Synthesis And Application Of Porphyrin And Thiophene-Drived Covalent Organic Framework Photosensitizers For Photocatalysis

Photocatalysis is a promising technology which has been applied broadly in many fields such as organic synthesis,organic degradation,photoelectric converting,photocatalytic hydrogen/oxygen evolution and so on.One of the most core issues is to find an efficient and controllable photosensitizer,which can absorb and transform solar energy.However,many photosensitizers have poor capacities of absorption and transformation for solar energy.Herein,porphyrin and thiophene-drived covalent organic framework?COF?were prepared and regarded as effective photosensitizer for photocatalytic oxidation and photodynamics therapy?PDT?.In addition,the mechanism of photocatalytic oxidation and PDT were studies carefully.In order to investigate the property effect of different substituents on porphyin,cyano and methoxy-substitutional porphyrin derivatives were prepared firstly.For a further study the properties of metalloporphyrin,Zn was introduced into the center of porphyrin derivatives.The structure of porphyrin derivatives are confirmed by high-resolution mass spectrometer and NMR.The reaction rate of Zn-porphyrin in the photooxidation reaction of1,5-dihydroxynaphthalene is 1.4 times higher than undoped porphyrin.In addition,singlet oxygen quantum yield of Zn-porphyrin is 1.02 which is higher than porphyrin?0.62?.ESR was used to study the functional mechanism of Zn-4CN-TPP.It turned out that there is an interconversion between Zn⁺and Zn²⁺in the process of photocatalysis.In addition,introducing of cyano-group enhance the electronic transmission ability,resulting in a high PDT performance.Althrough the introduction of metal can improve the catalytic performance,it also increase the cost of raw materials and operating.So,in order to avoid the use of metal,a novel COF-S based on the condensation between amino and aldehyde group were synthetized.It turned out that the prepared COF-S possess good solvent dispersion,well-developed porous structure,large specific surface area and high absorption capacity for visible light.With 2 mg COF-S as photosensitizer,the conversion of1,5-dihydroxynaphthalene was over 80%wthin 2h.In addition,ESR results indicate that this COF-S can effectively generate singlet oxygen?¹O₂?under visible light irradiation.So the COF-S has its own excited triplet state and it can transfer the triplet state energy to other triplet state acceptors.As a non-metal and free heavy atom triplet photosensitizer,its has promising and broad potential applications.In order to study the effect of temperature on COF-S properties,the COF-S were prepared in three different temperatures?100,120,150oC?.Results indicate that COF-S-100 had the best performance for the generation of ¹O₂.In addition,the catalytic conversion 1,5-dihydroxynaphthalene mechanism of COF-S was also studed and discussed.