Porphyrin-based 2D Covalent Organic Frameworks For Photocatalytic Redox Reactions

Utilization of solar energy can help people to solve the increasing energy and environmental problems.However,the efficient use of solar energy relies on highly active photocatalysts.Covalent organic frameworks(COFs)is a kind of highly porous and crystalline polymers which can be categorized into two-dimensional(2D)and three-dimensional(3D)COFs.For 2D COFs which are comprised of 2D polymeric layers and stacked in a columnar fashion,could offer a long-range eclipsed alignment of?-chromophores with pre-organized transport of long-lived photoexcited states.These semiconducting properties have made 2D COFs an excellent choice for heterogeneous photocatalysis.More importantly,compared with other amorphous polymers,it is possible for scientists to build structure-activity relationship from a molecular level with the ordered and well-defined structure.In this context,we choose porphyrin as the photo functional unit and constructed a series of porphyrin-based 2D COFs.Through the adjustment of their linker and linkage respectively,we could efficiently tune the photocatalytic properties of the resulted COFs.The specific contents are as follow:1.We have come up with a strategy of designing isostructural COFs with porphyrinic nodes and varying the electronic parameters systematically upon metal coordination.Keeping structural factors the same,we might get straightforward property-activity correlation in isostructural COFs.With this approach,a series of isostructural hydrazone linked 2D porphyrinic COFs(MPor-DETH-COF,M=H2,Co,Ni,Zn)with similar crystallinity and porosity were constructed for photocatalytic hydrogen evolution from water.These COFs exhibited active and tunable photocatalytic activities during the photocatalytic hydrogen evolution experiments.This work demonstrates isostructural 2D COFs can simplify and give new insight to structure-activity-property relationship for fundamental understanding of controlled photocatalytic water splitting properties at molecular label.2.In this part,we have described the synthesis of a novel porphyrin-based sp~2carbon-conjugated COF through Knoevenagel condensation reaction.With various characterizations,our results clearly showed that Por-sp~2c-COF has a permanent porosity and high chemical stability,even under harsh conditions.Por-sp~2c-COF has been used as a metal-free heterogeneous photocatalyst for the visible-light-induced aerobic oxidation of amines to imines,and more importantly,the inherent structure equips Por-sp~2c-COF with several advantages as a photocatalyst(for example,reusability and a high photocatalytic performance)compared to imine-linked Por-COF.Therefore,we believe that 2D sp~2 carbon-linked COFs can provide an interesting platform for developing heterogeneous photocatalytic systems.