No abstract

Ordered interlayer stacking is intrinsic in twodimensional covalent organic frameworks (2D COFs) and has strong implications on COF's optoelectronic properties. Reversible interlayer sliding, corresponding to shearing of 2D layers along their basal plane, is an appealing dynamic control of both structures and properties, yet it remains unexplored in the 2D COF field. Herein, we demonstrate that the reversible interlayer sliding can be realized in an imine-linked tetrathiafulvalene (TTF)-based COF TTF-DMTA. The solvent treatment induces crystalline phase changes between the proposed staircase-like sql net structure and a slightly slipped eclipsed sql net structure. The solvation-induced crystallinity changes correlate well with reversible spectroscopic and electrical conductivity changes as demonstrated in oriented COF thin films. In contrast, no reversible switching is observed in a related TTF-TA COF, which differs from TTF-DMTA in terms of the absence of methoxy groups on the phenylene linkers. This work represents the first 2D COF example of which eclipsed and staircase-like aggregated states are interchangeably accessed via interlayer sliding, an uncharted structural feature that may enable applications such as chemiresistive sensors.

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. A new monomer 2-aminoterephthalohydrazide (NH2-Th) bearing both amine and hydrazide functionalities is designed to react with benzene-1,3,5-tricarbaldehyde (Bta). Remarkably, the different activity of amine and hydrazide groups toward aldehyde underpin the highly site-selective synthesis of an unprecedented NH2-Th-Bta COF with abundant free amine groups anchored in the well-defined pore channels. Interestingly, NH2-Th-Bta COF exhibits dramatically enhanced iodine uptake capacity (3.58 g g–1) in comparison to that of the nonfunctionalized Th-Bta COF counterpart (0.68 g g–1), and many reported porous adsorbents, despite its low specific surface area. Moreover, NH2-Th-Bta COF possesses exceptional cycling capability and retained high iodine uptake, even after six cycles. This work not only provides a simple and straightforward route for the de novo synthesis of amine-functionalized COFs but also uncovers the great potential of amine-functionalized COFs as adsorbents in the efficient removal of radioiodine and beyond.

Covalent organic frameworks are a new class of crystalline porous materials that have various potential applications. However, utilization of covalent organic frameworks as new stationary phases for gas chromatography separation has been less explored. In this work, a hydrazone‐linked chiral covalent organic framework has been covalently bonded onto the inner surface of fused silica capillary. The fabricated hydrazone‐linked covalent organic framework‐bound capillary column displays a moderate polarity nature and exhibits relatively high resolution performances for separation of linear alkanes and alcohols, as well as aromatic positional isomers including xylene, nitrotoluene, chloronitrobenzene, benzenediol, and naphthol isomers. The present study reveals that the hydrazone‐linked covalent organic framework‐bound capillary column is quite promising for the gas chromatography separation of aromatic positional isomers.

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 welldefined 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. We have further demonstrated that the helical chirality and circular dichroism signal can be facilely inversed by simply adjusting the amount of acetic acid during synthesis. Moreover, by transferring chirality to achiral fluorescent molecular adsorbents, the helical COF nanostructures can effectively induce circularly polarized luminescence with the highest luminescent asymmetric factor (g lum ) up to � 0.01.