Study On Covalent Organic Framework And Properties Constructed By Triazine Ring And Porphyrin Unit

Porphyrin compounds are widely present in the natural environment.It is the core substance involved in life activities in most organisms.Porphyrin-based covalent organic framework（Porphyrin COFs）using porphyrin as the structural unit is a new type of porous organic polymer,and have the characteristics of regular and orderly structure,rich porosity,and good stability.Therefore,in the past five years,they have received more and more attention in the fields of gas storage,photoelectric catalysis and energy storage.Porphyrin COFs composed of light elements have low density and good crystallinity,in which strong coordination ability（M-N）between nitrogen atoms and metal ions in the porphyrin ring provides the possibility to meet different application requirements.At present,people have developed a variety of porphyrin covalent organic framework construction methods and successfully applied them in various catalytic reactions,but there are still certain limitations.On the one hand,the stability of porphyrin COFs,such as those formed by borateization,is poor,and they are easily oxidized or hydrolyzed in the air,leading to low recycling rates.On the other hand,most of the porphyrin COFs reported in the literature are formed by the expansion of porphyrin molecules in the direction of four meso-sites,but the framework structure extended by porphyrin molecules in the direction of two meso-sites is almost a blank area.Studies have shown that in COFs constructed by phenyl,when C on the benzene ring is substituted by N,it is beneficial to increase the flatness and improve the catalytic activity.Therefore,we first used the Lindsey route to synthesize the organic unit block for the construction of triazine-cyclic porphyrin COF,that is,trans A₂B₂-type porphyrin-5,15-bis（4-p-cyanophenyl）porphyrin[trans-Por-（CN）₂],and then use the triazine ring to connect with the porphyrin molecule to construct a new hyperconjugation type of COF（TA-Por-sp²-COF）without continuous single bonds.In the past,the construction of such hyperconjugated COFs generally used Schiff base reactions.In our design,the triazinyl group formed by self-polymerization from the cyano group in porphyrin unit was developed in two directions.In this way,a highly ordered two-dimensional topological structure is constructed.The hyperconjugation system constructed by porphyrin molecule and triazine ring exhibits high-efficiency photocatalytic performance for the oxidative coupling reaction of benzylamine and its derivatives.Without sacrificial agents and co-catalysts,TA-Por-sp²-COF has a selectivity and conversion rate of more than 99%for the photocatalytic oxidative coupling of benzylamine to imine reaction within 2.5 hours.Finally,we hope that these works can provide references for enriching the types of porphyrin COFs library and their specific applications.