Layer-stacking structures are very common in two-dimensional covalent organic frameworks (2D COFs). While their structures are normally determined under solvent-free conditions, the structures of solvated 2D COFs are largely unexplored. We report herein the in situ determination of solvated 2D COF structures, which exhibit an obvious difference as compared to that of the same COF under dried state. Powder X-ray diffraction (PXRD) data analyses, computational modeling, and Pawley refinement indicate that the solvated 2D COFs experience considerable interlayer shifting, resulting in new structures similar to the staggered AB stacking, namely, quasi-AB-stacking structures, instead of the AA-stacking structures that are usually observed in the dried COFs. We attribute this interlayer shifting to the interactions between COFs and solvent molecules, which may weaken the attraction strength between adjacent COF layers. Density functional theory (DFT) calculations confirm that the quasi-AB stacking is energetically preferred over the AA stacking in solvated COFs. All four highly crystalline 2D COFs examined in the present study exhibit considerable interlayer shifting upon solvation, implying the universality of the solvent-induced interlayer stacking rearrangement in 2D COFs. These findings prompt re-examination of the 2D COF structures in solvated state and suggest new opportunities for the applications of COF materials under wet conditions.

Resolving single-crystal structures of two-dimensional covalent organic frameworks (2D COFs) is a great challenge, hindered in part by limited strategies for growing high-quality crystals. A better understanding of the growth mechanism facilitates development of methods to grow high-quality 2D COF single crystals. Here, we take a different perspective to explore the 2D COF growth process by tracing growth intermediates. We discover two different growth mechanisms, nucleation and self-healing, in which self-assembly and pre-arrangement of monomers and oligomers are important factors for obtaining highly crystalline 2D COFs. These findings enable us to grow micron-sized 2D single crystalline COF Py-1P. The crystal structure of Py-1P is successfully characterized by three-dimensional electron diffraction (3DED), which confirms that Py-1P does, in part, adopt the widely predicted AA stacking structure. In addition, we find the majority of Py-1P crystals (>90%) have a previously unknown structure, containing 6 stacking layers within one unit cell.

Acetylene (C 2 H 2) removal from ethylene (C 2 H 4) is a crucial step in the production of polymer-grade C 2 H 4 but remains a daunting challenge because of the similar physicochemical properties of C 2 H 2 and C 2 H 4. Currently energyintensive cryogenic distillation processes are used to separate the two gases industrially. A robust ultramicroporous metalorganic framework (MOF), Ni 3 (pzdc) 2 (7 Hade) 2 , is reported for efficient C 2 H 2 /C 2 H 4 separation. The MOF comprises hydrogen-bonded linked one-dimensional (1D) chains, and features high-density open metal sites (2.7 nm À3) and electronegative oxygen and nitrogen sites arranged on the pore surface as cooperative binding sites. Theoretical calculations, in situ powder X-ray diffraction and Fourier-transform infrared spectroscopy revealed a synergistic adsorption mechanism. The MOF possesses S-shaped 1D pore channels that efficiently trap trace C 2 H 2 at 0.01 bar with a high C 2 H 2 uptake of 60.6 cm 3 cm À3 and C 2 H 2 /C 2 H 4 selectivity.

A new type of photolabile, surface-initiated, atom-transfer radical polymerization (SI-ATRP) initiator 3-(2bromo-2-methylpropanamido)-3-(2-nitrophenyl)propanoic acid was synthesized, and immobilized via an aminosilane linker onto a flat silicon surface. Poly(lauryl methacrylate) and polystyrene brushes were grown from the surface via SI-ATRP, and the surface-tethered polymer chains cleaved off under UV irradiation. The kinetics of the cleavage process were investigated, and an apparent effect of osmotic forces within the polymer brush could be observed. The molecular weight of the cleaved polymers could be readily determined by means of size-exclusion chromatography.

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