Constructing Photosensitizers Based On Electron Donor-Acceptor Structure And Their Application In Photooxidation

Solar energy is clean and renewable energy,which has been widely used in the field of photocatalysis.In solar photochemical conversion,energy transfer and electron transfer play a fundamental role.However,most photosensitizers showed inferior efficiency of electron transfer and energy transfer ability,limiting the development of photocatalysis.Therefore,constructing efficient photosensitizers to control the electron transfer and energy transfer processes is the key to the efficient utilization of solar energy.Herein,covalent organic frameworks（COFs）and graphitic carbon nitride（g-C₃N₄）were used for constructing high-efficiency photosensitizer containing electron-withdrawing electron（D-A）structures,which were applied to the field of photocatalysis,and further explored the influence of D-A structure on electron/energy transfer and photooxidation performance.The D-A structure of COF-Tp Pa with benzene ring as electron-donating group and cycloketone structure as electron-withdrawing group was prepared by solvothermal method using Tp and p-phenylenediamine as raw materials.The ESR and DFT proved that the D-A structure can reduce the energy gap(ΔE_ST)between the singlet-triplet state,promote the ISC process,and realize the energy transfer pathway.Compared with COF-LZU1,a pure electron donating system,COF-Tp Pa showed excellent photocatalytic selectivity in the oxidation of 1,5-DHN and the yield of Juglone was up to 48.93%.CN-Tp photosensitizer in which g-C₃N₄ is regarded as an electron donating component and cycloketone structure is considered to be an electron withdrawing component,was prepared by solvothermal method ESR,time-resolved fluorescence spectroscopy and DFT calculations showed that the electron-withdrawing component can realize the directional transfer of energy in g-C₃N₄ and promote the ISC process.CN-Tp has excellent performance in photocatalytic oxidation of 1,5-DHN,and the yield of Juglone increased from 8.61%to 49.02%.CN/Tp containing electron-donating groups was synthesized by one-step thermal polymerization using Tp and urea as raw materials.The time-resolved fluorescence spectroscopy and DFT calculations proved that the introduction of electron-donating groups successfully promoted the electron transfer process of g-C₃N₄,enabling it to selectively generate O₂^·-.Under mild reaction conditions,CN/Tp has excellent catalytic oxidative styrene epoxidation performance,and the conversion of styrene can reach 45.7%after irradiation for12 h.