Synthesis And Photocatalytic Performance Of Boron-containing Porous Organic Polymers

Photocatalytic technology can utilize green and sustainable solar energy for organic conversion,degradation of pollutants and decomposition of hydrogen in aquatic products,so as to effectively alleviate environmental and energy problems.Organic fluorescent dye molecules,especially boron-containing fluorescent dyes,have excellent photophysical properties due to the introduction of boron,such as large fluorescence quantum yield,low band gap and excellent ability to activate oxygen.Therefore,they have attracted much attention in the field of photocatalytic organic synthesis.However,as homogeneous small molecule photocatalyst,boron-containing fluorescent dyes have inherent problems,such as poor stability,easy photobleaching,and poor recycling caused by difficult separation of products and catalysts,which seriously restrict their further application.In this paper,aiming at the problems existing in the traditional boron-containing fluorescent dyes as homogeneous photocatalyst,we tried to use boron-containing fluorescent dyes as the key construction unit.Through the strategy of chemical bond polymerization,the boron-containing fluorescent dyes with photocatalytic activity were anchored in heterogeneous materials in the form of covalent bonds,so as to solve the problems of poor stability and difficult separation from the source.Firstly,two novel conjugated microporous polymers TPA-B-CMP and TPB-B-CMP were prepared by Sonogashira coupling reaction usingβ-diketone boron fluoride dye as the key active center.The chemical structure and photoelectric properties of the polymers were characterized by FT-IR,¹³C NMR CP/MAS,XRD,SEM,solid UV absorption spectroscopy and electrochemical tests.The polymer has medium porosity,strong physical and chemical stability,adjustable band gap and high photoelectric activity.In addition,the band gap,energy level and photocurrent response of the two boron-containing polymers can be easily adjusted by enhancing the donor-acceptor characteristics in the framework.For the first time,TPA-B-CMP and TPB-B-CMP were used as metal-free heterogeneous photocatalysts for oxidative coupling of primary amines and hydroxylation of arylboronic acids.TPA-B-CMP and TPB-B-CMP showed excellent photocatalytic performance,wide substrate adaptability and good cycling performance in both photocatalytic aerobic oxidation reactions.In addition,polymers have the properties of photosensitizers,which can well generate singlet oxygen and superoxide radicals under visible light irradiation.We found that the introduction of effective electron donor-acceptor structure into the polymer could adjust and optimize the optical properties of the photocatalyst.Therefore,we introduced electron-rich carbazole groups as strong electron-donating structures and polymerization sites,and obtained fluorine-and phenyl-coordinated conjugated microporous polymers Cz-BF₂-CMP and Cz-BPh₂-CMP by oxidative coupling reaction catalyzed by cheap and nontoxic Fe Cl₃.The chemical structure and photoelectric properties of the polymer were characterized by FT-IR,¹³C NMR CP/MAS,XRD,SEM,solid ultraviolet absorption spectroscopy and electrochemical tests.The obtained CMP has high specific surface area,strong physical and chemical stability and excellent photoelectric properties.In a green and mild system,Cz-BF₂-CMP has good photocatalytic performance for the oxidation of benzimidazole and sulfide to prepare organic sulfoxide,and has excellent substrate universality and recycling.In contrast,the phenyl-coordinated Cz-BPh₂-CMP has low activity in the photocatalytic reaction,and the superoxide radical test reaction that generates singlet oxygen through reactive oxygen species test also reflects the excellent photosensitivity of Cz-BF₂-CMP.