Guest-Induced Conformational Transformations in Tiara[5]arene Crystals: A Pathway for Molecular Sieving

In pursuit of environmental sustainability and energy efficiency, assorted macrocyclic compounds have recently emerged as crystalline adsorbents for the efficient molecular sieving of various chemical commodities. Herein, we delve into the conformational characteristics and solid-state packing modes of tiara[5]arenes (T[5]), a rim-differentiated pillar[5]arene derivative. By meticulously exploring the conformational space, we have successfully identified a multitude of distinct T[5] conformers within a relatively narrow energy range of 22 kJ/mol. This finding underscores the inherent conformational flexibility of this macrocyclic scaffold, enabling T[5] to adapt diverse packing arrangements in the solid state. While solvent-free T[5] crystals do not exhibit permanent porosity, they undergo solvomorphic interconversions when exposed to various guest compounds. Our study demonstrates that T[5]-based crystalline materials exhibit a notable preference for selectively capturing aromatic and olefinic solvents, such as benzene, toluene, chlorobenzene, and cyclohexene, over their aliphatic hydrocarbon counterparts from equivalent volume liquid mixtures, achieving up to 10:1 selectivity between benzene and cyclohexane.

Leveraging Halogen Interactions for a Supramolecular Nanotube

We demonstrate the formation of supramolecular nanotubes from molecular triangles in a single crystal by balancing the hydrogen bonds and halogen interactions between individual macrocycles. Thereby, we template the supramolecular nanotube growth by intermolecular interactions encoded directly in the macrocycles instead of those provided by the crystallization solvent. Ultimately, we show that replacing bromines for iodines in the macrocycle is necessary to achieve this supramolecular organization by enhancing the strength of the halogen interactions and concomitant reduction of the detrimental hydrogen bonds. We investigated the nature and the interplay of the individual intermolecular interactions by analysis of the experimental single crystal data and quantum chemical calculations. This work enriches the available toolbox of supramolecular interactions and will aid and abet the development of rationally-designed materials with a long-range 1D tubular organization.

Quantum Size-Driven Spectral Variations in Pillar[n]arene Systems: A Density Functional Theory and Wave Function Assessment

This study explores the quantum size effects on the optical properties of pillar[n]arene (n = 5, 6, 7, 8) utilizing density functional theory (DFT) and wave function analysis. The mechanisms of electron transitions in one-photon absorption (OPA) and two-photon absorption (TPA) spectra are investigated, alongside the calculation of electron circular dichroism (ECD) for these systems. Transition Density Matrix (TDM) and electron-hole pair density maps are employed to study the electron excitation characteristics, unveiling a notable size dependency. Analysis of the transition electric dipole moment (TEDM) and the transition magnetic dipole moment (TMDM) reveals the electromagnetic interaction mechanism within pillar[n]arene. Raman spectra computations further elucidate vibrational modes, while interactions with external environments are studied using electrostatic potential (ESP) analysis, and electron delocalization is assessed under an external magnetic field, providing insights into the magnetically induced current phenomena within these supramolecular structures. The thermal stability of pillar[n]arene was investigated by ab initio molecular dynamics (AIMD).

White-Light Emission from a Host-Guest Composite between Carboxylatopillar[5]arene-Modified N-Doped Carbon Dots and Rhodamine 6G for Rutin Detection

The construction of tunable white-light-emitting materials has garnered increasing attention in the scientific community. In this study, N-doped carbon dots (N-CDs) were surface-modified with carboxylatopillar[5]arene (CP[5]) using an EDC-NHS coupling reaction to create CCDs. CCDs were then conjugated with rhodamine 6G (R6G) through host-guest interactions to fabricate the CCDs-R6G composites. These composites produced two-color fluorescence emission peaks at 447 and 557 nm when excited by a wavelength of 340 nm. Excitingly, white-light emission (0.28, 0.30) can be readily achieved by varying the R6G concentration. To further explore potential applications, a new detection method for rutin (RT) based on the inner filter effect (IFE) was developed. Experimental results verify the practicality and reliability of the fluorescence sensor based on CCDs-R6G composites for RT detection in real samples.

Pillararene-Based Supramolecular Polymers for Adsorption and Separation

Supramolecular polymers have attracted increasing attention in recent years due to their perfect combination of supramolecular chemistry and traditional polymer chemistry. The design and synthesis of macrocycles have driven the rapid development of supramolecular chemistry and polymer science. Pillar[n]arenes, a new generation of macrocyclic compounds possessing unique pillar-shaped structures, nano-sized cavities, multi-functionalized groups, and excellent host-guest complexation abilities, are promising candidates to construct supramolecular polymer materials with enhanced properties and functionalities. This review summarizes recent progress in the design and synthesis of pillararene-based supramolecular polymers (PSPs) and illustrates their diverse applications as adsorption and separation materials. All performances are evaluated and analyzed in terms of efficiency, selectivity, and recyclability. Typically, PSPs can be categorized into three typical types according to their topologies, including linear, cross-linked, and hybrid structures. The advances made in the area of functional supramolecular polymeric adsorbents formed by new pillararene derivatives are also described in detail. Finally, the remaining challenges and future perspectives of PSPs for separation-based materials science are discussed. This review will inspire researchers in different fields and stimulate creative designs of supramolecular polymeric materials based on pillararenes and other macrocycles for effective adsorption and separation of a variety of targets.

Enhanced Desalination Polyamide Membranes Incorporating Pillar[5]arene through in-Situ Aggregation-Interfacial Polymerization-isAGRIP

Membrane-based desalination have an important role in water purification. Inspired by highly performant biological proteins, artificial water channels (AWC) have been proposed as active components to overcome the permeability/selectivity trade-off of desalination processes. Promising performances have been reported with Pillararene crystalline phases revealing impressive molecular-scale separation performances, when used as selective porous materials. Herein, we demonstrate that Pillar[5]arene PA[5] aggregates are in-situ generated and incorporated during the interfacial polymerization, within industrially relevant reverse osmosis polyamide-PA membranes. In particular, we explore the best combination between PA[5] aggregates and m-phenylenediamine (MPD) and trimesoylchloride (TMC) monomers to achieve their seamless incorporation in a defect-free hybrid polyamide PA[5]-PA membranes for enhanced desalination. The performances of the reference and hybrid membranes are evaluated by cross-flow filtration under real reverse osmosis conditions (15.5 bar of applied pressure) by filtration of brackish feed streams. The optimized membranes achieve a ∼40 % improvement, in water permeance of ∼2.76±0.5 L m^-2  h^-1  bar^-1 and high 99.5 % NaCl rejection with respect to the reference TFC membrane and a similar water permeance compared to one of the best commercial BW30 membranes (3.0 L m^-2  h^-1  bar^-1 and 99.5 % NaCl rejection).

A pillar[5]arene-based covalent organic framework with pre-encoded selective host-guest recognition

It is highly desirable to maintain both permanent accessible pores and selective molecular recognition capability of macrocyclic cavitands in the solid state. Integration of well-defined discrete macrocyclic hosts into ordered porous polymeric frameworks (e.g., covalent organic frameworks, COFs) represents a promising strategy to transform many supramolecular chemistry concepts and principles well established in the solution phase into the solid state, which can enable a broad range of practical applications, such as high-efficiency molecular separation, heterogeneous catalysis, and pollution remediation. However, it is still a challenging task to construct macrocycle-embedded COFs. In this work, a novel pillar[5]arene-derived (P5) hetero-porous COF, denoted as P5-COF, was rationally designed and synthesized. Featuring the unique backbone structure, P5-COF exhibited selective adsorption of C2H2 over C2H4 and C2H6, as well as significantly enhanced host-guest binding interaction with paraquat, in comparison with the pillar[5]arene-free COF analog, Model-COF. The present work established a new strategy for developing COFs with customizable molecular recognition/separation properties through the bottom-up "pre-porous macrocycle to porous framework" design.

Intrinsically Porous Molecular Materials (IPMs) for Natural Gas and Benzene Derivatives Separations

ConspectusSeparating and purifying chemicals without heat would go a long way toward reducing the overall energy consumption and the harmful environmental footprint of the process. Molecular separation processes are critical for the production of raw materials, commodity chemicals, and specialty fuels. Over 50% of the energy used in the production of these materials is spent on separation and purification processes, which primarily includes vacuum and cryogenic distillations. Chemical manufacturers are now investigating modest thermal approaches, such as membranes and adsorbent materials, as they are more cognizant than ever of the need to save energy and prevent pollution. Porous materials, such as zeolites, metal-organic frameworks (MOFs), and covalent organic frameworks (COFs), have dominated the field of industrial separations as their high surface areas and robust pores make them ideal candidates for molecular separations of gases and hydrocarbons. Separation processes involving porous materials can save 70%-90% of energy costs compared to that of thermally driven distillations. However, most porous materials have low thermal, chemical, and moisture stability, in addition to limited solution processability, which tremendously constrain their broad industrial translation. Intrinsically porous molecular materials (IPMs) are a subclass of porous molecular materials that are comprised of molecular host macrocycles or cages that absorb guests in or around their intrinsic cavity. IPMs range from discrete porous molecules to assemblies with amorphous or highly crystalline structures that are held together by weak supramolecular interactions. Compared to the coordination or dynamic covalent bond-constructed porous frameworks, IPMs possess high thermal, chemical, and moisture stability and maintain their porosity under critical conditions. Moreover, the intrinsic porosity endows IPMs with excellent host-guest properties in solid, liquid (organic or aqueous), and gas states, which can be further utilized to construct diverse separation strategies, such as solid-gas adsorption, solid-liquid absorption, and liquid-liquid extraction. The diversity of host-guest interactions in the engineered IPMs affords a plethora of possibilities for the development of the ideal "molecular sieves". Herein, we present a different take on the applicability of intrinsically porous materials such as cyclodextrin (CD), cucurbiturils (CB), pillararene (P), trianglamines (T), and porous organic cages (POCs) that showed an impressive performance in gas purification and benzene derivatives separation. IPMs can be easily scaled up and are quite stable and solution processable that consequently facilitates a favorable technological transformation from the traditional energy-intensive separations. We will account for the main advances in molecular host-guest chemistry to design "on-demand" separation processes and also outline future challenges and opportunities for this promising technology.

Supramolecular AIE polymer-based rare earth metallogels for the selective detection and high efficiency removal of cyanide and perchlorate

Two novel supramolecular AIE polymer-based rare earth metallogels (PT-GEu and PT-GTb) have been rationally designed and synthesized for the efficient detection and removal of cyanide (CN⁻) and perchlorate (ClO₄⁻).

Pillararene-based conjugated porous polymers

The synthesis and application of promising polymeric materials–pillararene-based conjugated porous polymers–are discussed and summarized in this review.

Engineering Magnetic Guanidyl-Functionalized Supramolecular Organic Framework for Efficient Enrichment of Global Phosphopeptides

Comprehensive mass spectrometry-based proteomics analysis is currently available but remains challenging, especially for post-translational modifications of phosphorylated proteins. Herein, multifunctional magnetic pillar[5]arene supramolecular organic frameworks were fabricated and immobilized with arginine (mP5SOF-Arg) for highly effective enrichment of global phosphopeptides. The specific phosphate-P5/phosphate-guanidine affinities and large surface area with regular porosity contribute to the high enrichment capacity. By coupling with mass spectrometry, high detection sensitivity (0.1 fmol), excellent selectivity (1:5000 molar ratios of β-casein/cytochrome c), and high recyclability (seven cycles) were achieved for phosphopeptide analysis. mP5SOF-Arg can efficiently enrich phosphopeptides from practical samples, including defatted milk, egg yolk, and human saliva. Notably, a total of 450 phosphopeptides were explored for highly selective identification from A594 cells and 1445 phosphopeptides were identified from mouse liver tissue samples. mP5SOF-Arg exhibited great potential to serve as the basis for peptidomic research to identify phosphopeptides and provided insight for biomarker discovery.

Synthetic Macrocycle-Based Nonporous Adaptive Crystals for Molecular Separation

The exploitation of new materials for adsorptive separation of industrially important hydrocarbons is of great importance in both scientific research and petrochemical industry. Nonporous adaptive crystals (NACs) as a robust class of synthetic materials have drawn much attention during the past five years for their superior performance in adsorption and separation. Pillararenes are the main family of macrocyclic arenes used for NACs construction, where the structure-function relationship has been intensively studied. In the past two years, some emerging types of synthetic macrocyclic arenes have been successfully brought into this research field, showing the gradual enrichment and diversification of NACs materials. This Minireview summarizes the recent advances of synthetic macrocycle-based NACs, which are categorized by various practical applications in molecular separation. Besides, NACs-based vapochromic supramolecular systems are also discussed. Finally, future perspectives and challenges of NACs are given. We envisage that this Minireview will be a useful and timely reference for those who are interested in new molecular and supramolecular crystals for storage and separation applications.

Supramolecular-Macrocycle-Based Crystalline Organic Materials

Supramolecular macrocycles are well known as guest receptors in supramolecular chemistry, especially host-guest chemistry. In addition to their wide applications in host-guest chemistry and related areas, macrocycles have also been employed to construct crystalline organic materials (COMs) owing to their particular structures that combine both rigidity and adaptivity. There are two main types of supramolecular-macrocycle-based COMs: those constructed from macrocycles themselves and those prepared from macrocycles with other organic linkers. This review summarizes recent developments in supramolecular-macrocycle-based COMs, which are categorized by various types of macrocycles, including cyclodextrins, calixarenes, resorcinarenes, pyrogalloarenes, cucurbiturils, pillararenes, and others. Effort is made to focus on the structures of supramolecular-macrocycle-based COMs and their structure-function relationships. In addition, the application of supramolecular-macrocycle-based COMs in gas storage or separation, molecular separation, solid-state electrolytes, proton conduction, iodine capture, water or environmental treatment, etc., are also presented. Finally, perspectives and future challenges in the field of supramolecular-macrocycle-based COMs are discussed.

Conjugated Macrocycle Polymer Nanoparticles with Alternating Pillarenes and Porphyrins as Struts and Cyclic Nodes

Conjugated macrocycle polymers (CMPs) integrated using the macrocyclic confinement effect make imposing restrictions feasible on the growth of metal nanoparticles with confined size and high dispersion. For a proof-of-concept exploration, a novel nanoscale CMP is reported, denoted as DMP[5]-TPP-CMP, comprising two representative types of macrocyclic compounds, i.e., pillararene and porphyrin, as alternating strut/node components in the skeleton. With abundant anchoring sites, CMP implanted with Pd nanoparticles (Pd@DMP[5]-TPP-CMP, Pd@CMP for short) is successfully obtained through a simple post-treatment, exhibiting remarkable catalytic activity in Suzuki-Miyaura coupling (SMC) and nitrophenol reduction. The as-prepared Pd@CMP material shows favorable performance in expediting the process of SMC with an appreciable yield even under mild conditions, as well as in facilitating the electron transfer process from borohydride to nitrophenol through metal-hydride complex to produce aminophenol with a very short transformation time of 3 min and superior apparent kinetic rate constant k _app of 1.9 × 10^-2 s^-1 , higher than most palladium supports. Significantly, this multifunctional Pd@CMP composite material not only enriches the family of CMPs, but also sheds light on the development of green catalysts with excellent stability and easy recyclability without deactivation.

Janus triple tripods build up a microporous manifold for HgCl2 and I2 uptake

Three tripods for a versatile molecular scaffold: combining the Janus core for supramolecular recognition and the planar carboxyl tripod for framework construction enables metal uptake and iodine removal applications.

Multi-stimuli-responsive supramolecular gel constructed by pillar[5]arene-based pseudorotaxanes for efficient detection and separation of multi-analytes in aqueous solution

Here, a novel pseudorotaxanes-type crosslinker of a supramolecular polymer network (WP5-PN) has been constructed from a host water-soluble pillar[5]arene (WP5) and a guest naphthalene dimethylamine derivative (PN) via a stepwise process involving multiple non-covalent interactions. The obtained supramolecular polymers were able to transform into a supramolecular polymer gel (WP5-PN-G) and show AIE properties in DMSO-H2O binary solution. Interestingly, due to the dynamic and reversible nature of non-covalent interactions, the resultant supramolecular polymer gels exhibited external stimuli-responsiveness to different parameters, such as temperature, acid-base, competitive guest and mechanical stress. Moreover, WP5-PN-G showed fluorescent response for Fe3+ and Cu2+, while its xerogel showed excellent recyclable separation properties for these metal ions with adsorption rates up to 98.07% and 95.38%, respectively. Moreover, by rational introduction of these metal ions into the WP5-PN-G, corresponding metal ion coordinated metallogels, such as WP5-PN-FeG and WP5-PN-CuG were obtained. These metallogels could selectively and sensitively sense F- and CN-, respectively. The detection limits of these metallogels for F- and CN- were about 1 × 10-8 M. The WP5-PN-G has potential applications in multi-analytes detection and separation as well as fluorescent display materials.

Near-Ideal Xylene Selectivity in Adaptive Molecular Pillar[ n]arene Crystals

The energy-efficient separation of alkylaromatic compounds is a major industrial sustainability challenge. The use of selectively porous extended frameworks, such as zeolites or metal–organic frameworks, is one solution to this problem. Here, we studied a flexible molecular material, perethylated pillar[n]arene crystals (n = 5, 6), which can be used to separate C8 alkylaromatic compounds. Pillar[6]arene is shown to separate para-xylene from its structural isomers, meta-xylene and ortho-xylene, with 90% specificity in the solid state. Selectivity is an intrinsic property of the pillar[6]arene host, with the flexible pillar[6]arene cavities adapting during adsorption thus enabling preferential adsorption of para-xylene in the solid state. The flexibility of pillar[6]arene as a solid sorbent is rationalized using molecular conformer searches and crystal structure prediction (CSP) combined with comprehensive characterization by X-ray diffraction and ¹³C solid-state NMR spectroscopy. The CSP study, which takes into account the structural variability of pillar[6]arene, breaks new ground in its own right and showcases the feasibility of applying CSP methods to understand and ultimately to predict the behavior of soft, adaptive molecular crystals.

Tetraphenylethylene-Interweaving Conjugated Macrocycle Polymer Materials as Two-Photon Fluorescence Sensors for Metal Ions and Organic Molecules

A luminescent conjugated macrocycle polymer (CMP) with strong two-photon fluorescence property, namely, P[5]-TPE-CMP, is constructed from ditriflate-functionalized pillar[5]arene and a 1,1,2,2-tetrakis(4-ethynylphenyl)ethylene (TPE) linker through a Sonogashira-Hagihara cross-coupling reaction. Significantly, in sharp contrast with the corresponding conjugated microporous polymer without synthetic macrocycles, P[5]-TPE-CMP shows an outstanding stability against photobleaching and exhibits highly selective cation sensing capability toward Fe³⁺ at different excitation wavelengths (both UV and red-near-infrared regions). Meanwhile, its fluorescence could also be sufficiently quenched by 4-amino azobenzene, a frequently used organic dye that is certified to be carcinogenic, as compared with a group of common organic compounds. This work paves a new way for enhancing the properties of porous organic polymers through the introduction of supramolecular macrocycles like macrocyclic arenes.

Rational construction of an ssa-type of MOF through pre-organizing the ligand's conformation and its exceptional gas adsorption properties

A ligand conformation-controlled assembly strategy has been successfully employed to construct a copper-based MOF with the desired ssa-type topology, which exhibits exceptional C₂H₂ and CO₂ adsorption properties.

Macrocycle crosslinked mesoporous polymers for ultrafast separation of organic dyes

Mesoporous polymers were synthesized by interfacial polymerization of macrocycles (sulfonatocalix[4]arenes and pillar[5]arenes) and terephthaloyl chloride.

Multiple Efficient Fluorescence Emission from Cucurbit[10]uril-[Cd4Cl16]8--Based Pillared Diamond Porous Supramolecular Frameworks

Cucurbit[10]uril (Q[10] or CB[10]), with the largest rigid cavity (ca. 1.0 nm) yet characterized in the cucurbiturils family, and indeed among all artificial macrocyclic receptors to date, has been successfully exploited to construct a novel Q[10]-[Cd₄Cl₁₆]^8--based pillared diamond porous supramolecular framework. Single-crystal X-ray diffraction analysis revealed that the three-dimensional open-nanotube-type porous framework is constructed from free Q[10] molecules and [Cd₄Cl₁₆]^8- cluster anions through the outer surface interactions of Q[10]. Notably, the Q[10]-based porous framework host can accommodate guest dyes, such as rhodamine B (G1), pyrenemethanamine hydrochloride (G2), and bathocuproine hydrochloride (G3), to form solid materials with efficient red-green-blue (RGB) fluorescence. This work not only exemplifies a facile approach for the construction of macrocycle-based porous frameworks but also offers a simple, lower cost, yet still highly efficient means of preparing multi-emitting, including white-light-emitting, solid luminescent materials.