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This review discusses the design and syntheses of molecular-scale pillar[n]arene-based porous materials with promising applications and summarises the development of using pillar[n]arenes as the building blocks of porous materials. From the perspective of 'role of participation' in the syntheses of molecular-scale pillar[n]arene-based porous materials, the content can be divided into pillar[n]arenes serving as supramolecular nanovalves on surfaces and as ligands for metal-organic frameworks and covalent organic polymers. By integrating pillararenes, which possess rigid pillar-like structures, electron-rich cavities and desirable host-guest properties, with porous polymers of large surface areas and abundant active sites, applications of the resulting materials in drug release platforms, molecular recognition, sensing, detection, gas adsorption, removal of water pollution, organic photovoltaic materials and heterogeneous catalysis can be realised simultaneously and efficiently. Finally, in the conclusion and prospect part, we put forward the challenges and viewpoints of the current research on pillar[n]arene-based porous materials. We hope this article can provide a timely and valuable reference for researchers interested in synthetic macrocycles and porous materials.

Summary Supramolecular macrocyclic compounds including cyclodextrin, pillararene, calixarene, and cucurbituril are a family of multifarious hosts capable of selectively binding with guests via their intrinsic cavities. They have been used as ideal functional entities on the surface of inorganic nanoparticles to improve their solubility, stability, and biocompatibility in vivo. Macrocyclic compounds can be attached onto the surface of inorganic nanoparticles via covalent or noncovalent bonds, thus acting as a versatile anchoring point, which allows reversible complexation with small molecules via host-guest recognitions. A variety of functional tags including imaging probes, targeting groups, and therapeutic agents can be introduced for further functionalization of the organic-inorganic hybrid nanoparticles. The macrocycles-based organic-inorganic nanohybrids have shown remarkable properties and significant potential in various biomedical applications thanks to the surface modification of macrocycles. Here, we review the versatile construction of macrocycles-based hybrid nanomaterial platforms and discuss their significant potential in biomedical and related applications.

A dicarboxylatopillar[5]arene (DCP5)-based coordination polymer, namely DCP5-EuxTby, with color-tunable emission and capable of nitroaromatic pollutant detection, has been designed and fabricated via a typical metal–ligand coordination approach. Due to its rigid skeleton and electron-rich cavity, DCP5 plays an important role in this multi-color framework, not only as a linker but also as a blue-color fluorescence donor. Intriguingly, the fluorescent color of DCP5-EuxTby can be tuned from green to red simply by mediating the molar ratio of Eu3+ : Tb3+ in the functional system. More importantly, a white-color emitting system, that is, DCP5-Eu1Tb3, is discovered when the ratio of Eu3+ : Tb3+ is 1 : 3, and the white-light emissive DCP5-Eu1Tb3 exhibits good detection performance toward nitroaromatic pollutants in a wide application field. We envision that this work will open a new avenue for the exploration of synthetic macrocycle-based new materials in the construction of new fluorescent sensors and detectors for environmental sustainability and bio-related fields.

Synthetic fungicides have been widely used to protect crops from fungal diseases. However, excessive use of synthetic fungicides leads to the generation of fungicide resistance in fungal pathogens. Recently, smart cargo delivery systems have been introduced for the construction of a pesticide delivery nanoplatform, benefiting from their controlled release performance. Herein, a fungal pathogen microenvironment-responsive supramolecular fungicide nanoplatform has been designed and constructed, using quaternary ammonium salt (Q)-modified mesoporous silica nanoparticles (MSN-Q NPs) as nanocarriers loaded with berberine hydrochloride (BH) and carboxylatopillar[5]arene (CP[5]A) as nanogates to form BH-loaded CP[5]A@MSN-Q NPs for effective inhibition of Botrytis cinerea. CP[5]A as nanogates can endow the fungicide nanoplatform with pH stimuli-responsive release features for the control of fungicide release. The loaded BH, as a natural plant fungicide, provides an ecofriendly alternative to synthetic fungicides for controlling B. cinerea. Interestingly, we use oxalic acid (OA) secreted by B. cinerea as a trigger so that BH can be released from the fungicide nanoplatform on demand under pathogen microenvironments for controlling B. cinerea. The experimental results indicate that the fabricated fungicide nanoplatform could effectively inhibit the mycelial growth and spore germination, providing a new way for the management of B. cinerea in actual application.

The fabrication of smart materials is gradually becoming a research focus in nanotechnology and materials science. An important criterion of smart materials is the capacity of stimuli-responsiveness, while another lies in selective recognition. Accordingly, supramolecular host-guest chemistry has proven a promising support for building intelligent, responsive systems; hence, synthetic macrocyclic hosts, such as calixarenes, cucurbiturils, cyclodextrins, and pillararenes, have been used as ideal building blocks. Meanwhile, manipulating and harnessing light artificially is always an intensive attempt for scientists in order to meet the urgent demands of technological developments. Fluorescence resonance energy transfer (FRET), known as a well-studied luminescent activity and also a powerful tool in spectroscopic area, has been investigated from various facets, of which the application range has been broadly expanded. In this review, the innovative collaboration between FRET and supramolecular macrocyclic chemistry will be presented and depicted with typical examples. Facilitated by the dynamic features of supramolecular macrocyclic motifs, a large variety of FRET systems have been designed and organized, resulting in promising optical materials with potential for applications in protein assembly, enzyme assays, diagnosis, drug delivery monitoring, sensing, photosynthesis mimicking and chemical encryption.

Supramolecular nanovalves are an emerging class of important elements that are functionalized on the surfaces of inorganic or hybrid nanocarriers in the constructions of smart cargo delivery systems. Taking advantage of the pseudorotaxane structure via host-guest complexation and the dynamic nature of supramolecular interactions, macrocyclic arene-based supramolecular nanovalves have shown great promise in the applications of drug delivery and controlled release. Careful selection of diverse external stimuli, such as pH variations, temperature changes, redox, enzymes, light irradiation, and competitive binding, can activate the opening and closing of the nanovalves by altering the supramolecular structure or binding affinities. Meanwhile, the porous solid supports in controlled release systems also play an important role in the functionalities of the nanocarriers, which include, but not limited to, mesoporous silica nanoparticles (MSNs), metal-organic frameworks (MOFs), core-shell nanomaterials, and rare-earth porous nanomaterials. The elaborate decoration by macrocyclic arenes-based supramolecular nanovalves on porous nanomaterials has provided intelligent controlled release platforms. In this review, we will focus on the overview of supramolecular nanovalves based on two typical macrocyclic arenes, that is, calixarenes and pillarenes, and their operation manners in the controlled release processes.