Constructing a 3D Covalent Organic Framework from 2D hcb Nets through Inclined Interpenetration

Three-dimensional covalent organic frameworks (3D COFs) have been of great interest due to their inherent numerous open sites and pore confinement effect. However, it has remained challenging to build 3D frameworks via interdigitation (also known as inclined interpenetration) by generating an entangled network formed by multiple 2D layers inclined with respect to each other. Herein, we report the first case of constructing a 3D COF, termed COF-904, through interdigitating 2D hcb nets, which was formed via [3+2] imine condensation reactions by the use of 1,3,5-triformylbenzene and 2,3,5,6-tetramethyl-1,4-phenylenediamine. The single-crystal structure of COF-904 is solved, and the locations of all non-hydrogen atoms are determined by 3D electron diffraction with a resolution up to 0.8 Å. These results not only broaden the strategy for achieving 3D COFs via interdigitation but also demonstrate that structurally complex extended frameworks can arise from simple molecules.

A Heteromeric Carboxylic-acid-based Single Crystalline Crosslinked Organic Framework

The development of large pore single-crystalline covalently linked organic frameworks is critical in revealing the detailed structure-property relationship with substrates. One emergent approach is to photo-crosslink hydrogen-bonded molecular crystals. Introducing complementary hydrogen-bonded carboxylic acid building blocks is promising to construct large pore networks, but these molecules often form interpenetrated networks or non-porous solids. Herein, we introduced heteromeric carboxylic acid dimers to construct a non-interpenetrated molecular crystal. Crosslinking this crystal precursor with dithiols afforded a large pore single-crystalline hydrogen-bonded crosslinked organic framework HCOF-101. X-ray diffraction analysis revealed HCOF-101 as an interlayer connected hexagonal network, which possesses flexible linkages and large porous channels to host a hydrazone photoswitch. Multicycle Z/E-isomerization of the hydrazone took place reversibly within HCOF-101, showcasing the potential use of HCOF-101 for optical information storage.

A novel hydrogen-bonded organic framework for the sensing of two representative organic arsenics

A novel fluorescent hydrogen-bonded organic framework with a double fold interpenetrated structure, HOF-22, has been successfully constructed and structurally characterized. HOF-22 is capable of sensitive detection of two representative organic arsenics from aqueous solution.

Supramolecular networks in molecular complexes of pyridine boronic acids and polycarboxylic acids: synthesis, structural characterization and fluorescence properties

3- and 4-pyridineboronic acids have been combined with trimesic and pyromellitic acids to give three molecular complexes.

A Series of Layered Assemblies of Hydrogen-Bonded, Hexagonal Networks of C3-Symmetric π-Conjugated Molecules: A Potential Motif of Porous Organic Materials

Hydrogen-bonded porous organic crystals are promising candidates for functional organic materials due to their easy construction and flexibility arising from reversible bond formation-dissociation. However, it still remains challenging to form porous materials with void spaces that are well-controlled in size, shape, and multiplicity because even well-designed porous frameworks often fail to generate pores within the crystal due to unexpected disruption of hydrogen bonding networks or interpenetration of the frameworks. Herein, we demonstrate that a series of C3-symmetric π-conjugated planar molecules (Tp, T12, T18, and Ex) with three 4,4'-dicarboxy-o-terphenyl moieties in their periphery can form robust hydrogen-bonded hexagonal networks (H-HexNets) with dual or triple pores and that the H-HexNets stack without interpenetration to yield a layered assembly of H-HexNet (LA-H-HexNet) with accessible volumes up to 59%. Specifically, LA-H-HexNets of Tp and T12 exhibit high crystallinity and permanent porosity after desolvation (activation): SABET = 788 and 557 m(2) g(-1), respectively, based on CO2 sorption at 195 K. We believe that the present design principle can be applied to construct a wide range of two-dimensional noncovalent organic frameworks (2D-nCOFs) and create a pathway to the development of a new class of highly porous functional materials.

A fluorescent paramagnetic Mn metal-organic framework based on semi-rigid pyrene tetra-carboxylic acid: sensing of solvent polarity and explosive nitroaromatics

An Mn metal-organic framework (Mn-MOF), Mn-L, based on a pyrene-tetraacid linker (H4 L), displays a respectable fluorescence quantum yield of 8.3% in spite of the presence of the paramagnetic metal ions, due presumably to fixation of the metal ions in geometries that do not allow complete energy/charge-transfer quenching. Remarkably, the porous Mn-L MOF with ∼25% solvent-accessible volume exhibits a heretofore unprecedented solvent-dependent fluorescence emission maximum, permitting its use as a probe of solvent polarity; the emission maxima in different solvents correlate excellently with Reichardt's solvent polarity parameter (E T (N)). Further, the applicability of Mn-L to the sensing of nitroaromatics via fluorescence quenching is demonstrated; the detection limit for TNT is shown to be 125 p.p.m. The results bring out the fact that MOFs based on paramagnetic metal ions can indeed find application when the quenching mechanisms are attenuated by certain geometries of the organic linkers of the MOF.

A C3-symmetric macrocycle-based, hydrogen-bonded, multiporous hexagonal network as a motif of porous molecular crystals

A C3-symmetric π-conjugated macrocycle combined with an appropriate hydrogen bonding module (phenylene triangle) allowed the construction of crystalline supramolecular frameworks with a cavity volume of up to 58%. The frameworks were obtained through non-interpenetrated stacking of a hexagonal sheet possessing three kinds of pores with different sizes and shapes. The activated porous material absorbed CO2 up to 96 cm(3) g(-1) at 195 K under 1 atm.

High surface area and Z′ in a thermally stable 8-fold polycatenated hydrogen-bonded framework

Permanent porosity, a large surface area, and unprecedented Z′ was exhibited in an 8-fold polycatenated hydrogen-bonded organic framework.