Construction And Research Of Photosensitive Metal-Organic Frameworks:Regulation And Application Of The Electron-Transfer Behavior

Controllable photoinduced electron transfer process is key to the efficient photocatalytic transformation and photobiochemistry process,while the orderly assembly of molecules provides a structural basis for the controllable electron transfer process.Coordination induced molecular self-assembly can accurately control the arrangement,distance and packing mode of molecules,thus this strategy can be used to construct structural carriers which can regulate the photoinduced electron transfer process on spatial scale.Metal-organic frameworks（MOFs）,as a type of crystalline porous materials composed of metal nodes and organic ligands by coordination self-assembly,have programmable structures and modifiable functions.Taking advantage of the crystal engineering strategy,photosensitive units can be orderly introduced into MOFs and thus the photoinduced electron transfer behavior can be regulated in this manner.In this thesis,photoredox ligands based on triphenylamine and phenazine derivatives were chosen as building blocks to construct photosensitive MOFs with redox-inert（such as Mg2+,Zn2+）and redox-active metal ions(such as Cu²⁺),respectively.The electron transfer processes between ligands,metal nodes and guests within MOFs were regulated by thermodynamic and kinetic methods.Then the synthesized photosensitive MOFs were used as the catalysts in photocatalysis and the therapy agents in cancer therapy,respectively.Specific research contents are as follows:1.The driving force of the photoinduced electron transfer process was first regulated from the perspective of thermodynamics,by inserting different numbers of thiophene moieties into triphenylamine skeleton to modify the molecular conjugation degree,the photophysical and electrochemical properties of the ligands were continuously regulated.Then,ligands with suitable photo/electronic properties were selected to construct the photosensitive MOFs with Mg2+ and Zn2+,respectively.The synergistic effect between the Lewis acidic metal nodes and the photosensitive ligands was used to regulate the confined electron transfer processes between photosensitive MOFs and the guests on a spatial scale.And the synthesized MOFs were used as catalysts in the radical addition-oxidation casade reaction of styrenes and the sulfonylationcyclamation casade reaction of α,β-unsaturated olefins,respectively.2.By decorating bulky auxiliaries into a photoreductive triphenylamine-based ligand,a photosensitive MOF with twisted conjugation between the triphenylamine-based ligand and the Cu（Ⅱ）nodes was constructed.The twisted Cu（Ⅱ）-dye conjunction endows the MOF with diodelike photoelectronic behaviors,which inhibits the ineffective electron transfer process from the photocatalytic center to the Cu（Ⅱ）catalytic center,enhances the photoinduced electron transfer from the photocatalytic center to the guest molecules（such as free radical precursors）,and allows the electron retrieve from the Cu（Ⅰ）species generated by reductive elimination to the oxidized photocatalytic center.Thus,the photocatalytic cycle and Cu（Ⅱ）catalytic cycle are synergized within MOFs for the decaboxylative C（sp3）-heteroatom couplings and chlorotrifluoromethylation of olefins.And the well-retained Cu（Ⅱ）sites during photoirradiation and the surrounding chiral microenvironment exhibit unique modulation effects to substrates and intermediates,improving the regioselectivity and stereoselectivity of these reactions.3.A phenazine-based radical cationic ligand H3PDPA·+ was designed and synthesized,by merging this ligand with Cu²⁺,we constructed a radical cationic MOF,named Cu-PDPA·+.The stable oxidized state Cu-PDPA·+ can not interact with O2 to produce reactive oxygen species,thus exhibiting low systemic toxicity to normal tissues.After entering the cancer cells,CuPDPA·+ can be reduced by the overexpressed GSH in the tumor microenvironment,and the generated Cu-PDPA can undergo the photoinduced ligand-to-metal electron transfer process,generating Cu（I）species to convert the overexpressed H2O2 into ·OH for photodynamic therapy.In addition,the weak acidic tumor microenvironment can also induce partial decomposition of this MOF,releasing the redox-active Cu²⁺ ions and ligands for chemodynalic therapy.