Visible-Light-Driven Rotation of Molecular Motors in Discrete Supramolecular Metallacycles

Light switching for product selectivity control in photocatalysis

Artificial switchable catalysis is a new, rapidly expanding field that offers great potential advantages for both homogeneous and heterogeneous catalytic systems. Light irradiation is widely accepted as the best stimulus to artificial switchable chemical systems. In recent years, tremendous progress has been made in the synthesis and application of photo-switchable catalysts that can control when and where bond formation and dissociation take place in reactant molecules. Photo-switchable catalysis is a niche area in current catalysis, on which systematic analysis and reviews are still lacking in the scientific literature, yet it offers many intriguing and versatile applications, particularly in organic synthesis. This review aims to highlight the recent advances in photo-switchable catalyst systems that can result in two different chemical product outcomes and thus achieve a degree of control over organic synthetic reactions. Furthermore, this review evaluates different approaches that have been employed to achieve dynamic control over both the catalytic function and the selectivity of several different types of synthesis reactions, along with the remaining challenges and potential opportunities. Owing to the great diversity of the types of reactions and conditions adopted, a quantitative comparison of efficiencies between considered systems is not the focus of this review, instead the review showcases how insights from successful adopted strategies can help better harness and channel the power of photoswitchability in this new and promising area of catalysis research.

Photoswitching in a Liquid Crystalline Pt(II) Coordination Complex

Photoswitching of photoluminescence has sparked tremendous research interests for super-resolution imaging, high-security-level anti-counterfeiting, and other high-tech applications. However, the excitation of photoluminescence is usually ready to trigger the photoswitching process, making the photoluminescence readout unreliable. Herein, we report a new photoswitch by the marriage of spiropyran with platinum(II) coordination complex. Viable photoluminescence can be achieved upon excitation by 480 nm visible light while the photoswitching can be easily triggered by 365 nm UV light. The feasible photoswitching may be benefited from the formed liquid crystalline (LC) phase of the designed photoswitch as a crystalline spiropyran is normally unable to implement photoswitching. Compared to the counterparts, this LC photoswitch can show distinct and reliable apparent colors and emission colors before and after photoswitching, which may promise the utility in high-security-level anti-counterfeiting and other advanced information technologies.

Light-Responsive Supramolecular Liquid-Crystalline Metallacycle for Orthogonal Multimode Photopatterning

The development of multimode photopatterning systems based on supramolecular coordination complexes (SCCs) is considerably attractive in supramolecular chemistry and materials science, because SCCs can serve as promising platforms for the incorporation of multiple functional building blocks. Herein, we report a light-responsive liquid-crystalline metallacycle that is constructed by coordination-driven self-assembly. By exploiting its fascinating liquid crystal features, bright emission properties, and facile photocyclization capability, a unique system with spatially-controlled fluorescence-resonance energy transfer (FRET) is built through the introduction of a photochromic spiropyran derivative, which led to the realization of the first example of a liquid-crystalline metallacycle for orthogonal photopatterning in three-modes, namely holography, fluorescence, and photochromism.

Light-driven micro/nanomotors in biomedical applications

Nanotechnology brings hope for targeted drug delivery. However, most current drug delivery systems use passive delivery strategies with limited therapeutic efficiency. Over the past two decades, research on micro/nanomotors (MNMs) has flourished in the biomedical field. Compared with other driven methods, light-driven MNMs have the advantages of being reversible, simple to control, clean, and efficient. Under light irradiation, the MNMs can overcome several barriers in the body and show great potential in the treatment of various diseases, such as tumors, and gastrointestinal, cardiovascular and cerebrovascular diseases. Herein, the classification and mechanism of light-driven MNMs are introduced briefly. Subsequently, the applications of light-driven MNMs in overcoming physiological and pathological barriers in the past five years are highlighted. Finally, the future prospects and challenges of light-driven MNMs are discussed as well. This review will provide inspiration and direction for light-driven MNMs to overcome biological barriers in vivo and promote the clinical application of light-driven MNMs in the biomedical field.

Motorized Photomodulator: Making A Non-photoresponsive Supramolecular Gel Switchable by Light

Introducing photo-responsive molecules offers an attractive approach for remote and selective control and dynamic manipulation of material properties. However, it remains highly challenging how to use a minimal amount of photo-responsive units to optically modulate materials that are inherently inert to light irradiation. Here we show the application of a light-driven rotary molecular motor as a "motorized photo-modulator" to endow a typical H-bond-based gel system with the ability to respond to light irradiation and create a reversible sol-gel transition. The key molecular design feature is the introduction of a minimal amount (2 mol %) of molecular motors into the supramolecular network as photo-switchable non-covalent crosslinkers. Advantage is taken of the subtle interplay of the large geometry change during photo-isomerization of the molecular motor guest and the dynamic nature of a supramolecular gel host system. As a result, a tiny amount of molecular motors is enough to switch the mechanical modulus of the entire supramolecular systems. This study proves the concept of designing photo-responsive materials with minimum use of non-covalent light-absorbing units.

A visible-light-driven molecular motor based on barbituric acid

We present a class of visible-light-driven molecular motors based on barbituric acid. Due to a serendipitous reactivity we observed during their synthesis, these motors possess a tertiary stereogenic centre on the upper half, characterised by a hydroxy group. Using a combination of femto- and nanosecond transient absorption spectroscopy, molecular dynamics simulations and low-temperature 1H NMR experiments we found that these motors operate similarly to push-pull second-generation overcrowded alkene-based molecular motors. Interestingly, the hydroxy group at the stereocentre enables a hydrogen bond with the carbonyl groups of the barbituric acid lower half, which drives a sub-picosecond excited-state isomerisation, as observed spectroscopically. Computational simulations predict an excited state "lasso" mechanism where the intramolecular hydrogen bond pulls the molecule towards the formation of the metastable state, with a high predicted quantum yield of isomerisation (68%) in gas phase.

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.

Accounts of applied molecular rotors and rotary motors: recent advances

Molecular machines are nanoscale devices capable of performing mechanical works at molecular level. These systems could be a single molecule or a collection of component molecules that interrelate with one another to produce nanomechanical movements and resulting performances. The design of the components of molecular machine with bioinspired traits results in various nanomechanical motions. Some known molecular machines are rotors, motors, nanocars, gears, elevators, and so on based on their nanomechanical motion. The conversion of these individual nanomechanical motions to collective motions via integration into suitable platforms yields impressive macroscopic output at varied sizes. Instead of limited experimental acquaintances, the researchers demonstrated several applications of molecular machines in chemical transformation, energy conversion, gas/liquid separation, biomedical use, and soft material fabrication. As a result, the development of new molecular machines and their applications has accelerated over the previous two decades. This review highlights the design principles and application scopes of several rotors and rotary motor systems because these machines are used in real applications. This review also offers a systematic and thorough overview of current advancements in rotary motors, providing in-depth knowledge and predicting future problems and goals in this area.

[2,2] Paracyclophanes-based double helicates for constructing artificial light-harvesting systems and white LED device

The construction of efficient artificial light-harvesting systems (ALHSs) is of vital importance in utilizing solar energy. Herein, we report the non-covalent syntheses of double helicates PCP-TPy1/2 and Rp,Rp-PCP-TPy1/2 by metal-coordination interaction and their applications in ALHSs and white light-emitting diode (LED) device. All double helicates exhibit significant aggregation-induced emission in tetrahydrofuran/water (1:9, v/v) solvent. The aggregated double helicates can be used to construct one-step or sequential ALHSs with fluorescent dyes Eosin Y (EsY) and Nile red (NiR) with the energy transfer efficiency up to 89.3%. Impressively, the PMMA film of PCP-TPy1 shows white-light emission when doped 0.075% NiR, the solid of double helicates (Rp,Rp-) PCP-TPy2 can be used as the additive of a blue LED bulb to achieve white-light emission. In this work, we provided a general method for the preparation of novel double helicates and explored their applications in ALHSs and fluorescent materials, which will promote future construction and application of helicates as emissive devices.

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.

Photoexcitation-Induced Assembly: A Bottom-Up Physical Strategy for Driving Molecular Motion and Phase Evolution

ConspectusIn the field of molecular assembly, photodriven self-assembly is a smart and crucial strategy to regulate the molecular orderliness, multiscale structure, and optoelectronic properties. Traditionally, photodriven self-assembly is based on photochemical processes, through molecular structural change induced by photoreactions. Despite great progress in the photochemical self-assembly, there still exists disadvantages (e.g., the photoconversion rate never reaches 100% with the possible side reactions). Therefore, the photoinduced nanostructure and morphology are often difficult to predict due to insufficient phase transition or defects. In contrast, the physical processes based on photoexcitation are straightforward and can fully utilize photons to avoid the drawbacks of photochemistry. The photoexcitation strategy excludes the change of molecular structure, only utilizing the molecular conformational change from the ground state to excited state. Then, the excited state conformation is employed to drive molecular movement and aggregation, further promoting the synergistic assembly or phase transition of the entire material system. The regulation and exploration of molecular assembly upon photoexcitation can open up a new paradigm to deal with the "bottom-up" behavior and develop unprecedented optoelectronic functional materials.This Account starts with a brief introduction to the problems faced by photocontrolled self-assembly and presents the photoexcitation-induced assembly (PEIA) strategy. Then, we focus on exploring PEIA strategy based on persulfurated arenes as the prototype. The molecular conformational transition of persulfurated arenes from the ground state to the excited state is conducive to the formation of intermolecular interactions, successively driving molecular motion, aggregation, and assembly. Next, we describe our progress in exploring PEIA of persulfurated arenes at the molecular level and then demonstrate that the PEIA of persulfurated arenes can synergistically drive molecular motion and phase transition in various block copolymer systems. Moreover, we provide the potential applications of PEIA in dynamic visual imaging, information encryption, and surface property regulation. Finally, an outlook on further development of PEIA is prospected.

Designing supramolecular self-assembly nanomaterials as stimuli-responsive drug delivery platforms for cancer therapy

Stimuli-responsive nanomaterials have attracted substantial interest in cancer therapy, as they hold promise to deliver anticancer agents to tumor sites in a precise and on-demand manner. Interestingly, supramolecular chemistry is a burgeoning discipline that entails the reversible bonding between components at the molecular and nanoscale levels, and the recent advances in this area offer the possibility to design nanotherapeutics with improved controllability and functionality for cancer therapy. Herein, we provide a comprehensive summary of typical non-covalent interaction modes, which primarily include hydrophobic interaction, hydrogel bonding, host-guest interaction, π-π stacking, and electrostatic interaction. Special emphasis is placed on the implications of these interaction modes to design novel stimuli-responsive drug delivery principles and concepts, aiming to enhance the spatial, temporal, and dosage precision of drug delivery to cancer cells. Finally, future perspectives are discussed to highlight current challenges and future opportunities in self-assembly-based stimuli-responsive drug delivery nanotechnologies for cancer therapy.

A Nitrogen Out-of-Plane (NOOP) Mechanism for Imine-Based Light-Driven Molecular Motors

Light-driven molecular motors have generated considerable interest due to their potential applications in material and biological systems. Recently, Greb and Lehn reported a new class of molecular motors, chiral N-alkyl imines, which undergo unidirectional rotation induced by light and heat. The mechanism of unidirectional motion in molecular motors containing a C═N group has been assumed to consist of photoinduced torsion about the double bond. In this work, we present a computational study of the photoisomerization dynamics of a chiral N-alkyl imine motor. We find that the location and energetics of minimal energy conical intersections (MECIs) alone are insufficient to understand the mechanism of the motor. Furthermore, a key part of the mechanism consists of out-of-plane distortions of the N atom (followed by isomerization about the double bond). Dynamic effects and out-of-plane distortions are critical to understand the observed (rather low) quantum yield for photoisomerization. Our results provide hints as to how the photoisomerization quantum yield might be increased, improving the efficiency of this class of molecular motors.

Selective Binding and Isomerization of Oximes in a Self-Assembled Capsule

A series of straight-chain (C7-C13) alkyl-O-methyl aldoximes (R-C(H)═NOMe) were synthesized with various functional groups at the remote ends (alkenes, halogen, -COOH, and NH₂). Their isomers about the C═N bond showed ∼60-40% E-Z-ratio in organic solutions. Surprisingly, their confinement in a water-soluble capsule with benzoselenodiazole walls shows high selectivity for the cis-/Z-isomer. Their relative affinities for the chalcogen-bonded capsule at room temperature depend mainly on the guest chain length and functional groups. A chain length of 14 heavy atoms showed especially high E- to Z-isomer selectivity (>99%) and was used in separation. The E-Z isomerization occurred only in the capsular cavity at room temperature and was accelerated 10-fold by sonication. The Z-isomer selective binding, separation, and E-Z isomerization are supported by NMR, DOSY, and computational studies.

Adaptive 2D and Pseudo-2D Systems: Molecular, Polymeric, and Colloidal Building Blocks for Tailored Complexity

Two-dimensional and pseudo-2D systems come in various forms. Membranes separating protocells from the environment were necessary for life to occur. Later, compartmentalization allowed for the development of more complex cellular structures. Nowadays, 2D materials (e.g., graphene, molybdenum disulfide) are revolutionizing the smart materials industry. Surface engineering allows for novel functionalities, as only a limited number of bulk materials have the desired surface properties. This is realized via physical treatment (e.g., plasma treatment, rubbing), chemical modifications, thin film deposition (using both chemical and physical methods), doping and formulation of composites, or coating. However, artificial systems are usually static. Nature creates dynamic and responsive structures, which facilitates the formation of complex systems. The challenge of nanotechnology, physical chemistry, and materials science is to develop artificial adaptive systems. Dynamic 2D and pseudo-2D designs are needed for future developments of life-like materials and networked chemical systems in which the sequences of the stimuli would control the consecutive stages of the given process. This is crucial to achieving versatility, improved performance, energy efficiency, and sustainability. Here, we review the advancements in studies on adaptive, responsive, dynamic, and out-of-equilibrium 2D and pseudo-2D systems composed of molecules, polymers, and nano/microparticles.

Rotors tailoring molecular stacking for constructing multi-stimuli-responsive luminescent materials

We report a multi-stimuli-responsive luminescent material containing rotor moieties. It forms two types of crystals, G and O. The emission of G can be modulated by multiple external stimuli, whereas O does not show such responsiveness. The X-ray structure analysis reveals that the rotors are critical for the polymorphic emission and stimuli response properties.

Solvato-Controlled Assembly and Structural Transformation of Emissive Poly-NHC-Based Organometallic Cages and Their Applications in Amino Acid Sensing and Fluorescence Imaging

Stimuli-induced structural transformation of supramolecular cages has drawn increasing attention because of their sensitive feature to external variations as model systems to simulate biological processes. However, combining structural transformation and useful functions has remained a difficult task. This study reports the solvato-controlled self-assembly of two unique topologies with different emission characteristics, a water-soluble Ag₈ L₄ cage (A) and an Ag₄ L₂ cage (B), produced from the same sulfonate-pendant tetraphenylethene (TPE) bridged tetrakis-(1,2,4-triazolium) ligand. Both cages show interesting solvent-responsive reversible structural transformation, and the change of fluorescence signals can efficiently track the process. Additionally, water-soluble cage A exhibits unique properties in thermochromism, thiol amino acid sensing, and subcellular imaging in aqueous media.

Non-equilibrium Nanoassemblies Constructed by Confined Coordination on a Polymer Chain

Biological systems employ non-equilibrium self-assembly to create ordered nanoarchitectures with sophisticated functions. However, it is challenging to construct artificial non-equilibrium nanoassemblies due to lack of control over assembly dynamics and kinetics. Herein, we design a series of linear polymers with different side groups for further coordination-driven self-assembly based on shape-complementarity. Such a design introduces a main-chain confinement which effectively slows down the assembly process of side groups, thus allowing us to monitor the real-time evolution of lychee-like nanostructures. The function related to the non-equilibrium nature is further explored by performing photothermal conversion study. The ability to observe and capture non-equilibrium states in this supramolecular system will enhance our understanding of the thermodynamic and kinetic features as well as functions of living systems.

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.

Stepping Out of the Blue: From Visible to Near-IR Triggered Photoswitches

Light offers unique opportunities for controlling the activity of materials and biosystems with high spatiotemporal resolution. Molecular photoswitches are chromophores that undergo reversible isomerization between different states upon irradiation with light, allowing a convenient means to control their influence over the system of interest. However, a significant limitation of classical photoswitches is the requirement to initiate the switching in one or both directions using deleterious UV light with poor tissue penetration. Red-shifted photoswitches are hence in high demand and have attracted keen recent research interest. In this Review, we highlight recent progress towards the development of visible- and NIR-activated photoswitches characterized by distinct photochromic reaction mechanisms. We hope to inspire further endeavors in this field, allowing the full potential of these tools in biotechnology and materials chemistry applications to be realized.

Through the Eyes of Creators: Observing Artificial Molecular Motors

Inspired by molecular motors in biology, there has been significant progress in building artificial molecular motors, using a number of quite distinct approaches. As the constructs become more sophisticated, there is also an increasing need to directly observe the motion of artificial motors at the nanoscale and to characterize their performance. Here, we review the most used methods that tackle those tasks. We aim to help experimentalists with an overview of the available tools used for different types of synthetic motors and to choose the method most suited for the size of a motor and the desired measurements, such as the generated force or distances in the moving system. Furthermore, for many envisioned applications of synthetic motors, it will be a requirement to guide and control directed motions. We therefore also provide a perspective on how motors can be observed on structures that allow for directional guidance, such as nanowires and microchannels. Thus, this Review facilitates the future research on synthetic molecular motors, where observations at a single-motor level and a detailed characterization of motion will promote applications.

Solid-state photochromic arylazopyrazole based transition metal complexes

A new class of photoactive and chelating ligands L1-3 have been designed and synthesized by incorporating arylazo-3,5-dimethylpyrazole units in the ligand frameworks. Significantly they are designed in such a way...

Phosphorus guiding palladium: [4+4] metallomacrocyclic PdII complex and self-assembly of heterometallic PdII/ZnII grid-type complex

The reaction of heteroditopic ligand 1 featuring a hard pyridine-hydrazone-pyrimidine (N,N,N) site and a softer pyrimidine-hydrazone-phosphane (N,N,P) pocket with [Pd(CH3CN4)](OTf)2 in different metal-to-ligand ratios (M:L) gave the homobimetallic PdII complex...

Visible Light-Driven Molecular Switches and Motors: Recent Developments and Applications

Inspired by human vision, a diverse range of light-driven molecular switches and motors has been developed for fundamental understanding and application in material science and biology. Recently, the design and synthesis of visible light-driven molecular switches and motors have been actively pursued. This emerging trend is partly motivated to avoid the harmful effects of ultraviolet light, which was necessary to drive the classical molecular switches and motors at least in one direction, impeding their employment in biomedical and photopharmacology applications. Moreover, visible light-driven molecular switches and motors are demonstrated to enable benign optical materials for advanced photonic devices. Therefore, during the past several years, visible light-driven molecular switches based on azobenzene derivatives, diarylethenes, 1,2-dicyanodithienylethenes, hemithioindigo derivatives, iminothioindoxyls, donor-acceptor Stenhouse adducts, and overcrowded alkene based molecular motors have been judiciously designed, synthesized, and used in the development of functional materials and systems for a wide range of applications. In this Review, we present the recent developments toward the design of visible light-driven molecular switches and motors, with their applications in the fabrication of functional materials and systems in material science, bioscience, pharmacology, etc . The visible light-driven molecular switches and motors realized so far undoubtedly widen the scope of these interesting compounds for technological and biological applications. We hope this Review article could provide additional impetus and inspire further research interests for future exploration of visible light-driven advanced materials, systems, and devices.

Metal complexes bearing photochromic ligands: photocontrol of functions and processes

Metal complexes associated with photochromic molecules are attractive platforms to achieve smart light-switching materials with innovative and exciting properties due to specific optical, electronic, magnetic or catalytic features of metal complexes and by perturbing the excited-state properties of both components to generate new reactivity and photochemical properties. In this overview, we focus on selected achievements in key domains dealing with optical, redox, magnetic properties, as well as application in catalysis or supramolecular chemistry. We also try to point out scientific challenges that are still faced for future developments and applications.

Synergistic regulation of nonbinary molecular switches by protonation and light

We report a molecular switching ensemble whose states may be regulated in synergistic fashion by both protonation and photoirradiation. This allows hierarchical control in both a kinetic and thermodynamic sense. These pseudorotaxane-based molecular devices exploit the so-called Texas-sized molecular box (cyclo[2]-(2,6-di(1H-imidazol-1-yl)pyridine)[2](1,4-dimethylenebenzene); 1⁴⁺, studied as its tetrakis-PF₆ ^- salt) as the wheel component. Anions of azobenzene-4,4'-dicarboxylic acid (2H⁺•2) or 4,4'-stilbenedicarboxylic acid (2H⁺•3) serve as the threading rod elements. The various forms of 2 and 3 (neutral, monoprotonated, and diprotonated) interact differently with 1⁴⁺, as do the photoinduced cis or trans forms of these classic photoactive guests. The net result is a multimodal molecular switch that can be regulated in synergistic fashion through protonation/deprotonation and photoirradiation. The degree of guest protonation is the dominating control factor, with light acting as a secondary regulatory stimulus. The present dual input strategy provides a complement to more traditional orthogonal stimulus-based approaches to molecular switching and allows for the creation of nonbinary stimulus-responsive functional materials.

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.

Photocatalysis in Supramolecular Fluorescent Metallacycles and Metallacages

The utilization of photocatalytic techniques for achieving light-to-fuel conversion is a promising way to ease the shortage of energy and degradation of the ecological environment. Fluorescent metallacycles and metallacages have drawn considerable attention and have been used in widespread fields due to easy preparation and their abundant functionality including photocatalysis. This review covers recent advances in photocatalysis in discrete supramolecular fluorescent metallacycles and metallacages. The developments in the utilization of the metallacycles skeletons and the effect of fluorescence-resonance energy transfer for photocatalysis are discussed. Furthermore, the use of the ligands decorated by organic chromophores or redox metal sites in metallacages as photocatalysts and their ability to encapsulate appropriate catalytic cofactors for photocatalysis are summarized. For the sake of brevity, macrocycles and cages with inorganic coordination complexes such as ruthenium complexes and iridium complexes are not included in this minireview.

Light-fueled transient supramolecular assemblies in water as fluorescence modulators

Dissipative self-assembly, which requires a continuous supply of fuel to maintain the assembled states far from equilibrium, is the foundation of biological systems. Among a variety of fuels, light, the original fuel of natural dissipative self-assembly, is fundamentally important but remains a challenge to introduce into artificial dissipative self-assemblies. Here, we report an artificial dissipative self-assembly system that is constructed from light-induced amphiphiles. Such dissipative supramolecular assembly is easily performed using protonated sulfonato-merocyanine and chitosan based molecular and macromolecular components in water. Light irradiation induces the assembly of supramolecular nanoparticles, which spontaneously disassemble in the dark due to thermal back relaxation of the molecular switch. Owing to the presence of light-induced amphiphiles and the thermal dissociation mechanism, the lifetimes of these transient supramolecular nanoparticles are highly sensitive to temperature and light power and range from several minutes to hours. By incorporating various fluorophores into transient supramolecular nanoparticles, the processes of aggregation-induced emission and aggregation-caused quenching, along with periodic variations in fluorescent color over time, have been demonstrated. Transient supramolecular assemblies, which act as fluorescence modulators, can also function in human hepatocellular cancer cells.

Dissipative self-assembly, which requires a continuous supply of fuel to maintain the assembled states far from equilibrium, is the foundation of biological systems but it remains a challenge to introduce light as fuel into artificial dissipative self-assemblies. Here, the authors report an artificial dissipative self-assembly system that is constructed from light-induced amphiphiles.

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.

Coordination-Driven Selective Formation of D2 Symmetric Octanuclear Organometallic Cages

The coordination-driven self-assembly of organometallic half-sandwich iridium(III)- and rhodium(III)-based building blocks with asymmetric ambidentate pyridyl-carboxylate ligands is described. Despite the potential for obtaining a statistical mixture of multiple products, D₂ symmetric octanuclear cages were formed selectively by taking advantage of the electronic effects emanating from the two types of chelating sites - (O,O') and (N,N') - on the tetranuclear building blocks. The metal sources and the lengths of bridging ligands influence the selectivity of the self-assembly. Experimental observations, supported by computational studies, suggest that the D₂ symmetric cages are the thermodynamically favored products. Overall, the results underline the importance of electronic effects on the selectivity of coordination-driven self-assembly, and demonstrate that asymmetric ambidentate ligands can be used to control the design of discrete supramolecular coordination complexes.

Self-assembled luminescent Cu(i) tetranuclear metallacycles based on 3,3′-bipyridine ligands

Three luminescent tetranuclear macrocycles are obtained selectively, applying coordination-driven supramolecular processes to the reaction of 3,3′-bipyridine ligand with in situ formed Cu(i) bimetallic units bearing a coordination angle of ca. 120°.

Dinuclear helicate or mononuclear pincer lanthanide complexes from one ligand: stereo-controlled assembly and catalysis

By varying the metal/ligand ratio, either dinuclear triple helicate or mononuclear pincer can be stereo-selectively obtained from the same chiral ligand. Their catalytic properties have been demonstrated with the asymmetric FC alkylation reactions.

A supramolecular dual-donor artificial light-harvesting system with efficient visible light-harvesting capacity

A supramolecular dual-donor artificial light-harvesting system with efficient visible light-harvesting capacity was constructed through the hierarchical self-assembly approach.