Publications by authors named "Xihao Tang"

Aqueous asymmetric catalysis using chiral covalent organic frameworks (COFs) represents a significant advancement but remains to be explored. Herein, we present the first example of aqueous asymmetric catalysis catalyzed by a primary amine-tagged chiral -ADP-TAPB COF. The -ADP-TAPB COF was synthesized by the postsynthetic deprotection of -ADP-TAPB-Boc bearing a protective tert-butoxycarbonyl (Boc) group, which was constructed by a Schiff-base reaction between an alanine-derived chiral building block (-ADP-Boc) and 1,3,5-tris(4-aminophenyl)benzene (TAPB).

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Article Synopsis
  • Researchers have successfully created the first self-standing chiral covalent organic framework (COF) films using a new polymerization-dispersion-filtration method, which was previously challenging in the field.
  • These films are transparent, smooth, and crack-free, exhibiting strong circular polarized luminescence (CPL) and tunability in properties like thickness and roughness.
  • The chiral COF films can also load achiral organic dyes, enhancing their chiral characteristics and achieving a record high luminescence factor, indicating their potential for innovative optical applications.
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The design and synthesis of chiral covalent organic frameworks (COFs) with controlled defect sites are highly desirable but still remain largely unexplored. Herein, we report the synthesis of a defective chiral HD-TAPB-DMTP COF by modifying the chiral monomer helicid (HD) into the framework of an achiral imine-linked TAPB-DMTP COF using a chiral monomer exchange strategy. Upon the introduction of the chiral HD unit, the obtained defective chiral HD-TAPB-DMTP COF not only displays excellent crystallinity, large specific surface area (up to 2338 m/g) and rich accessible chiral functional sites but also exhibits fluorescence emission, rendering it a good candidate for discrimination of amino acids.

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Chiral covalent organic frameworks (COFs) hold considerable promise in the realm of heterogeneous asymmetric catalysis. However, fine-tuning the pore environment to enhance both the activity and stereoselectivity of chiral COFs in such applications remains a formidable challenge. In this study, we have successfully designed and synthesized a series of clover-shaped, hydrazone-linked chiral COFs, each with a varying number of accessible chiral pyrrolidine catalytic sites.

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Tuning the topology of two-dimensional (2D) covalent organic frameworks (COFs) is of paramount scientific interest but remains largely unexplored. Herein, we present a site-selective synthetic strategy that enables the tuning of 2D COF topology by simply adjusting the molar ratio of an amine-functionalized dihydrazide monomer (NH -Ah) and 4,4',4''-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde (Tz). This approach resulted in the formation of two distinct COFs: a clover-like 2D COF with free amine groups (NH -Ah-Tz) and a honeycomb-like COF without amine groups (Ah-Tz).

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The development of chiral covalent organic frameworks (COFs) by postsynthetic modification is challenging due to the common occurrences of racemization and crystallinity decrement under harsh modification conditions. Herein, we employ an effective site-selective synthetic strategy for the fabrication of an amine-functionalized hydrazone-linked COF, NH-Th-Tz COF, by the Schiff-base condensation between aminoterephthalohydrazide (NH-Th) and 4,4',4″-(1,3,5-triazine-2,4,6-triyl)tribenzaldehyde (Tz). The resulting NH-Th-Tz COF with free amine groups on the pore walls provides an appealing platform to install desired chiral moieties through postsynthetic modification.

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Despite significant progress on the design and synthesis of covalent organic frameworks (COFs), precise control over microstructures of such materials remains challenging. Herein, two chiral COFs with well-defined one-handed double-helical nanofibrous morphologies were constructed via an unprecedented template-free method, capitalizing on the diastereoselective formation of aminal linkages. Detailed time-dependent experiments reveal the spontaneous transformation of initial rod-like aggregates into the double-helical microstructures.

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Porous spherical silica-based chiral stationary phases (CSPs) have been commercially used in the field of chiral separation, however, the scope of their application is, to some extent, limited by the instability of silica towards mobile phase containing strong base or acid. As such, developing new matrix-based CSPs is one of the effective strategies to overcome this bottleneck in studies of chiral separation materials. In this work, we have demonstrated that stable spherical covalent organic frameworks (SCOFs) can be utilized as matrixes for the fabrication of new CSPs for the first time.

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Amine-functionalized covalent organic frameworks (COFs) hold great potential in diversified applications. However, the synthesis is dominated by postsynthetic modification, while the de novo synthesis allowing for direct installation of amine groups remains a formidable challenge. Herein, we develop a site-selective synthetic strategy for the facile preparation of amine-functionalized hydrazone-linked COF for the first time.

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With the aid of an azo directing group, Pd-catalyzed ortho-sp(2) C-H bond activation/functionalization of azoarenes with aryl acyl peroxides has been explored. This transformation provides easy access to regioselectively introducing acyloxyl and aryl groups into azoarenes by simply changing the reaction temperature and solvent.

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