Donor-Acceptor Assembly of Amphiphilic Molecules Based on 9,10-Distyrylanthracene Derivatives with Terminal Naphthalene Groups.

Amphiphilic rod-coil compounds have excellent photophysical properties and can be assembled into supramolecular nanostructures of different sizes in water or polar solvents. Herein, we synthesized the amphiphilic compounds 2N-DSA, 4N-DSA, and 6N-DSA with 9,10-distyrylanthracene (DSA) as the core and a naphthalene unit as the terminal group that connected DSA through a tetraethylene glycol chain. These compounds have excellent aggregation-induced emission (AIE) properties in aqueous solution and are assembled into worm-like fragments or different sizes of spherical assemblies, defending the volume ratio of the rod to coil segments. Notably, the donor-acceptor interaction between DSA and electron- deficient compounds 2,4,6-trinitrophenol (TNP), 2,4,5,7-tetranitrofluorenone (TNF), and tetraethylene glycol dinitrobenzoate (TGDNB) forms a charge transfer complex, which can be used as a nanoreactor to improve the yield of the Suzuki coupling reaction about 8-10 times. The experimental results reveal that the synergy effect of the donor-acceptor, intermolecular π-π stacking, and hydrophobic-hydrophilic interactions significantly influences the morphology of aggregates and the efficiency of the nanoreactor.

Chirality-induced supramolecular nanodishes: enantioselectivity and energy transfer.

Self-assembly is one of the most important issues of fabricating materials with precise chiral nanostructures. Herein, we constructed a chiral assembly system from amphiphiles containing hydrophobic/hydrophilic chiral coils bonded to hexabiphenyl, exhibiting controllable enantioselectivity over various aggregation behaviors. The chiral coils aroused various steric hindrances affecting intrinsic stacking tendency and compactness, leading to different aggregating behaviors, as concluded from the self-assembly investigation. The strong π-π stacking interaction between the long hexabiphenyl groups gave rise to a relatively compact arrangement in the aqueous solution, whereas the methyl side groups on the coil segments raised steric hindrance at the rigid-flexible interface, resulting in loose stacking and formation of nanostructures with a larger curvature. Compared with the achiral molecule 1 that formed micron-sized large sheets, molecules 2-4 containing chiral coils aggregated into nanodishes, which looked exactly like mosquito-repellent incense, to overcome surface tension. The helical structures effectively amplified chirality and exhibited strong circular dichroism (CD) signals, which indicate enantioselectivity. In addition, the relatively loose packing behavior permitted their co-assembly with a dye and aided efficient energy transfer, providing a foundation for the chiral application of supramolecules. Thus, by introducing a simple methyl side group in amphiphilic molecules, asymmetric synthesis and energy transfer efficiency can be realized.

Recent Developments of Fluorescence Sensors Constructed from Pillar[n]arene-Based Supramolecular Architectures Containing Metal Coordination Sites.

The field of fluorescence sensing, leveraging various supramolecular self-assembled architectures constructed from macrocyclic pillar[n]arenes, has seen significant advancement in recent decades. This review comprehensively discusses, for the first time, the recent innovations in the synthesis and self-assembly of pillar[n]arene-based supramolecular architectures (PSAs) containing metal coordination sites, along with their practical applications and prospects in fluorescence sensing. Integrating hydrophobic and electron-rich cavities of pillar[n]arenes into these supramolecular structures endows the entire system with self-assembly behavior and stimulus responsiveness. Employing the host-guest interaction strategy and complementary coordination forces, PSAs exhibiting both intelligent and controllable properties are successfully constructed. This provides a broad horizon for advancing fluorescence sensors capable of detecting environmental pollutants. This review aims to establish a solid foundation for the future development of fluorescence sensing applications utilizing PSAs. Additionally, current challenges and future perspectives in this field are discussed.

Chirality Amplification Over the Morphology Control of the Rod-Coil Molecules with Lateral Methyl Groups.

In the context of sustainable development, research regarding chirality has aroused enormous attention. Concurrently, chiral self-assembly is one of the most important subjects in supramolecular research, which can broaden the applications of chiral materials. This study focuses on the morphology control of amphiphilic rod-coil molecules composed of the rigid hexaphenyl unit and flexible oligoethylene and butoxy groups containing lateral methyl groups, carried out using an enantioseparation application. The methyl side chain being located on different blocks influences the driving force through steric hindrance, which determines the direction and degree of tilted packing during the π-π stacking of the self-assembly process. Interestingly, the amphiphilic rod-coil molecules aggregated into long helical nano-fibers, which further hierarchically aggregated into nano-sheets or nano-tubes upon increasing the concentration of the THF/H2O solution. In particular, the hierarchical-chiral assembly effectively amplified the chirality and was validated by the strong Cotton signals; playing a vital role in the enantioselective nucleophilic substitution reaction. These results provide new insights into the applications of chiral self-assemblies and soft chiral materials.

Photoresponsive reversible self-assembly of rod-coil amphiphiles containing spiropyran groups.

Stimuli-responsive assembly deformation is a key feature in constructing smart soft materials, which makes them versatile and autonomous. In this study, rod-coil amphiphilic compounds containing spiropyran (SP) groups were developed and synthesized to investigate their stimuli-responsive assembly in a solution system with 99% water content. In addition to photochromic phenomena, reversible light-mediated morphological alterations occurred in these molecular aggregates. Based on the different flexible chain segments of rod-coil amphiphiles, the initial assemblies underwent a dissociation-reassembly process under ultraviolet (UV) irradiation, whereupon they deformed or disassembled to assemblies. Furthermore, as the UV source was removed, the original nanostructures were gradually recovered again via the ring-closing reaction process. These compounds, interestingly, can selectively combine with copper ions to produce cross-linked co-assembled nanostructures. The copper ion complex solution of rod-coil amphiphilic compounds emitted unique bright blue fluorescence, which allowed for the specific visual identification of copper ions in aqueous solutions.

Supramolecular nanostructures of coil-rod-coil molecules containing a 9,10-distyrylanthracene group in aqueous solution and their optical properties of assemblies.

A series of coil-rod-coil molecules containing a 9,10-distyrylanthracene (DSA) core was successfully synthesized. The flexible parts of these molecules are composed of different polyethylene oxide chains. These molecules with aggregation-induced luminescence properties can be assembled into micelles, spheres, and sheet-like nano-assemblies in aqueous solution and have a strong ability to form charge-transfer complexes with the electron-deficient small molecules 2,4,5,7-tetranitro-9-fluorenone and 2,4,6-trinitrophenol. Interestingly, under ultraviolet light irradiation, the DSA structure undergoes photolysis and induces the disappearance of the aggregation-induced luminescence phenomena, giving these molecules application potential as a photodegradable material. In addition, these molecules are suitable organic dyes for information encryption and anti-counterfeiting applications.

Stimuli-Responsive Supramolecular Chirality Switching and Nanoassembly Constructed by n-Shaped Amphiphilic Molecules in Aqueous Solution.

Self-assembled nanomaterials composed of amphiphilic oligomers with functional groups have been applied in the fields of biomimetic chemistry and on-demand delivery systems. Herein, we report the assembly behavior and unique properties of an emergent n-shaped rod-coil molecule containing an azobenzene (AZO) group upon application of an external stimulus (thermal, UV light). The n-shaped amphiphilic molecules comprising an aromatic segment based on anthracene, phenyl linked with azobenzene groups, and hydrophilic oligoether (chiral) segments self-assemble into large strip-like sheets and perforated-nanocage fragments in an aqueous environment, depending on the flexible oligoether chains. Interestingly, the nano-objects formed in aqueous solution undergo a morphological transition from sheets and nanocages to small one-dimensional nanofibers. These molecules exhibit reversible photo- and thermal-responsiveness, accompanied by a change in the supramolecular chirality caused by the conformational transitions of the rod backbone. The architecture of n-shaped amphiphilic molecules with a photosensitive group makes them ideal candidates for intelligent materials for applications in advanced materials science.

Self-assembly of propeller-shaped amphiphilic molecules: control over the supramolecular morphology and photoproperties of their aggregates.

The aggregation-induced emission (AIE) effect is an important feature for luminescence studies, which can offer a broader range of applications for fluorescent materials. Herein, we report the morphological control and photoproperties of amphipathic propeller-shaped rod-coil molecules based on a benzene-1,3,5-tricarboxamide (BTA) unit, which restricts the intramolecular rotation and leads to the AIE effect during the self-assembly process. Investigations on the assembly of these molecules have revealed that tetragonal perforated lamella, hexagonal columnar, body-centered tetragonal micellar, and hexagonal close-packed nanostructures were spontaneously formed in the solid-state. In the solution-state, these molecules assemble into nanosheet-like aggregates, bowl-like objects, and spherical nanoparticles, respectively. The morphology of the molecular aggregates can be controlled by modifying the molecular chain length or introducing lateral methyl groups in the coil chain. Notably, these molecular assemblies exhibit strong AIE phenomena in a mixed THF/H2O solution and can be used as smart soft materials due to the restriction of their intramolecular motion.

The mechanism of the selective binding ability between opiate metabolites and acyclic cucurbit[4]uril: an MD/DFT study.

Subtle changes in molecular structure often lead to significant differences in host-guest interactions, which result in different host-guest recognition capabilities and dynamics behaviours in complex formation. Herein, we reveal the influence of the guest substituents on host-guest molecular recognition by molecular dynamics (MD) simulation and density functional theory (DFT) approaches. The results suggest that the binding energy barrier of acyclic cucurbit[4]uril (ACB[4]) with opiate metabolites gradually decreases. The methyl group in morphine (MOR) and morphine-3-glucuronide (M3G) strengthens the hydrophobicity of the guest, while depressing the energy loss of the desolvation of polar groups (e.g. hydroxyl) inside the ACB[4] cavity. However, in M3G, the 3-glucuronide group located outside the ACB[4] host cavity effectively alleviates the unfavourable desolvation effect of the hydroxyl and increases the binding constant by two orders of magnitude (compared with normorphine (NMOR)). Our findings stressed the essentiality of the binding mode and intermolecular noncovalent interactions in the host-guest selective binding ability.

Improved Efficiency Roll-Off and Operational Lifetime of Organic Light-Emitting Diodes with a Tetradentate Platinum(II) Complex by Using an n-Doped Electron-Transporting Layer.

The efficiency roll-off and operational lifetime of organic light-emitting diodes (OLEDs) with a tetradentate Pt(II) emitter is improved by engaging an n-doped electron-transporting layer (ETL). Compared to those devices with non-doped ETL, the driving voltage is lowered, the charged carrier is balanced, and the exciton density in the emissive layer (EML) is decreased in the device with n-doped ETL with 8-hydroxyquinolinolatolithium (Liq). High luminance of almost 70,000 cd m-2 and high current efficiency of 40.5 cd A-1 at high luminance of 10,000 cd m-2 is achieved in the device with 50 wt%-Liq-doped ETL. More importantly, the extended operational lifetime of 1945 h is recorded at the initial luminance of 1000 cd m-2 in the 50 wt%-Liq-doped device, which is longer than that of the device with non-doped ETL by almost 10 times. This result manifests the potential application of tetradentate Pt(II) complexes in the OLED industry.

The relationship between molecular structure and supramolecular morphology in the self-assembly of rod-coil molecules with oligoether chains.

Controlling the morphology of rod-coil molecular aggregates is crucial for studying and obtaining functional materials with exceptional properties. In this paper, we report the construction of rod-coil molecular nanoaggregates with well-defined structures. The rod-coil molecules, labeled 1a-1d, consist of a rod section, composed of phenyl and biphenyl groups, and oligoether chains with 7 and 12 repeating units. The final assembled structures showed either oblique or hexagonal columnar structures, depending on the length of the coils in the bulk state. Interestingly, in water, molecules 1a and 1c self-assemble into scrolled nanofibers and cylindrical micelles. Instead, molecules 1b and 1d, which have methyl groups decorated at the interface of the rod and coil sections, self-organize into helical nanofibers and nanorings, respectively. Thus, controlling the length of the coil chains and inserting lateral methyl groups is an effective strategy to construct precise rod-coil molecular assemblies in the bulk and in aqueous solution.

Supramolecular nanostructures constructed by rod-coil molecular isomers: effect of rod sequences on molecular assembly.

Coil-rod-coil molecules, composed of flexible oligoether chains and conjugated rod blocks, have a well-known ability to produce various nanostructures in bulk and in aqueous solution. Herein we report the synthesis and self-assembly of coil-rod-coil molecules based on the sequence of the rod building block and the type of oligoether coil chain. These molecules consist of conjugated rod segments, which are composed of biphenyl, terphenyl, and acetylenic bonds, with chiral oligoether chains as flexible coil segments. The experimental results imply that the sequence of the rod segments markedly influences the self-assembled nanostructures of coil-rod-coil molecules in the bulk state, and that the type of coil chain strongly affects the morphology of the supramolecular nanoassemblies of these molecules in aqueous solution. In the bulk state, molecules 1a and 1b, which contain biphenyl units connected to the end of the coil segments self-organize into a hexagonal perforated lamellar phase, and oblique columnar and body-centred tetragonal structures, respectively. However, molecules 2a and 2b bearing terphenyl units linked to the end of the coil segments self-assemble into lamellar, hexagonal perforated lamellar and hexagonal columnar structures. In aqueous solution, rod-coil molecular isomers with linear chiral oligoether chains self-assemble into helical nanofibres of various lengths. Meanwhile, isomers with chiral oligoether dendron chains self-organize into sheet-like nanoribbons of different sizes.

Morphological Control of Coil-Rod-Coil Molecules Containing m-Terphenyl Group: Construction of Helical Fibers and Helical Nanorings in Aqueous Solution.

Rod-coil molecules, composed of rigid segments and flexible coil chains, have a strong intrinsic ability to self-assemble into diverse supramolecular nanostructures. Herein, we report the synthesis and the morphological control of a new series of amphiphilic coil-rod-coil molecular isomers 1-2 containing flexible oligoether chains. These molecules are comprised of m-terphenyl and biphenyl groups, along with triple bonds, and possess lateral methyl or butyl groups at the coil or rod segments. The results of this study suggest that the morphology of supramolecular aggregates is significantly influenced by the lateral alkyl groups and by the sequence of the rigid fragments in the bulk and in aqueous solution. The molecules with different coils self-assemble into lamellar or oblique columnar structures in the bulk state. In aqueous solution, molecule 1a, with a lack of lateral groups, self-assembled into large strips of sheets, whereas exquisite nanostructures of helical fibers were obtained from molecule 1b, which incorporated lateral methyl groups between the rod and coil segments. Interestingly, molecule 1c with lateral butyl and methyl groups exhibited a strong self-organizing capacity to form helical nanorings. Nanoribbons, helical fibers, and small nanorings were simultaneously formed from the 2a-2c, which are structural isomers of 1a, 1b, and 1c. Accurate control of these supramolecular nanostructures can be achieved by tuning the synergistic interactions of the noncovalent driving force with hydrophilic-hydrophobic interactions in aqueous solution.

Supramolecular helical nanostructures from self-assembly of coil-rod-coil amphiphilic molecules incorporating the dianthranide unit.

Coil-rod-coil amphipathic oligomers composed of a rigid dianthranide unit and a hydrophilic branched oligoether as the coil segment were synthesized. These amphiphilic molecules self-assemble into clew-like aggregates composed of fibres or helical nanofibers in aqueous solution. Subsequently, supramolecular polymers were produced from the above objects through charge-transfer interactions by adding 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (4F-TCNQ). Interestingly, temperature-sensitive supramolecular chirality was induced by lateral methyl units located at the interface of the rigid and flexible segments. However, upon addition of the electron-acceptor molecule, 4F-TCNQ, strong donor-acceptor interactions restrict any change in supramolecular chirality with temperature.

Control of supramolecular nanoassemblies by tuning the interactions of bent-shaped rod-coil molecules.

Rod-coil molecules 1a, 1b and 2a, 2b, consisting of biphenyl and phenyl units connected by an acetylene bond as the rod segment and oligo(ethylene glycol) (OEG) as the coil segment, were synthesized and characterized. Molecules 1a and 1b incorporate a butoxy group at the apex of their bent-shaped rigid building blocks, while both 1b and 2b contain a lateral methyl group between the rod and coil segments. The self-assembling behavior of these molecules was investigated using DSC, SAXS, CD, AFM, and TEM in bulk and aqueous solutions. In the bulk state, 1a self-assembles into oblique columnar structures, whereas 1b, incorporating butoxy and lateral methyl groups, self-assembles into three-dimensional body-centered tetragonal structures. Molecules 2a and 2b with no butoxy groups, and 2b incorporating a lateral methyl group, self-assemble into hexagonal perforated lamellar and oblique columnar structures, respectively. In dilute aqueous solutions, 1a assembles into tubular nanoassemblies, while 1b self-organizes into micelles and nanoparticles. On the other hand, 2a and 2b spontaneously aggregate into nanoribbons and nanofibers. Furthermore, CD experiments together with AFM investigations of 2b indicate the creation of self-organized helical fibers, implying that the lateral methyl group induces the helical stacking of the rod building block. These results reveal that the butoxy and lateral methyl groups between the rod and coil segments dramatically influence the creation of supramolecular nanostructures and morphologies.

Self-organizing p-quinquephenyl building blocks incorporating lateral hydroxyl and methoxyl groups into supramolecular nano-assemblies.

The self-assembling behavior of coil-rod-coil molecules 1a, 1b, and 2a, 2b was investigated using DSC, POM, SAXS, and AFM in bulk and aqueous solutions. These molecules contain p-quinquephenyl groups as rod segments incorporating lateral hydroxyl or methoxyl groups in the center positions and oligo(ethylene oxide)s as the coil segments. Molecules 1a and 1b, with lateral methoxyl groups in the rod segments, self-assemble into oblique columnar structures in the crystalline phase and transform into nematic phases. On the other hand, molecules 2a and 2b, with hydroxyl groups in the center of their rod segments, self-organize into hexagonal perforated lamellar and oblique columnar nano-structures in the crystalline and liquid crystalline phase, respectively. In aqueous solutions, these molecules aggregate into nano-ribbons and vesicles, depending on their lateral groups and oligo(ethylene oxide) chain lengths. These results imply that the lateral methoxyl or hydroxyl groups, present in the center of the rod segments, significantly influence the formation of various supramolecular nano-structures in the bulk state and in aqueous solution. This is achieved via tuning of the non-covalent interactions of the rod building blocks.

Liquid crystalline assembly of coil-rod-coil molecules with lateral methyl groups into 3-D hexagonal and tetragonal assemblies.

In this paper, we report the synthesis and self-assembly behavior of coil-rod-coil molecules, consisting of three biphenyls linked through a vinylene unit as a conjugated rod segment and poly(ethylene oxide) (PEO) with a degree of polymerization (DP) of 7, 12 and 17, incorporating lateral methyl groups between the rod and coil segments as the coil segment. Self-organized investigation of these molecules by means of differential scanning calorimetry (DSC), thermal polarized optical microscopy (POM) and X-ray diffraction (XRD) reveals that the lateral methyl groups attached to the surface of rod and coil segments, dramatically influence the self-assembling behavior in the liquid-crystalline mesophase. Molecule 1 with a relatively short PEO coil length (DP=7) self-assembles into rectangular and oblique 2-dimensional columnar assemblies, whereas molecules 2 and 3 with DP of 12 and 17 respectively, spontaneously self-organize into unusual 3-dimensional hexagonal close-packed or body-centered tetragonal assemblies.

Palladium-catalyzed asymmetric decarboxylative cycloaddition of vinylethylene carbonates with Michael acceptors: construction of vicinal quaternary stereocenters.

An efficient method for the diastereo- and enantioselective construction of vicinal all-carbon quaternary stereocenters through palladium-catalyzed decarboxylative cycloaddition of vinylethylene carbonates with activated Michael acceptors was developed. By using a palladium complex generated in situ from [Pd2(dab)3]⋅CHCl3 and a phosphoramidite ligand as a catalyst under mild reaction conditions, the process provides multifunctionalized tetrahydrofurans bearing vicinal all-carbon quaternary stereocenters in high yields with a high level of absolute and relative stereocontrol.

Applications of Supramolecular Polymers Generated from Pillar[n]arene-Based Molecules.

Supramolecular chemistry enables the manipulation of functional components on a molecular scale, facilitating a "bottom-up" approach to govern the sizes and structures of supramolecular materials. Using dynamic non-covalent interactions, supramolecular polymers can create materials with reversible and degradable characteristics and the abilities to self-heal and respond to external stimuli. Pillar[n]arene represents a novel class of macrocyclic hosts, emerging after cyclodextrins, crown ethers, calixarenes, and cucurbiturils. Its significance lies in its distinctive structure, comparing an electron-rich cavity and two finely adjustable rims, which has sparked considerable interest. Furthermore, the straightforward synthesis, uncomplicated functionalization, and remarkable properties of pillar[n]arene based on supramolecular interactions make it an excellent candidate for material construction, particularly in generating interpenetrating supramolecular polymers. Polymers resulting from supramolecular interactions involving pillar[n]arene find potential in various applications, including fluorescence sensors, substance adsorption and separation, catalysis, light-harvesting systems, artificial nanochannels, and drug delivery. In this context, we provide an overview of these recent frontier research fields in the use of pillar[n]arene-based supramolecular polymers, which serves as a source of inspiration for the creation of innovative functional polymer materials derived from pillar[n]arene derivatives.

Self-assembly of ß-cyclodextrin-pillar[5]arene molecules into supramolecular nanoassemblies: morphology control by stimulus responsiveness and host-guest interactions.

Macrocyclic molecules have attracted considerable attention as new functional materials owing to their unique pore size structure and excellent host-guest properties. With the development of macrocyclic compounds, the properties of mono-modified macrocyclic materials can be improved by incorporating pillar[n]arene or cyclodextrin derivatives through bridge bonds. Herein, we report the self-assembly of amphiphilic di-macrocyclic host molecules (H1-2) based on ß-cyclodextrin and pillar[5]arene units linked by azophenyl or biphenyl groups. In a H2O/DMSO (19 : 1, v/v) mixed polar solvent, an amphiphile H1 with an azophenyl group self-assembled into unique nanorings and exhibited an obvious photoresponsive colour change. This photochromic behaviour makes H1 suitable for application in carbon paper materials on which arbitrary patterns can be erased and rewritten. The amphiphile H2, with a biphenyl unit, self-assembled into spherical micelles. These differences indicate that various linker units lead to changes in the intermolecular and hydrophilic-hydrophobic interactions. In a CHCl3/DMSO (19 : 1, v/v) mixed low-polarity solvent, the amphiphile H1 self-assembled into fibrous aggregates, whereas the molecule H2 assembled into unique nanoring aggregates. In this CHCl3/DMSO mixed solvent system, small nanosheet aggregates were formed by the addition of a guest molecule (G) composed of tetraphenylethene and hexanenitrile groups. With prolonged aggregation time, the small sheet aggregates further aggregated into cross-linked nanoribbons and eventually formed large nanosheet aggregates. The data reveal that the morphology of H1-2 can be controlled by tuning the intermolecular interactions of the molecules via the formation of host-guest complexes. Moreover, the polyhydroxy cyclodextrin unit on H1-2 can be strongly adsorbed on the stationary phase in column chromatography via multiple hydrogen bonds, and the singly modified pillar[5]arenes can be successfully separated by host-guest interactions.