| Two-dimensional(2D)covalent organic frameworks(COFs),as a new network structure completely composed of light elements and linked by strong covalent bonds,show some excellent physical and chemical properties.COFs have many advantages,including designable structure,excellent crystallinity,specific porosity,high specific surface area and good physicochemical stability,which provide a promising platform for gas storage and separation,photocatalysis,electrocatalysis,fluorescent sensors,and energy storage.In recent years,with the rapid development of the preparation and application for COFs materials,a series of COFs with new linkage types and unique properties have been synthesized,and applied in various fields.Although some progress in the research of COFs materials was achieved,the studies of COFs in many fields still remain in their infancy,and many challenges have to be overcome in developing the emerging COFs materials.Therefore,it is urgent to synthesize COFs with new structures and explore their potential applications.To solve the bottleneck problems,this work explores the cutting-edge applications of COFs in some intriguing fields.In addition,new 2D COFs were designed and synthesized and their applications were investigated.The main content and innovative results achieved are as follows.(1)The BTA-NPDA-COF and BTA-BPDA-COF materials were synthesized through Knoevenagel condensation reactions between 2,2’,2"-(benzene-1,3,5-triyl)triacetonitrile(BTA)and naphthalene-2,6-dicarbaldehyde(NPDA)or[1,1’biphenyl]-4,4’-dicarbaldehyde(BPDA).The C=C linked frameworks exhibited excellent solvent stability,excellent crystallinity,and strong photoluminescence,and BTA-NPDA-COF achieved the absolute photoluminescent quantum yield of 21.53%in solid state.The ultrathin porous nanosheets with thicknesses of 2-4 nm were obtained by liquid-phase exfoliation.Fluorescent properties of the films were further studied in various solvents.In addition,the BTA-NPDA-COF nanosheets were firstly employed as the sensor with a high detection limit of 57 ppb for silver ions.(2)The high crystalline PTTA-NPDA and PTTA-ATDA were obtained by Schiff base condensation of 4.4’,4",4’"-(pyrene-1,3,6,8-tetrayl)-tetraaniline(PTTA)and naphthalene-2.6-dicarbaldehyde(NPDA)or anthracene-9,10-dicarbaldehyde(ATDA).Both PTTA-NPDA and PTTA-ATDA showed high surface area and porosity,even the surface area of the PTTA-NPDA can reach up to 1,870 m2 g-1.Our study revealed that PTTA-NPDA exhibited a very fast response and high sensitivity to the presence of gaseous HCl and NH3.PTTA-NPDA showed a high sensitivity toward NH3 vapor with an exposure limit of 8 ppm.We utilized the two COFs as adsorption materials for the removal of organic dyes(methyl orange,methyl blue,rhodamine B,and congo red)in the water.The UV-vis spectra suggested that both COFs have the effect on removing the dyes,which can be attributed to their specific pore sizes and high surface areas in the frameworks.(3)We have prepared 2D porous frameworks of ADA-PTM through the polymerization of anthracene-2,6-diamine(ADA)and[1,1’-biphenyl]-4carboxaldehyde,4’-[bis(2,3,5,6-tetrachloro-4’-formyl-[1,1 ’-biphenyl]-4-yl)methyl]2’,3’,5’,6’-tetrachloro(PTM)by Schiff base reaction.The porous radical frameworks of ADA-PTMR were then synthesized by deprotonation to obtain PTM anions and further oxidation to generate PTM radicals in the prior ADA-PTM skeletons.ESR spectra of the ADA-PTM and ADA-PTMR suggested the existing carbon-center radicals in both porous organic frameworks.Compared with the induced radicals of the ADA-PTM by the conjugated skeletons,there are relatively high spin concentration of carbon-center radicals in the ADA-PTMR structure.At 2 K,the saturation magnetization(Ms)of ADA-PTMR were estimated to be 2.24 emu g-1.Electronic structures and spin density of the ADA-PTMR were investigated using density functional theory(DFT)calculations.The microscopic origin of the magnetic moments in the structure was further explained.For the ADA-PTMR,magnetic states mainly focused on the central methyl carbon atom(αC)(0.32 μB),while partially reside on the ortho-positioned carbon(0.03 μB)and para-positioned carbon atoms(0.04 μB)of the chlorinated benzene rings linked with the aC.The solution synthesis of few-layer ADA-PTM films was carried out via imine condensation of the precursors at the liquid/liquid interface.Moreover,the 2D ADA-PTM films were obtained by means of interface method based on reactions between liquid phases,and they were firstly applied in the organic spin valves(OSVs)device with a typical 5%positive magnetoresistance(MR)at 50 K.(4)PDA-PTM and BTA-PTM were synthesized through Knoevenagel condensation reaction of[1,1 ’-biphenyl]-4-carboxaldehyde,4’-[bis(2,3,5,6tetrachloro-4’-formyl-[1,1-biphenyl]-4-yl)methyl]-2’,3’,5’,6’-tetrachloro(PTM)and 2,2’-(1.4-phenylene)-diacetonitrile(PDA)or 2,2’,2"-(benzene-],3,5triyl)triacetonitrile(BTA)for the first time.Using p-chloranil as an oxidant,the radical frameworks of PDA-PTMR and BTA-PTMR with high spin concentrations were further prepared by the oxidation of PDA-PTM or BTA-PTM frameworks in the alkaline solutions,respectively.ESR spectra of the four COFs revealed the existing radicals in their structures,and the PDA-PTMR even exhibited a spin concentration of 5.45 × 1023 spins mol-1,which is among the highest value in most of reported pure PTM-based porous frameworks.The magnetism of the radical frameworks is further investigated.At 2 K,the saturation paramagnetic moments of the PDA-PTMR and BTA-PTMR reached 2.04 and 2.20 emu g-1,respectively.Electronic structures and spin densities of the radical frameworks were studied through systematic DFT calculations.The microscopic origin of the magnetic moments in the structures was further explained.The magnetic states of PDAPTMR mainly focused on the central methyl carbon atom(αC)(0.34μB),while partially reside on the ortho-positioned carbon(0.03 μB)and para-positioned carbon atoms(0.04 μB)of the chlorinated benzene rings linked with αC.For the BTA-PTMR,the magnetic states mainly focused on the αC(0.31 μB),while partially reside on the ortho-positioned carbon(0.03 μB)and para-positioned carbon atoms(0.04 μB)of the chlorinated benzene rings linked with the αC. |
