Stimuli-responsive fluorescent supramolecular polymer network based on a monofunctionalized leaning tower[6]arene

Recent Developments of Fluorescence Sensors Constructed from Pillar[n]arene-Based Supramolecular Architectures Containing Metal Coordination Sites

The field of fluorescence sensing, leveraging various supramolecular self-assembled architectures constructed from macrocyclic pillar[n]arenes, has seen significant advancement in recent decades. This review comprehensively discusses, for the first time, the recent innovations in the synthesis and self-assembly of pillar[n]arene-based supramolecular architectures (PSAs) containing metal coordination sites, along with their practical applications and prospects in fluorescence sensing. Integrating hydrophobic and electron-rich cavities of pillar[n]arenes into these supramolecular structures endows the entire system with self-assembly behavior and stimulus responsiveness. Employing the host-guest interaction strategy and complementary coordination forces, PSAs exhibiting both intelligent and controllable properties are successfully constructed. This provides a broad horizon for advancing fluorescence sensors capable of detecting environmental pollutants. This review aims to establish a solid foundation for the future development of fluorescence sensing applications utilizing PSAs. Additionally, current challenges and future perspectives in this field are discussed.

Multi-Responsive Molecular Encapsulation and Release Based on Hydrogen-Bonded Azo-Macrocycle

Research on stimuli-responsive host-guest systems is at the cutting edge of supramolecular chemistry, owing to their numerous potential applications such as catalysis, molecular machines, and drug delivery. Herein, we present a multi-responsive host-guest system comprising azo-macrocycle 1 and 4,4'-bipyridinium salt G1 for pH-, photo-, and cation- responsiveness. Previously, we reported a novel hydrogen-bonded azo-macrocycle 1. The size of this host can be controlled through light-induced E↔Z photo-isomerization of the constituent azo-benzenes. The host is found in this work to be capable of forming stable complexes with bipyridinium/pyridinium salts, and implementing guest capture and release with G1 under light in a controlled manner. The binding and release of the guest in the complexes can also be easily controlled reversibly by using acid and base. Moreover, the cation competition-induced dissociation of the complex 1a₂⊃G1 is achieved. These findings are expected to be useful in regulating encapsulation for sophisticated supramolecular systems.

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.

Separation of Low-Molecular-Weight Organics by Water-Soluble Macrocyclic Arenes

In this study, we fabricate a series of water-soluble anionic macrocyclic arenes, including pillar[5]arene (WP5), pillar[6]arene (WP6), leaning pillar[6]arene (WLT6), and biphenyl-extended pillar[6]arene (WBpP6), which show different separation capabilities toward low-molecular-weight organics, such as short chain haloalkanes, cyclic aliphatics, and aromatics, in water. The liquid-liquid distribution experiments are carried out at room temperature. The separation factor for low-molecular-weight organics is evaluated in the extraction of equimolar mixtures. WP6 demonstrates a high extraction efficiency of up to 89% in separating toluene/methylcyclohexane mixtures. These adsorbents also have the advantages of rapid adsorption, high separation efficiency, remarkable selectivity, and good recyclability. This work not only expands the application scope of macrocyclic chemistry, but also has practical research value for organics separation and water purification.

Pillararene-Inspired Macrocycles: From Extended Pillar[n]arenes to Geminiarenes

chemistry since their establishment due to their innate functional features of molecular recognition and complexation. The rapid development of modern supramolecular chemistry has also significantly benefited from creating new macrocycles with distinctive geometries and properties. For instance, pillar[n]arenes (pillarenes), a relatively young generation of star macrocyclic hosts among the well-established ones (e.g., crown ethers, cyclodextrins, cucurbiturils, and calixarenes), promoted a phenomenal research hotspot all over the world in the past decade. Although the synthesis, host-guest properties, and various supramolecular functions of pillarenes have been intensively studied, many objective limitations and challenges still cannot be ignored. For example, high-level pillar[n]arenes (n > 7) usually do not possess applicable large-sized cavities due to structural folding and cannot be synthesized on a large scale because of the uncompetitive cyclization process. Furthermore, two functional groups must be covalently para-connected to each repeating phenylene unit, which severely limits their structural diversity and flexibility. In this context, we have developed a series of pillarene-inspired macrocycles (PIMs) using a versatile and modular synthetic strategy during the past few years, aiming to break through the synthetic limitations in traditional pillarenes and find new opportunities and challenges in supramolecular chemistry and beyond. Specifically, by grafting biphenyl units into the pillarene backbones, extended pillar[n]arenes with rigid and nanometer-sized cavities could be obtained with reasonable synthetic yields by selectively removing hydroxy/alkoxy substitutes on pillarene backbones, leaning pillar[6]arenes and leggero pillar[n]arenes with enhanced structural flexibility and cavity adaptability were obtained. By combining the two types of bridging modes in pillarenes and calixarenes, a smart macrocyclic receptor with two different but interconvertible conformational features, namely geminiarene, was discovered. Benefiting from the synthetic accessibility, facile functionalization, and superior host-guest properties in solution or the solid state, this new family of macrocycles has exhibited a broad range of applications, including but not limited to supramolecular assembly/gelation/polymers, pollutant detection and separation, porous organic polymers, crystalline/amorphous molecular materials, hybrid materials, and controlled drug delivery. Thus, in this Account, we summarize our research efforts on these PIMs. We first present an overview of their design and modular synthesis and a summary of their derivatization strategies. Thereafter, particular attention is paid to their structural features, supramolecular functions, and application exploration. Finally, the remaining challenges and perspectives are outlined for their future development. We hope that this Account and our works can stimulate further advances in synthetic macrocyclic chemistry and supramolecular functional systems, leading to practical applications in various research areas.

Supramolecular systems prepared using terpyridine-containing pillararene

Recent progresses about the preparation of terpyridine-containing pillararene, as well as the utilization of those building blocks for making external stimulud-responsive supramolecular systems were summarized in this review.

Barbier single-atom polymerization induced emission as a one-pot approach towards stimuli-responsive luminescent polymers

A one-pot strategy for the design of stimuli-responsive luminescent polymers has been demonstrated through Barbier PIE, where the N,N-dimethyl moiety endows the polymers with both stimuli-responsive and red-shifted nonconjugated emission properties.

Aggregation-Induced Emission-Active Gels: Fabrications, Functions, and Applications

Chromophores that exhibit aggregation-induced emission (i.e., aggregation-induced emission luminogens [AIEgens]) emit intense fluorescence in their aggregated states, but show negligible emission as discrete molecular species in solution due to the changes in restriction and freedom of intramolecular motions. As solvent-swollen quasi-solids with both a compact phase and a free space, gels enable manipulation of intramolecular motions. Thus, AIE-active gels have attracted significant interest owing to their various distinctive properties and promising application potential. Herein, a comprehensive overview of AIE-active gels is provided. The fabrication strategies employed are detailed, and the applications of AIEgens are summarized. In addition, the gel functions arising from the AIE moieties are revealed, along with their structure-property relationships. Furthermore, the applications of AIE-active gels in diverse areas are illustrated. Finally, ongoing challenges and potential means to address them are discussed, along with future perspectives on AIE-active gels, with the overall aim of inspiring research on novel materials and ideas.

Pillar[n]arene-Based Supramolecular Switches in Solution and on Surfaces

The design and synthesis of new synthetic macrocycles has driven the rapid development of supramolecular chemistry and materials. Pillar[n]arenes, as a new type of macrocyclic compounds, are used as a promising type of building blocks for switchable supramolecular systems due to their versatile functionalization and the ability of binding toward various guest molecules. A number of guests can form inclusion complexes with pillar[n]arenes and their derivatives in solution, which are sensitive to different external triggers. Interestingly, the pursuit of complex stimuli-responsive functional materials and devices has largely motivated the shift of pillar[n]arene-based switches from solution media to surfaces for controllable macroscopic motions on solid platforms. Facilitated by the facile modification of pillar[n]arenes on various solid supports and the dynamic binding of host-guest complexes, numerous functional hybrid materials with adjustable physical or chemical properties and integrated functionalities have been reported in the last decade. Here, the advance of supramolecular switches in solution and on surfaces based on pillar[n]arenes and derivatives with an emphasis on the efforts and the latest contributions from the field is discussed.