Photocatalytic reduction of molecular oxygen is a promising route toward sustainable production of hydrogen peroxide (H 2 O 2 ). This challenging process requires photoactive semiconductors enabling solar energy driven generation and separation of electrons and holes with high charge transfer kinetics. Covalent organic frameworks (COFs) are an emerging class of photoactive semiconductors, tunable at a molecular level for high charge carrier generation and transfer. Herein, we report two newly designed two-dimensional COFs based on a (diarylamino)benzene linker that form a Kagome ( kgm ) lattice and show strong visible light absorption. Their high crystallinity and large surface areas (up to 1165 m 2 ·g –1 ) allow efficient charge transfer and diffusion. The diarylamine (donor) unit promotes strong reduction properties, enabling these COFs to efficiently reduce oxygen to form H 2 O 2 . Overall, the use of a metal-free, recyclable photocatalytic system allows efficient photocatalytic solar transformations.

A novel Cu(I)-based two-dimensional (2D, 4 4 net) metal−organic framework (MOF) [Cu(L)(I)] 2n •2nDMF• nMeCN (1); L = 4′-(4-methoxyphenyl)-4,2′:6′,4″-terpyridine; DMF = N,N-dimethylformamide, MeCN = acetonitrile) has been synthesized and found to behave as a colorimetric detector for the widest variety of small molecules such as different solvents, halobenzenes, N-heterocycles, amine, and nitroaromatic explosives all in vapor phase through a single crystal to single crystal (SCSC) transformation. The 2D 4 4 nets are interdigitated with each other to form a supramolecular 3D MOF having 1D pore. The interdigitated layers are stabilized by π•••π interactions and CH•••π interactions and provide extreme stability up to 380 °C. Interestingly, all guest exchange and encapsulation processes are reversible without loss of structural integrity. Positions of the guest molecules in the host−guest complex have been identified from the crystal structure and found to involve weak interactions with the framework. Notably, this is the first time for a report of any material which encapsulates such a large number of small molecules in the vapor phase from different chemical classes in SCSC fashion with visible color changes. Tests confirm the selectivity toward most polar molecule in a class. In the presence of guest molecules, the MOF exhibits a blue shift in fluorescence emission spectra and the extent of the blue shift is appreciably high. It also shows high selectivity toward diethylamine (dea) among N-heterocycles, amine, and highly explosive trinitrophenol (TNP) among nitroaromatic explosives as revealed from concurrent luminescence quenching in solution. Finally, the MOF represents one of the best hosts reported so far having extreme stability and selectivity and meets the benchmark of reversibility for material applications.

Rise of porous covalent triazine frameworks (CTFs) for sustainable applications.

The stability of metal−organic frameworks (MOFs) typically decreases with an increasing number of defects, limiting the number of defects that can be created and limiting catalytic and other applications. Herein, we use a hemilabile (Hl) linker to create up to a maximum of six defects per cluster in UiO-66. We synthesized hemilabile UiO-66 (Hl-UiO-66) using benzene dicarboxylate (BDC) as linker and 4-sulfonatobenzoate (PSBA) as the hemilabile linker. The PSBA acts not only as a modulator to create defects but also as a coligand that enhances the stability of the resulting defective framework. Furthermore, upon a postsynthetic treatment in H 2 SO 4 , the average number of defects increases to the optimum of six missing BDC linkers per cluster (three per formula unit), leaving the Zr-nodes on average sixfold coordinated. Remarkably, the thermal stability of the materials further increases upon this treatment. Periodic density functional theory calculations confirm that the hemilabile ligands strengthen this highly defective structure by several stabilizing interactions. Finally, the catalytic activity of the obtained materials is evaluated in the acid-catalyzed isomerization of α-pinene oxide. This reaction is particularly sensitive to the Brønsted or Lewis acid sites in the catalyst. In comparison to the pristine UiO-66, which mainly possesses Brønsted acid sites, the Hl-UiO-66 and the postsynthetically treated Hl-UiO-66 structures exhibited a higher Lewis acidity and an enhanced activity and selectivity. This is further explored by CD 3 CN spectroscopic sorption experiments. We have shown that by tuning the number of defects in UiO-66 using PSBA as the hemilabile linker, one can achieve highly defective and stable MOFs and easily control the Brønsted to Lewis acid ratio in the materials and thus their catalytic activity and selectivity.

Recently, covalent organic frameworks (COFs) have emerged as an interesting class of porous materials, featuring tunable porosity and fluorescence properties based on reticular construction principles. Some COFs display highly emissive monocolored luminescence, but attaining white-light emission from COFs is difficult as it must account for a wide wavelength range. White-light emission is highly desired for solid-state lighting applications, and obtaining it usually demands the combination of red-, green-, and blue-light components. Hence, to achieve the targeted white-light emission, we report for the first time grafting of lanthanides (Eu 3+ /Tb 3+ ) on a two-dimensional imine COF (TTA-DFP-COF). We studied the luminescence properties of the hybrid materials prepared by anchoring Eu 3+ (red light) and Tb 3+ (green light) β-diketonate complexes onto the TTA-DFP-COF. Reticular construction is exploited to design strong coordination of Eu 3+ and Tb 3+ ions into nitrogen-rich pockets of the imine COF. Mixed Eu 3+ /Tb 3+ materials are then prepared to incorporate red and green components along with the inherent blue light from the organic moieties of the COF to produce white-light emission. We show that COFs have the potential for hosting Eu 3+ and Tb 3+ complexes, which can be tuned to obtain desired excitations for applications in the field of optoelectronics, microscopy, optical sensing, and bioassay.

In this article, a set of fluorine functionalized covalent triazine frameworks have been synthesized with 2,2′,3,3′,5,5′,6,6′-octafluoro-4,4′-biphenyldicarbonitrile as the monomer under ionothermal conditions.

We present, for the first time, covalent triazine frameworks functionalized with acetylacetonate group (acac-CTFs). They are obtained from the polymerization of 4,4′-malonyl­dibenzonitrile under ionothermal conditions and exhibit BET surface areas up to 1626 m2/g. The materials show excellent CO2 uptake (3.30 mmol/g at 273 K and 1 bar), H2 storage capacity (1.53 wt % at 77 K and 1 bar), and a good CO2/N2 selectivity (up to 46 at 298 K). The enhanced CO2 uptake value and good selectivity are due to the presence of dual polar sites (N and O) throughout the material. In addition, acac-CTF was used to anchor VO­(acac)2 as a heterogeneous catalyst. The V@acacCTF showed outstanding reactivity and reusability for the modified Mannich-type reaction with a higher turnover number than the homogeneous catalyst. The higher reactivity and reusability of the catalyst come from the coordination of the vanadyl ions to the acetyl acetonate groups present in the material. The strong metalation is confirmed from Fourier transform infrared analysis, 13C MAS NMR spectral analysis, and X-ray photoelectron spectroscopy measurement. Detailed characterization of the V@acac-CTF reveals that electron donation from O∧O of the acetylacetonate group to VO­(acac)2, combined with the very high surface area of acac-CTF, is responsible for the stabilization of the catalyst. Overall, this contribution highlights the necessity of stable catalytic binding sites on heterogeneous supports to fabricate greener catalysts for sustainable chemistry.

UiO-66 is regarded as an epitome of metal−organic frameworks (MOFs) because of its stability. Defect engineering has been used as a toolbox to alter the performance of MOFs. UiO-66 is among the most widely explored MOFs because of its capability to bear a high number of defects without undergoing structural collapse. Several representative works in the field of MOF-based defect engineering are available based on UiO-66. In this review, more emphasis is given toward the construction of catalytic sites by engineering defects in UiO-66 as a representative including all the detailed synthesis procedures for inducing defects, and the characterization techniques used to analyze these defects in UiO-66 are discussed. Furthermore, a comprehensive review for the defects themselves and the support using defects in catalysis is provided to accentuate the importance of defect engineering.