Daisy Chain Rotaxanes Research Articles

Simultaneous Hydrogenation of an Insulated Diarylacetylene Dimer Incorporated as Axle Molecules in a Cyclodextrin-Based [c2]Daisy Chain Rotaxane.

The [c2]daisy chain rotaxane is an attractive interlocked molecule for the development of functional materials because of its unique mechanical properties that respond to various external stimuli, resulting in extension and contraction motions along the molecular axis. The synthesis of several 'impossible' [2]rotaxanes that do not exhibit obvious binding motifs between their axle and wheel moieties has been achieved through further chemical modification of their axle moieties within pre-prepared [2]rotaxanes. However, no 'impossible' [c2]daisy chain rotaxane has been synthesized using similar strategies until now. In this study, we investigated the hydrogenation of diarylacetylene moieties within a permethylated α-cyclodextrin (PM α-CD)-based [c2]daisy chain rotaxane using Pd/C or Pd/CaCO3 under hydrogen. A new [c2]daisy chain rotaxane featuring two diarylethane moieties was successfully synthesized through the simultaneous full hydrogenation of the insulated diarylacetylene moieties under optimized conditions. The new rotaxane is classified as an 'impossible' [c2]daisy chain rotaxane due to the lack of obvious binding motifs between diarylethane and the PM α-CD. This work demonstrates for the first time that the insulated axle moieties of [c2]daisy chain rotaxanes can undergo novel chemical modifications using a synthetic strategy employing transition-metal-catalyzed hydrogenation, which can potentially advance the development of nanoarchitectures with functional interlocked molecules.

Force-activated ratiometric fluorescence switching of tensile mechano-fluorophoric polyurethane elastomers with enhanced toughnesses improved by mechanically interlocked [c2] daisy chain rotaxanes

The extended and contracted conformations of [c2] daisy chain rotaxanes were introduced in mechano-fluorophoric polyurethane (PU) scaffolds via step-growth polymerizations to obtain distinct mechanical and optical features upon external forces. Particularly, the inherent ductile and stretchable capabilities along with notable toughnesses of PU films containing very low contents of [c2] daisy chain moieties with long-range sliding motions were obviously improved. Furthermore, appealing Förster resonance energy transfer (FRET) behaviors with the optimum energy transfer efficiency ca. 26.02% between blue-emitting tetraphenylethylene (TPE) and yellow-orange-emitting rhodamine derivatives could be acquired in the PU film under tensile conditions, which could be assigned to the incorporation of bi-fluorophoric daisy chain rotaxane into PU frameworks to gain reversible dual fluorescence switching behaviors upon stretching and relaxation processes. Additionally, the stretching deformations of PU films were inspected by X-ray diffraction (XRD) and FTIR techniques for the verification of correlated morphological properties of stretching states in the oriented daisy chain rotaxane-based PU films. Interestingly, impressive shape recovery and reversible ratiometric mechano-fluorophoric fluorescence switching properties of [c2] daisy chain rotaxane-based PU films could be attained upon heating, suggesting potential applications of PU films comprising artificial molecular muscles with glorious mechanical and optical behaviors in advanced polymer networks.

One-Pot Synthesis of Stable Poly([c2]Daisy–chain Rotaxane) with Pseudo-Stopper via Metathesis Reaction and Thiol-Ene Reaction

Rotaxanes, known as supramolecular compounds, are expected to find applications in functional materials due to their high degree of freedom. However, their synthesis requires multistep reactions, and there is a demand for more convenient methods to synthesize rotaxane materials. In this study, we aimed to investigate a simpler method for synthesizing highly functional rotaxane materials and explore the diversity of molecular designs. To achieve this, we successfully synthesized a host–guest conjugated compound that incorporates both crown ether as the host unit and secondary ammonium salts as the guest unit within the same molecule. Subsequently, the metathesis reaction of these compounds, which construct [c2]daisy-chain rotaxanes, enabled the one-pot synthesis of a topological polymer called “poly([c2]daisy-chain rotaxane)” with a pseudo-stopper. This methodology achieves the stabilization and polymerization of rotaxanes simultaneously, contributing to the easy materialization of rotaxanes. Furthermore, the thiol-ene reaction achieved the extension of the distance between rotaxane units and provided a useful approach to diversify the design of functional materials with rotaxane structures.

Controllable Aggregation-Induced Emission and Förster Resonance Energy Transfer Behaviors of Bistable [c2] Daisy Chain Rotaxanes for White-Light Emission and Temperature-Sensing Applications.

Bistable [c2] daisy chain rotaxanes with respective extended and contracted forms of [c2]A and [c2]B containing a blue-emissive anthracene (AN) donor and orange-emissive indandione-carbazole (IC) acceptor were successfully synthesized via click reaction. Tunable-emission bistable [c2] daisy chain rotaxanes with fluorescence changes from blue to orange, including bright-white-light emissions, could be modulated by the aggregation-induced emission (AIE) characteristics and Förster resonance energy transfer (FRET) processes through altering water fractions and shuttling processes (i.e., acid/base controls). Accordingly, as a result of excellent fine-tuning AIE (at 60% water content of H2O/THF) and FRET (with a compatible energy transfer of EFRET = 33.2%) behaviors after the shuttling process (by adding base), the brightest white-light emission at CIE (0.31, 0.37) with a quantum yield of Φ = 15.64% was obtained in contracted [c2]B with good control of molecular shuttling to possess higher photoluminescence (PL) quantum yields and better energy transfer efficiencies (i.e., the manipulation of reduced PET and enhanced FRET processes) due to their intramolecular aggregations of blue AN donors and orange IC acceptors with a proper water content of 60% H2O. Furthermore, dynamic light-scattering (DLS) and time-resolved photoluminescence (TRPL) measurements, along with theoretical calculations, were utilized to investigate and confirm AIE and FRET phenomena of bistable [c2] daisy chain rotaxanes. Especially, both bistable [c2] daisy chain rotaxanes [c2]A and [c2]B and noninterlocked monomer M could be exploited for the applications of ratiometric fluorescence temperature sensing due to the temperature effects on the AIE and FRET features. Based on these desirable bistable [c2] daisy chain rotaxane structures, this work provides a potential strategy for the future applications of tunable multicolor emission and ratiometric fluorescence temperature-sensing materials.

Reversible fluorescence and Förster resonance energy transfer switching behaviours of bistable photo-switchable [c2] daisy chain rotaxanes and photo-patterning applications

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.

Maximizing the [c2]daisy chain to lasso ratio through competitive self-templating clipping reactions.

Self-templating two-component coupling reactions allowed the isolation of two threaded products with different molecular sizes: a lasso-type [1]rotaxane and a [c2]daisy chain rotaxane. Their distribution in the final reaction mixture varies as a factor of the concentration of the reactants. Through this methodology we obtained a large 84-membered cyclic multistation [2]rotaxane.

Template-Directed Synthesis of Redox-Active [c3]Daisy Chain Rotaxanes

Cyclic daisy chain rotaxanes represent a particularly intriguing class of mechanically interlocked molecules with the potential to generate precisely controlled molecular movements by internal sliding of their chains. In this issue of <i>Chem</i>, Stoddart and collaborators introduce an efficient template-directed strategy for accessing [<i>c</i>3]daisy chain rotaxanes capable of redox switching between a relaxed macrocycle and a tensed trisarm-shaped conformation.

Radical Cyclic [3]Daisy Chains

Summary Mechanically interlocked molecules (MIMs) that undergo controllable internal motions of their component parts in more than one dimension are rare entities in the molecular world. Cyclic [2]daisy chains ([c2]DCs) are a class of MIMs that have been identified as prototypes for molecular muscles. It remains, however, a challenge to synthesize [cn]DCs with n > 2 selectively and efficiently. Herein, we report the design and synthesis of [c3]DCs employing radical and anionic templates. Two mechanically interlocked [c3]DCs with 18 positive charges were obtained in >90% yields. One [c3]DC displayed good air stability in its radical cationic form, while the other underwent reversible “co-conformational” switching between open macrocyclic and closed trisarm-shaped forms under electrochemical control. These findings provide not only two-dimensional MIMs with attractive electronic and switchable properties, but also a starting point for the design of extended molecular arrays, which could become the forerunners of adjustable molecular nets and breathable molecular membranes.

Daisy Chain Dendrimers: Integrated Mechanically Interlocked Molecules with Stimuli-Induced Dimension Modulation Feature.

The precise construction of the high-order mechanically interlocked molecules (MIMs) with well-defined topological arrangements of multiple mechanically interlocked units has been a great challenge. Herein, we present the first successful preparation of a new family of daisy chain dendrimers, in which the individual [c2]daisy chain rotaxane units serve as the branches of dendrimer skeleton. In particular, the third-generation daisy chain dendrimer with 21 [c2]daisy chain rotaxane moieties was realized, which might be among the most complicated discrete high-order MIMs comprised of multiple [c2]daisy chain rotaxane units. Interestingly, such unique topological arrangements of multiple stimuli-responsive [c2]daisy chain rotaxanes endowed the resultant daisy chain dendrimers controllable and reversible nanoscale dimension modulation through the collective and amplified extension/contraction of each [c2]daisy chain rotaxane branch upon the addition of acetate anions or DMSO molecules as external stimulus. Furthermore, on the basis of such an intriguing size switching feature of daisy chain dendrimers, dynamic composite polymer films were constructed through the incorporation of daisy chain dendrimers into polymer films, which could undergo fast, reversible, and controllable shape transformations when DMSO molecules were employed as stimulus. The successful merging of [c2]daisy chain rotaxanes and dendrimers described herein provides not only a brand-new type of high-order mechanically interlocked systems with well-defined topological arrangements of [c2]daisy chain rotaxanes, but also a successful and practical approach toward the construction of supramolecular dynamic materials.

Design, assembly, characterization, and operation of double-stranded interlocked DNA nanostructures.

Mechanically interlocked DNA nanostructures are useful as flexible entities for operating DNA-based nanomachines. Interlocked structures made of double-stranded (ds) DNA components can be constructed by irreversibly threading them through one another to mechanically link them. The interlocked components thus remain bound to one another while still permitting large-amplitude motion about the mechanical bond. The construction of interlocked dsDNA architectures is challenging because it usually involves the synthesis and modification of small dsDNA nanocircles of various sizes, dependent on intrinsically curved DNA. Here we describe the design, generation, purification, and characterization of interlocked dsDNA structures such as catenanes, rotaxanes, and daisy-chain rotaxanes (DCRs). Their construction requires precise control of threading and hybridization of the interlocking components at each step during the assembly process. The protocol details the characterization of these nanostructures with gel electrophoresis and atomic force microscopy (AFM), including acquisition of high-resolution AFM images obtained in intermittent contact mode in liquid. Additional functionality can be conferred on the DNA architectures by incorporating proteins, molecular switches such as photo-switchable azobenzene derivatives, or fluorophores for studying their mechanical behavior by fluorescence quenching or fluorescent resonance energy transfer experiments. These modified interlocked DNA architectures provide access to more complex mechanical devices and nanomachines that can perform a variety of desired functions and operations. The assembly of catenanes can be completed in 2 d, and that of rotaxanes in 3 d. Addition of azobenzene functionality, fluorophores, anchor groups, or the site-specific linkage of proteins to the nanostructure can extend the time line.

Cover Feature: Unsymmetric Bistable [c2]Daisy Chain Rotaxanes which Combine Two Types of Electroactive Stoppers (Eur. J. Org. Chem. 21/2019)

The Cover Feature shows contracted (top) and extended (bottom) molecular models of unsymmetric bistable [c2]daisy chain rotaxanes with two different units as stoppers: an electron donor triarylamine and an electron acceptor perylene bisimide. The distinct cyclic voltammograms of the extended (blue) and contracted (red) structures highlight how the electrochemical properties of the stoppers can be altered by the shuttling event, that is controlled here by pH stimulation. This use of the mechanical bond could be, in principle, implemented towards the design of sensing devices. More information can be found in the Full Paper by E. Moulin, N. Giuseppone et al.

C 2]Daisy Chain Rotaxanes as Molecular Muscles

Bistable [ c2]daisy chain rotaxanes represent a particularly intriguing class of interlocked molecules that can produce internal sliding movements with a net contraction or extension at the single-molecule level. These nanometric motions show some analogies with the sliding motions of actin and myosin filaments in sarcomeres, and this is why [ c2]daisy chain rotaxanes have been also named as “molecular muscles,” as their first synthesis in 2000. In this minireview, the authors discuss the recent history of these molecules, their modular chemical structures, and the various synthetic pathways described in the literature to access them. The authors also detail how their internal motions can be controlled and characterized by a number of chemical and physical tools. The authors finally show that their integration within polymers and materials can give access to synchronized motions and amplifications up to the macroscopic scale. Overall, the numerous examples that have been described in the literature to date demonstrate that this family of molecules has already strongly influenced the entire field of research on artificial molecular machines, and has the potential to be implemented as actuators working at all scales, from nanometric-switchable devices to mechanically active soft matter materials.

Unsymmetric Bistable [c2]Daisy Chain Rotaxanes which Combine Two Types of Electroactive Stoppers

Mechanically interlocked molecules (MIMs) have emerged as intriguing building blocks for the construction of stimuli‐responsive devices and materials. A particularly interesting and well‐implemented subclass of MIMs is composed of symmetric bistable [c2]daisy chain rotaxanes. Topologically, they consist in the double thread of two symmetric macrocycles that are covalently linked to an axle bearing two switchable stations and a bulky stopper to avoid unthreading. Herein we report the synthesis and characterization of a series of unsymmetric bistable [c2]daisy chain rotaxanes that present two different electroactive units as stoppers (an electron donor triarylamine and an electron acceptor perylene bisimide unit). Using a combination of 1D and 2D NMR along with cyclic voltammetry, we demonstrate that the pH actuation of the mechanical bond can be used to modulate the electrochemical properties of the bistable [c2]daisy chain rotaxanes when switching between the contracted and extended forms.

Bistable [c2] Daisy Chain Rotaxanes as Reversible Muscle-like Actuators in Mechanically Active Gels

The implementation of molecular machines in polymer science is of high interest to transfer mechanical motions from nanoscale to macroscale in order to access new kinds of active devices and materials. Toward this objective, thermodynamic and topological aspects need to be explored for reaching efficient systems capable of producing a useful work. In this paper we describe the branched polymerization of pH-sensitive bistable [c2] daisy chain rotaxanes by using copper(I)-catalyzed Huisgen 1,3-dipolar cycloaddition ("click chemistry"). With this cross-linked topology, the corresponding materials in the form of chemical gels can be contracted and expanded over a large variation of volume (∼50%) by changing the protonation state of the system. HR-MAS 1H NMR and neutron scattering experiments reveal that this macroscopic response of the gels results from the synchronized actuation of the mechanical bonds at the molecular level.

Controlled Sol-Gel Transitions by Actuating Molecular Machine Based Supramolecular Polymers.

The implementation of artificial molecular machines in polymer science is an important objective that challenges chemists and physicists in order to access an entirely new class of smart materials. To design such systems, the amplification of a mechanical actuation from the nanoscale up to a macroscopic response in the bulk material is a central issue. In this article we show that bistable [c2]daisy chain rotaxanes (i.e., molecular muscles) can be linked into main-chain Upy-based supramolecular polymers. We then reveal by an in depth quantitative study that the pH actuation of the mechanically active rotaxane at the nanoscale influences the physical reticulation of the polymer chains by changing the supramolecular behavior of the Upy units. This nanoactuation within the local structure of the main chain polymer results in a mechanically controlled sol-gel transition at the macroscopic level.

Daisy Chain Rotaxanes Made from Interlocked DNA Nanostructures.

We report the stepwise assembly of supramolecular daisy chain rotaxanes (DCR) made of double‐stranded DNA: Small dsDNA macrocycles bearing an axle assemble into a pseudo‐DCR precursor that was connected to rigid DNA stoppers to form DCR with the macrocycles hybridized to the axles. In presence of release oligodeoxynucleotides (rODNs), the macrocycles are released from their respective hybridization sites on the axles, leading to stable mechanically interlocked DCRs. Besides the expected threaded DCRs, certain amounts of externally hybridized structures were observed, which dissociate into dumbbell structures in presence of rODNs. We show that the genuine DCRs have significantly higher degrees of freedom in their movement along the thread axle than the hybridized DCR precursors. Interlocking of DNA in DCRs might serve as a versatile principle for constructing functional DNA nanostructures where the movement of the subunits is restricted within precisely confined tolerance ranges.

Daisy Chain Rotaxanes Made from Interlocked DNA Nanostructures

AbstractWe report the stepwise assembly of supramolecular daisy chain rotaxanes (DCR) made of double‐stranded DNA: Small dsDNA macrocycles bearing an axle assemble into a pseudo‐DCR precursor that was connected to rigid DNA stoppers to form DCR with the macrocycles hybridized to the axles. In presence of release oligodeoxynucleotides (rODNs), the macrocycles are released from their respective hybridization sites on the axles, leading to stable mechanically interlocked DCRs. Besides the expected threaded DCRs, certain amounts of externally hybridized structures were observed, which dissociate into dumbbell structures in presence of rODNs. We show that the genuine DCRs have significantly higher degrees of freedom in their movement along the thread axle than the hybridized DCR precursors. Interlocking of DNA in DCRs might serve as a versatile principle for constructing functional DNA nanostructures where the movement of the subunits is restricted within precisely confined tolerance ranges.

PH and light-controlled self-assembly of bistable [c2] daisy chain rotaxanes.

A logic gate based on a bistable [c2] daisy chain rotaxane decorated with lateral triarylamine units is described, giving rise to an INHIBIT logic function using proton concentration and light as inputs, and producing dual color change and supramolecular self-assembly as outputs.

Redox Switchable Daisy Chain Rotaxanes Driven by Radical–Radical Interactions

We report the one-pot synthesis and electrochemical switching mechanism of a family of electrochemically bistable 'daisy chain' rotaxane switches based on a derivative of the so-called 'blue box' (BB(4+)) tetracationic cyclophane cyclobis(paraquat-p-phenylene). These mechanically interlocked molecules are prepared by stoppering kinetically the solution-state assemblies of a self-complementary monomer comprising a BB(4+) ring appended with viologen (V(2+)) and 1,5-dioxynaphthalene (DNP) recognition units using click chemistry. Six daisy chains are isolated from a single reaction: two monomers (which are not formally 'chains'), two dimers, and two trimers, each pair of which contains a cyclic and an acyclic isomer. The products have been characterized in detail by high-field (1)H NMR spectroscopy in CD3CN-made possible in large part by the high symmetry of the novel BB(4+) functionality-and the energies associated with certain aspects of their dynamics in solution are quantified. Cyclic voltammetry and spectroelectrochemistry have been used to elucidate the electrochemical switching mechanism of the major cyclic daisy chain products, which relies on spin-pairing interactions between V(•+) and BB(2(•+)) radical cations under reductive conditions. These daisy chains are of particular interest as electrochemically addressable molecular switches because, in contrast with more conventional bistable catenanes and rotaxanes, the mechanical movement of the ring between recognition units is accompanied by significant changes in molecular dimensions. Whereas the self-complexed cyclic monomer-known as a [c1]daisy chain or molecular 'ouroboros'-conveys sphincter-like constriction and dilation of its ultramacrocyclic cavity, the cyclic dimer ([c2]daisy chain) expresses muscle-like contraction and expansion along its molecular length.