Design And Synthesis Of Severl Novel Chiral Covalent Organic Frameworks

Due to their inherent porosity and structural periodicity,Covalent organic frameworks?COFs?,especially chiral COFs?CCOFs?recently have been considered as competitive candidates for catalysis,sensor,optoelectronics,and energy storage,attracting widespread attention.However,it remains challenging to construct CCOFs,because of the discrepancy between asymmetry and crystallinity.In this thesis,we report the effective synthesis of a series of COFs with novel structure and unique performances through the bottom-up strategy,taking tetraaryl-1,3-dioxolane-4,5-dimethanols?TADDOL?or salicylaldehydoethylenediamine?salen?as backbones.For the first time,a series of CCOFs based on achiral diamine or triamine linkers were successfully assembled in the presence of chiral catalyst.The performances of these CCOFs in catalysis,separation and circularly polarized luminescence properties were studied.This paper is divided into six chapters:In Chapter 1,the recent development of COFs and the design and synthesis of CCOFs,including their unique structural characteristics and their applications in asymmetric catalysis and separation,together with the problems and the challenges that they are encountering were introduced in details.The overviews of the thesis topic and progress are also discussed and presented.In Chapter 2,two CCOFs were metal-directed synthesized by imine-condensations of enantiopure 1,2-diaminocyclohexane with C₃-symmetric trisalicylaldehydes.The Zn?salen?modules in the CCOFs allowed for installing multivariate metals into the frameworks by postsynthetic metal exchange.The exchanged CCOFs could serve as efficient and recyclable heterogeneous catalysts with maintained high crystallinity and porosity for asymmetric cyanation of aldehydes,Diels-Alder reaction,alkene epoxidation,epoxide ring-opening and related sequential reactions with up to 97%ee.In Chapter 3,eight Zn?salen?-based CCOFs with circularly polarized luminescence?CPL?were prepared by Schiff-base condensation of enantiopure 1,2-diaminocyclohexane with trisalicylaldehydes or tetra?salicylaldehyde?derivatives in the presence of zinc ions.The monomer structure in CCOFs finely tune the pore interior and affinity for circularly polarized luminescence while the maximum of luminescence dissymmetry factor(g_lum)was about 3.7×10^-2.The addition of tetrabutylammonium fluoride to the THF dispersion of CCOFs generated enhanced fluorescence efficiency with maintained g_lum value.In Chapter 4,the first example of 3D CCOFs were synthesized through bottom-up approach by imine condensation of an enantiopure 2-fold symmetric TADDOL-derived tetraaldehyde with a tetrahedral tetra?4-anilyl?methane.After postsynthetic oxidation of imine linkages,the frameworks were transformed into an amide-linked CCOFs with retention of crystallinity and porosity,as well as enhanced chemical stability.Both CCOFs could be used as chiral stationary phases for high performance liquid chromatography to enantioseparate racemic alcohols,sulfoxides,carboxylic acids and esters.The oxidized CCOFs finely optimized the pore interior and showed superior separation performance compared to the pristine frameworks.In Chapter 5,a total of nine 2D CCOFs were crystallized from achiral organic precursors by chiral catalytic induction.CCOF TpTab showed high enantioselectivity toward chiral carbohydrates in fluorescence quenching.After post-synthetic modification of enaminone groups located in chiral channels with Cu?II?ions,CCOF TpTab could also be utilized as a heterogeneous catalyst for the asymmetric organic reaction.In Chapter 6,a briefly conclusion and prospects were given.