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The preparation of highly rigid cobalt(II)- and copper(II)–organic frameworks incorporating a tetralactam [2]rotaxane as a ligand is described. The interlocked ligand is functionalized with two pairs of carboxylate groups placed at each counterpart, thus limiting its dynamics within the crystal. The solid structure of the metal–organic rotaxane frameworks showed different, unprecedented polycatenation modes of grids, depending on the employed metal, providing great rigidity to the structures. This rigidity has been evaluated by using single crystal X-ray diffraction analyses of the cobalt(II)–organic frameworks embedded in different solvents, observing that the lattices remain unchanged. Thus, this research demonstrates that rigid and robust materials with permanent porosity can be achieved using dynamic ligands. [ABSTRACT FROM AUTHOR]

The interactions between ether naphthotube and a series of dication guests in organic solution were investigated. It was found that ether naphthotube formed stable host‐guest complexes selectively with these guests in a 1 : 1 stoichiometric ratio with association constants ranging from 102 to 106 M−1, which were confirmed by 1H‐NMR spectra and ITC experiments. The host‐guest interactions are driven by enthalpy change as the entropic factors are unfavorable. Positive correlations between ΔH and ΔS have been observed in the host‐guest complexes. Furthermore, the para‐substitution of the guests can significantly affect the binding affinities through a combination of field/inductive and resonance effects by following a linear free energy relationship. Based on the host‐guest complexes composed of ether naphthotube and organic cations, two interlocked [2]rotaxanes were prepared by cationization reaction and Huisgen cycloaddition between the cations and the stopper components. The ether naphthotube‐based host‐guest complexes are useful for creating sophisticated interlocked molecules. [ABSTRACT FROM AUTHOR]

Brønsted basicity is a fundamental chemical property featured by several kinds of inorganic and organic compounds. In this Review, we treat a particularly high basicity resulting from the mechanical entanglement involving two or more molecular subunits in catenanes and rotaxanes. Such entanglement allows a number of basic sites to be in close proximity with each other, highly increasing the proton affinity in comparison with the corresponding, non-entangled counterparts up to obtain superbases, properly defined as mechanically interlocked superbases. In the following pages, the development of this kind of superbases will be described with a historical perusal, starting from the initial, serendipitous findings up to the most recent reports where the strong basic property of entangled molecular units is the object of a rational design. Brønsted basicity can be greatly enhanced by the mechanical entanglement of two or more interlocked molecular subunits within catenanes and rotaxanes. Here, the authors discuss the development of such mechanically interlocked superbases, and outline challenges and opportunities for future directions of research. [ABSTRACT FROM AUTHOR]

We report that the use of a hydrogen-bonded pyrimidine-macrocycle complex can efficiently facilitate the threading of two bispyridinium ethylenes into four rings, as evidenced by X-ray crystallography of its precursor, offering a rare example of a doubly threaded [6]rotaxane in 91% yield. The unusual architecture is found to be stable with no dethreading despite the large ring size of the macrocycle with respect to the stopper. [ABSTRACT FROM AUTHOR]

The first example of a [2]rotaxane shuttle capable of selective optical sensing of chloride anions over other halides is reported. The rotaxane was synthesised via a chloride ion template‐directed cyclisation of an isophthalamide macrocycle around a multi‐station axle containing peripheral naphthalene diimide (NDI) stations and a halogen bonding (XB) bis(iodotriazole) based station. Proton NMR studies indicate the macrocycle resides preferentially at the NDI stations in the free rotaxane, where it is stabilised by aromatic donor‐acceptor charge transfer interactions between the axle NDI and macrocycle hydroquinone moieties. Addition of chloride ions in an aqueous‐acetone solvent mixture induces macrocycle translocation to the XB anion binding station to facilitate the formation of convergent XB⋅⋅⋅Cl− and hydrogen bonding HB⋅⋅⋅Cl− interactions, which is accompanied by a reduction of the charge‐transfer absorption band. Importantly, little to no optical response was induced by addition of bromide or iodide to the rotaxane, indicative of the size discriminative steric inaccessibility of the interlocked cavity to the larger halides, demonstrating the potential of using the mechanical bond effect as a potent strategy and tool in chloride‐selective chemo‐sensing applications in aqueous containing solvent environments. [ABSTRACT FROM AUTHOR]

Mechanically interlocked molecules (MIMs) represent an exciting yet underexplored area of research in the context of carbon nanoscience. Recently, work from our group and others has shown that small carbon nanotube fragments—[n]cycloparaphenylenes ([n]CPPs) and related nanohoop macrocycles—may be integrated into mechanically interlocked architectures by leveraging supramolecular interactions, covalent tethers, or metal‐ion templates. Still, available synthetic methods are typically difficult and low yielding, and general methods that allow for the creation of a wide variety of these structures are limited. Here we report an efficient route to interlocked nanohoop structures via the active template Cu‐catalyzed azide‐alkyne cycloaddition (AT−CuAAC) reaction. With the appropriate choice of substituents, a macrocyclic precursor to 2,2′‐bipyridyl embedded [9]CPP (bipy[9]CPP) participates in the AT−CuAAC reaction to provide [2]rotaxanes in near‐quantitative yield, which can then be converted into the fully π‐conjugated catenane structures. Through this approach, two nanohoop[2]catenanes are synthesized which consist of a bipy[9]CPP catenated with either Tz[10]CPP or Tz[12]CPP (where Tz denotes a 1,2,3‐triazole moiety replacing one phenylene ring in the [n]CPP backbone). [ABSTRACT FROM AUTHOR]

Mechanically interlocked molecules (MIMs) represent an exciting yet underexplored area of research in the context of carbon nanoscience. Recently, work from our group and others has shown that small carbon nanotube fragments—[n]cycloparaphenylenes ([n]CPPs) and related nanohoop macrocycles—may be integrated into mechanically interlocked architectures by leveraging supramolecular interactions, covalent tethers, or metal‐ion templates. Still, available synthetic methods are typically difficult and low yielding, and general methods that allow for the creation of a wide variety of these structures are limited. Here we report an efficient route to interlocked nanohoop structures via the active template Cu‐catalyzed azide‐alkyne cycloaddition (AT−CuAAC) reaction. With the appropriate choice of substituents, a macrocyclic precursor to 2,2′‐bipyridyl embedded [9]CPP (bipy[9]CPP) participates in the AT−CuAAC reaction to provide [2]rotaxanes in near‐quantitative yield, which can then be converted into the fully π‐conjugated catenane structures. Through this approach, two nanohoop[2]catenanes are synthesized which consist of a bipy[9]CPP catenated with either Tz[10]CPP or Tz[12]CPP (where Tz denotes a 1,2,3‐triazole moiety replacing one phenylene ring in the [n]CPP backbone). [ABSTRACT FROM AUTHOR]

The spontaneous generation of transmembrane gradients is an important fundamental research goal for artificial nanotechnology. The active transport processes that give rise to such gradients directly mirror the famous Maxwell's Demon thought experiment, where a Demon partitions particles between two chambers to generate a nonequilibrium state. Despite these similarities, discussion of Maxwell's Demon is absent in the literature on artificial membrane transport. By contrast, the emergence of rational design principles for nonequilibrium artificial molecular motors can trace its intellectual roots directly to this famous thought experiment. This perspective highlights the links between Maxwell's Demon and nonequilibrium machines, and argues that understanding the implications of this 19th century thought experiment is crucial to the future development of transmembrane active transport processes. [ABSTRACT FROM AUTHOR]

Processive catalysts remain attached to a substrate and perform multiple rounds of catalysis. They are abundant in nature. This review highlights artificial processive catalytic systems, which can be divided into (A) catalytic rings that move along a polymer chain, (B) catalytic pores that hold polymer chains and decompose them, (C) catalysts that remain attached to and move around a cyclic substrate via supramolecular interactions, and (D) anchored catalysts that remain in contact with a substrate via multiple catalytic interactions (see frontispiece). [ABSTRACT FROM AUTHOR]

"Improbable" rotaxanes consisting of interlocked conjugated components represent non‐trivial synthetic targets, not to mention those with all‐benzene scaffolds. Herein, a modular synthetic strategy has been established using an isolable azo‐linked pre‐rotaxane as the core module, in which the azo group functions as a tracelessly removable template to direct mechanical bond formations. Through versatile connections of the pre‐rotaxane and other customizable modules, [2]‐ and [3]rotaxanes derived from all‐benzene scaffolds have been accomplished, demonstrating the utility and potential of the synthetic design for all‐benzene interlocked supramolecules. [ABSTRACT FROM AUTHOR]

The transmission of chiral information between the molecular, meso and microscopic scales is a facet of biology that remains challenging to understand mechanistically and to mimic with artificial systems. Here we demonstrate that the dynamic change in the expression of the chirality of a rotaxane can be transduced into a change in pitch of a soft matter system. Shuttling the position of the macrocycle from far‐away‐from to close‐to a point‐chiral center on the rotaxane axle changes the expression of the chiral information that is transmitted across length scales; from nanometer scale constitutional chirality that affects the conformation of the macrocycle, to the centimeter scale chirality of the liquid crystal phase, significantly changing the pitch length of the chiral nematic structure. [ABSTRACT FROM AUTHOR]

"Improbable" rotaxanes consisting of interlocked conjugated components represent non‐trivial synthetic targets, not to mention those with all‐benzene scaffolds. Herein, a modular synthetic strategy has been established using an isolable azo‐linked pre‐rotaxane as the core module, in which the azo group functions as a tracelessly removable template to direct mechanical bond formations. Through versatile connections of the pre‐rotaxane and other customizable modules, [2]‐ and [3]rotaxanes derived from all‐benzene scaffolds have been accomplished, demonstrating the utility and potential of the synthetic design for all‐benzene interlocked supramolecules. [ABSTRACT FROM AUTHOR]

The transmission of chiral information between the molecular, meso and microscopic scales is a facet of biology that remains challenging to understand mechanistically and to mimic with artificial systems. Here we demonstrate that the dynamic change in the expression of the chirality of a rotaxane can be transduced into a change in pitch of a soft matter system. Shuttling the position of the macrocycle from far‐away‐from to close‐to a point‐chiral center on the rotaxane axle changes the expression of the chiral information that is transmitted across length scales; from nanometer scale constitutional chirality that affects the conformation of the macrocycle, to the centimeter scale chirality of the liquid crystal phase, significantly changing the pitch length of the chiral nematic structure. [ABSTRACT FROM AUTHOR]

Inspired by interlocked oligonucleotides, peptides and knotted proteins, synthetic systems where a macrocycle cages a bioactive species that is "switched on" by breaking the mechanical bond have been reported. However, to date, each example uses a bespoke chemical design. Here we present a platform approach to mechanically caged structures wherein a single macrocycle precursor is diversified at a late stage to include a range of trigger units that control ring opening in response to enzymatic, chemical, or photochemical stimuli. We also demonstrate that our approach is applicable to other classes of macrocycles suitable for rotaxane and catenane formation. [ABSTRACT FROM AUTHOR]

Inspired by interlocked oligonucleotides, peptides and knotted proteins, synthetic systems where a macrocycle cages a bioactive species that is "switched on" by breaking the mechanical bond have been reported. However, to date, each example uses a bespoke chemical design. Here we present a platform approach to mechanically caged structures wherein a single macrocycle precursor is diversified at a late stage to include a range of trigger units that control ring opening in response to enzymatic, chemical, or photochemical stimuli. We also demonstrate that our approach is applicable to other classes of macrocycles suitable for rotaxane and catenane formation. [ABSTRACT FROM AUTHOR]

Over the last two decades ratchet mechanisms have transformed the understanding and design of stochastic molecular systems—biological, chemical and physical—in a move away from the mechanical macroscopic analogies that dominated thinking regarding molecular dynamics in the 1990s and early 2000s (e.g. pistons, springs, etc), to the more scale‐relevant concepts that underpin out‐of‐equilibrium research in the molecular sciences today. Ratcheting has established molecular nanotechnology as a research frontier for energy transduction and metabolism, and has enabled the reverse engineering of biomolecular machinery, delivering insights into how molecules ‘walk’ and track‐based synthesisers operate, how the acceleration of chemical reactions enables energy to be transduced by catalysts (both motor proteins and synthetic catalysts), and how dynamic systems can be driven away from equilibrium through catalysis. The recognition of molecular ratchet mechanisms in biology, and their invention in synthetic systems, is proving significant in areas as diverse as supramolecular chemistry, systems chemistry, dynamic covalent chemistry, DNA nanotechnology, polymer and materials science, molecular biology, heterogeneous catalysis, endergonic synthesis, the origin of life, and many other branches of chemical science. Put simply, ratchet mechanisms give chemistry direction. Kinetic asymmetry, the key feature of ratcheting, is the dynamic counterpart of structural asymmetry (i.e. chirality). Given the ubiquity of ratchet mechanisms in endergonic chemical processes in biology, and their significance for behaviour and function from systems to synthesis, it is surely just as fundamentally important. This Review charts the recognition, invention and development of molecular ratchets, focussing particularly on the role for which they were originally envisaged in chemistry, as design elements for molecular machinery. Different kinetically asymmetric systems are compared, and the consequences of their dynamic behaviour discussed. These archetypal examples demonstrate how chemical systems can be driven inexorably away from equilibrium, rather than relax towards it. [ABSTRACT FROM AUTHOR]

An aqueous solution of chlorinated polyethylene glycol (Cl-PEG-Cl) and α-cyclodextrin (α-CD) was used to form inclusion complexes, which several α-CDs are threaded into the linear PEG chain and produced a so-called polypseudorotaxane (PPRx). By attaching 4-ethylaniline as the blocking agent to the chlorinated PEG chain ends, the complex will be stabilized, resulting in the formation of so-called polyrotaxane (PRx) (also known as molecular necklace). Finally, crosslinked αCD-based PRx with a tubular structure was formed via the condensation reactions between α-cyclodextrins and epichlorohydrin. Using concentrated NaOH solution, polymer chains were then removed from complexes, resulting in the so-called molecular tube (MT). This novel method led to the improvement in polyrotaxane conversion with less production steps and reduced materials overall costs. Resulting products in each section were characterized by 1H and 13C nuclear magnetic resonance spectroscopies (1H-NMR and 13C-NMR), from which complex inclusion ratio and length of the nanotubes were estimated. XRD was also used to confirm tubular structure of the inclusion complexes. [ABSTRACT FROM AUTHOR]

The concept of polyrotaxane comes from the rotaxane structure in the supramolecular field. It is a mechanically interlocked supramolecular assembly composed of linear polymer chains and cyclic molecules. Over recent decades, the synthesis and application of polyrotaxanes have seen remarkable growth. Particularly, cyclodextrin‐based polyrotaxanes have been extensively reported due to the low‐price raw materials, good biocompatibility, and ease of modification. Hence, it is also one of the most promising mechanically interlocking supramolecules for wide industrialization in the future. Polyrotaxanes are widely introduced into materials such as elastomers, hydrogels, and engineering polymers to improve their mechanical properties or impart functionality to the materials. In these materials, polyrotaxane acts as a slidable cross‐linker to dissipate energy through sliding or assist in dispersing stress concentration in the cross‐linked network, thereby enhancing the toughness of the materials. Further, the unique sliding‐ring effect of cyclodextrin‐based polyrotaxanes has pioneered advancements in stretchable electronics and energy storage materials. This includes their innovative use in stretchable conductive composite and binders for anodes, addressing critical challenges in these fields. In this mini‐review, our focus is to highlight the current progress and potential wider applications in the future, underlining their transformative impact across various domains of material science. [ABSTRACT FROM AUTHOR]

'Impossible' rotaxanes, which are constituted by interlocked components without obvious binding motifs, have attracted the interest of the mechanically interlocked molecules (MIMs) community. Within the synthetic efforts reported in the last decades towards the preparation of MIMs, some innovative protocols for accessing 'impossible' rotaxanes have been developed. This short review highlights different selected synthetic examples of 'impossible' rotaxanes, as well as suggests some future directions of this research area. [ABSTRACT FROM AUTHOR]

Aiming at the construction of novel stimuli‐responsive fluorescent system with precisely tunable emissions, the typical 9,14‐diphenyl‐9,14‐dihydrodibenzo[a, c]phenazine (DPAC) luminogen with attractive vibration‐induced emission (VIE) behavior has been introduced into [2]rotaxane as a stopper. Taking advantage of their unique dual stimuli‐responsiveness towards solvent and anion, the resultant [2]rotaxanes reveal both tunable VIE and switchable circularly polarized luminescence (CPL). Attributed to the formation of mechanical bonds, DPAC‐functionalized [2]rotaxanes display interesting VIE behaviors including white‐light emission upon the addition of viscous solvent, as evaluated in detail by femtosecond transient absorption (TA) spectra. In addition, ascribed to the regulation of chirality information transmission through anion‐induced motions of chiral wheel, the resolved chiral [2]rotaxanes reveal unique switchable CPL upon the addition of anion, leading to significant increase in the dissymmetry factors (glum) values with excellent reversibility. Interestingly, upon doping the chiral [2]rotaxanes in stretchable polymer, the blend films reveal remarkable emission change from white light to light blue with significant 6.5‐fold increase in glum values up to −0.035 under external tensile stresses. This work provides not only a new design strategy for developing molecular systems with fluorescent tunability but also a novel platform for the construction of smart chiral luminescent materials for practical use. [ABSTRACT FROM AUTHOR]

Aiming at the construction of novel stimuli‐responsive fluorescent system with precisely tunable emissions, the typical 9,14‐diphenyl‐9,14‐dihydrodibenzo[a, c]phenazine (DPAC) luminogen with attractive vibration‐induced emission (VIE) behavior has been introduced into [2]rotaxane as a stopper. Taking advantage of their unique dual stimuli‐responsiveness towards solvent and anion, the resultant [2]rotaxanes reveal both tunable VIE and switchable circularly polarized luminescence (CPL). Attributed to the formation of mechanical bonds, DPAC‐functionalized [2]rotaxanes display interesting VIE behaviors including white‐light emission upon the addition of viscous solvent, as evaluated in detail by femtosecond transient absorption (TA) spectra. In addition, ascribed to the regulation of chirality information transmission through anion‐induced motions of chiral wheel, the resolved chiral [2]rotaxanes reveal unique switchable CPL upon the addition of anion, leading to significant increase in the dissymmetry factors (glum) values with excellent reversibility. Interestingly, upon doping the chiral [2]rotaxanes in stretchable polymer, the blend films reveal remarkable emission change from white light to light blue with significant 6.5‐fold increase in glum values up to −0.035 under external tensile stresses. This work provides not only a new design strategy for developing molecular systems with fluorescent tunability but also a novel platform for the construction of smart chiral luminescent materials for practical use. [ABSTRACT FROM AUTHOR]

ABA types triblock copolymers, specifically poly(L‐lactide)‐co‐poly(ethylene glycol)‐co‐poly(L‐lactide) (PLLA‐PEG‐PLLA) and poly(D‐lactide)‐co‐poly(ethylene glycol)‐co‐poly(D‐lactide) (PDLA‐PEG‐PDLA), are employed for stereocomplexes (SCs) formation. These SCs are subsequently utilized as axles, in conjunction with various cyclodextrins (CDs) as ring moieties to create pseudo‐polyrotaxane (PPRX). The authors referred to this new construct as "SC PPRX", to distinguish it from the earlier study, denoted as "PPRX SC", which primarily focuses on SC within the PPRX. When attempting to form PPRXs in aqueous solutions, the authors encountered challenges related to the inclusion of CDs due to the robust presence of the SC structure. However, by using mixed solvents, such as water/acetone (10/1, v/v), a partial relaxation of the SC structure is observed. This allows for the successful inclusion of CDs, thereby facilitating the PPRX formation. These observations highlight the significance of axle–axle interaction, which, in this case, prevailed over axle–ring interactions in determining the outcome of the formation process. The authors propose the term, 'SC pseudo‐capping effect' to describe this unique phenomenon, underscoring the role of interactions among polymer chains, including polymer–polymer and axle–axle interactions, in shaping the architecture of rotaxanes. This study thus unveils a novel dimension of polymer‐polymer interactions within the realm of rotaxane. [ABSTRACT FROM AUTHOR]

Oligo(para‐phenylene) (PPn) is a compound composed of directly connected 1,4‐phenylene moieties. The synthesis of PPn composed of six or more phenylene moieties with no substituent at the internal phenylene moiety has been challenging because of its low solubility. Herein we synthesized oligo(para‐phenylene)[2]rotaxanes, including a deca(para‐phenylene)[2]rotaxane, with a defined number of phenylene moieties. Biaryl coupling of iodoarenes mediated by macrocyclic dibenzodihydrophenanthroline‐Ni complex was utilized for the first time to synthesize the [2]rotaxanes. Compared to the non‐interlocked deca(para‐phenylene), the deca(para‐phenylene)[2]rotaxane showed higher solubility. The properties of the oligo(para‐phenylene)[2]rotaxanes and non‐interlocked oligo(para‐phenylene)s were analyzed by spectroscopic methods. [ABSTRACT FROM AUTHOR]

Topological gels possess structures that are cross‐linked only via physical constraints; ideally, no attractive intermolecular interactions act between their components, which yields interesting physical properties. However, most reported previous topological gels were synthesized based on supramolecular interlocked structures such as polyrotaxane, for which attractive intermolecular interactions are essential. Here, we synthesize a water‐soluble "molecular net" (MN) with a large molecular weight and three‐dimensional network structure using poly(ethylene glycol). When a water‐soluble monomer (N‐isopropylacrylamide) is polymerized in the presence of the MNs, the extending polymer chains penetrates the MNs to form an ideal topological MN gel with no specific attractive interactions between its components. The MN gels show unique physical properties as well a significantly high degree of swelling and high extensibility due to slipping of the physical cross‐linking. We postulate this method to yield a new paradigm in gel science with unprecedented physical properties. [ABSTRACT FROM AUTHOR]

Topological gels possess structures that are cross‐linked only via physical constraints; ideally, no attractive intermolecular interactions act between their components, which yields interesting physical properties. However, most reported previous topological gels were synthesized based on supramolecular interlocked structures such as polyrotaxane, for which attractive intermolecular interactions are essential. Here, we synthesize a water‐soluble "molecular net" (MN) with a large molecular weight and three‐dimensional network structure using poly(ethylene glycol). When a water‐soluble monomer (N‐isopropylacrylamide) is polymerized in the presence of the MNs, the extending polymer chains penetrates the MNs to form an ideal topological MN gel with no specific attractive interactions between its components. The MN gels show unique physical properties as well a significantly high degree of swelling and high extensibility due to slipping of the physical cross‐linking. We postulate this method to yield a new paradigm in gel science with unprecedented physical properties. [ABSTRACT FROM AUTHOR]

A supramolecular photovoltaic strategy is applied to enhance power conversion efficiencies (PCE) of photoelectrochemical devices by suppressing electron–hole recombination after photoinduced electron transfer (PET). Here, the author exploit supramolecular localization of the redox mediator—in close proximity to the dye—through a rotaxane topology, reducing electron–hole recombination in p‐type dye‐sensitized solar cells (p‐DSSCs). Dye PRotaxane features 1,5‐dioxynaphthalene recognition sites (DNP‐arms) with a mechanically‐interlocked macrocyclic redox mediator naphthalene diimide macrocycle (3‐NDI‐ring), stoppering synthetically via click chemistry. The control molecule PStopper has stoppered DNP‐arms, preventing rotaxane formation with the 3‐NDI‐ring. Transient absorption and time‐resolved fluorescence spectroscopy studies show ultrafast (211 ± 7 fs and 2.92 ± 0.05 ps) PET from the dye‐moiety of PRotaxane to its mechanically interlocked 3‐NDI‐ring‐acceptor, slowing down the electron–hole recombination on NiO surfaces compared to the analogue. p‐DSSCs employing PRotaxane (PCE = 0.07%) demonstrate a 30% PCE increase compared to PStopper (PCE = 0.05%) devices, combining enhancements in both open‐circuit voltages (VOC = 0.43 vs 0.36 V) and short‐circuit photocurrent density (JSC = −0.39 vs −0.34 mA cm−2). Electrochemical impedance spectroscopy shows that PRotaxane devices exhibit hole lifetimes (τh) approaching 1 s, a 16‐fold improvement compared to traditional I−/I3−‐based systems (τh = 50 ms), demonstrating the benefits obtained upon nanoengineering of interfacial dye‐regeneration at the photocathode. [ABSTRACT FROM AUTHOR]

Rotaxanes are interlocked molecules that consist of a macrocycle encircling a stoppered thread. The ability to control relative component positions makes rotaxanes ideal building blocks for constructing functional and responsive molecular machines. Despite the potential of rotaxanes, their challenging synthesis limits their application. One approach to construct rotaxanes is to use an active template synthesis, where a reaction that forms the thread is accelerated in the cavity of a macrocycle. An emerging method of active template synthesis that exploits the ability of crown ether macrocycles to accelerate simple organic reactions is discussed herein. Crown ether active template synthesis (CEATS) permits the rapid and simple synthesis of rotaxanes containing a wide range of functionality. Integrating rotaxane formation with chemical reaction networks has permitted the construction of molecular machines. The simplification of rotaxane synthesis will facilitate their widespread study and application. [ABSTRACT FROM AUTHOR]

Mechanically interlocked polymers (MIPs) are promising candidates for the construction of elastomeric materials with desirable mechanical performance on account of their abilities to undergo inherent rotational and translational mechanical movements at the molecular level. However, the investigations on their mechanical properties are lagging far behind their structural fabrication, especially for linear polyrotaxanes in bulk. Herein, we report stretchable poly[2]rotaxane elastomers (PREs) which integrate numerous mechanical bonds in the polymeric backbone to boost macroscopic mechanical properties. Specifically, we have synthesized a hydroxyfunctionalized [2]rotaxane that subsequently participates in the condensation polymerization with diisocyanate to form PREs. Benefitting from the peculiar structural and dynamic characteristics of the poly[2]rotaxane, the representative PRE exhibits favorable mechanical performance in terms of stretchability (∼1200%), Young's modulus (24.6 MPa), and toughness (49.5 MJ/m3). Moreover, we present our poly[2]rotaxanes as model systems to understand the relationship between mechanical bonds and macroscopic mechanical properties. It is concluded that the mechanical properties of our PREs are mainly determined by the unique topological architectures which possess a consecutive energy dissipation pathway including the dissociation of host-guest interaction and consequential sliding motion of the wheel along the axle in the [2]rotaxane motif. [ABSTRACT FROM AUTHOR]

This article explores the use of ionic ligand-substrate interactions in enantioselective palladium-catalyzed Suzuki-Miyaura reactions. Traditionally, stereochemical control in asymmetric catalysis has relied on steric repulsion, but recent research has investigated the use of noncovalent interactions, such as ionic interactions, to enhance stereoselectivity. The article focuses on the challenges and advancements in utilizing ionic interactions in transition-metal catalysis and presents recent work on developing chiral dialkyl biarylphosphine ligands with nonligating ionic groups for long-range stereocontrol in Suzuki-Miyaura reactions. The authors demonstrate the successful creation of chirality at remote quaternary stereocenters through the use of ionic substrate-catalyst interactions. Further research is needed to fully understand the complex networks of ionic interactions and explore the potential of ionic chiral catalysts. [Extracted from the article]

The development of efficient and selective organic synthetic approaches for complex molecules has garnered significant attention due to the need for precise control over molecular structures and functions. Rotaxanes, a type of mechanically interlocked molecules (MIMs), have shown promising applications in various fields including sensing, catalysis, and material science. However, the highly selective synthesis of oligo[n]rotaxanes (mostly n≥3) through controlling host‐guest complexation and supramolecular threading assembly process still remains an ongoing challenge. In particular, the utilization of two‐dimensional (2D) macrocycles with structural shape‐persistency for the synthesis of oligo[n]rotaxanes is rare. In this concept, research on cooperatively threaded host‐guest complexation with hydrogen‐bonded (H‐bonded) aramide macrocycles and selective synthetic protocols of oligo[n]rotaxanes has been summarized. The high efficiency and selectivity in synthesis are ascribed to the synergistic interplay of multiple non‐covalent bonding interactions such as hydrogen bonding and intermolecular π–π stacking of macrocycles within the unique supramolecular structure of threaded host‐guest complexes. This review focuses on the latest progress in the concepts, synthesis, and properties of H‐bonded aramide macrocycle‐based oligorotaxanes, and presents an in‐depth outlook on challenges in this emerging field. [ABSTRACT FROM AUTHOR]

Rotaxanes can serve as scaffolds for the generation of bifunctional catalysts. We have now generated acid–base functionalized rotaxanes featuring two chiral subunits. The mechanical bond leads to increased reaction rates and also to strongly altered enantioselectivites in comparison to the non-interlocked control catalysts. [ABSTRACT FROM AUTHOR]

Diamine reagents have been used to functionalize a [2]rotaxane building block bearing an activated pentafluorophenyl ester stopper. Upon a first acylation, an intermediate host‐guest complex with a terminal amine function is obtained. Dissociation of the intermediate occurs in solution and acylation of the released axle generates a [2]rotaxane with an elongated axle subunit. In contrast, the corresponding [3]rotaxane can be obtained if the reaction conditions are appropriate to stabilize the inclusion complex of the mono‐amine intermediate and the pillar[5]arene. This is the case when the stopper exchange is performed under mechanochemical solvent‐free conditions. Alternatively, if the newly introduced terminal amide group is large enough to prevent the dissociation, the second acylation provides exclusively a [3]rotaxane. On the other hand, detailed conformational analysis has been also carried out by variable temperature NMR investigations. A complete understanding of the shuttling motions of the pillar[5]arene subunit along the axles of the rotaxanes reported therein has been achieved with the help of density functional theory calculations. [ABSTRACT FROM AUTHOR]

Rotaxane‐type fluorescence dyes promise applications of optical and biological interest because their inner fluorescence cores are protected in inseparable host–guest systems. However, there are few relevant reports of such rotaxane‐type fluorescence dyes due to the difficulty of their syntheses. Here, a versatile synthetic method is established for [5]rotaxane‐type fluorescence dyes by employing a cooperative capture strategy. Using this method, [5]rotaxanes with emission colors ranging from blue to red are synthesized successfully. These [5]rotaxanes show higher emission quantum yields than the corresponding naked fluorescence dyes in water and even in the solid state. Furthermore, these rotaxanes show photostability and chemical stability, demonstrating the high applicability of [5]rotaxane‐type fluorescence dyes for a variety of emitting materials. [ABSTRACT FROM AUTHOR]

Important biological processes, such as signaling and transport, are regulated by dynamic binding events. The development of artificial supramolecular systems in which binding between different components is controlled could help emulate such processes. Herein, we describe stiff‐stilbene‐containing macrocycles that can be switched between (Z)‐ and (E)‐isomers by light, as demonstrated by UV/Vis and 1H NMR spectroscopy. The (Z)‐isomers can be effectively threaded by pyridinium halide axles to give pseudorotaxane complexes, as confirmed by 1H NMR titration studies and single‐crystal X‐ray crystallography. The overall stability of these complexes can be tuned by varying the templating counteranion. However, upon light‐induced isomerization to the (E)‐isomer, the threading capability is drastically reduced. The axle component, in addition, can form a heterodimeric complex with a secondary isophthalamide host. Therefore, when all components are combined, light irradiation triggers axle exchange between the macrocycle and this secondary host, which has been monitored by 1H NMR spectroscopy and simulated computationally. [ABSTRACT FROM AUTHOR]

Important biological processes, such as signaling and transport, are regulated by dynamic binding events. The development of artificial supramolecular systems in which binding between different components is controlled could help emulate such processes. Herein, we describe stiff‐stilbene‐containing macrocycles that can be switched between (Z)‐ and (E)‐isomers by light, as demonstrated by UV/Vis and 1H NMR spectroscopy. The (Z)‐isomers can be effectively threaded by pyridinium halide axles to give pseudorotaxane complexes, as confirmed by 1H NMR titration studies and single‐crystal X‐ray crystallography. The overall stability of these complexes can be tuned by varying the templating counteranion. However, upon light‐induced isomerization to the (E)‐isomer, the threading capability is drastically reduced. The axle component, in addition, can form a heterodimeric complex with a secondary isophthalamide host. Therefore, when all components are combined, light irradiation triggers axle exchange between the macrocycle and this secondary host, which has been monitored by 1H NMR spectroscopy and simulated computationally. [ABSTRACT FROM AUTHOR]

Biodegradable polyrotaxanes (PRXs) are important scaffolds for the development of biomaterials. However, the degradation behavior of PRXs constructed via physical crosslinking remains largely unexplored. Herein, a degradable PRX exhibiting physical hydrogen bonds as crosslinks between α‐cyclodextrins (α‐CDs) as the cyclic molecules is synthesized by introducing hyperbranched polyglycerol (HPG) containing numerous terminal 1,2‐diols into the α‐CDs with an incorporation ratio of HPG (HPG/PRX) varying from 2 to 19 via anion ring‐opening polymerization of glycidol. Rheological analysis by a frequency sweep test reveals that a typical HPG‐PRX forms hydrogels by physical crosslinking via hydrogen bonding, whereas a low branched degree of HPG in HPG‐PRX weakens the physical crosslinking. The obtained gels recover their original shape upon pulling and releasing, which is consistent with a pulley effect. Degradation and erosion tests in water show that increasing the molecular weight of the introduced HPG changes the degradation behavior from bulk degradation to surface erosion. Owing to its controllable degradation or erosion by tuning the rate of water ingress according to the number of hydrogen bonds and the branched degree, this HPG‐modified PRX paves the way for the development of new biodegradable/erodible gels. [ABSTRACT FROM AUTHOR]

Detailed investigations into the stepwise bis‐functionalization of a pillar[5]arene‐containing rotaxane building block have been carried out. Upon a first stopper exchange, the pillar[5]arene moiety of the mono‐acylated product is preferentially located close to its reactive pentafluorophenyl ester stopper, thus limiting the accessibility to the reactive carbonyl group by the nucleophilic reagents. Selective mono‐functionalization is thus very efficient. Introduction of a second stopper is then possible to generate dissymmetrical rotaxanes with different amide stoppers. Moreover, when dethreading is possible upon the second acylation, the pillar[5]arene plays the role of a protecting group allowing the synthesis of dissymmetrical axles that are particularly difficult to prepare under statistical conditions. Finally, detailed conformation analysis of the rotaxanes revealed that the position of the pillar[5]arene moiety on its axle subunit is mainly governed by polar interactions in nonpolar organic solvents, whereas solvophobic effects play a major role in polar solvents. [ABSTRACT FROM AUTHOR]

Over the last few decades, research on mechanically interlocked molecules has significantly evolved owing to their unique structural features and interesting properties. A substantial percentage of the reported works have focused on the synthetic strategies, leading to the preparation of functional MIMs for their applications in the chemical, materials, and biomedical sciences. Importantly, various macrocyclic wheels with specific heteroditopicity (including phenanthroline, amide, amine, oxy-ether, isophthalamide, calixarene and triazole) and threading axles (bipyridine, phenanthroline, pyridinium, triazolium, etc.) have been designed to synthesize targeted multifunctional mononuclear/multinuclear pseudorotaxanes, rotaxanes and catenanes. The structural uniqueness of these interlocked systems is advantageous owing to the presence of mechanical bonds with specific three-dimensional cavities. Furthermore, their multi-functionalities and preorganised structural entities exhibit a high potential for versatile applications, like switching, shuttling, dynamic properties, recognition and sensing. In this feature article, we describe some of the most recent advances in the construction and chemical behaviour of a new generation of interlocked molecules, primarily focusing on heteroditopic wheels and their applications in different directions of the modern research area. Furthermore, we outline the future prospects and significant perspectives of the new generation heteroditopic wheel based interlocked molecules in different emerging areas of science. [ABSTRACT FROM AUTHOR]

We describe a rotaxane molecular shuttle encompassing triazolium and tertiary ammonium units as weak recognition sites for the ring. Such a design, which differs from that of typical controllable rotaxanes, allows the precise tuning of the ring distribution among the two sites – i.e., the coconformational equilibrium – by changing the solvent polarity or the nature of the counteranions. Shuttling of the ring between the two stations can also be toggled by acid–base stimuli. Such an approach is paradigmatic to obtain rotaxanes that can sense environmental changes and transduce them into a coconformational response and opens avenues for novel applications in sensing and stimuli-responsive materials. [ABSTRACT FROM AUTHOR]

Inherent chirality represents a distinct category of molecular chirality that does not fall within the traditional classification of four chiral elements: central, axial, planar, and helical chirality. While extensive research has been conducted on the catalytic enantioselective construction of these conventional chiralities, the corresponding synthesis of inherently chiral molecules has remained largely unexplored. This minireview provides a comprehensive summary of recent advancements in this field, focusing on the catalytic asymmetric synthesis of inherently chiral calixarenes, saddle‐shaped tetraphenylenes and their heterocycle derivatives, mechanically planar chiral rotaxanes and chiral multilayer 3D frameworks, as well as our perspective in this field. [ABSTRACT FROM AUTHOR]

Chemical topology refers to the three-dimensional arrangement (i.e., connectivity and spatial relationship) of a molecule's constituent atoms and bonds. The molecular mechanism for translation defines the linear configuration of all nascent proteins. Nontrivial protein topology arises only upon post-translational processing events and often imparts functional benefits such as enhanced stability, making topology a unique dimension for protein engineering. Utilizing the assembly-reaction synergy, our group has developed several methods for the effective and convenient cellular synthesis of a variety of topological proteins, such as lasso proteins, protein rotaxanes, and protein catenanes. The work opens the access to new protein classes and paves the road toward illustrating the topological effects on structure-function relationship of proteins, which lays solid foundation for exploring topological proteins' practical application. [ABSTRACT FROM AUTHOR]

A series of pseudorotaxanes with supramolecular organometallic silver(I) and gold(I) pillarplexes acting as rings and different α,ω‐dicarboxylic acids as axle components are reported. The successful formation of the host‐guest complexes is shown by 1H NMR spectroscopy and respective NMR titration. Additional evaluation with ITC titration experiments yielded dissociation constants (Kd) ranging from 10−5 to 10−7 M. Single‐crystal X‐Ray diffraction analysis reveals a particularly exciting pore alignment of different examples in the solid state depending on the length of the guest. The work highlights, that dicarboxylic acids can penetrate the tight tubular pillarplex pore, paving the way to future mechanically interlocked molecules and materials. [ABSTRACT FROM AUTHOR]

A novel method for extracting and measuring trace amounts of indium, gallium, and thallium using a synthesized [2]rotaxane hydroxamic acid is proposed. The method involves extracting the elements at specific pH levels using chloroform and measuring them using spectrophotometry and inductively couples plasma atomic emission spectrometry (ICP-AES). The extraction mechanism and the factors that influence the extraction process are also discussed. The method is shown to be effective for measuring these elements in a variety of samples, such as alloys, environmental samples, minerals, water, and biological samples. The sensitivity of this method is enhanced 60 times by ICP-AES measurements, which makes it useful for trace determination of In, Ga, and Tl. [ABSTRACT FROM AUTHOR]

The active metal template (AMT) strategy is a powerful tool for the formation of mechanically interlocked molecules (MIMs) such as rotaxanes and catenanes, allowing the synthesis of a variety of MIMs, including π‐conjugated and multicomponent macrocycles. Cycloparaphenylene (CPP) is an emerging molecule characterized by its cyclic π‐conjugated structure and unique properties. Therefore, diverse modifications of CPPs are necessary for its wide application. However, most CPP modifications require early stage functionalization and the direct modification of CPPs is very limited. Herein, we report the synthesis of a catenane consisting of [9]CPP and a 2,2′‐bipyridine macrocycle as a new CPP analogue that contains a reliable synthetic scaffold enabling diverse and concise post‐modification. Following the AMT strategy, the [9]CPP‐bipyridine catenane was successfully synthesized through Ni‐mediated aryl‐aryl coupling. Catalytic C−H borylation/cross‐coupling and metal complexation of the bipyridine macrocycle moiety, an effective post‐functionalization method, were also demonstrated with the [9]CPP‐bipyridine catenane. Single‐crystal X‐ray structural analysis revealed that the [9]CPP‐bipyridine catenane forms a tridentated complex with an Ag ion inside the CPP ring. This interaction significantly enhances the phosphorescence lifetime through improved intermolecular interactions. [ABSTRACT FROM AUTHOR]

We have developed a new approach for the synthesis of "improbable" rotaxanes by using malonate‐centered rotaxanes as interlocked surrogate precursors. Here, the desired dumbbell‐shaped structure can be assembled from two different, completely separate, portions, with the only residual structure introduced from the malonate surrogate being a methylene group. We have synthesized improbable [2]‐ and [3]rotaxanes with all‐hydrocarbon dumbbell‐shaped components to demonstrate the potential structural flexibility and scope of the guest species that can be interlocked when using this approach. [ABSTRACT FROM AUTHOR]

The active metal template (AMT) strategy is a powerful tool for the formation of mechanically interlocked molecules (MIMs) such as rotaxanes and catenanes, allowing the synthesis of a variety of MIMs, including π‐conjugated and multicomponent macrocycles. Cycloparaphenylene (CPP) is an emerging molecule characterized by its cyclic π‐conjugated structure and unique properties. Therefore, diverse modifications of CPPs are necessary for its wide application. However, most CPP modifications require early stage functionalization and the direct modification of CPPs is very limited. Herein, we report the synthesis of a catenane consisting of [9]CPP and a 2,2′‐bipyridine macrocycle as a new CPP analogue that contains a reliable synthetic scaffold enabling diverse and concise post‐modification. Following the AMT strategy, the [9]CPP‐bipyridine catenane was successfully synthesized through Ni‐mediated aryl‐aryl coupling. Catalytic C−H borylation/cross‐coupling and metal complexation of the bipyridine macrocycle moiety, an effective post‐functionalization method, were also demonstrated with the [9]CPP‐bipyridine catenane. Single‐crystal X‐ray structural analysis revealed that the [9]CPP‐bipyridine catenane forms a tridentated complex with an Ag ion inside the CPP ring. This interaction significantly enhances the phosphorescence lifetime through improved intermolecular interactions. [ABSTRACT FROM AUTHOR]

We have developed a new approach for the synthesis of "improbable" rotaxanes by using malonate‐centered rotaxanes as interlocked surrogate precursors. Here, the desired dumbbell‐shaped structure can be assembled from two different, completely separate, portions, with the only residual structure introduced from the malonate surrogate being a methylene group. We have synthesized improbable [2]‐ and [3]rotaxanes with all‐hydrocarbon dumbbell‐shaped components to demonstrate the potential structural flexibility and scope of the guest species that can be interlocked when using this approach. [ABSTRACT FROM AUTHOR]

In situ switching of the associated anions of a rotaxane catalyst between Cl− and TFPB− exposes its dialkylammonium and imidazolium stations, respectively, thereby selectively catalyzing the reactions of a mixture of trans‐cinnamaldehyde and an aliphatic thiol to yield the Michael adduct and the thioacetal product, respectively. [ABSTRACT FROM AUTHOR]

In situ switching of the associated anions of a rotaxane catalyst between Cl− and TFPB− exposes its dialkylammonium and imidazolium stations, respectively, thereby selectively catalyzing the reactions of a mixture of trans‐cinnamaldehyde and an aliphatic thiol to yield the Michael adduct and the thioacetal product, respectively. [ABSTRACT FROM AUTHOR]

Advanced Organic Chemical Materials Co‐constructed Mechanically bonded amphiphiles (MBAs), also known as mechanically interlocked molecules (MIMs), have emerged as an important kind of functional building block for the construction of artificial molecular machines and soft materials. Herein, a novel MBA, i. e., bistable [2]rotaxane H2 was designed and synthesized. In the solution state, H2 demonstrated pH and metal ion‐responsive emissions due to the presence of a distance‐dependent photoinduced electron transfer (PET) process and the fluorescence resonance energy transfer (FRET) process, respectively. Importantly, the amphiphilic feature of H2 has endowed it with unique self‐assembly capability, and nanospheres were obtained in a mixed H2O/CH3CN solvent. Moreover, the morphology of H2 aggregates can be tuned from nanospheres to vesicles due to the pH‐controlled shuttling motion‐induced alternation of H2 amphiphilicity. Interestingly, larger spheres with novel pearl‐chain‐like structures from H2 were observed after adding stoichiometric Zn2+. In particular, H2 shows pH‐responsive emissions in its aggregation state, allowing the visualization of the shuttling movement by just naked eyes. It is assumed that the well‐designed [2]rotaxane, and particularly the proposed concept of MBA shown here, will further enrich the families of MIMs, offering prospects for synthesizing more MIMs with novel assembly capabilities and bottom‐up building dynamic smart materials with unprecedented functions. [ABSTRACT FROM AUTHOR]