Covalent organic frameworks (CoFs) are a class of important porous materials that allow atomically precise integration of building blocks to achieve pre-designable pore size and geometry; however, pore surface engineering in CoFs remains challenging. Here we introduce pore surface engineering to CoF chemistry, which allows the controlled functionalization of CoF pore walls with organic groups. This functionalization is made possible by the use of azideappended building blocks for the synthesis of CoFs with walls to which a designable content of azide units is anchored. The azide units can then undergo a quantitative click reaction with alkynes to produce pore surfaces with desired groups and preferred densities. The diversity of click reactions performed shows that the protocol is compatible with the development of various specific surfaces in CoFs. Therefore, this methodology constitutes a step in the pore surface engineering of CoFs to realize pre-designed compositions, components and functions.

A series of two-dimensional covalent organic frameworks (2D COFs) locked with intralayer hydrogen-bonding (H-bonding) interactions were synthesized. The H-bonding interaction sites were located on the edge units of the imine-linked tetragonal porphyrin COFs, and the contents of the H-bonding sites in the COFs were synthetically tuned using a three-component condensation system. The intralayer H-bonding interactions suppress the torsion of the edge units and lock the tetragonal sheets in a planar conformation. This planarization enhances the interlayer interactions and triggers extended π-cloud delocalization over the 2D sheets. Upon AA stacking, the resulting COFs with layered 2D sheets amplify these effects and strongly affect the physical properties of the material, including improving their crystallinity, enhancing their porosity, increasing their light-harvesting capability, reducing their band gap, and enhancing their photocatalytic activity toward the generation of singlet oxygen. These remarkable effects on the structure and properties of the material were observed for both freebase and metalloporphyin COFs. These results imply that exploration of supramolecular ensembles would open a new approach to the structural and functional design of COFs.

Organic batteries free of toxic metal species could lead to a new generation of consumer energy storage devices that are safe and environmentally benign. However, the conventional organic electrodes remain problematic because of their structural instability, slow ion-diffusion dynamics, and poor electrical conductivity. Here, we report on the development of a redox-active, crystalline, mesoporous covalent organic framework (COF) on carbon nanotubes for use as electrodes; the electrode stability is enhanced by the covalent network, the ion transport is facilitated by the open meso-channels, and the electron conductivity is boosted by the carbon nanotube wires. These effects work synergistically for the storage of energy and provide lithium-ion batteries with high efficiency, robust cycle stability, and high rate capability. Our results suggest that redox-active COFs on conducting carbons could serve as a unique platform for energy storage and may facilitate the design of new organic electrodes for high-performance and environmentally benign battery devices.

We report a synthetic strategy for construction of the first example of organocatalytic covalent organic frameworks via pore surface engineering. The COF catalyst combines a number of striking features, including enhanced activity, broad applicability, good recyclability, and high capability, to perform catalytic transformation under continuous flow conditions.

We report the assembly of graphene oxide (G-O) building blocks into a vertical and radially aligned structure by a bidirectional freeze-casting approach. The crystallization of water to ice assembles the G-O sheets into a structure, a G-O aerogel whose local structure mimics turbine blades. The centimeter-scale radiating structure in this aerogel has many channels whose width increases with distance from the center. This was achieved by controlling the formation of the ice crystals in the aqueous G-O dispersion that grew radially in the shape of lamellae during freezing. Because the shape and size of ice crystals is influenced by the G-O sheets, different additives (ethanol, cellulose nanofibers, and chitosan) that can form hydrogen bonds with HO were tested and found to affect the interaction between the G-O and formation of ice crystals, producing ice crystals with different shapes. A G-O/chitosan aerogel with a spiral pattern was also obtained. After chemical reduction of G-O, our aerogel exhibited elasticity and absorption capacity superior to that of graphene aerogels with "traditional" pore structures made by conventional freeze-casting. This methodology can be expanded to many other configurations and should widen the use of G-O (and reduced G-O and "graphenic") aerogels.

Covalent organic frameworks (COFs) are a class of designable crystalline polymers with structural periodicity and inherent porosity. [1][2][3][4][5][6][7][8][9] COFs have emerged as new porous materials for gas adsorption and storage because of their high porosity, robust thermal stability, and low densities. [1,2,7] In addition, the layered structure of 2D COFs provides periodic arrays of p clouds that can greatly facilitate charge-carrier transport; [1f, 3, 9] this structural feature is not seen in conventional 1D and 3D polymers. To date, COFs containing boronate ester, boroxine, imine, triazine, and hydrazone linkages have been synthesized. [1][2][3][4][5][6][7][8][9] The development of new reactions to synthesize such covalent and crystalline frameworks is critical for further progress in this emerging field.We report herein a new reaction based on squaraine that allows for the synthesis of a new type of 2D COF. Squaraines are interesting dyes with a zwitterionic resonance structure and have broad applications in areas such as imaging, nonlinear optics, photovoltaics, photodynamic therapy, and ion sensing. [10] Squaraines are usually prepared through the condensation of squaric acid (SA) with aromatic, heteroaromatic, or olefinic compounds in a simple one-step reaction. [10] For example, the condensation of SA with p-toludine as the donating molecule gives a squaraine (SQ) with a planar yet zigzagged zwitterionic resonance structure (Scheme 1 a and b). By using this linkage, we expect to form a conjugated COF with a zigzagged skeleton. We synthesized copper(II) 5,10,15,20-tetrakis(4-aminophenyl)porphyrin (TAP-CuP) as a building block for the SA condensation and constructed a crystalline 2D conjugated COF (CuP-SQ COF; Scheme 1 c) with a tetragonal mesoporous skeleton. We demonstrated that the SQ-linked COFs have a zigzagged conformation that protects the layered structure from sideslip, are highly stable in solvents, provide an extended p conjugation over the 2D sheets, and have lower band gap energy and greatly enhanced absorbance capability compared to existing COFs. These features extend the structural and functional scope of COFs.The CuP-SQ COF was synthesized under solvothermal conditions through the condensation of SA and TAP-CuP in o-dichlorobenzene/n-butanol (1:1 by vol.) at 85 8C for 7 days. The resulting precipitate was collected by filtration, washed with THF and acetone, and dried at 150 8C under vacuum to provide the CuP-SQ COF as a dark purple powder in 94 % yield. When combinations of n-butanol with other aromatic solvents, such as mesitylene and 1,3,5-tricholorobenzene, were used, the resulting solid had a lower crystallinity. To investiagte the ratio of o-dichlorobenzene to nBuOH, ratios of 1:3, 1:2, 1:1, 2:1, and 3:1 were used; the product with the highest crystallinity was obtained when the 1:1 volume ratio was used. The model compound SQ was synthesized under the same reaction conditions in 99 % yield (Scheme 1 a and the Supporting Information). Thermal gravimetric analysis shows that the...

Crystallinity and porosity are crucial for crystalline porous covalent organic frameworks (COFs). Here we report synthetic control over the crystallinity and porosity of COFs by managing interlayer interactions based on self-complementary π-electronic forces. Fluoro-substituted and nonsubstituted aromatic units at different molar ratios were integrated into the edge units that stack to trigger self-complementary π-electronic interactions in the COFs. The interactions improve the crystallinity and enhance the porosity by maximizing the total crystal stacking energy and minimizing the unit cell size. Consequently, the COF consisting of equimolar amounts of fluoro-substituted and nonsubstituted units showed the largest effect. These results suggest a new approach to the design of COFs by managing the interlayer interactions.

Conjugated microporous polymers are developed as a new platform for lithium-battery energy storage, which features a near-unity coulombic efficiency, high capacity and cycle stability. The polymers exhibit synergistic structural effects on facilitating charge dynamics by virtue of their built-in redox skeletons, open nanopores and large surface areas.