFBD）was synthesized using the p-hydroxybiphenyl skeleton and urotropine.Subsequently,a two-dimensional luminescent covalent organic framework,TFBD-Py-COF,was synthesized with triple recognition sites through the aldehyde amine condensation strategy of TFBD with the tetra-connected building block,1,3,6,8-tetra-（p-aminophenyl）pyrene（Py TTA）,which contains a fluorescent moiety.The triple recognition site consists of hydrogen bonds,reversibly protonated N and O-H...N=C chelate units as well as forming recognition traps.Due to hydrogen bonding and hole-limiting domain effect,TFBD-Py-COF exhibits fluorescence sensing ability for nitro compounds,especially for p-nitroaniline with high sensitivity and low detection limit of 4.0×10^-2 ppm.In addition,as a result of the imine N protonation,TFBD-Py-COF showed reversible acid-chromogenic behavior and different fluorescence colors for different p H.The selective fluorescence quenching of TFBD-Py-COF for Fe³⁺was attributed to the coordination of Fe³⁺with O-H...N=C chelating units to form non-luminescent ground state compounds with a detection limit of 0.2μM.This work achieved the first integration of multiple recognition sites into a framework to form a recognition trap strategy,further enriching the diversity of structural site design for materials.（2）Synthesis and proton conduction properties of two-dimensional sulfonic acid-based covalent organic framework（TFBD-TA-COF-SO₃H）:In order to improve the conjugation and electrical conductivity of the material,we chose the structural block 4,4’,4’’,4’’’-[pyrene-1,3,6,8-tetradecyltetrakis（acetylene-2,1-diyl）]tetraphenylamine（TAEPY）containing acetylene group and TFBD to synthesize a two-dimensional covalent organic framework material TFBD-TA-COF with high crystallinity and high specific surface area by aldehyde amine condensation.Based on the"click"reaction,the hydroxyl group in the framework was modified with 1,3-propanesulfonic acid to a sulfonic acid group,thus obtaining TFBD-TA-COF-SO₃H with higher intrinsic proton conductivity.PXRD showed that the framework structure of the TFBD-TA-COF-SO₃H material was not destroyed.Proton conduction experiments show that at 98%RH and 90°C,the proton conductivity of TFBD-TA-COF-SO₃H reached 1.1×10^-3 S/cm,the excellent conductivity is attributed to the introduction of the sulfonic acid moiety which provides additional proton transfer sites.The calculated activation energy for TFBD-TA-COF-SO₃H is 0.55 e V,indicating that the material exhibits a transport（Vehicular）mechanism at 98%RH.This work paves the way for the development of more novel plasmonic conductors.（3）Synthesis and photocatalytic hydrogen peroxide production performance of two-dimensional anthracene-based covalent organic framework（TFBD-DA-COF）:A two-dimensional covalent organic framework material TFBD-DA-COF with homoporous structure was synthesized by aldehyde amine condensation reaction with TFBD and the photosensitive unit 2,6-diaminoanthracene（DA）as the building block monomer.The anthracene group was introduced into TFBD-DA-COF material and applied to the photocatalytic hydrogen peroxide production by utilizing its photosensitivity,we found that the hydrogen peroxide production rate of TFBD-DA-COF was 374μmol g^-1 h^-1 without sacrificial agent,and the hydrogen peroxide production rate reached 505μmol g^-1 h^-1 when ethanol:water=1:9,which improved the performance by 1.35 times.Notably,hydroxyl groups provide hydrogen bonding sites that not only enhance the stability of the framework,but also help the framework to absorb water and increase the rate of photocatalytic hydrogen peroxide production.This chapter opens up new avenues for solar-driven metal-free photocatalysis.