Design,Synthesis And Application Of [3+6] Topological Porous Organic Cages

Porous organic cages(POCs)are one kind of crystalline porous molecular materials.POCs are regarded as a kind of molecules with pore structure constructed by discrete building blocks through covalent bonds,it also represents the unique porous solid assembled by POCs molecules tight packing via supramolecular interactions.Therefore,POCs have both molecular and supramolecular characteristics.They can be used as either molecular hosts or supramolecular porous materials.In addition,POCs have many materials advantages including well-defined molecular structures,good chemical stability,high surface areas,three-dimensional cross channels,easy device processing,and so on.Thus far,POCs have the wide applications in the field of adsorption and separation,heterogeneous catalysis,fluorescence recognition,and it has been increasingly concerned by researchers.In recent years,POCs have evolved into a new class of synthons due to their good solubility and molecular pore structure.Their applications have been further expanded by post-modification synthesis,organic cage-to-framework,and encapsulation of functional nanoparticles strategies.In this doctoral thesis,a series of research work was carried out to exclusively prepare[3+6]topological functional POCs based on the synthesis strategy of dynamic covalent chemistry.Four novel POCs were constructed by the reaction of different functional building blocks with chiral cyclohexanediamine enantiomers.The application research of POCs was extended to the field of heterogeneous visible light catalysis,iodine capture,chiral recognition,and preparation of covalent organic frameworks with POCs as starting materials.Moreover,the correlation between the structures and properties of these obtained materials is also discussed.The specific research contents are listed as follows:(1)Design,Synthesis,and Heterogeneous Photocatalysis of Microporous Porphyrin Organic CageA novel porphyrin tetraaldehyde building block,5,15-di[3’,5’-diformyl(1,1’biphenyl)]porphyrin(H2DBPP),was designed and synthesized.The reactions of H2DBPP with cyclohexanediamine enanotiomers afford a pair of novel porphyrin tubular organic cages,PTC-1(2H).They are characterized by single crystal X-ray diffraction analysis and various spectroscopies.Transient absorption spectroscopy of PTC-1(2H)in toluene reveals much prolonged triplet lifetime(102.20 μs)relative to monomer reference(53.98 μs)due to the rigid POC molecular structure,illustrating the unique photophysical behavior of cagelike photosensitizer.Homogeneous photo-bleach experiments of 1,3-diphenyliso-benzofuran in DMF discloses that PTC-1(2H)had good homogeneous singlet oxygen photocatalytic performance.This is further demonstrated by electron spin-resonance spectroscopy and aerobic photo-oxidation of benzylamine.Furthermore,microporous supramolecular framework of PTC-1(2H)is able to promote the heterogeneous photo-oxidation of various primary amines with conversion efficiency above 99%under visible light irradiation.Such prominent molecular photocatalytic activity,in combination with the porous structure of the cage-based supramolecular framework,renders the solid PTC-1(2H)to exhibit faster reaction rate in heterogeneous visible light catalysis of the aerobic photo-oxidation of primary amines than the reference monomer solid and two well-known porphyrin-containing metal-organic frameworks(MOFs),PCN-222 and PCN-224.These results indicate the great application potentials of porous organic cages in heterogeneous phase.(2)Synthesis,Crystal Structure,and Application of Bithiophene Porous Organic CageThe enantiomeric porous organic cages,(R)/(S)-BTPOC,have been devised and prepared by dynamic covalent chemistry of imine bond formed between bithiophene-based tetraaldehyde and cyclohexanediamine building blocks.These two cage molecules with inner porosity,stable aromatic backbones,and multiple electron-rich building units have been fully characterized by a variety of spectroscopies and single crystal X-ray diffraction studies.The physical adsorption data of carbon dioxide at 196 K confirms that BTPOC has permanent microporosity with Brunauer-Emmett-Teller surface area of 605 m2 g-1,representing one of moderately porous molecular materials.The degassed POC show the selevtive CO2,CH4,and N2 adsorption behaviors.The ideal adsorbed solution theory calculations introduce the CO2/CH4 selectivity coefficients of 9.3 at 273 K and 10.6 at 298 K.The separation selectivity is consistent with those moderate porous molecular crystals.Moreover,BTPOC is able to accommodate a large amount of I2 with a high uptake value of 3.21 g g-1,being superior to almost all the porous molecular crystals reported thus far.This stable material has also excellent recyclability,keeping above 85%capacity in the fourth cycles.Mechanism investigations reveal that the high I2 vapor capture capability associated with the the abundant porosity,π-conjugated structure,and high imine bonds content.The present work shows the great application potentialities of these microporous POCs in the field of I2 vapor capture.(3)Enantioselective Assembly and Recognition of Heterochiral Porous Organic Cages Deduced from Binary Chiral ComponentsChiral recognition and discrimination is not only of significance in biological processes but also a powerful method to fabricate functional supramolecular materials.Herein,a pair of heterochiral porous organic cages,(R,S)-HPOC-1 and(S,R)-HPOC-1,out of four possible enantiomeric products,with mirror stereoisomeric crystal structures were cleanly prepared by condensation occurring in the exclusive combination of cyclohexanediamine and binaphthol-based tetraaldehyde enantiomers.Fluorescence spectroscopy was used to trace the reaction kinetics,revealing that the assembly mechanism is derived from the direct stereoselective assembly of chiral building blocks,which is different from the reported narcissistic or social self-sorting mechanisms in mono-heterochiral organic cage assembly.In addition,circular dichroism spectroscopy studies show that HPOC-1 can chiral recognize carvone,and the possible binding sites of HPOC1 are explored by 1H NMR and theoretical simulations.According to the standard curve drawn by the circular dichroism spectral data,the ee value of the rac-carvone can be determined more accurately.(4)Synthesis,Transformation and Properties of Nitrogen-Rich Porous Organic Cages and Covalent Organic FrameworksReaction of 5,5’-([2,2’-bipyridine]-5,5’-diyl)diisophthalaldehyde(BPDDP)with cyclohexanediamine and[benzidine(BZ)/[2,2’-bipyridine]-5,5’-diamine(BPDA)],respectively,affords a nitrogen-rich porous organic cage BPPOC and two two-dimensional COFs,USTB-1 and USTB-2,under suitable conditions.Interestingly,BPPOC is able to successfully transform into USTB-1 and USTB-2(newly conversed COFs denoted as USTB-1 c and USTB-2c,respectively)upon the imine unit exchange from cyclohexanedimine in cage to BZ and BPDA in COFs.Such a transformation also enables the isolation of analogous COFs(USTB-3c and USTB-4c)on the basis of a previously reported isostructural POC,BTPOC.Due to the poor solubility of BTDDP,the prepared USTB-4 contains incomplete converted tetraaldehydes.In addition to the single crystal and powder X-ray diffraction structural analysis,the newly prepared cage and COFs have been characterized by nuclear magnetic resonance spectroscopy,Fourier transform infrared spectroscopy,scanning electron microscopy,and transmission electron microscopy.BPPOC was revealed to be able to adsorb the iodine vapor with an uptake of 5.64 g g-1,breaking the POCs record of 3.78 g g-1.Nevertheless,the cage-derived COFs exhibit improved iodine vapor adsorption capability in comparison with the directly synthesized counterparts,with the highest uptake of 5.80 g g-1 disclosed for USTB1c.Mechanism investigation unveils the superiority of nitrogen atoms to sulfur atoms for POCs in iodine vapor capture with the assistance of the definite crystal structures.In addition,organic cage compounds can be used as raw materials for a new class of covalent organic frameworks due to their good solubility and purity.This work further bridges two distinct porous organic mate-rials through the chemical transformation and deeply understanding of their structure-performance relationships.