In 2008, we reported a new class of pillar-shaped macrocyclic hosts, known as “pillar[n]arenes”. Today, pillar[n]arenes are recognized as key players in supramolecular chemistry because of their facile synthesis, unique pillar shape, versatile functionality, interesting host–guest properties, and original supramolecular assembly characteristics, which have resulted in numerous electrochemical and biomedical material applications. In this Review, we have provided historical background to macrocyclic chemistry, followed by a detailed discussion of the fundamental properties of pillar[n]arenes, including their synthesis, structure, and host–guest properties. Furthermore, we have discussed the applications of pillar[n]arenes to materials science, as well as their applications in supramolecular chemistry, in terms of their fundamental properties. Finally, we have described the future perspectives of pillar[n]arene chemistry. We hope that this Review will provide a useful reference for researchers working in th...

Pillar-Shaped Macrocyclic Hosts Pillar[n]arenes: New Key Players for Supramolecular Chemistry

Macrocycles are molecular entities that display a combination of molecular recognition and complexation properties with vital implications for host–guest/supramolecular chemistry. Since the accidental discovery of the crown ethers by Pedersen half a century ago, the chemistry of wholly synthetic macrocycles for structure-specific, highly selective, host–guest complexation has experienced rapid development. While the structural diversity and host–guest chemistry of the original macrocycles are well-known, new derivatives of them are being investigated continuously and reported on today in order to improve their recognition properties as well as to unleash new opportunities in supramolecular chemistry. In this Review, we survey the recent developments of the chemistry of naturally occurring cyclodextrins, along with a variety of synthetic flexible and rigid macrocycles that have drawn their inspiration from Pedersen's ground-breaking discovery of crown ethers in the mid-1960s.

Surveying macrocyclic chemistry: from flexible crown ethers to rigid cyclophanes

Medicine can benefit significantly from advances in nanotechnology because nanoscale assemblies promise to improve on previously established therapeutic and diagnostic regimes. Over the past decade, the use of delivery platforms has attracted attention as researchers shift their focus toward new ways to deliver therapeutic and/or diagnostic agents and away from the development of new drug candidates. Metaphorically, the use of delivery platforms in medicine can be viewed as the "bow-and-arrow" approach, where the drugs are the arrows and the delivery vehicles are the bows. Even if one possesses the best arrows that money can buy, they will not be useful if one does not have the appropriate bow to deliver the arrows to their intended location. Currently, many strategies exist for the delivery of bioactive agents within living tissue. Polymers, dendrimers, micelles, vesicles, and nanoparticles have all been investigated for their use as possible delivery vehicles. With the growth of nanomedicine, one can envisage the possibility of fabricating a theranostic vector that could release powerful therapeutics and diagnostic markers simultaneously and selectively to diseased tissue. In our design of more robust theranostic delivery systems, we have focused our attention on using mesoporous silica nanoparticles (SNPs). The payload "cargo" molecules can be stored within this robust domain, which is stable to a wide range of chemical conditions. This stability allows SNPs to be functionalized with stimulus-responsive mechanically interlocked molecules (MIMs) in the shape of bistable rotaxanes and psuedorotaxanes to yield mechanized silica nanoparticles (MSNPs). In this Account, we chronicle the evolution of various MSNPs, which came about as a result of our decade-long collaboration, and discuss advances in the synthesis of novel hybrid SNPs and the various MIMs which have been attached to their surfaces. These MIMs can be designed in such a way that they either change shape or shed off some of their parts in response to a specific stimulus, such as changes in redox potential, alterations in pH, irradiation with light, or the application of an oscillating magnetic field, allowing a theranostic payload to be released from the nanopores to a precise location at the appropiate time. We have also shown that these integrated systems can operate not only within cells, but also in live animals in response to pre-existing biological triggers. Recognizing that the theranostics of the future could offer a fresh approach to the treatment of degenerative diseases including cancer, we aim to start moving out of the chemical domain and into the biological one. Some MSNPs are already being tested in biological systems.

Mechanized Silica Nanoparticles: A New Frontier in Theranostic Nanomedicine

Pillar[5]arene tetramers with tetraphenylethene cores and different lengths of alkyl ether chains (H1-4C4P and H2-2C4P) and a 9,10-distyrylanthrace-bridged neutral guest linker (DSA-G) are synthesized to fabricate tunable solid-state fluorescent materials through supramolecular assemblies of DSA-G⊂H1-4C4P and DSA-G⊂H2-2C4P. Their fluorescence emission is strongly enhanced and their colors are changed upon assembly, which can be ascribed to the supramolecular assembly-induced enhanced emission and Forster resonance energy transfer (FRET) processes between H1-4C4P (or H2-2C4P) and DSA-G. Both ensembles of DSA-G⊂H1-4C4P and DSA-G⊂H2-2C4P exhibit thermo and solvent dual-responsive features, while DSA-G⊂H2-2C4P shows higher sensitivity toward external stimuli as compared to DSA G⊂H1-4C4P due to the shorter distance between fluorophores. The use of these fluorescent materials as inks confirms their efficiencies in the solid-state, paving the way for new potential applications of smart optical materials based on supramolecular assemblies.

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Jie Han

Papers

Activation-Enabled Syntheses of Functionalized Pillar[5]arene Derivatives.