Structural Design, Synthesis And Application Of Novel Boron-containing Organic Molecules In Catalysis And Sensin

The vigorous development of organic boron chemistry has brought new vitality to many application fields such as biomedicine,new energy and new materials.Boron atoms have unique electron deficient properties.Embedding them into the conjugated system can greatly regulate the electronic structure,orbital energy level,redox properties and photoelectric properties of materials.At present,the core scientific problem facing the field of energy conversion technology and sensing(such as polymer solar cells,metal air cells,gas/ion sensing,etc.)is to develop efficient new material systems,explore and regulate the charge density distribution and orbital energy level structure of the system.Therefore,from two starting points,this paper designed and synthesized non-metallic oxygen reduction electrocatalytic cathode materials based on three/four coordinated boron and applied them in zinc air batteries;Further,the application prospect of tri coordinated boron as gas/ion sensing material is explored by using its electron deficient properties.The main research contents are as follows:(1)Traditional carbon materials enhance the electrocatalytic activity of materials by adding heteroatoms and constructing defects.This method has achieved some results,but it is always difficult to grasp the precise regulation and mechanism of material active sites.The electrocatalyst based on non-metallic organic molecules has adjustable structure and controllable electronic environment of active sites.Therefore,asymmetric molecular design strategy is used to regulate the charge distribution of active sites.By introducing boron nitrogen coordination bond(B←N)into symmetrical molecules to change the local charge environment of active sites,and then introducing thiophene heterocycle on one side,asymmetric structure design is adopted to regulate the charge distribution of molecules,in order to increase the molecular dipole and induce the formation of highly active sites.The results show that asymmetric as-BNT and as-PYT have higher ORR performance than symmetric s-BN,s-PY,s-BN2T and s-PY2T.In particular,as-BNT co regulated by B←N and thiophene heterocycle has an onset and half wave potential of 0.92 V and 0.69 V respectively.DFT theoretical calculation results show that the active site changes from site 12 C atom of symmetrical molecule to site 14 amino N atom of asymmetric molecule,and the asymmetric molecule has uneven charge distribution,efficient electrocatalytic activity and controllable catalytic reaction process dynamics.(2)Starting from fluorene based molecules,we replaced one of the benzene rings with thiophene in order to break its symmetrical molecular structure,and then further introduced boron nitrogen covalent bond(B-N)to construct non-metallic organic boron electrocatalytic materials with higher activity.Because porphyrins have the advantages of strong charge transfer ability and high chemical stability,the conjugated microporous polymer catalyst was obtained by the polymerization of largeπ-conjugated porphyrins with triaryl boron,fluorene and Indeno Thiophene Units by Buchwald Hartwig reaction.The experimental results show that compared with fluorene based(BBAP)and Indeno thiophene(BTAP)based polymer catalytic systems,triarylboroxy polymer catalyst bnap has larger dipole moment,uneven charge distribution,higher ORR catalytic activity,and the starting and half wave potentials are 0.93 V and 0.7 V respectively.The results show that the triarylboroxy catalytic system can significantly improve its electrocatalytic activity.DFT theoretical calculation results show that the additional charge generated by bnap helps to increase the active site and electrocatalytic activity.(3)Due to the strong Lewis acid of triarylboron structure,it can effectively reduce the LUMO/HOMO energy level of the unit.Therefore,this part of work innovatively uses triarylboron structure to construct room temperature ammonia sensing materials.The results show that this type of B-N organic small molecule ammonia sensor shows excellent response/recovery,stability and high efficiency selectivity of ammonia.Its detection limit is as low as 198 ppb,well below the maximum allowable limit for ammonia(25 ppm)during long-term exposure.More importantly,the B-N conjugated polymer sensor developed by us has a response value of up to 3.2×10~4,which is the highest response value of organic ammonia sensor reported at present.The gas sensing mechanism of this kind of material is explored through theoretical calculation.In addition,the polymer treated by fluorine ion has obvious characteristics of sunlight and fluorescence transformation,which provides a new and efficient material system for the development of optical sensors and displays,and has broad application prospects.