This tutorial review highlights the representative advances in the new synthetic strategies toward covalent organic frameworks.

Covalent organic frameworks (COFs) with reversible redox behaviors are potential electrode materials for lithium‐ion batteries (LIBs). However, the sluggish lithium diffusion kinetics, poor electronic conductivity, low reversible capacities, and poor rate performance for most reported COF materials limit their further application. Herein, a new 2D COF (TFPB‐COF) with six unsaturated benzene rings per repeating unit and ordered mesoporous pores (≈2.1 nm) is designed. A chemical stripping strategy is developed to obtain exfoliated few‐layered COF nanosheets (E‐TFPB‐COF), whose restacking is prevented by the in situ formed MnO2 nanoparticles. Compared with the bulk TFPB‐COF, the exfoliated TFPB‐COF exhibits new active Li‐storage sites associated with conjugated aromatic π electrons by facilitating faster ion/electron kinetics. The E‐TFPB‐COF/MnO2 and E‐TFPB‐COF electrodes exhibit large reversible capacities of 1359 and 968 mAh g−1 after 300 cycles with good high‐rate capability.

2D conductive metal–organic frameworks (2D c‐MOFs) feature promising applications as chemiresistive sensors, electrode materials, electrocatalysts, and electronic devices. However, exploration of the spin‐polarized transport in this emerging materials and development of the relevant spintronics have not yet been implemented. In this work, layer‐by‐layer assembly was applied to fabricate highly crystalline and oriented thin films of a 2D c‐MOF, Cu3(HHTP)2, (HHTP: 2,3,6,7,10,11‐hexahydroxytriphenylene), with tunable thicknesses on the La0.67Sr0.33MnO3 (LSMO) ferromagnetic electrode. The magnetoresistance (MR) of the LSMO/Cu3(HHTP)2/Co organic spin valves (OSVs) reaches up to 25 % at 10 K. The MR can be retained with good film thickness adaptability varied from 30 to 100 nm and also at high temperatures (up to 200 K). This work demonstrates the first potential applications of 2D c‐MOFs in spintronics.

We herein develop a two-in-one molecular design strategy for facile synthesis of 2D imine based covalent organic frameworks (COFs). The integration of two different functional groups (i.e., formyl and amino groups) in one simple pyrene molecule affords a bifunctional building block: 1,6-bis­(4-formylphenyl)-3,8-bis­(4-aminophenyl)­pyrene (BFBAPy). Highly crystalline and porous Py-COFs can be easily prepared by the self-condensation of BFBAPy in various solvents, such as CH2Cl2, CHCl3, tetrahydrofuran, methanol, ethanol, acetonitrile, and dimethylacetamide, etc. The current work, to the best of our knowledge, is a rare case of COF synthesis that exhibits excellent solvent adaptability. Highly crystalline Py-COF thin films have been facilely fabricated on various substrates and exhibit potential applications in hole transporting layers for perovskite solar cells. Furthermore, the versatility of this two-in-one strategy was also verified by two additional examples. The current work dramatically reduces the difficulty of COF synthesis, and such two-in-one strategy is anticipated to be applicable for the synthesis of other COFs constructed by different building blocks and linkages.

Photocatalytic covalent organic frameworks were facilely constructed via the integration of alternative donor–acceptor units into the 2D extended and crystalline scaffolds, which exhibit excellent photodegradation efficiency toward aqueous Cr(vi).

A mesoporous imine COF with densely arranged vinyl groups (COF-V) was inverse-vulcanized with sulfur and used as an efficient cathode material for Li–S batteries.

Two imine-based two-dimensional covalent organic frameworks (2D COFs: TPT-Azine-COF and TPT-TAPB-COF) which exhibit large surface areas and good crystallinity were synthesized from flexible building blocks. Both of them exhibit a prominent adsorption capacity for Rhodamine B (970 mg g–1) and volatile iodine (225 wt %) with good recyclability.

The integration of redox-active sites into the skeleton of open-framework materials is an efficient strategy toward high-performance organic electrodes for energy storage devices. In this work, stepwise introduction of ketone (KT) groups to the skeletons of isostructural two-dimensional (2D) covalent organic frameworks (COFs) was realized by the condensation of 2,4,6-triformylphloroglucinol (Tp, as nodes) with a series of ditopic diamines, which contained none, one, two, and four KT moieties in each linker units, respectively. The precise control of the redox functionalities at the molecular level, combined with regular built-in channels in these KT-Tp COFs endowed them with superior capacitances and excellent rate capabilities for energy storage. In particular, 2KT-Tp COF and 4KT-Tp COF electrodes exhibited high capacitances of 256 and 583 F g −1 at a discharge rate of 0.2 A g −1 , respectively, which outperformed most reported COF-based electrodes. More importantly, exceptional long-term cyclabilities (> 92% capacitance retention) were achieved even after 20,000 cycles at a high current density of 5 A g −1 for these KT-Tp COFs. Our results demonstrated that orthoquinone moieties rendered enhanced performance than the redox COFs with isolated carbonyl groups.