Design And Construction Of Novel Functional Chiral Covalent Organic Frameworks

Covalent organic frameworks（COFs）with high porosity and well-defined tunable structures have emerged as a novel platform for material design and functional explorations.However,the COFs with chiral structures are still in the initial stage of research because of their challenging synthesis and poor stability.Here,a series of chiral covalent organic frameworks（CCOFs）with novel functions were constructed and their structures were well characterized to broaden the application field of CCOFs,especially for the first utilization on transmembrane transport of chiral molecules and asymmetric electrochemical catalysis.This dissertation includes the following contents:1.By three-component imine condensations of a C₃-symmetric trialdehyde,diamines with different lengths,and a diamine with divinyl groups,two vinyl-functionalized two-dimensional（2D）COFs were crystallized.Both multivariant COFs afford straight 1D mesoporous channels formed by AA or AB stacking of layered hexagonal networks.After postmodification with chiralβ-cyclodextrin（β-CD）via thiol-ene click reactions,the COFs were further mixed with polyethersulfone and fabricated into free-standing mixed matrix membranes（MMMs）that could selectively transport amino acids,as revealed by monitoring not only transmembrane ionic current signature but also concentration changes of permeated substrates.Especially,in the system,the AA stacked COF exhibited higher chiral recognition capability toward histidine enantiomers than the AB stacked COF because of its uniform open channels decorated withβ-CD.2.A family of three-component 2D CCOFs was prepared by crystallizing mixtures of a triamine with Mac Millan catalyst,triamines with different steric groups,and a dialdehyde derivative of thieno-[3,2-b]thiophene.The COF stacking modes,which could be synthetically tuned using different three-component condensation systems,greatly affected the chemical stability and crystallinity.With the Mac Millan imidazolidinones homogeneously appended to their channels,the three CCOFs containing an electroactive thiophene moiety could work as efficient chiral catalysts for the electrochemical asymmetricα-arylation of aldehydes.Under mild redox conditions,the CCOFs gave access to products by the cooperation of anodic oxidation and asymmetric organocatalytic protocol for theα-arylation of aldehydes with good yields and up to 97%enantiomeric excesses.3.By Knoevenagel polycondensation of chiral tetrabenzaldehyde of dibinaphthyl-22-crown-6 with 1,4-phenylenediacetonitrile or 4,4′-biphenyl-diacetonitrile,two olefin-linked chiral COFs with 2D layered tetragonal structure were prepared.The in-situ reduction of olefin linkages of the as-prepared CCOFs produced two C-C bond-linked frameworks via crystal-to-crystal transformation,which retained high crystallinity and porosity as well as high chemical stability in both strong acids and bases.Compared to the pristine structures,the reduced CCOFs displayed blueshifted emission with enhanced quantum yields and fluorescence lifetimes,while the parent CCOFs exhibited higher enantioselectivity than the reduced frameworks when frameworks were used as fluorescent sensors to detect chiral amino alcohols.