Motorized Macrocycle: A Photo-responsive Host with Switchable and Stereoselective Guest Recognition

Dynamic control of circumrotation of a [2]catenane by acid-base switching

Dynamic control of the motion in a catenane remains a big challenge as it requires precise design and sophisticated well-organized structures. This paper reports the design and synthesis of a donor-acceptor [2]catenane through mechanical interlocking, employing a crown ether featuring two dibenzylammonium salts on its side arms as the host and a cyclobis(paraquat-p-phenylene) (CBPQT ⋅ 4PF6 ) ring as the guest molecule. By addition of external acid or base, the catenane can form self-complexed or decomplexed compounds to alter the cavity size of the crown ether ring, consequently affecting circumrotation rate of CBPQT ⋅ 4PF6 ring of the catenane. This study offers insights for the design and exploration of artificial molecular machines with intricate cascading responsive mechanisms.

A Photoswitchable Macrocycle Controls Anion-Templated Pseudorotaxane Formation and Axle Relocalization

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 1 H NMR spectroscopy. The (Z)-isomers can be effectively threaded by pyridinium halide axles to give pseudorotaxane complexes, as confirmed by 1 H 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 1 H NMR spectroscopy and simulated computationally.

Photoresponsive Supramolecular Cages and Macrocycles

The utilisation of light to achieve precise manipulation and control over the structure and function of supramolecular assemblies has emerged as a highly promising approach in the development of complex, configurable, or multifunctional systems and nanoscopic machine-like entities. In this minireview, we highlight recent examples of self-assembled and covalently bound cages and macrocycles with a focus on the external and internal functionalisation of a structure with a photoswitchable unit or the embedment of a photoswitch into the framework of a structure. Functionalising the interior or exterior of a supramolecular cage or macrocycle with a photoresponsive group enables control over different properties, such as guest binding or assembly in the solid-state, while the overall shape of the assembly often undergoes no significant change. By directly integrating a photoswitchable unit into the framework of a supramolecular structure, the isomerisation can either induce a geometry change, the disassembly, or the disassembly and reassembly of the structure. Historical and recent examples covered in this review are based on azobenzene, diarylethene, stilbene photoswitches, or alkene motors that were incorporated into macrocycles and cages constructed by metal-organic, dynamic covalent, or covalent bonds.

Dual-Stimulus-Driven Dynamically Controllable [3]Rotaxane with Tunable Organic Room-Temperature Phosphorescence

A dual-stimulus-driven stiff-stilbene-based dynamic [3]rotaxane has been facilely developed using the threading-stoppering strategy and exhibits reversible shuttling motions and bidirectional rotations upon encountering acid-base and distinct light stimulations, respectively. Herein, the two dibenzo-24-crown-8 macrocycles can undergo reversible switching motion between two different stations along the axle suffered from acid-base stimulation, and simultaneously, the two rotaxanes can also perform cis-trans rotations upon irradiation with distinct light. In other words, the constructed rotaxanes can conduct two modes of regular motions without interference. Interestingly, reciprocating switching motion of the rings along the axle enabled the rotaxanes to exhibit controllable and reversible photoisomerization speed, conversion yield, and quantum yield. Crucially, these rotaxanes also manifest adjustable solid-state organic room-temperature phosphorescence (RTP) and photoluminescence stimulated by dual factors (acid-base and diverse light), which are further applied in information encryption and anticounterfeiting. The presented study provides an instructive way for precisely boosting photoisomerization performances and the fabrication of dual-stimuli-induced molecular machines with functions of two-mode mechanical motions and controllable pure organic RTP switches.

Synthesis of Large Macrocycles with Chiral Sulfur Centers via Enantiospecific SuFEx and SuPhenEx Click Reactions

Here we report the first asymmetric synthesis of large chiral macrocycles with chiral sulfur atoms. Building on stereospecific SuFEx and SuPhenEx click chemistries, this approach utilizes disulfonimidoyl fluorides and disulfonimidoyl p-nitrophenolates─which are efficient building blocks with two chiral sulfur centers, and diphenols to efficiently form novel S-O bonds. Characteristic results include the enantiospecific one-step synthesis of rings consisting of 21-58 members and characterization of both enantiomers (R,R and S,S) by e.g. X-ray crystallography.

Water-soluble organic macrocycles based on dye chromophores and their applications

Traditional water-soluble organic macrocyclic receptors generally lack photofunctionality, thus monitoring the drug delivery and the phototheranostic applications of these host-guest macrocyclic systems has been greatly restricted. To address this issue, incorporating π-conjugated dye chromophores as building blocks into macrocyclic molecules is a straightforward and promising strategy. This approach not only imparts intrinsic optical features to the macrocycles themselves but also enhances the host-guest binding ability due to the large planar structures of the dyes. In this feature article, we focus on recent advances in water-soluble macrocyclic compounds based on organic dye chromophores, such as naphthalimide (NDI), perylene diimides (PDI), azobenzene (azo), tetraphenylethylene (TPE) and anthracene, and provide an overview of their various applications including molecular recognition, drug release, biological imaging, photothermal therapy, etc. We hope that this article could be helpful and instructive for the design of water-soluble dye-based macrocycles and the further development of their biomedical applications, particularly in combination with drug therapy and phototheranostics.

A Chiral Emissive Conjugated Macrocycle for High-Affinity and Highly Enantioselective Recognition in Water

Accurately distinguishing between enantiomeric molecules is a fundamental challenge in the field of chemistry. However, there is still significant room for improvement in both the enantiomeric selectivity (KR(S) /KS(R) ) and binding strength of most reported macrocyclic chiral receptors to meet the demands of practical application scenarios. Herein, we synthesized a water-soluble conjugated tubular host-namely, corral[4]BINOL-using a chiral 1,1'-bi-2-naphthol (BINOL) derivative as the repeating unit. The conjugated chiral backbone endows corral[4]BINOL with good fluorescent emission (QY=34 % ) and circularly polarized luminescence (|glum | up to 1.4×10-3 ) in water. Notably, corral[4]BINOL exhibits high recognition affinity up to 8.6×1010  M-1 towards achiral guests in water, and manifested excellent enantioselectivity up to 18.7 towards chiral substrates, both of which represent the highest values observed among chiral macrocycles in aqueous solution. The ultrastrong binding strength, outstanding enantioselectivity, and facile accessibility, together with the superior fluorescent and chiroptical properties, endow corral[4]BINOL with great potential for a wide range of applications.

Enlightening dynamic functions in molecular systems by intrinsically chiral light-driven molecular motors

Chirality is a fundamental property which plays a major role in chemistry, physics, biological systems and materials science. Chiroptical artificial molecular motors (AMMs) are a class of molecules which can convert light energy input into mechanical work, and they hold great potential in the transformation from simple molecules to dynamic systems and responsive materials. Taking distinct advantages of the intrinsic chirality in these structures and the unique opportunity to modulate the chirality on demand, chiral AMMs have been designed for the development of light-responsive dynamic processes including switchable asymmetric catalysis, chiral self-assembly, stereoselective recognition, transmission of chirality, control of spin selectivity and biosystems as well as integration of unidirectional motion with specific mechanical functions. This review focuses on the recently developed strategies for chirality-led applications by the class of intrinsically chiral AMMs. Finally, some limitations in current design and challenges associated with recent systems are discussed and perspectives towards promising candidates for responsive and smart molecular systems and future applications are presented.

Allosteric control of olefin isomerization kinetics via remote metal binding and its mechanochemical analysis

Allosteric control of reaction thermodynamics is well understood, but the mechanisms by which changes in local geometries of receptor sites lower activation reaction barriers in electronically uncoupled, remote reaction moieties remain relatively unexplored. Here we report a molecular scaffold in which the rate of thermal E-to-Z isomerization of an alkene increases by a factor of as much as 104 in response to fast binding of a metal ion to a remote receptor site. A mechanochemical model of the olefin coupled to a compressive harmonic spring reproduces the observed acceleration quantitatively, adding the studied isomerization to the very few reactions demonstrated to be sensitive to extrinsic compressive force. The work validates experimentally the generalization of mechanochemical kinetics to compressive loads and demonstrates that the formalism of force-coupled reactivity offers a productive framework for the quantitative analysis of the molecular basis of allosteric control of reaction kinetics. Important differences in the effects of compressive vs. tensile force on the kinetic stabilities of molecules are discussed.

A photochemical method to evidence directional molecular motions

Light driven synthetic molecular motors represent crucial building blocks for advanced molecular machines and their applications. A standing challenge is the development of very fast molecular motors able to perform rotations with kHz, MHz or even faster frequencies. Central to this challenge is the direct experimental evidence of directionality because analytical methods able to follow very fast motions rarely deliver precise geometrical insights. Here, a general photochemical method for elucidation of directional motions is presented. In a macrocyclization approach the molecular motor rotations are restricted and forced to proceed in two separate ~180° rotation-photoequilibria. Therefore, all four possible photoinduced rotation steps (clockwise and counterclockwise directions) can be quantified. Comparison of the corresponding quantum yields to the unrestricted motor delivers direct evidence for unidirectionality. This method can be used for any ultrafast molecular motor even in cases where no high energy intermediates are present during the rotation cycle.

Stimulus-Controlled Anion Binding and Transport by Synthetic Receptors

Anionic species are omnipresent and involved in many important biological processes. A large number of artificial anion receptors has therefore been developed. Some of these are capable of mediating transmembrane transport. However, where transport proteins can respond to stimuli in their surroundings, creation of synthetic receptors with stimuli-responsive functions poses a major challenge. Herein, we give a full overview of the stimulus-controlled anion receptors that have been developed thus far, including their application in membrane transport. In addition to their potential operation as membrane carriers, the use of anion recognition motifs in forming responsive membrane-spanning channels is discussed. With this review article, we intend to increase interest in transmembrane transport among scientists working on host-guest complexes and dynamic functional systems in order to stimulate further developments.

Reversible Inversion of Circularly Polarized Luminescence in a Coassembly Supramolecular Structure with Achiral Sulforhodamine B Dyes

The dynamic control of circularly polarized luminescence (CPL) has far-reaching significance in optoelectronics, information storage, and data encryption. Herein, we reported the reversible inversion of CPL in a coassembly supramolecular system consisting of chiral molecules L4, which contain two positively charged viologen units, and achiral ionic surfactant sodium dodecyl sulfate (SDS) by introducing achiral sulforhodamine B (SRB) dye molecules. The chirality of CPL in the coassemblies can be efficiently regulated and inverted by simply adjusting the amount of SRB. A series of experimental characterization, including optical spectroscopy, electron microscope, ¹H NMR, and X-ray scattering measurements, suggested that SRB could coassemble with L4/SDS to establish a new stable L4/SDS/SRB supramolecular structure through electrostatic interactions. Moreover, the negative-sign CPL could revert to the positive-sign CPL if titanium dioxide (TiO₂) nanoparticles were used to decompose SRB molecules. The evolution of the CPL inversion process could be cycled at least 5 times without a significant decline in CPL signals when SRB was refueled to the system. Our results provide a facile approach to dynamically regulating the handedness of CPL in a multiple-component supramolecular system via achiral species.

Multi-Responsive Molecular Encapsulation and Release Based on Hydrogen-Bonded Azo-Macrocycle

Research on stimuli-responsive host-guest systems is at the cutting edge of supramolecular chemistry, owing to their numerous potential applications such as catalysis, molecular machines, and drug delivery. Herein, we present a multi-responsive host-guest system comprising azo-macrocycle 1 and 4,4'-bipyridinium salt G1 for pH-, photo-, and cation- responsiveness. Previously, we reported a novel hydrogen-bonded azo-macrocycle 1. The size of this host can be controlled through light-induced E↔Z photo-isomerization of the constituent azo-benzenes. The host is found in this work to be capable of forming stable complexes with bipyridinium/pyridinium salts, and implementing guest capture and release with G1 under light in a controlled manner. The binding and release of the guest in the complexes can also be easily controlled reversibly by using acid and base. Moreover, the cation competition-induced dissociation of the complex 1a₂⊃G1 is achieved. These findings are expected to be useful in regulating encapsulation for sophisticated supramolecular systems.

Supramolecular Gel-to-Gel Transition Induced by Nanoscale Structural Perturbation via the Rotary Motion of Feringa's Motor

Supramolecular rather than covalent molecular engineering on Feringa motors can provide an alternative toolkit for tuning the properties of motorized materials through appropriate supramolecular structural perturbations, which are underexplored. Herein, a multicomponent supramolecular gel system is successfully prepared by employing an ultra-low molecular weight gelator and a modulator-Feringa motor. The electron microscopic, spectroscopic, and rheological data revealed that the morphology and mechanical properties of the gel can be tuned via a crystallographic mismatch branching (CMB) mechanism simply by adding varied amounts of motor modulators. Notably, the rotary motion of the motor is preserved in such a multicomponent gel system, and the morphology and rheology of the gel can be further altered by the motor's rotary motion that promotes the structural perturbation, resulting in seldomly seen gel-to-gel transition events. The work shown here offers prospects to utilize a supramolecular perturbation strategy to deliver responsiveness from molecular motors to the corresponding bulk materials.

Light-Driven Aqueous Dissipative Pseudorotaxanes with Tunable Fluorescence Enabling Deformable Nano-Assemblies

Developing an artificial dynamic nanoscale molecular machine that dissipatively self-assembles far from equilibrium is fundamentally important but is significantly challenging. Herein, we report dissipatively self-assembling light-activated convertible pseudorotaxanes (PRs) that show tunable fluorescence and enable deformable nano-assemblies. A pyridinium-conjugated sulfonato-merocyanine derivative (EPMEH) and cucurbit[8]uril (CB[8]) form the 2EPMEH ⊂ CB[8] [3]PR in a 2:1 stoichiometry, which phototransforms into a transient spiropyran containing 1:1 EPSP ⊂ CB[8] [2]PR when exposed to light. The transient [2]PR thermally relaxes (reversibly) to the [3]PR in the dark accompanied by periodic fluorescence changes that include near-infrared emission. Moreover, octahedral and spherical nanoparticles are formed through the dissipative self-assembly of the two PRs, and the Golgi apparatus is dynamically imaged using fluorescent dissipative nano-assemblies.

Singlet Oxygen Responsive Molecular Receptor to Modulate Atropisomerism and Cation Binding

In switchable molecular recognition, ¹ O₂ stimulus responsive receptors offer a unique structural change that is rarely exploited. The employed [4+2] reaction between ¹ O₂ and anthracene derivatives is quantitative, reversible and easily implemented. To evaluate the full potential of this new stimulus, a non-macrocyclic anthracene-based host was designed for the modular binding of cations. The structural investigation showed that ¹ O₂ controlled the atropisomerism in an on/off fashion within the pair of hosts. The binding studies revealed higher association constants for the endoperoxide receptor compared to the parent anthracene, due to a more favoured preorganization of the recognition site. The fatigue of the ¹ O₂ switchable hosts and their complexes was monitored over five cycles of cycloaddition/cycloreversion.

Supramolecular Enhancement of Charge Transport through Pillar[5]arene-Based Self-Assembled Monolayers

Intermolecular charge transport is one of the essential modes for modulating charge transport in molecular electronic devices. Supermolecules are highly promising candidates for molecular devices because of their abundant structures and easy functionalization. Herein, we report an efficient strategy to enhance charge transport through pillar[5]arene self-assembled monolayers (SAMs) by introducing cationic guests. The current density of pillar[5]arene SAMs can be raised up to about 2.1 orders of magnitude by inserting cationic molecules into the cavity of pillar[5]arenes in SAMs. Importantly, we have also observed a positive correlation between the charge transport of pillar[5]arene-based complex SAMs and the binding affinities of the pillar[5]arene-based complexation. Such an enhancement of charge transport is attributed to the efficient host-guest interactions that stabilize the supramolecular complexes and lower the energy gaps for charge transport. This work provides a predictive pattern for the regulation of intermolecular charge transport in guiding the design of next generation switches and functional sensors in supramolecular electronics.

Hierarchical Materials from High Information Content Macromolecular Building Blocks: Construction, Dynamic Interventions, and Prediction

Hierarchical materials that exhibit order over multiple length scales are ubiquitous in nature. Because hierarchy gives rise to unique properties and functions, many have sought inspiration from nature when designing and fabricating hierarchical matter. More and more, however, nature's own high-information content building blocks, proteins, peptides, and peptidomimetics, are being coopted to build hierarchy because the information that determines structure, function, and interfacial interactions can be readily encoded in these versatile macromolecules. Here, we take stock of recent progress in the rational design and characterization of hierarchical materials produced from high-information content blocks with a focus on stimuli-responsive and "smart" architectures. We also review advances in the use of computational simulations and data-driven predictions to shed light on how the side chain chemistry and conformational flexibility of macromolecular blocks drive the emergence of order and the acquisition of hierarchy and also on how ionic, solvent, and surface effects influence the outcomes of assembly. Continued progress in the above areas will ultimately usher in an era where an understanding of designed interactions, surface effects, and solution conditions can be harnessed to achieve predictive materials synthesis across scale and drive emergent phenomena in the self-assembly and reconfiguration of high-information content building blocks.

Photoswitchable molecular tweezers: isomerization to control substrate binding, and what about vice versa?

The linkage of two identical binding motifs by a molecular photoswitch has proven to be a straightforward and versatile strategy to control substrate binding affinity by light. Stimulus control of binding properties in artificial receptors is partly inspired by the dynamic behavior of proteins and is highly attractive as it could, for example, improve extraction processes and allow (de)activation of membrane transport on demand. This feature article summarizes the development and design principles of molecular tweezers containing a molecular photoswitch as the core unit. Besides the control of binding affinity by isomerization, the effect of substrate binding on the isomerization behavior is discussed where data is available. While the latter often receives less attention, it could be of benefit in the future creation of multi-stimuli-controlled molecular switching and machine-like systems.

Systematic Synthesis of Macrocycles Bearing up to Six 2,2'-Bipyridine Moieties through Self-Assembled Double Helix Structure

A new synthetic strategy for macrocycles bearing multiple coordination moieties was developed. A self-assembled double helix structure, composed of two linear strands bearing 2,2'-bipyridine units and Cu(I) ions, provided access to macrocycles bearing a defined number of 2,2'-bipyridine moieties and a defined ring size, via an olefin-metathesis reaction between two linear strands in the helix. The double helix structure improved the selectivity of the macrocycle synthesis by bringing the reaction points in close proximity even in the case of large macrocycles.

The Influence of Strain on the Rotation of an Artificial Molecular Motor

In artificial small‐molecule machines, molecular motors can be used to perform work on coupled systems by applying a mechanical load—such as strain—that allows for energy transduction. Here, we report how ring strain influences the rotation of a rotary molecular motor. Bridging the two halves of the motor with alkyl tethers of varying sizes yields macrocycles that constrain the motor's movement. Increasing the ring size by two methylene increments increases the mobility of the motor stepwise and allows for fine‐tuning of strain in the system. Small macrocycles (8–14 methylene units) only undergo a photochemical E/Z isomerization. Larger macrocycles (16–22 methylene units) can perform a full rotational cycle, but thermal helix inversion is strongly dependent on the ring size. This study provides systematic and quantitative insight into the behavior of molecular motors under a mechanical load, paving the way for the development of complex coupled nanomachinery.

Visible-light controlled supramolecular transformations of donor-acceptor Stenhouse adducts amphiphiles at multiple length-scale

Designing responsive, adaptive, and dynamic supramolecular systems in water, the incorporation of photoresponsive units in amphiphilic molecular structures enables functional responses in a non-invasive way by using light. However, in aqueous media, vast majority of reported synthetic photoresponsive molecular amphiphiles are commonly driven by high energy and bio-damaging UV-light for supramolecular transformation at multiple length-scale. Herein, we present newly designed visible-light controlled supramolecular assembly of donor-acceptor Stenhouse adducts amphiphiles (DA) with excellent stability and solubility in aqueous media. The excellent photoswitchability in organic media and photoresponsiveness in aqueous media driven by visible-light are found, as confirmed with UV-vis absorption and NMR spectroscopies. Supramolecular assembly at multiple length-scale of DAs is investigated with electron microscopies and X-ray diffraction to show large aspect-ratio of nanostructures assembled into macroscopic soft scaffolds. Upon visible-light irradiation, the large geometrical transformation of DAs enables supramolecular transformations, and subsequently destabilizes the macroscopic soft scaffold to release fluorophores from the scaffolds. These results provide the feasibility in developing the next generation of visible-light controlled macroscopic soft functional scaffold from supramolecular assembly across multiple length-scale without and offer ample opportunity to design future soft robotic materials and functional biomaterials.

Light-controlled shape-changing azomacrocycles exhibiting reversible modulation of pyrene fluorescence emission

We report the design, synthesis, and study of light-induced shape-changing azomacrocycles. These systems have been incorporated with azobenzene photoswitches using alkoxy tethers and triazole units to afford flexibility and binding. We envision that such azomacrocycles are capable of reversibly binding with the guest molecule. Remarkably, we have demonstrated fully light-controlled fluorescence quenching and enhancement in the monomeric emission of pyrene (guest). Such modulations have been achieved by the photoisomerization of the azomacrocycle and, in turn, host-guest interactions. Also, the azomacrocycles tend to aggregate and can also be controlled by light or heat. We uncovered such phenomena using spectroscopic, microscopic, and isothermal titration calorimetry (ITC) studies and computations.

Active Mechanical Threading by a Molecular Motor

Molecular motors transform external energy input into directional motions and offer exquisite precision for nano‐scale manipulations. To make full use of molecular motor capacities, their directional motions need to be transmitted and used for powering downstream molecular events. Here we present a macrocyclic molecular motor structure able to perform repetitive molecular threading of a flexible tetraethylene glycol chain through the macrocycle. This mechanical threading event is actively powered by the motor and leads to a direct translation of the unidirectional motor rotation into unidirectional translation motion (chain versus ring). The mechanism of the active mechanical threading is elucidated and the actual threading step is identified as a combined helix inversion and threading event. The established molecular machine function resembles the crucial step of macroscopic weaving or sewing processes and therefore offers a first entry point to a “molecular knitting” counterpart.

Synergistic Effect of Chiral Nanofibers Amplifying the Orbit Angular Momentum To Enhance Optomagnetic Coupling

Manipulating magnetic bits by photon in spintronics, opto-magnetic coupling, is lagging far behind what we could expect. To investigate the issue, one should face the problem to find photon dependence of spin dynamics and spin manipulation. In this work, through introducing chiral orbit in organic crystals, circularly polarized photon can manipulate spin via the channel of photon-orbit-spin interactions. Under the stimulus of the magnetic field, strong spin polarization will feed back to the change in polarized state of light. Moreover, twisting several chiral nanofibers into a thick one, a more pronounced opto-magnetic coupling is clearly observed due to the chirality generated larger chiral orbit. Meanwhile, spin dynamics (or spin response times) inside the aggregated thick chiral fiber can be further tuned by circularly polarized light. Hopefully, this study can deepen the understanding of organic chiral spin-photonics and enhance the application of organic functional crystals in the future.

Benzimidazole-Piperazine-Coumarin/Cucurbit[7]uril Supramolecular Photoinduced Electron Transfer Fluorochromes for Detection of Carnosol by Stimuli-Responsive Dye Displacement and pK a Tuning

A new fluorescent dye (4PBZC) comprising coumarin (C), piperazine (P), and benzimidazole (BZ) was designed, prepared, and complexed to cucurbit[7]uril (CB7) to detect carnosol (CAR), an anti-breast cancer drug, in sub-nanomolar concentrations utilizing the supramolecular indicator displacement assay strategy, the CB7-assisted pK _a shift, and the CB7-retarded photoinduced electron transfer process. The host-guest complexation was confirmed by UV-visible absorption, fluorescence, and ¹H NMR spectroscopy, which established the binding of 4PBZC to CB7. CB7 preferentially binds the indicator dye (4PBZC) via the protonated BZ residue compared to the neutral BZ one, demonstrated by a higher binding constant of the complex in its di-protonated form, which led to an increase in the pK _a of the BZ moiety by ca. 3.0 units after the addition of CB7. In aqueous solution (pH 6), switching the emission signals between 4PBZH⁺C/CB7 (ON state) and 4PBZC (OFF state) was achieved by displacement of the protonated dye from the cavity of CB7 by the CAR analyte. An efficient sensor was obtained for the sensitive detection of CAR in aqueous solution with a low detection limit of 0.148 ng/mL (0.45 nM) and a linear range from 20 to 627 ng/mL.

Fine-Tuning Macrocycle Cavity to Selectively Bind Guests in Water for Near-Infrared Photothermal Conversion

The rational and specific synthesis of the required organic macrocycles to bind the size-matched targeted guests without undesired macrocyclic byproducts remains a great challenge. Herein, based on a new naphthalimide...

Coordination-directed self-assembly of molecular motors: towards a two-wheel drive nanocar

Designing and constructing hierarchical and stimuli-responsive motorized nanocar systems to perform useful tasks on-demand is highly imperative towards molecular nanotechnology. In this work, a most simplified two-wheel nanocar was successfully prepared through a facile strategy of coordination-directed self-assembly. The nanocar meso-AgL2 features a central pseudo square-planar Ag(I) which was bridged by two enantiomeric motors as the wheels that ensure the car moves in the same direction when observed externally. Thanks to the electronic push-pull characteristic of L and ³ILCT triplet sensitization, this nanocar can be driven by visible light up to 500 nm. Furthermore, it could be disassembled into individual motor elements through the addition of pyridine, thus allowing dynamic regulation over the function of the nanocar. Importantly, our STM imaging results showed very organized tilted layered structures for meso-AgL2 on highly oriented pyrolytic graphite (HOPG) that are quite similar to its crystalline ones, paving the way for future single molecule manipulations. The nanocar reported here represents the first example of integrating individual motors into a hierarchical motorized nanocar system via the facile coordination-directed self-assembly method and may offer a good starting point to realize its robotic functions, e.g., metal transportation and release.

Motorized Macrocycle: A Photo-responsive Host with Switchable and Stereoselective Guest Recognition

Designing photo-responsive host-guest systems can provide versatile supramolecular tools for constructing smart systems and materials. We designed photo-responsive macrocyclic hosts, modulated by light-driven molecular rotary motors enabling switchable chiral guest recognition. The intramolecular cyclization of the two arms of a first-generation molecular motor with flexible oligoethylene glycol chains of different lengths resulted in crown-ether-like macrocycles with intrinsic motor function. The octaethylene glycol linkage enables the successful unidirectional rotation of molecular motors, simultaneously allowing the 1:1 host-guest interaction with ammonium salt guests. The binding affinity and stereoselectivity of the motorized macrocycle can be reversibly modulated, owing to the multi-state light-driven switching of geometry and helicity of the molecular motors. This approach provides an attractive strategy to construct stimuli-responsive host-guest systems and dynamic materials.

D–π–A type ferrocene-substituted azobenzene photochromic switches: synthesis, structures, and electrochemical and photoisomerization studies

A series of D–π–A type azobenzenes with a ferrocenyl/ferrocenylethynyl electron donor at the para/meta-position have been synthesized and characterized by electrochemistry and UV-vis spectroscopy.