Removal of dyes using polymers of intrinsic microporosity (PIMs): a recent approach.

Removal of dyes from various industrial effluents is a great challenge, and cost-effective methods and materials with high dye removal efficacy are in high demand. Adsorption, nanofiltration and photocatalytic degradation are three major techniques that have been investigated for dye removal. PIMs are promising materials for use in these three methods based on their attributes, such as microporosity, solution processibility, high chemical stability and tunability through facile synthesis and easy postmodification. Although the number of reports on dye removal employing PIMs are limited, some of the materials have been shown to exhibit good dye separation properties, which are comparable to those of the state-of-the-art material activated carbon. In this highlight, we make an account of progress in PIMs and PIM-based composite materials in different dye removal processes over the last decade. Furthermore, we discuss the existing challenges of PIM-based materials and aim to analyze the key parameters for improving their dye removal properties.

Polymers of Intrinsic Microporosity Based on Dibenzodioxin Linkage: Design, Synthesis, Properties, and Applications.

The development of polymers of intrinsic microporosity (PIMs) over the last two decades has established them as a distinct class of microporous materials, which combine the attributes of microporous solid materials and the soluble nature of glassy polymers. Due to their solubility in common organic solvents, PIMs are easily processable materials that potentially find application in membrane-based separation, catalysis, ion separation in electrochemical energy storage devices, sensing, etc. Dibenzodioxin linkage, Tröger's base, and imide bond-forming reactions have widely been utilized for synthesis of a large number of PIMs. Among these linkages, however, most of the studies have been based on dibenzodioxin-based PIMs. Therefore, this review focuses precisely on dibenzodioxin linkage chemistry. Herein, the design principles of different rigid and contorted monomer scaffolds are discussed, as well as synthetic strategies of the polymers through dibenzodioxin-forming reactions including copolymerization and postsynthetic modifications, their characteristic properties and potential applications studied so far. Towards the end, the prospects of these materials are examined with respect to their utility in industrial purposes. Further, the structure-property correlation of dibenzodioxin PIMs is analyzed, which is essential for tailored synthesis and tunable properties of these PIMs and their molecular level engineering for enhanced performances making these materials suitable for commercial usage.

Porous flexible frameworks: origins of flexibility and applications.

Porous crystalline frameworks including zeolites, metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and hydrogen-bonded organic frameworks (HOFs) have attracted great research interest in recent years. In addition to their assembly in the solid-state being fundamentally interesting and aesthetically pleasing, their potential applications have now pervaded in different areas of chemistry, biology and materials science. When framework materials are endowed with 'flexibility', they exhibit some properties (e.g., stimuli-induced pore breathing and reversible phase transformations) that are distinct from their rigid counterparts. Benefiting from flexibility and porosity, these framework materials have shown promise in applications that include separation of toxic chemicals, isotopes and hydrocarbons, sensing, and targeted delivery of chemicals. While flexibility in MOFs has been widely appreciated, recent developments of COFs and HOFs have established that flexibility is not just limited to MOFs. In fact, zeolites-that are considered rigid when compared with MOFs-are also known to exhibit dynamic modes. Despite flexibility may be conceived as being detrimental to the formation and stability of periodic structures, the landscape of flexible framework structures continues to expand with discovery of new materials with promising applications. In this review, we make an account of different flexible framework materials based on their framework types with a more focus on recent examples and delve into the origin of flexibility in each case. This systematic analysis of different flexibility types based on their origins enables understanding of structure-property relationships, which should help guide future development of flexible framework materials based on appropriate monomer design and tailoring their properties by bottom-up approach. In essence, this review provides a summary of different flexibility types extant to framework materials and critical analysis of importance of flexibility in emerging applications.

Salt loading in MOFs: solvent-free and solvent-assisted loading of NH4NO3 and LiNO3 in UiO-66.

While the loading of liquid or solid materials in the pores of metal-organic frameworks (MOFs) can yield composite materials with novel and useful emergent properties, the loading of solids, and ionic solids in particular, can be challenging. We report the loading of the salts NH4NO3 and LiNO3 in the MOF UiO-66. The relatively low-melting NH4NO3 is loaded in UiO-66 in a solvent-free method, and loading is complete in 8 h at 75 °C, far below the melting point of NH4NO3. The higher-melting LiNO3 requires a small amount of solvent (water) for loading, and active removal of water assists in loading of the salt to form a composite that is 38% by mass LiNO3. These and similar salt-MOF composites are of interest for applications such as solid-ion conductors and energetic materials.

Exceptional hydrogen storage achieved by screening nearly half a million metal-organic frameworks.

Few hydrogen adsorbents balance high usable volumetric and gravimetric capacities. Although metal-organic frameworks (MOFs) have recently demonstrated progress in closing this gap, the large number of MOFs has hindered the identification of optimal materials. Here, a systematic assessment of published databases of real and hypothetical MOFs is presented. Nearly 500,000 compounds were screened computationally, and the most promising were assessed experimentally. Three MOFs with capacities surpassing that of IRMOF-20, the record-holder for balanced hydrogen capacity, are demonstrated: SNU-70, UMCM-9, and PCN-610/NU-100. Analysis of trends reveals the existence of a volumetric ceiling at ∼40 g H2 L-1. Surpassing this ceiling is proposed as a new capacity target for hydrogen adsorbents. Counter to earlier studies of total hydrogen uptake in MOFs, usable capacities in the highest-capacity materials are negatively correlated with density and volumetric surface area. Instead, capacity is maximized by increasing gravimetric surface area and porosity. This suggests that property/performance trends for total capacities may not translate to usable capacities.

Nitrogen-Free Bifunctional Bianthryl Leads to Stable White-Light Emission in Bilayer and Multilayer OLED Devices.

White organic light-emitting diodes (WOLEDs) are at the center stage of OLED research today because of their advantages in replacing the high energy-consuming lighting technologies in vogue for a long time. New materials that emit white light in simple devices are much sought after. We have developed two novel electroluminescent materials, referred to as BABZF and BATOMe, based on a twisted bianthryl core, which are brilliantly fluorescent, thermally highly stable with high T d and T g, and exhibit reversible redox property. Although inherently blue emissive, BABZF leads to white-light emission (CIE ≈ 0.28, 0.33) with a moderate power efficiency of 2.24 lm/W and a very high luminance of 15 600 cd/m2 in the fabricated multilayer nondoped OLED device. This device exhibited excellent color stability over a range of applied potential. Remarkably, similar white-light emission was captured even from a double-layer device, attesting to the innate hole-transporting ability of BABZF despite it being non-nitrogenous, that is, lacking any traditional hole-transporting di-/triarylamino group(s). Similar studies with BATOMe led to inferior device performance results, thereby underscoring the importance of dibenzofuryl groups in BABZF. Experimental as well as theoretical studies suggest the possibility of emission from multiple species involving BABZF and its exciplex and electroplex in the devices. The serendipitously observed white-light emission from a double-layer device fabricated with an unconventional hole-transporting material (HTM) opens up new avenues to create new non-nitrogenous HTMs that may lead to more efficient white-light emission in simple double-layer devices.

Metal Effects on the Sensitivity of Isostructural Metal-Organic Frameworks Based on 5-Amino-3-nitro-1H-1,2,4-triazole.

Two energetic metal-organic frameworks (MOFs), Co-ANTA and Zn-ANTA, are synthesized from 5-amino-3-nitro-1H-1,2,4-triazole (ANTA) and exhibit superior oxygen balance, density, and thermal stability compared to ANTA. The superior oxygen balance is achieved through a combination of hydroxide ligands and deprotonated linkers. Although the materials are isostructural and have similar density, oxygen balance, and sensitivity to heat, their impact sensitivities are significantly different. Similar to ANTA, Zn-ANTA is fairly insensitive to impact. By contrast, the impact sensitivity of ANTA is increased significantly after coordination polymerization with cobalt. The disparate impact sensitivities of the compounds might be attributed to the different electronic configurations of the metal ions constituting the frameworks.

Coordination Polymerization of 5,5'-Dinitro-2H,2H'-3,3'-bi-1,2,4-triazole Leads to a Dense Explosive with High Thermal Stability.

High-energy coordination polymers (CPs) based on nitrogen-rich ligands are an emerging class of explosives. However, modulation of the energetic properties of high-energy CPs and the establishment of their structure-function relationship remain in their infancy. In the present study, the utility of coordination polymerization as a technique to modulate the application of critical energetic properties, such as density and thermal stability, of a secondary explosive, 5,5'-dinitro-2H,2H'-3,3'-bi-1,2,4-triazole (DNBT), is presented. Ni-DNBT is a discrete octahedral complex with density lower than that of DNBT. Cu-DNBT also contains octahedral metal coordination, similar to that in Ni-DNBT, as the building unit; however, the partial reduction of CuII to CuI ions during the reaction and their unique geometrical preferences lead to linking of the octahedral CuII complexes by tetrahedral CuI ions and render the resultant material a one-dimensional polymer with high density. In fact, Cu-DNBT has the highest density among all of the DNBT-based energetics. Furthermore, Cu-DNBT exhibits thermal stability superior to that of both Ni-DNBT and DNBT. Cu-DNBT is one of the two DNBT-based energetic materials and one of the few energetics that are stable at temperatures higher than 300 °C.

Benzophenones as Generic Host Materials for Phosphorescent Organic Light-Emitting Diodes.

Despite the fact that benzophenone has traditionally served as a prototype molecular system for establishing triplet state chemistry, materials based on molecular systems containing the benzophenone moiety as an integral part have not been exploited as generic host materials in phosphorescent organic light-emitting diodes (PhOLEDs). We have designed and synthesized three novel host materials, i.e., BP2-BP4, which contain benzophenone as the active triplet sensitizing molecular component. It is shown that their high band gap (3.91-3.93 eV) as well as triplet energies (2.95-2.97 eV) permit their applicability as universal host materials for blue, green, yellow, and red phosphors. While they serve reasonably well for all types of dopants, excellent performance characteristics observed for yellow and green devices are indeed the hallmark of benzophenone-based host materials. For example, maximum external quantum efficiencies of the order of 19.2% and 17.0% were obtained from the devices fabricated with yellow and green phosphors using BP2 as the host material. White light emission, albeit with rather poor efficiencies, has been demonstrated as a proof-of-concept by fabrication of co-doped and stacked devices with blue and yellow phosphors using BP2 as the host material.

Carbon Dioxide Capture by a Metal-Organic Framework with Nitrogen-Rich Channels Based on Rationally Designed Triazole-Functionalized Tetraacid Organic Linker.

A semirigid tetraacid linker H4L functionalized with 1,2,3-triazole was rationally designed and synthesized to access nitrogen-rich MOFs for selective adsorption of CO2. The cadmium MOF, that is, Cd-L, obtained by the reaction of H4L with Cd(NO3)2, is found to be a 3D porous framework structure that is robust to desolvation. Crystal structure analysis reveals channels that are decorated by the triazole moieties of L. Gas adsorption studies show that Cd-L MOF permits remarkable CO2 uptake to the extent of 99 and 1000 cc/g at 1 and 30 bar, respectively, at 0 °C. While literature survey reveals that MIL-112, constructed from a 1,2,3-triazole functionalized linker, exhibits no porosity to gas adsorption due to structural flexibility, the results with Cd-L MOF described herein emphasize how rigidification of the organic linker improves gas uptake properties of the resultant MOF.

Porous coordination polymers of diverse topologies based on a twisted tetrapyridylbiaryl: application as nucleophilic catalysts for acetylation of phenols.

Porous coordination polymers (CPs) with partially uncoordinated pyridyl rings based on rationally designed polypyridyl linkers are appealing from the point of view of their application as nucleophilic catalysts. A D2d -symmetric tetradentate organic linker L, that is, 2,2',6,6'-tetramethoxy-3,3',5,5'-tetrakis(4-pyridyl)biphenyl, was designed and synthesized for metal-assisted self-assembly aimed at porous CPs. Depending on the nature of the metal ion and the counter anion, the ligand L is found to function as a 3- or 4-connecting building block leading to porous CPs of diverse topologies. The reaction of L with Zn(NO3 )2 and Cd(NO3 )2 yields porous 2 D CPs of "fes" topology, in which the tetrapyridyl linker L serves as a 3-connecting unit with its free pyridyl rings well exposed into the pores. The functional utility of these porous CPs containing uncoordinated pyridyl rings is demonstrated by employing them as efficient heterogeneous nucleophilic catalysts for acetylation of a number of phenols with varying electronic properties and reactivities.