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.
Advanced porous materials (APMs)—such as metal‐organic frameworks (MOFs) and porous organic polymers (POPs)—have emerged as an exciting research frontier of chemistry and materials science. Given their tunable pore size and extensive diversity, APMs have found widespread applications. In addition, adding dynamic functional groups to porous solids furthers the development of stimuli‐responsive materials. By incorporating moving elements—molecular rotors—into the porous frameworks, molecular‐rotor‐driven advanced porous materials (MR‐APMs) can respond reversibly to chemical and physical stimuli, thus imparting dynamic functionalities that have not been found in conventional porous materials. This Minireview discusses exemplary MR‐APMs in terms of their design, synthesis, rotor dynamics, and potential applications.
Porous
organic cages (POCs) have many advantages, including superior
microenvironments, good monodispersity, and shape homogeneity, excellent
molecular solubility, high chemical stability, and intriguing host–guest
chemistry. These properties enable POCs to overcome the limitations
of extended porous networks such as metal–organic frameworks
(MOFs) and covalent organic frameworks (COFs). However, the applications
of POCs in bioimaging remain limited due to the problems associated
with their rigid and hydrophobic structures, thus leading to strong
aggregation-caused quenching (ACQ) in aqueous biological media. To
address this challenge, we report the preparation of aggregation-induced
emission (AIE)-active POCs capable of stimuli responsiveness for enhanced
bioimaging. We rationally design a hydrophilic, structurally flexible
tetraphenylethylene (TPE)-based POC that is almost entirely soluble
in aqueous solutions. This POC’s conformationally flexible
superstructure allows the dynamic rotation of the TPE-based phenyl
rings, thus endowing impressive AIE characteristics for responses
to environmental changes such as temperature and viscosity. We employ
these notable features in the bioimaging of living cells and obtain
good performance, demonstrating that the present AIE-active POCs are
suitable candidates for further biological applications.
Given its abundance and clean combustion, natural gas (NG) is one of the leading sources of energy to meet present demands. However, the storage and transportation of NG remain challenging. Besides the commonly used NG storage methods such as compression and liquefaction, adsorbed NG is an attractive alternative. Here, the requirements for vehicles to be powered by adsorbed natural gas (ANG) are examined. Despite top‐performing adsorbents and present‐day engineering solutions, there remain obstacles that prevent vehicles fueled by ANG from becoming commonplace. Herein, these challenges are highlighted to inspire engineering solutions for onboard ANG systems.
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