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Understanding the fundamental reactivity of polymetallic complexes is challenging due to the complexity of their structures with many possible bond breaking and forming processes. Here, we apply ion mobility mass spectrometry coupled with density functional theory to investigate the disassembly mechanisms and energetics of a family of heterometallic rings and rotaxanes with the general formula [NH

Anion receptors employing two distinct sensory mechanisms are rare. Herein, we report the first examples of halogen‐bonding porphyrin BODIPY [2]rotaxanes capable of both fluorescent and redox electrochemical sensing of anions. 1H NMR, UV/visible and electrochemical studies revealed rotaxane axle triazole group coordination to the zinc(II) metalloporphyrin‐containing macrocycle component, serves to preorganise the rotaxane binding cavity and dramatically enhances anion binding affinities. Mechanically bonded, integrated‐axle BODIPY and macrocycle strapped metalloporphyrin motifs enable the anion recognition event to be sensed by the significant quenching of the BODIPY fluorophore and cathodic perturbations of the metalloporphyrin P/P+. redox couple., The first examples of porphyrin‐BODIPY halogen bonding [2]rotaxanes have been prepared according to an active metal template strategy. Capitalising on the augmented anion affinities by virtue of axle triazole ligation to macrocyclic zinc(II) metalloporphyrin, the incorporation of fluorogenic BODIPY and redox‐active porphyrin transducing groups allows dual‐channel sensing of anions by quenching BODIPY emission and through cathodic perturbations of porphyrin oxidation redox couples.

The nature of mechanically interlocked molecules (MIMs) has continued to encourage researchers to design and construct a variety of high-performance materials. Introducing mechanically interlocked structures into polymers has led to novel polymeric materials, called mechanically interlocked polymers (MIPs). Rotaxane-based MIPs are an important class, where the mechanically interlocked characteristic retains a high degree of structural freedom and mobility of their components, such as the rotation and sliding motions of rotaxane units. Therefore, these MIP materials are known to possess a unique set of properties, including mechanical robustness, adaptability and responsiveness, which endow them with potential applications in many emerging fields, such as protective materials, intelligent actuators, and mechanisorption. In this review, we outline the synthetic strategies, structure-property relationships, and application explorations of various polyrotaxanes, including linear polyrotaxanes, polyrotaxane networks, and rotaxane dendrimers.

Integrating individual microscopic motion to perform tasks in macroscopic sale is common in living organisms. However, developing artificial materials in which molecular-level motions could be amplified to behave macroscopically is still challenging. Herein, we present a class of mechanically interlocked networks (MINs) carrying densely rotaxanated backbones as a model system to understand macroscopic mechanical properties stemmed from the integration and amplification of intramolecular motion of the embedded [2]rotaxane motifs. On the one hand, the motion of mechanical bonds introduces the original dangling chains into the network, and the synergy of numerous such microscopic motions leads to an expansion of entire network, imparting good stretchability and puncture resistance to the MINs. On the other hand, the dissociation of host−guest recognition and subsequent sliding motion represent a peculiar energy dissipation pathway, whose integration and amplification result in the bulk materials with favorable toughness and damping capacity. Thereinto, we develop a continuous stress-relaxation method to elucidate the microscopic motion of [2]rotaxane units, which contributes to the understanding of the relationship between cumulative microscopic motions and amplified macroscopic mechanical performance. The fundamental insights gained from the study of high-density mechanically bonded networks would facilitate the fabrication and application of mechanically interlocked materials.

The synthesis of chiral mechanically interlocked molecules has attracted a lot of attention in the last few years, with applications in different fields, such as asymmetric catalysis or sensing. Herein we describe the synthesis of orientational mechanostereoisomers, which include a benzylic amide macrocycle with a stereogenic center, and nonsymmetric N-(arylmethyl)fumaramides as the axis. The base-promoted cyclization of the initial fumaramide thread allows enantioenriched value-added compounds, such as lactams of different ring sizes and amino acids, to be obtained. The chiral information is effectively transmitted across the mechanical bond from the encircling ring to the interlocked lactam. High levels of enantioselectivity and full control of the regioselectivity of the final cyclic compounds are attained.

The distribution of the ring component in [2]rotaxanes was modulated by the introduction of a less symmetric spiro ring.

The self-trapping nano-loop structures of [1]rotaxanes exhibited multiple Förster resonance energy transfer (FRET) OFF/ON patterns via dual and sequential locking/unlocking upon UV exposure.

Mechanically interlocked molecules (MIMs) have gained attention in the field of catalysis due to their unique molecular properties. Central to MIMs, rotaxanes are highly promising and attractive supramolecular catalysts due to their unique three‐dimensional structures and the flexibility of their subcomponents. This Minireview discusses the use of rotaxanes in organocatalysis and transition‐metal catalysis., Rotaxanes are highly promising and attractive supramolecular catalysts. They offer conceptually novel possibilities in catalysis, such as switchability, the generation of highly congested reaction spaces or the development of bifunctional catalyst systems. This Minireview describes recent advances in the use of rotaxanes in organo‐ and transition‐metal catalysis, classified by the role of the macrocycle in each catalyst system.

Advances in supramolecular chemistry are often underpinned by the development of fundamental building blocks and methods enabling their interconversion. In this work, we report the use of an underexplored dynamic covalent reaction for the synthesis of stimuli-responsive [2]rotaxanes. The formamidinium moiety lies at the heart of these mechanically interlocked architectures, because it enables both dynamic covalent exchange and the binding of simple crown ethers. We demonstrated that the rotaxane self-assembly follows a unique reaction pathway and that the complex interplay between crown ether and thread can be controlled in a transient fashion by addition of base and fuel acid. Dynamic combinatorial libraries, when exposed to diverse nucleophiles, revealed a profound stabilizing effect of the mechanical bond as well as intriguing reactivity differences between seemingly similar [2]rotaxanes.

Electrochemically controllable rotaxanes are prime examples of supramolecular switches and promising prototypes for artificial molecular machines. This perspective discusses recent progress and applications beyond classical molecular shuttles., Are they still electrifying? Electrochemically switchable rotaxanes are well known for their ability to efficiently undergo changes of (co-)conformation and properties under redox-control. Thus, these mechanically interlocked assemblies represent an auspicious liaison between the fields of molecular switches and molecular electronics. Since the first reported example of a redox-switchable molecular shuttle in 1994, improved tools of organic and supramolecular synthesis have enabled sophisticated new architectures, which provide precise control over properties and function. This perspective covers recent advances in the area of electrochemically active rotaxanes including novel molecular switches and machines, metal-containing rotaxanes, non-equilibrium systems and potential applications.

The relation between the chemical structure and the mechanical behavior of molecular machines is of paramount importance for a rational design of superior nanomachines. Here, we report on a mechanistic study of a nanometer scale translational movement in two bistable rotaxanes. Both rotaxanes consist of a tetra-amide macrocycle interlocked onto a polyether axle. The macrocycle can shuttle between an initial succinamide station and a 3,6-dihydroxy- or 3,6-di-tert-butyl-1,8-naphthalimide end stations. Translocation of the macrocycle is controlled by a hydrogen-bonding equilibrium between the stations. The equilibrium can be perturbed photochemically by either intermolecular proton or electron transfer depending on the system. To the best of our knowledge, utilization of proton transfer from a conventional photoacid for the operation of a molecular machine is demonstrated for the first time. The shuttling dynamics are monitored by means of UV–vis and IR transient absorption spectroscopies. The polyether axle accelerates the shuttling by ∼70% compared to a structurally similar rotaxane with an all-alkane thread of the same length. The acceleration is attributed to a decrease in activation energy due to an early transition state where the macrocycle partially hydrogen bonds to the ether group of the axle. The dihydroxyrotaxane exhibits the fastest shuttling speed over a nanometer distance (τshuttling ≈ 30 ns) reported to date. The shuttling in this case is proposed to take place via a so-called harpooning mechanism where the transition state involves a folded conformation due to the hydrogen-bonding interactions with the hydroxyl groups of the end station.

The syntheses of two novel mechanically chiral rotaxanes containing urea and squaramide motifs (in yields of 33% and 22% respectively) are presented. 1H NMR spectroscopic titrations reveal shuttling of the macrocycle - detectable by modulation of the expression of mechanical chirality in the NMR spectrum - is possible through the addition of achiral chloride anions, a process which is reversed by the addition of sodium cations.

Rotaxanes are currently one of the most promising objects of study in the field of artificial molecular machines. A rotaxane molecule is composed by two or more molecular components that are connected by a mechanical bond. 51 years ago, the first synthesis of this type of molecules was performed, since then, there has been a great effort in obtaining new models to study its molecular movements and application as molecular machines. Here, we present an overview of intercomponent interactions in rotaxanes and how these interactions affect the major movements presented by this class of molecules. For this, different approaches to assess these interactions are discussed, both in solution and solid state.

Room temperature phosphorescent (RTP) γ-CD-CB[6]-cowheeled [4]rotaxanes were synthesized by implanting a naphthalene axle into the cavity of iodine-substituted γ-CDs. The strong green RTP was quenched exclusively by Trp while no RTP quenching was observed with other major physiological amino acids or with the Trp-containing protein HSA, demonstrating a highly specific sensing of free Trp.

The advancements in the field of mechanically interlocked molecular systems (MIMs) has concurrently restructured the material chemistry frontiers and provided ample scope to explore new dimensions for applications and diversity creation. Among all these molecular entities, rotaxanes have a special locale and many research groups over the globe have contributed to their current niche in supramolecular chemistry. From refinements for better yielding synthetic strategies to their application oriented designs, this field has come a long way and is well inclined for further developments. In this review, we aim to document the contemporary developments in the synthesis of phenanthroline (phen) based rotaxanes. In addition to providing a comprehensive account of various subtypes of these rotaxanes and their stitching strategies, their applications, wherever discernible, will be duely highlighted.

Ring size is a critically important parameter in many interlocked molecules as it directly impacts many of the unique molecular motions that they exhibit. Reported herein are studies using one of the largest macrocycles reported to date to synthesize doubly threaded [3]rotaxanes. A large ditopic 46 atom macrocycle containing two 2,6-bis(

Reversible FRET ON-OFF switching and fluorescence photo-patterning applications of acid-base controlled extended and contracted [c2] daisy chain rotaxanes containing photochromic spiropyran and triphenylamine-chalcone chromophores were investigated.

[1]Rotaxanes based on monosubstituted phosphorus-containing pillar[5]arenes have been synthesized by the Kabachnik–Fields reaction for the first time in good yields.

Bulky photolabile masked alkyne equivalents (MAEs) are needed for the synthesis of polyyne polyrotaxanes, as insulated molecular wires and as stabilized forms of the linear polymeric allotrope of carbon, carbyne. We have synthesized a novel MAE based on phenanthrene and compared it with an indane-based MAE. Photochemical unmasking of model compounds was studied at different wavelengths (250 and 350 nm), and key products were identified by NMR spectroscopy and X-ray crystallography. UV irradiation at 250 nm leads to unmasking of both MAEs. Irradiation of the phenanthrene system at 350 nm results in quantitative dimerization via [2 + 2] cycloaddition to form a [3]-ladderane; irradiation of this ladderane at 250 nm generates a dihydrotriphenylene, which can be oxidized easily to a triphenylene. Irradiation of the indane-based MAE at 350 nm in the presence of traces of oxygen forms an endoperoxide and a bisepoxide. Both MAEs have been incorporated into rotaxanes via copper-mediated active metal template Glaser or Cadiot–Chodkiewicz coupling. The identity of the rotaxanes was confirmed by NMR spectroscopy and mass spectrometry. The phenanthrene rotaxane decomposes during attempted photochemical unmasking, whereas photolysis of the indane rotaxane results in unmasking of the polyyne thread to form a rotaxane with a chain of 16 sp-hybridized carbon atoms. This approach opens avenues toward the synthesis of encapsulated carbon allotropes.

Rotaxane building blocks bearing 3,5‐bis(trifluoromethyl) benzenesulfonate (BTBS) stoppers have been efficiently prepared from a pillar[5]arene derivative, 3,5‐bis(trifluoromethyl) benzenesulfonyl chloride (BTBSCl) and different diols, namely 1,10‐decanediol and 1,12‐dodecanediol. The BTBS moieties of these compounds are good leaving groups and stopper exchange reactions could be achieved by treatment with different nucleophiles thus affording rotaxanes with ester, thioether or ether stoppers., Rotaxanes, just pop the stoppers: Rotaxane building blocks bearing 3,5‐bis(trifluoromethyl) benzenesulfonate (BTBS) stoppers have been efficiently prepared. The BTBS moieties of these compounds are good leaving groups allowing to perform stopper exchange by treatment with different nucleophiles to afford rotaxanes with ester, ether or thioether stoppers.

Heterobifunctional rotaxanes serve as efficient catalysts for the addition of malonates to Michael acceptors. We report a series of four different heterobifunctional rotaxanes, featuring an amine‐based thread and a chiral 1,1′‐binaphthyl‐phosphoric‐acid‐based macrocycle. High‐level DFT calculations provided mechanistic insights and enabled rational catalyst improvements, leading to interlocked catalysts that surpass their non‐interlocked counterparts in terms of reaction rates and stereoselectivities., Heterobifunctional rotaxanes, featuring an amine‐based thread and a macrocyclic chiral 1,1′‐binaphthyl‐phosphoric acid, serve as efficient organocatalysts for the stereoselective addition of malonates to Michael acceptors. High‐level DFT calculations provided mechanistic insights and enabled rational catalyst improvements, leading to interlocked catalysts that surpass their non‐interlocked counterparts in terms of reaction rates and stereoselectivities.

Unexpected strongly luminescent complexes were constructed via the weakly luminescent [1]rotaxane coordinating with Zn2+ specifically due to the coordination-induced emission effect.

Dedicated to Prof. Tomás Torres on the occasion of his 70th birthday; International audience; Our groups are involved in a research program on the development of molecular and supramolecular systems combining pillar[5]arene building blocks with porphyrins. Functionalization of both rims of the pillar[5]arene scaffold with metalloporphyrins generated giant molecular machines mimicking the blooming of a flower as well as light-harvesting devices. On the other hand, we have also used the host-guest properties of pillar[5]arene derivatives to prepare photoactive mechanically interlocked molecules. In such compounds, complementary subunits are associated into a single molecular ensemble but without being connected through covalent bonds. Inter-component photo-induced energy transfer processes remain however extremely fast in these systems despite the exclusive link through mechanical bonds. All these results are described in the present review.

Reversible switching between the closed cyclic dimeric assembly [Cu2(1)2]2+ (OFF state) and the extended dimeric homoleptic complex [FeCu2(1)2]4+ (ON State) by addition/removal of Fe2+ triggered catalysis of a double‐click reaction and high yield preparation of [2]rotaxanes. Mechanistic and computational studies provide valuable general insight for double‐click strategies by revealing cooperative effects in the second cycloaddition step due to a distance‐tolerant preorganization of the first‐click product by the two copper(I)‐loaded phenanthroline subunits of [FeCu2(1)2]4+., Like an eagle spreading its wings wide, the closed structure opens its hidden catalytic sites upon addition of an iron trigger thus furnishing a cavity for a double‐click conversion toward rotaxanes. Surprisingly, a close distance match is not needed for double activation.

The efficacy of many drugs can be limited by undesirable properties, such as poor aqueous solubility, low bioavailability, and "off-target" interactions. To combat this, various drug carriers have been investigated to enhance the pharmacological profile of therapeutic agents. In this work, we demonstrate the use of mechanical protection to "cage" a DNA-targeting metallodrug within a photodegradable rotaxane. More specifically, we report the synthesis of rotaxanes incorporating as a stoppering unit a known G-quadruplex DNA binder, namely a PtII -salphen complex. This compound cannot interact with DNA when it is part of the mechanically interlocked assembly. The second rotaxane stopper can be cleaved by either light or an esterase, releasing the PtII -salphen complex. This system shows enhanced cell permeability and limited cytotoxicity within osteosarcoma cells compared to the free drug. Light activation leads to a dramatic increase in cytotoxicity, arising from the translocation of PtII -salphen to the nucleus and its binding to DNA.

A series of azobenzene-bridged dipillar[5]arenes were conveniently synthesized by coupling reaction of aminoalkyl-functionalized pillar[5]arenes with azobenzene-4,4’-dioxyacetic acid or azobenzene-4,4’-dioxybutanoic acid in dry chloroform under the combinatorial catalysis of HOBt/EDCl. 1H NMR, 2D NOESY spectra and single crystal structure clearly indicated that the unique bis-[1]rotaxanes could be formed by threading two diaminoalkylene units into the two cavities of pillar[5]arenes depending on the length of the diaminoalkylene chains. Under light irradiation at 365 nm, the trans-azobenzene unit transferred to cis-configuration, while the basic bis-[1]rotaxane structure was kept unchanged.

The condensation reaction of mono-amido-functionalized pillar[5]arenes with tere- and iso-phthaloyl diisothiocyanates in acetone under ultrasonic irradiation afforded tere- and iso-phthaloylthiourea-bridged dipillar[5]arenes. The similar reaction of mono-amido-functionalized pillar[5]arenes with 1,ω-bis(4-isothiocyanatophenoxy)alkanes also afforded diphenoxyalkylene thiourea-bridged dipillar[5]arenes. 1H NMR and NOESY spectra clearly indicated that bis-[1]rotaxanes were formed by insertion of longer alkylene chains into the cavities of two pillar[5]arenes. On the other hand, the free-forms of dipillar[5]arenes were obtained with the shorter ethylene chains existing on the outside of the cavities of two pillar[5]arenes.

The synthesis of a pair of switchable interlocked prolinamides and their use as organocatalysts in three different enamine-activated processes are reported. A diacylaminopyridine moiety was incorporated into the thread for directing [2]rotaxane formation further allowing the association of complementary small molecules. The rotaxane-based systems were tested as organocatalysts in asymmetric enamine-mediated processes, revealing a significantly improved catalytic ability if compared with the non-interlocked thread. The presence of an electron-withdrawing nitro group at the macrocycle helps to achieve high conversions and enantioselectivities. These systems are able to interact with N-hexylthymine as a cofactor to form supramolecular catalysts displaying a divergent catalytic behaviour. The presence or absence of the cofactor controls the chemoselectivity in competitive reactions., The mechanical bonding and the cofactor assembly in interlocked prolinamide-based organocatalysts upgrade enamine-type transformations by increasing their yields and enantio- and chemo-selectivities.

We report on rotaxanes featuring a pyridyl-acyl hydrazone moiety on the axle as a photo-/thermalswitchable macrocycle binding site. The pyridyl-acyl E-hydrazone acts as a hydrogen bonding template that directs the assembly of a benzylic amide macrocycle around the axle to form [2]rotaxanes in up to 85 % yield; the corresponding Zhydrazone thread affords no rotaxane under similar conditions. However, the E-rotaxane can be smoothly converted into the Z-rotaxane in 98 % yield under UV irradiation. The X-ray crystal structures of the E- and Z-rotaxanes show different intercomponent hydrogen bonding patterns. In molecular shuttles containing pyridyl-acyl hydrazone and succinic amide ester binding sites, the change of position of the macrocycle on the thread can be achieved through a series of light irradiation and heating cycles with excellent positional integrity (>95 %) and switching fidelity (98 %) in each state.

Formation of pseudo[3]rotaxane assemblies by P4Q1 and H with bis-imidazolium and bis-pyridinium guests was established by NMR spectral analyses and high-resolution mass spectrometric analyses. Cooperativity in the formation of pseudo[3]rotaxane assemblies was thoroughly investigated from the binding constant values derived from 1H NMR titration experiments. The results indicated the preferential 1:1 host-guest binding of pillar[4]arene[1]quinone and 2:1 host-guest binding by functionalized pillar[4]arene[1]quinone via positive cooperativity. The presence of hydrogen bonding functional groups attached to the quinone motif of pillar[4]arene[1]quinone facilitated the inclusion formation, which resulted in the formation of pseudo[3]rotaxanes.

Poly(ethylene glycol) diamine 1,1’-disubstituted ferrocene was utilized as a size-com-plementary site to synthesize lower coverage pseudopolyrotaxanes (pPRs) from self-assemblies with β- and γ-cyclodextrins (CDs). After end-capping β-CD pPRs using N-(triphenylmethyl)glycine (Trt-Gly-OH), an exact β-CD [3]polyrotaxane (PR) was created. However, an unexpected γ-CD [2]PR and a predictive chain folded stranded γ-CD pPR were identified from end-capped γ-CD pPRs. After end-capping a β-CD pPR self-assembled from β-CDs with amine terminated PEG containing ferrocene as a site-complementary site using Trt-Gly-OH, an exact β-CD [3]PR is invariably created. However, an unexpected γ-CD [2]PR and a predictive chain folded stranded γ-CD pPR are identified from end-capping γ-CD pPRs with Trt-Gly-OH.

Exceptionally strong halogen bonding (XB) donor-chloride interactions are exploited for the chloride anion template synthesis of neutral XB [2]rotaxane host systems which contain perfluoroaryl-functionalised axle components, including a remarkably potent novel 4,6-dinitro-1,3-bis-iodotriazole motif. Halide anion recognition properties in aqueous-organic media, determined via extensive

The term chiral was introduced by Lord Kelvin over a century ago to describe objects that are distinct from their own mirror image. Chirality is relevant in many scientific areas, but particularly chemistry because different mirror image forms of a molecule famously have different biological properties. Chirality typically arises in molecules due to a rigidly chiral arrangement of covalently bonded atoms. Less generally appreciated is that molecular chirality can arise when molecules are threaded through one another to create a mechanical bond. For example, when two molecular rings with chemically distinct faces are joined like links in a chain the resulting structure is chiral even when the rings themselves are not. We re-examined the symmetry properties of such mechanically axially chiral catenanes and in doing so identified a straightforward route to these molecules from simple building blocks. This also led to the discovery of a previously overlooked mechanical stereogenic unit that can arise when such a ring encircles a dumbbell-shaped axle to generate a rotaxane. These insights allowed us to produce the first highly enantioenriched axially chiral catenane and the same approach gave access to a molecule containing the newly identified noncanonical axially chiral rotaxane motif. With methods to access these structures in hand, the process of exploring their properties and applications can now begin.

Aggregation-induced emission (AIE)-active switchable [2]rotaxane TR2 with two different molecular stations and arm-terminated TPE units at both ends, and their derivatives were synthesized by means of threading, followed by the stoppering tactic via click chemistry. The AIE behavior of thread A1 and [2]rotaxanes (TR1, TR2, and TR3) in CH3CN were activated by tuning water fractions (fw), which induced the development of various well-defined nanostructures including spheres, nanorods, truncated cubes, and nanocubes via the self-assembly of scaffolds. These AIE changes and distinct nanostructures formation verify that the reported analogous rotaxanes were controlled by the shuttling movements of the macrocycle along with wide ranges of multi-non-covalent interactions. The anion-templated construction of [2]rotaxane TR2 with a high level of structurally complex design always encounters more challenging tasks. Evidently, the key to the design involved encoding flexible arms on both triazolium motifs, and exhibited an impressive selectivity and sensitivity (with a detection limit of 0.20 μM) towards the complementary H2PO4− ion species. The specific mechanical molecular motion and host–guest interactions of mechanically interlocked molecules (MIMs) were also further explored by quantum mechanical calculations. Importantly, the AIE changes of [2]rotaxanes TR1, TR2, and TR3 were further supported by their bioimaging applications and specifically, [2]rotaxane TR2 could be applied to in vitro imaging with H2PO4− at subcellular levels. This flexible multi-component synthetic strategy affords access to the systematic tuning of molecular structures and self-assembled architectures, and it will inspire further studies on the self-assembly of TPE-containing MIMs for materials science and biological applications.

Asymmetric synthesis of mechanically planar chiral rotaxanes and topologically chiral catenanes has been a long-standing challenge in organic synthesis. Recently, an excellent strategy was developed based on diastereomeric synthesis of rotaxanes and catenanes with mechanical chirality followed by removal of the chiral auxiliary. On the other hand, its enantioselective approach has been quite limited. Here, we report enantioselective preparation of mechanically planar chiral rotaxanes by kinetic resolution of the racemates via remote asymmetric acylation of a hydroxy group in the axis component, which provides an unreacted enantiomer in up to >99.9% ee in 29% yield (the theoretical maximum yield of kinetic resolution of racemate is 50%). While the rotaxane molecules are expected to have conformational complexity, our original catalysts enabled to discriminate the mechanical chirality of the rotaxanes efficiently with the selectivity factors in up to 16., Since the discovery of mechanically planar chiral rotaxanes and topologically chiral catenanes, their asymmetric synthesis has been a long-standing challenge. Here, the authors report enantioselective preparation of mechanically planar chiral rotaxanes with up to 99.9% ee in 29% yield.

International audience; Despite the impressive number of interlocked molecules described in the literature over the past 30 years, only a few stereoselective syntheses of mechanically chiral rotaxanes have been reported so far. In this study, we present the first diastereoselective synthesis of mechanically planar chiral [1]rotaxanes, that has been achieved using the active template Cu-mediated alkyne-azide cycloaddition reaction. This synthetic method has been applied to the preparation of a [1]rotaxane bearing a labile stopper that can then be substituted without disruption of the mechanical bond. This approach paves the way for the synthesis of a wide variety of mechanically planar chiral [1]rotaxanes, hence allowing the study of the properties and potential applications of this class of interlocked molecular architectures.

Controlled and complete assembly of supramolecular systems on solid supports is a challenge that would elevate the function of interlocked architectures. Building on the success of other dynamic covalent synthetic methods, we present hydrazone exchange as a strategy to improve the formation of rotaxanes in solution and on solid surfaces. Solution-state analogues containing naphthalenediimide (NDI) or bipyridinium motifs and 1,5-dinaphtho[38]crown-10 were initially prepared to establish ideal conditions for maintaining thermal equilibrium throughout the exchange reaction. Solid-state rotaxanes were synthesised on hydrazide-functionalised TentaGel™ polymer resins and analysed with HR MAS 1H NMR spectroscopy. Surface rotaxane functionalisation of 80% was achieved for the NDI rotaxane, which is significantly higher than previously reported with either dynamic covalent or traditional irreversible synthetic strategies.

Although the construction and application of pillar[5]arene-based [1]rotaxanes have been extensively studied, the types of stoppers for them are limited. In this work, we designed and prepared three series of pillar[5]arene-based [1]rotaxanes (P5[1]Rs) with pentanedione derivatives, azobenzene derivatives, and salicylaldehyde derivatives as the stoppers, respectively. The obtained P5[1]Rs were fully characterized by NMR (1H, 13C, and 2D), mass spectra, and single-crystal X-ray analysis. We found that the synergic C–H···π, C–H···O interactions and N–H···O, O–H···N hydrogen bonding are the key to the stability of [1]rotaxanes. This work not only enriched the diversity of pillar[n]arene family but also gave a big boost to the pillar[n]arene-based mechanically interlocked molecules

The interlocking of ring and axle molecular components in rotaxanes provides a way to combine chromophoric, electron-donor and electron-acceptor moieties in the same molecular entity, in order to reproduce the features of photosynthetic reaction centers. To this aim, the photoinduced electron transfer processes involving a 1,8-naphthalimide chromophore, embedded in several rotaxane-based dyads, were investigated by steady-state and time-resolved absorption and luminescence spectroscopic experiments in the 300 fs-10 ns time window. Different rotaxanes built around the dialkylammonium/ dibenzo[24]crown-8 ether supramolecular motif were designed and synthesized to decipher the relevance of key structural factors, such as the chemical deactivation of the ammonium-crown ether recognition, the presence of a secondary site for the ring along the axle, and the covalent functionalization of the macrocycle with a phenothiazine electron donor. Indeed, the conformational freedom of these compounds gives rise to a rich dynamic behavior induced by light and may provide opportunities for investigating and understanding phenomena that take place in complex (bio)molecular architectures.

Chiral pseudo[1]rotaxanes and [1]rotaxanes constructed from macrocyclic arenes still remain a big challenge mainly owing to the lack of such chiral macrocycles. In this work, a new system of chiral pseudo[1]rotaxanes formed by self-inclusion of helic[6]arene containing amide linked with the terminal tertiary amines was first discovered. Based on an atom-economic stopping strategy, a pair of chiral [1]rotaxanes were conveniently obtained in almost quantitative yields by blocking the pseudo[1]rotaxanes with monobenzyl bromide of tetraphenylethene. The structures of pseudo[1]rotaxanes and [1]rotaxanes were characterized by 2D NMR spectra in solution, combining with the DFT calculations. The photophysical properties further revealed the efficient chirality transfer of helic[6]arene to the tetraphenylethene moiety, compared to their unthreaded chiral isomers. The discovery of the chiral pseudo[1]rotaxanes allows for a wide and available synthesis of chiral [1]rotaxanes, and also opening a new avenue to the design of chiral supramolecular materials.

Dynamic mechanical chirality of [2]rotaxane consisting of a Cs symmetric wheel and a C2v symmetric axle is discussed via the synthesis, enantiomer separation, racemization, and chiral-prochiral interconversion. This [2]rotaxane is achiral and/or prochiral when its wheel locates at the center of the axle, but becomes chiral when the wheel moves from the center of the axle. These were proved by the experiments on the enantiomer separation and racemization. The racemization energy of the isolated single enantiomers was controlled by the bulkiness of the central substituents on the axle. Furthermore, the chiral-prochiral interconversion was achieved by relative positional control of the components. The present systematic studies will provide new insight into mechanically chiral interlocked compounds as well as the utility as dynamic chiral sources.