Supramolecular materials, dynamic materials by nature, are defined as materials whose components are bridged via reversible connections and undergo spontaneous and continuous assembly/disassembly processes under specific conditions. On account of the dynamic and reversible nature of noncovalent interactions, supramolecular polymers have the ability to adapt to their environment and possess a wide range of intriguing properties, such as degradability, shape-memory, and self-healing, making them unique candidates for supramolecular materials. In this critical review, we address recent developments in supramolecular polymeric materials, which can respond to appropriate external stimuli at the fundamental level due to the existence of noncovalent interactions of the building blocks.

Because of the importance of novel macrocycles in supramolecular science, interest in the preparation of these substances has grown considerably. However, the discovery of a new class of macrocycles presents challenges because of the need for routes to further functionalization of these molecules and good host-guest complexation. Furthermore, useful macrocylic hosts must be easily synthesized in large quantities. With these issues in mind, the recently discovered pillararenes attracted our attention. These macrocycles contain hydroquinone units linked by methylene bridges at para positions. Although the composition of pillararenes is similar to that of calixarenes, they have different structural characteristics. One conformationally stable member of this family is pillar[5]arene, which consists of five hydroquinone units. The symmetrical pillar architecture and electron-donating cavities of these macrocycles are particularly intriguing and afford them with some special and interesting physical, chemical, and host-guest properties. Due to these features and their easy accessibility, pillararenes, especially pillar[5]arenes, have been actively studied and rapidly developed within the last 4 years. In this Account, we provide a comprehensive overview of pillararene chemistry, summarizing our results along with related studies from other researchers. We describe strategies for the synthesis, isomerization, and functionalization of pillararenes. We also discuss their macrocyclic cavity sizes, their host-guest properties, and their self-assembly into supramolecular polymers. The hydroxyl groups of the pillararenes can be modified at all positions or selectively on one or two positions. Through a variety of functionalizations, researchers have developed many pillararene derivatives that exhibit very interesting host-guest properties both in organic solvents and in aqueous media. Guest molecules include electron acceptors such as viologen derivatives and (bis)imidazolium cations and alkyl chain derivatives such as n-hexane, alkanediamines, n-octyltrimethyl ammonium, and neutral bis(imidazole) derivatives. These host-guest studies have led to the fabrication of (pseudo)rotaxanes or poly(pseudo)rotaxanes, supramolecular dimers or polymers, artificial transmembrane proton channels, fluorescent sensors, and other functional materials.

4.3.2. Hybrid Self-Assemblies Constructed from an Amphiphilic Calix[4]arene and Au Nanoparticles 7267 4.4. Photomodulated Fluorescence of Supramolecular Assemblies of Sulfonatocalixarenes and Tetraphenylethene 7267 4.5. Photodynamic Therapy System Fabricated from a Calixarene-Based Supramolecular Amphiphile 7268 4.6. Multi-Stimuli-Responsive Supramolecular Amphiphile as a Drug Delivery System 7269 4.7. Cholinesterase-Responsive Supramolecular Vesicles as Drug Delivery Carriers 7270 4.8. Supramolecular Amphiphiles Constructed from Calixarene Analogues 7271 4.8.1. Supramolecular Amphiphile Based on Calix[4]resorcinarene and a Cationic Surfactant for Controllable Self-Assembly 7271 4.8.2. Fabrication of Well-Defined Crystalline Azacalixarene Nanosheets Assisted by Se•••N Noncovalent Interactions 7272 5. Cucurbituril-Based Supramolecular Amphiphiles 7273 5.1. Supramolecular Vesicles Formed by Amphiphilc Cucurbit[6]uril and Multivalent Binding of Sugar-Decorated Vesicles to Lectin 7274 5.2. Supramolecular Photosensitizers with Enhanced Antibacterial Efficiency 7274 5.3. Supramolecular Approach To Fabricate Highly Emissive Smart Materials 7275 5.4. Cucurbit[8]uril-Based Ternary Supramolecular Amphiphiles 7276 5.4.1. Spontaneous Formation of Vesicles Triggered by Formation of a Charge-Transfer Complex in a Host 7276 5.4.2. Supramolecular Glycolipid Based on Host-Enhanced Charge-Transfer Interaction 7276 5.4.3. Supramolecular Peptide Amphiphile Vesicles through Host−Guest Complexation 7277 5.4.4. Biocompatible and Biodegradable Supramolecular Assemblies for Reduction-Triggered Release of Doxorubicin 7278 6. Pillar[n]arenes-Based Supramolecular Amphiphiles 7279 6.1. Pillar[n]arene-Based Enzyme-Responsive Supramolecular Amphiphiles 7279 6.2. Bola-Type Supramolecular Amphiphile Constructed from a Water-Soluble Pillar[5]arene and a Rod−Coil Molecule for Dual Fluorescent Sensing 7280 6.3. Cationic Water-Soluble Pillar[6]arene-Based Supramolecular Amphiphile 7281 6.4. Photoresponsive Self-Assembly Based on a Water-Soluble Pillar[6]arene and an Azobenzene-Containing Amphiphile in Water 7282 6.5. Four-Armed Supramolecular Amphiphile with Complexation-Induced Emission 7283 6.6. Supramolecular Amphiphiles as Multiwalled Carbon Nanotube Dispersants 7283 6.6.1. pH-Responsive Water-Soluble Pillar[6]arene-Based Supramolecular Amphiphile 7283 6.6.2. UV-Responsive Water-Soluble Pillar[6]arene-Based Supramolecular Amphiphile 7284 6.7. Supramolecular Amphiphiles Constructed on the Basis of Pillararene/Paraquat Recognition 7284 6.7.1. pH-Responsive Supramolecular Amphiphiles on the Basis of Molecular Recognition between Pillar[n]arenes (n = 6, 7, and 10) and Paraquat 7284 6.7.2. Supramolecular Hybrid Nanostructures Based on Pillar[6]arene Modified Gold Nanoparticles/Nanorods and Their Application in pH-and NIR-Triggered Controlled Release 7286 6.8. Water-Soluble Pillar[6]arene-Based Supramolecular Vesicles for Drug Delivery 7287 7. Supramolecular Amphiphiles Constructed by Other Macrocycle-Based Host−Guest Molecular Recognitions 7288 7.1.

Introduction 7399 2. Synthesis of Rotaxanes Based on Various Macrocycles 7400 2.1. Crown Ethers 7401 2.1.1. Bis(m-phenylene)-32-crown-10 and Crown Ethers with Larger Sizes 7401 2.1.2. Dibenzo-24-crown-8 7402 2.1.3. Benzo-21-crown-7 7406 2.1.4. Crown Ether-Based Cryptands 7407 2.2. Cyclodextrins 7410 2.3. Cucurbiturils 7413 2.3.1. Cucurbit[6]uril 7413 2.3.2. Cucurbit[7]uril 7414 2.3.3. Cucurbit[8]uril 7415 2.4. Calixarenes 7416 2.4.1. Calix[4]arenes as Linkers or Stoppers 7416 2.4.2. Calix[5]arenes and Calix[6]arenes as Wheels 7416 2.4.3. Heterocalix[n]arenes or Calix[n]heteroarenes 7417 2.5. Pillararenes 7418 2.5.1.