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.

Supramolecular polymers based on host-guest interactions for the construction of artificial light-harvesting systems

In the present work, artificial light-harvesting systems with a fluorescence resonance energy transfer (FRET) process were successfully obtained in the aqueous solution. We designed and synthesized an amphiphilic pyrene derivative with two 4-vinylpyridium arms (Pmvb), which can interact with cucurbit[8]uril (CB[8]) to form supramolecular polymer through host-guest interactions in aqueous solution. The formation of supramolecular polymers results in a significant enhancement of fluorescence, which makes Pmvb-CB[8] an ideal energy donor to construct artificial light-harvesting systems in the aqueous solution. Subsequently, two different fluorescence dyes Rhodamine B (RhB) and Sulforhodamine 101 (SR101) were introduced as energy acceptors into the solution of Pmvb-CB[8] respectively, to fabricate two different artificial light-harvesting systems. The obtained artificial light-harvesting systems can achieve an efficient energy transfer process from Pmvb-CB[8] to RhB or SR101 with high energy transfer efficiency.

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-assembled structures of bent-shaped π-conjugated compounds: effect of siloxane groups for nano-segregation

The tuning of nanostructures is successfully achieved by introduction of siloxane unit to bithiophene-modified bent-shaped skeleton.

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.

Construction of Supramolecular Nanostructures from V-Shaped Amphiphilic Rod-Coil Molecules Incorporating Phenazine Units

A series of bent-shaped molecules, consisting of dibenzo[a,c]phenazine and phenyl groups connected together as a rod segment, and poly(ethylene oxide) (PEO) with a degree of polymerization (DP) of 6 as the coil segment, were synthesized. The self-assembling behavior of these molecules by differential scanning calorimetry (DSC), thermal optical polarized microscopy (POM), small-angle X-ray scattering spectroscopy (SAXS), atomic force microscopy (AFM), and transmission electron microscopy (TEM), revealed that carboxyl or butoxy carbonyl groups at the 11 position of dibenzo[a,c]phenazine noticeably influence self-organization of molecules into supramolecular aggregates in bulk and aqueous solutions. Molecules 1 and 2 with chiral or non-chiral PEO coil chains and the carboxyl group at the rod segments self-organize into a hexagonal perforated lamellar structure and a hexagonal columnar structure in the solid state. In aqueous solution, molecules 1 and 2 self-assemble into diverse lengths of nanofibers, whereas molecules 3 and 4 with butoxy carbonyl groups exhibit a self-organizing capacity to form diverse sizes of spherical aggregates.

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.

Construction of Supramolecular Assemblies from Self-Organization of Amphiphilic Molecular Isomers

Amphiphilic coil-rod-coil molecules, incorporating flexible and rigid blocks, have a strong affinity to self-organize into various supramolecular aggregates in bulk and in aqueous solutions. In this paper, we report the self-assembling behavior of amphiphilic coil-rod-coil molecular isomers. These molecules consist of biphenyl and phenyl units connected by ether bonds as the rod segment, and poly(ethylene oxide) (PEO) with a degree of polymerization of 7 and 12 as the flexible chains. Their aggregation behavior was investigated by differential scanning calorimetry, thermal optical polarized microscopy, small-angle X-ray scattering spectroscopy, and transmission electron microscopy. The results imply that the molecular structure of the rod building block and the length of the PEO chains dramatically influence the creation of supramolecular aggregates in bulk and in aqueous solutions. In the bulk state, these molecules self-organize into a hexagonal perforated lamellar and an oblique columnar structure, respectively, depending on the sequence of the rod building block. In aqueous solution, the molecule with a linear rod segment self-assembles into sheet-like nanoribbons. In contrast, its isomer, with a rod building block substituted at the meta-position of the aryl group, self-organizes into nanofibers. This is achieved through the control of the non-covalent interactions of the rod building blocks.

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.