Clamparene: Synthesis, Structure, and Its Application in Spontaneous Formation of 3D Porous Crystals

Macrocyclic arenes have emerged as pivotal scaffolds in supramolecular chemistry. Despite their significant contributions to molecular recognition and diverse applications, challenges persist in the development of macrocyclic arene-based crystalline materials, particularly in achieving porosity and addressing limitations in adsorption efficiency resulting from the small cavity sizes of existing macrocyclic arenes. In this study, we present the design and synthesis of a novel macrocyclic arene, clamparene (CLP), featuring a rigid backbone, easy synthesis, and a sizable cavity. CLP self-assembles into one-dimensional sub-nanotubes that further organize into a three-dimensional porous framework in the solid state. The crystalline solid of CLP exhibits potential as a porous crystalline adsorbent for various benzene-based contaminants with rapid adsorption kinetics, large uptake amounts, and good recyclability.

Keto-Adamantane-Based Macrocycle Crystalline Supramolecular Assemblies Showing Selective Vapochromism to Tetrahydrofuran

Here, we report the synthesis of adamantane-based macrocycle 2 by combining adamantane building blocks with π-donor 1,3-dimethoxy-benzene units. An unpredictable keto-adamantane-based macrocycle 3 was obtained by the oxidation of 2 using DDQ as an oxidant. Moreover, a new type of macrocyclic molecule-based CT cocrystal was prepared through exo-wall CT interactions between 3 and DDQ. The cocrystal material showed selective vapochromism behavior towards THF, specifically, among nine volatile organic solvents commonly used in the laboratory. Powder X-ray diffraction; UV-Vis diffuse reflectance spectroscopy; 1H NMR; and single crystal X-ray diffraction analyses revealed that color changes are attributed to the vapor-triggered decomplexation of cocrystals.

Photodriven Methane Conversion on Transition Metal Oxide Catalyst: Recent Progress and Prospects

Methane as the main component in natural gas is a promising chemical raw material for synthesizing value-added chemicals, but its harsh chemical conversion process often causes severe energy and environment concerns. Photocatalysis provides an attractive path to active and convert methane into various products under mild conditions with clean and sustainable solar energy, although many challenges remain at present. In this review, recent advances in photocatalytic methane conversion are systematically summarized. As the basis of methane conversion, the activation of methane is first elucidated from the structural basis and activation path of methane molecules. The study is committed to categorizing and elucidating the research progress and the laws of the intricate methane conversion reactions according to the target products, including photocatalytic methane partial oxidation, reforming, coupling, combustion, and functionalization. Advanced photocatalytic reactor designs are also designed to enrich the options and reliability of photocatalytic methane conversion performance evaluation. The challenges and prospects of photocatalytic methane conversion are also discussed, which in turn offers guidelines for methane-conversion-related photocatalyst exploration, reaction mechanism investigation, and advanced photoreactor design.

Flexible Luminescent Hydrogen-bonded Organic Framework for the Separation of Benzene and Cyclohexane

A nonplanar phenothiazine derivative with three cyano moieties (PTTCN) is designed and synthesized to achieve functional crystals for absorptive separation of benzene and cyclohexane. PTTCN can crystallize into two kinds of crystals with different fluorescence colors in different solvent systems. The molecules in two crystals are in different stereo isomeric forms of nitrogen, quasi axial (ax), and quasi equatorial (eq). The crystals with blue fluorescence in ax form may selectively adsorb benzene by a single-crystal-to-single-crystal (SCSC) transformation, but separated benzene from a benzene/cyclohexane equimolar mixture with a low purity of 79.6%. Interestingly, PTTCN molecules with eq form and benzene co-assembled to construct a hydrogen-bonded framework (X-HOF-4) with S-type solvent channels and yellow-green fluorescence, and can release benzene to form nonporous guest-free crystal under heating. Such nonporous crystals strongly favor aromatic benzene over cyclohexane and may selectively reabsorb benzene from benzene/cyclohexane equimolar mixture to recover original framework, and the purity of benzene can reach ≈96.5% after release from framework. Moreover, reversible transformation between the nonporous crystals and the guest-containing crystals allows the material to be reused.

Industrial Separation Challenges: How Does Supramolecular Chemistry Help?

The chemical industry and the chemical processes underscoring it are under intense scrutiny as the demands for the transition to more sustainable and environmentally friendly practices are increasing. Traditional industrial separation systems, such as thermally driven distillation for hydrocarbon purification, are energy intensive. The development of more energy efficient separation technologies is thus emerging as a critical need, as is the creation of new materials that may permit a transition away from classic distillation-based separations. In this Perspective, we focus on porous organic cages and macrocycles that can adsorb guest molecules selectively through various host-guest interactions and permit molecular sieving behavior at the molecular level. Specifically, we summarize the recent advances where receptor-based adsorbent materials have been shown to be effective for industrially relevant hydrocarbon separations, highlighting the underlying host-guest interactions that impart selectivity and permit the observed separations. This approach to sustainable separations is currently in its infancy. Nevertheless, several receptor-based adsorbent materials with extrinsic/intrinsic voids or special functional groups have been reported in recent years that can selectively capture various targeted guest molecules. We believe that the understanding of the interactions that drive selectivity at a molecular level accruing from these initial systems will permit an ever-more-effective "bottom-up" design of tailored molecular sieves that, in due course, will allow adsorbent material-based approaches to separations to transition from the laboratory into an industrial setting.

Giant Cavity Macrocycle: Synthesis, Structure, and Its Complexation with Pagoda[5]arene

A novel stretched hexagon structure naphthalene diimides-extended-pillar[6]arene 1 with a giant cavity size of 18.769 Å in width and 17.109 Å in height is reported. 1 exhibits highly selective binding of pagoda[5]arene compared to pillar[5]arene and prism[5]arene. Size matching and charge transfer interactions play a key role in the formation of the ring-in-ring stable complex.

Potential of nonporous adaptive crystals for hydrocarbon separation

Hydrocarbon separation is an important process in the field of petrochemical industry, which provides a variety of raw materials for industrial production and a strong support for the development of national economy. However, traditional separation processes involve huge energy consumption. Adsorptive separation based on nonporous adaptive crystal (NAC) materials is considered as an attractive green alternative to traditional energy-intensive separation technologies due to its advantages of low energy consumption, high chemical and thermal stability, excellent selective adsorption and separation performance, and outstanding recyclability. Considering the exceptional potential of NAC materials for hydrocarbon separation, this review comprehensively summarizes recent advances in various supramolecular host-based NACs. Moreover, the current challenges and future directions are illustrated in detail. It is expected that this review will provide useful and timely references for researchers in this area. Based on a large number of state-of-the-art studies, the review will definitely advance the development of NAC materials for hydrocarbon separation and stimulate more interesting studies in related fields.

Pd-catalyzed regioselective rollover dual C-H annulation cascade: facile approach to phenanthrene derivatives

Annulations of unsaturated systems through C-H activation represent a powerful tool for producing multicyclic scaffolds. Having coordinating centers in both annulation partners (a dual coordination strategy) would afford remarkable selectivities in the outcomes. Along this concept, we report herein a Pd-catalyzed regioselective rollover cascade dual C-H annulation of o-arylphenols with alkynols for constructing phenanthrene scaffolds. Control, KIE and deuteration studies were conducted to determine the reaction mechanism, and downstream transformations and scaled-up reactions were carried out to assess the robustness of the transformation.

Binaphthyl-Based Chiral Macrocyclic Hosts for the Selective Recognition of Iodide Anions

In this study, we explorethe synthesis of binaphthyl-based chiral macrocyclic hosts for the first time. They exhibited the selective recognition abilities of iodide anions which can be favored over those of other anions (AcO^-, NO₃^-, ClO₄^-, HSO₄^-, Br^-, PF₆^-, H₂PO₄^-, BF₄^-, and CO₃F₃S^-), as confirmed by UV-vis, HRMS, and ¹H NMR spectroscopy experiments, as well as DFT calculations. Neutral aryl C-H···anion interactions play an important role in the formation complexes. The recognition process can be observed by the naked eye.

Water soluble macrocyclic host for recognition of N-methylquinolinium salts in water

In this paper, we reported the synthesis of water soluble macrocyclic arenes 1 containing anionic carboxylate groups. It was found that host 1 could form a 1 : 1 complex with N-methylquinolinium salts in water. Moreover, the complexation and decomplexation of the complexes between host and the guests could be achieved by changing the pH of the solution, and the process could also be observed by naked eye.

Recent advances in the synthesis and applications of macrocyclic arenes

Macrocyclic arenes including calixarenes, resorcinarenes, cyclotriveratrylene, pillararenes and so on have emerged as highly attractive synthetic macrocyclic hosts due to their unique structures, facile functionalization, and broad range of applications. In recent years, there has been growing interest in the development of novel macrocyclic arenes composed of various aromatic building blocks bridged by methylene groups, which have found applications in various research areas. Consequently, the development of novel macrocyclic arenes has become a frontier and hot topic in supramolecular and macrocyclic chemistry. In this review, we feature the recent advances in the synthesis and applications of novel macrocyclic arenes that have emerged in the last decade. The general synthetic strategies employed for these macrocyclic arenes are systematically summarized, and their wide applications in molecular recognition and assemblies, molecular machines, biomedical science and functional materials are highlighted.

A Benzothiadiazole-Based Self-Assembled Cage for Cadmium Detection

A turn-on fluorescent probe, cage 1, was efficiently self-assembled by condensing 4,4'-(benzothiadiazole-4,7-diyl)dibenzaldehyde and TREN in chloroform. The formation of cage 1 was characterized and confirmed by NMR spectroscopy, mass spectrometry, and theoretical calculations. The yield of cage 1 could be controlled by tuning the reaction conditions, such as the precursor concentration. Interestingly, the addition of 10 equiv of Cd²⁺ relative to cage 1 could increase the fluorescence almost seven-fold. ¹H NMR and fluorescence experiments indicating fluorescence enhancement may be caused by the decomposition of cage 1. Such a high selectivity toward Cd²⁺ implies that the cage could potentially be employed in cadmium detection.

Adsorptive separation of para-xylene by nonporous adaptive crystals of phenanthrene[2]arene

In this work, we developed a new method for the preparation of phenanthrene[2]arene on a large-scale. Meanwhile, the synthetic phenanthrene[2]arene has been successfully used as nonporous adaptive crystals for the separation of para-xylene (pX) from xylene isomers. The crystal structure revealed that one host molecule can adsorb one pX molecule to form the 1@pX complex, in which pX is located in the cavity of the host.

A new method for the preparation of phenanthrene[2]arene on a large-scale was developed. The synthetic phenanthrene[2]arene has been successfully used as nonporous adaptive crystals for the separation of para-xylene from xylene isomers.

An electron-deficient supramolecular macrocyclic host for the selective separation of aromatics and cyclic aliphatics

Host 1 with an electron-deficient nanometer-sized cavity were synthesized in two steps. Moreover, 1 has been successfully used as a gas chromatographic stationary phase to prepare a packed column for the separation of PhH/Cy and Tol/MCy.