Construction And Photocatalytic Properties Of Mixed-Ligand Metal-Organic Frameworks

As a new kind of multifunctional inorganic-organic hybrid material,metal-organic frameworks have been widely used in visible light photocatalytic organic synthesis due to the presence of organic dye molecules with high density and regular orderly arrangement within frameworks.The purpose of visible light photocatalysis is to maximize the utilization of abundant solar energy.However,many MOFs photocatalysts still have shortcomings such as low solar energy utilization efficiency and single function.By introducing a variety of photoactive ligands into one single framework,the photophysical and photochemical properties of MOFs can be significantly improved,so that the prepared photocatalysts have excellent photocatalytic performance.In this paper,a mixed-ligand construction strategy,was used to introduce two kinds of photoactive ligands into one single framework and coordinate with metal nodes to form porous metal-organic frameworks with various structures,good chemical stability,and excellent photocatalytic performance.Through the synergistic effect of the two kinds of ligands in structure and performance,the obtained mixed-ligand MOFs can realize the efficient transformation of organic reactions under the light source with lower energy.The specific work is as follows:(1)A series of mixed-ligand MOFs(ZJU-56-X)with different two-photon absorption abilities were prepared by replacing partial ligand H4L2 with similar H4L1·OH that had twophoton activity.Under the irradiation of 660 nm LED,ZJU-56-X has good catalytic effect on C-N coupling of benzylamine and C-C coupling of N-phenyl-tetrahydroisoquinoline with nitromethane.The unique two-photon absorption process of this series of photocatalysts enables them to form a high-energy excited state the irradiation of infrared light,which can not only activate the substrate,but also avoid excessive activation of sensitive groups by ultraviolet light source.This study provides a new research idea for how to use low-energy light source to realize photocatalytic organic reactions.(2)By introducing two kinds of photoactive triarylamine(Ar3N)ligands(H3TCA and NPy3)into one single metal-organic framework,the Ar3N fragments can be fixed and optimized into intermediates with special structures to reduce structural relaxation.The well modified redox potentials of Cd-MIX enable the direct generation of aromatic radicals via photoinduced electron transfer process(PET)between Cd-MIX and the substrate,wherein the in situ formed Ar3N·+ could be used as a HAT reagent to abstract a H atom at the most electron-rich site of the C-H nucleophile.The two substrate radicals formed in the above process are directly coupled to complete the whole SET/HAT catalytic cycle,providing a new way for the rapid acquisition of bioactive functional drugs.(3)Based on the above construction system,a mixed-ligand Co-MIX was obtained by introducing H3TCA,NPy3,and redox active Co2+ions into one single metal-organic framework.Co-MIX not only has large open channels,but also has high density of photoactive sites,and has high photocatalytic activity for the photocatalytic hydrogen production coupled with selective oxidation of benzylamine or 1,2,3,4-tetrahydroisoquinoline.A series of control experiments were conducted to verify the advantages of the mixed-ligand MOFs Co-MIX,indicating that the two photoactive ligands have synergistic effects in terms of structure and catalytic performance.