Rod-coil Molecules Research Articles

Chiral aggregates of rod-coil molecules inside nanopores as efficient nanoreactors for asymmetric synthesis.

An important subject of porous organic materials is their capacity to access enantioselectivity due to their high surface area, controllable pore size, and ease of functionalization. However, recyclability of enantio-separation is a challenge, mainly due to the complex procedures of recovery and refreshing from enantiomers. For the first time, we combined nanochannel technology and supramolecular chiral assembly to achieve efficient enantioselectivity. Fine-designed amphiphilic chiral rod-coil molecules 1-3 were immobilized to SBA-15 pore walls to form SA-M1-3 (abbreviation for amino-functionalized SBA-15 connected to molecules 1-3), which commenced chiral aggregation inside the channels. The experimental results indicated that the strong π-π stacking interaction between the rigid terphenyl groups, as well as hydrophilic-hydrophobic interaction of the amphiphiles, assisted in chiral arrangement in aqueous solution, and was accompanied by amplification of chirality. As a result, porous chiral channels exhibiting enhanced efficiency in asymmetric synthesis were manufactured, where enantioselectivity can be controlled by the initial structural design of amphiphiles that induce chiral aggregation behaviors. The chiral centers of SA-M1 and SA-M2 are located on hydrophobic and hydrophilic coils, respectively, while SA-M3 possesses both chiral coils. The SA-M materials proceeded with chiral aggregation and behaved efficiently for enantioselectivity. SA-M3, which contained the most chiral centers, showed the most optimal enantioselectivity with an enantiomeric excess (ee) value up to 71.75%, which occurred because of the strongly driven chiral aggregation of the hydrophobic and hydrophilic chiral coils. The covalent hybrid structures of the SA-M materials can be easily refreshed simply through washing, and exhibited excellent recyclability with negligible loss of efficiency. Therefore, the SA-M materials have the ability to provide sustainable and reliable application value for enantiomer separation.

Morphology study of light– and pH–responsive amphiphiles with DSA for detection of nitrobenzene derivatives

Supramolecular molecular self–assemblies with 9, 10-distyrylanthracene (DSA) frameworks have good application prospects in fluorescent probes and optical materials owing to the unique AIE effect of the DSA unit. In this study, amphiphilic rod–coil molecules with rigid DSA parts and flexible oligoether chains were designed and synthesised, and their assembly capacities were investigated. The amphiphilic molecule with a lateral methyl unit in the coil branch formed worm–like supramolecular assemblies, while the molecule without lateral group self–assembled into an interwoven ribbon like structure in aqueous solution. This is due to noncovalent molecular interactions, such as the π–π stacking interaction of the rigid segments for the former or the hydrophilic–hydrophobic effect of molecules in the aqueous solution for the latter. Interestingly, under irradiation with 365 nm UV light, the original UV absorption of the molecule decreased and fluorescence quenching occurred, accompanied by a decrease in the size of the original aggregates, which became more apparent with as irradiation time increased, indicating the presence of photo-degradation. These molecular morphologies were also significantly influenced by the pH of the aqueous solution and produced nanoparticles of various sizes. Furthermore, we investigated the adsorption capacity of nitro compounds and found that molecular aggregates could be used for the detection of nitroaromatic compounds with strong electron-withdrawing groups.

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.

Fast Photoresponsive Phototransistor Memory Using Star-Shaped Conjugated Rod-Coil Molecules as a Floating Gate.

With the explosive growth in data generation, photomemory capable of multibit data storage is highly desired to enhance the capacity of storage media. To improve the performance of phototransistor memory, an organic-molecule-based electret with an elaborate nanostructure is of great importance because it can enable multibit data storage in a memory device with high stability. In this study, a series of star-shaped rod-coil molecules consisting of perylenediimide (PDI) and biobased solanesol were synthesized in two-armed (PDI-Sol2), four-armed (PDI-Sol4), and six-armed (PDI-Sol6) architectures. Their molecular architecture-morphology relationships were investigated, and phototransistor memory was fabricated and characterized to evaluate the structure-performance relationship of these rod-coil molecules. Accordingly, the memory devices were enabled by photowriting with panchromatic light (405-650 nm) and electrical erasing using a gate bias. The PDI-Sol4-based memory device showed high memory ratios of 10 000 over 10 000 s and a rapid multilevel photoresponse of 50 ms. This achievement is related to the favorable energy-level alignment, isolated nanostructure, and face-on orientation of PDI-Sol4, which eliminated the charge tunneling barrier. The results of this study provide a new strategy for tailoring nanostructures in organic-molecule-based electrets by using a star-shaped rod-coil architecture for high-performance phototransistor memory.

Construction of nanoaggregates from amphiphilic supramolecules containing barbiturate and Hamilton wedge units

AbstractThe study of supramolecular morphology is gaining significant attention. This may be attributed to the fact that nanostructures of aggregates have been found to significantly influence the photoelectronic properties of supramolecular materials. In this study, the self‐assembling behaviour of rod–coil molecules with barbiturate (Ba) or Hamilton wedge (Hw) units and the supramolecule Ba‐Hw was investigated. In chloroform solution, molecule Hw consisted of an oligo‐ethylene chain with degree of polymerization of 17 as well as biphenyl, phenyl and Hw units. Ba molecules incorporated octyloxy, biphenyl, phenyl and Ba groups that self‐organized into nanofibres with different diameters. Supramolecular amphiphile Hw‐Ba self‐aggregated into different sizes of nanosheet‐like aggregates. In a dimethylsulfoxide/H2O (1:19 v/v) mixed polar solvent, molecules Hw and Ba aggregated into twist‐shaped and nanosheet aggregates, while the supramolecular Hw‐Ba aggregated into larger‐size microtubes. Experimental results obtained for these molecular assemblies suggest that combining Ba and Hw units by employing hydrogen bonds is an effective strategy for forming amphiphilic supramolecules. Compared with the individual rod–coil molecules Ba and Hw, supramolecule Hw‐Ba has stronger π–π intermolecular forces due to the presence of more planar Hw‐Ba building blocks, which form various supramolecular assemblies with less curvature than the rigid and flexible surfaces of the original molecules. © 2021 Society of Industrial Chemistry.

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.

Supramolecular Functionalization for Improving Thermoelectric Properties of Single-Walled Carbon Nanotubes-Small Organic Molecule Hybrids.

Single-walled carbon nanotube (SWCNTs-P)-small organic molecule hybrid materials are promising candidates for achieving high thermoelectric (TE) performance. In this study, we synthesized rod-coil amphiphilic molecules, that is, tri(ethylene oxide) chain-attached bis(bithiophenyl)-terphenyl derivatives (1 and 2). Supramolecular functionalization of SWCNTs-P with 1 or 2 induced charge-transfer interactions between them. Improved TE properties of the supramolecular hybrids (SWCNTs-1 and SWCNTs-2) are attributed to increased charge-carrier concentration (electrical conductivity), interfacial phonon scattering (thermal conductivity), and energy difference between the transport and Fermi levels (ETr - EF; Seebeck coefficient). SWCNTs-2 exhibited a ZT of 0.42 × 10-2 at 300 K, which is 350% larger than that of SWCNTs-P. Furthermore, 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ)-doped SWCNTs-2 showed the highest ZT value of 1.96 × 10-2 at 300 K among SWCNTs-P/small organic molecule hybrids known until now. These results demonstrated that the supramolecular functionalization of SWCNTs-P with small organic molecules could be useful for enhancement of TE performance and applications in wearable/flexible thermoelectrics.

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.

Synthesis of Rod-coil Molecules bearing Oligo-Phenylene Vinylene Motifs: Effect of PEO Chain Lengths on the Evolution of Nanostructures Morphology and their Photophysical Properties

The applications of nano-dispersed organic conjugated active compounds or materials as well as current research is concerned mainly with optimization and control of the optical properties, by particle size and supramolecular structure of the particles. The aromatic macromolecules consisting of conjugated rigid rod segment and hydrophilic flexible chain as coil in aqueous solution can aggregate into a variety of supramolecular structures through mutual interaction between aromatic rod and hydrophilic chains of molecules and water. Here we report the synthesis of newer oligo phenylene vinylene (OPV) based rod-coil molecules with varying chain-length polyethylene oxide (PEO) repeating units (n = 8, 17, 45). Formation and photophysical properties of their nanostructures in water are studied comparatively. The nanostructures evolution of these molecules is observed with simple reprecipitation method. The stable nanostructures were formed without addition of any surfactants. The fabricated nanostructures ultimately give the materials with ‘controlled’ aggregation induced enhanced photophysical properties. The self-assembly of such OPV type rod molecules in water without adding any surfactants, therefore, can provide a strategy for the construction of well-defined and stable nanostructures with certain chemical functionalities and physical properties as advanced materials for photonic, electronic and biological applications. Copyright © VBRI Press.

Photo-controlled reversible assemblies from rod-coil molecules with azobenzene group

Rod-coil amphiphilic molecules composed of hydrophilic polyethylene glycol chains and an aromatic domain based on biphenyl and azobenzene groups self-assembled into two-dimensional columnar and lamellar nanostructures in the solid state. In the aqueous solution, these molecules produced wormlike micelles, nanoribbons, and large sheets, depending on their chain length. Interestingly, the quenched fluorescence emission of these molecules was observed in methylene chloride; nevertheless, the intensity of fluorescence emission in aqueous solution significantly increased relative to that observed in methylene chloride because the molecular self-assembly strongly suppressed the energy transfer in aqueous solution. Notably, UV/vis illumination resulted in a trans/cis isomerism of the azobenzene unit of these rod-coil molecules. However, these molecules did not respond to light in the liquid crystal phase because the transformation temperature of the liquid crystal phase was higher than the trans/cis isomer critical temperature. In aqueous solution, the trans/cis isomerism of the azobenzene unit induced the conversion of corresponding nanostructures into dispersed wormlike micelles, wormlike micelles and small fragments, and sheets. These results revealed that the trans/cis isomerism of azobenzene could be used as an external stimulus for amphiphilic molecular self-assembling systems to build various stimuli-responsive nanostructures.

Archimedean Tiling Patterns Self-Assembled from X-Shaped Rod–Coil Copolymers with Hydrogen Bonds

On the basis of self-consistent field theory (SCFT), we demonstrate that X-shaped rod–coil molecules with hydrogen-bonding groups self-assemble into Archimedean tiling patterns including [36], [44], [63], [3.4.6.4], and [(3.6)2], and dual tiling patterns including dual-[32.4.3.4]. The rod blocks form the edges of polygons, coil blocks fill in the inner spaces of polygons, and the existence of hydrogen bonds further decreases the domain size. A new mechanism is proposed to guide the formation of Archimedean tiling patterns: the fabrication of tiling patterns is controlled by the relationship between the length–diameter ratio β and volume fraction fR of rigid cores in X-shaped supra-macromolecules. This study provides a concept of macromolecular tiling for producing Archimedean tilings and suggests X-shaped rod–coil supra-macromolecules with hydrogen-bonding groups as an ideal platform for the fabrication of two-dimensional nanoscale patterns.

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.

Construction of Various Supramolecular Assemblies from Rod-Coil Molecules Containing Biphenyl and Anthracene Groups Driven by Donor-Acceptor Interactions.

Rod-coil amphiphilic functional molecules, comprising a rigid aromatic building block and hydrophilic oligoether dendrons as the coil segments, were synthesized. These compounds exhibit a powerful self-organizing ability to form supramolecular nanoparticles and long nanofibers in tetrahydrofuran/water solution, by controlling the intermolecular interaction of the rigid blocks. These molecules are able to form supramolecular polymers and, subsequently, to form sheetlike nanoaggregates, through charge-transfer interactions by the addition of a guest molecule, tetracyanoquinodimethane. Notably, upon addition of water-soluble 2,4,6-trinitrophenol, the self-assembly of these molecules exhibits the antagonistic effect owing to donor-acceptor and hydrophobic-hydrophilic interactions among the molecules. The experimental results reveal that various morphologies of rod-coil molecular assemblies can be obtained by tuning the molecular interaction and the hydrophilicity of guest electron-acceptor molecules. Interestingly, the cross-coupling reaction between phenylboronic acid and chlorobenzene occurs within the charge complexes of these molecular aggregates. This occurs in the nanoenvironment that affords an extremely concentrated reaction zone and reduces the activation energy barrier required for the cross-coupling reaction.

Template-Assisted Benzannulation Route to Pentacene and Tetracene Derivatives and its Application to Construct Amphiphilic Acenes That Self-Assemble into Helical Wires.

Pentacene is one of the most versatile organic semiconductors. New synthetic strategies to construct the pentacene skeleton are imperative to produce pentacene derivatives with appropriate solubility, stability, and optoelectronic properties for various applications. This paper describes a template-directed approach to pentacene derivatives. In the retrosynthesis, the acene skeleton is viewed as a laddered double strand polyene instead of the more intuitive linearly fused hexagons. Based on this vision, the template strand of polyene is constructed with Wittig olefination, whereas the second strand is accomplished with Knoevenagel condensation to produce pentacene and tetracene derivatives. The synthetic scheme is flexible enough to generate an array of acene derivatives with substitution patterns that were hitherto difficult to access. Amphiphilic pentacene and tetracene derivatives were also synthesized by the template strategy. One pentacene based amphiphilic rod-coil molecule undergoes self-assembly to form helical wire structures that were visualized with TEM.

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.

Donor-acceptor interaction-driven self-assembly of amphiphilic rod-coil molecules into supramolecular nanoassemblies.

Rigid-flexible amphiphilic molecules consisting of an aromatic segment based on pyrene and biphenyl units and hydrophilic polyethylene oxide chains self-assemble into lamellar, hexagonal columnar, and two-dimensional columnar nanostructures in the bulk state. In aqueous solution, these molecules self-assemble into nanofibers, spherical micelles, and multilayer nanotubes, depending on the chain or rod length of the molecules. Notably, ordered nanostructures of supramolecular polymers, such as single-layer curving fragments, nanofibers, and nanosheets, were constructed through charge-transfer interactions between the nanoobjects and an electron-acceptor molecule, 2,4,5,7-tetranitrofluorenone. These experimental results reveal that diverse supramolecular morphologies can be controlled by tuning rod-coil molecular interactions or charge-transfer interactions between the donor and acceptor molecules.

Self-Assembly of n-Shaped Rod–Coil Molecules into Thermoresponsive Nanoassemblies: Construction of Reversible Helical Nanofibers in Aqueous Environment

Amphiphilic coil–rod–coil molecules 1–3, consisting of an n-shaped rod building block and poly(ethylene oxide) (PEO) with a degree of polymerization of 5 linked through a biphenyl unit as the coil segment, were synthesized. Molecule 1 self-assembles into lamellar and hexagonal perforated layer structures, in the crystalline and liquid crystalline phases, respectively. Remarkably, molecule 2 incorporating lateral methyl groups between the rod and coil segments spontaneously self-organizes into hexagonal perforated layer and oblique columnar structures. The additional incorporation of a lateral butyl group at the center of the rod segment of molecule 2 generates molecule 3, which assumes an exclusively oblique columnar structure in the solid state. In aqueous solutions, molecule 1 self-assembles into fibrous aggregates, whereas molecules 2 and 3 exhibit a self-organizing capacity to form helical fibers. Additionally, circular dichroism (CD) experiments and atomic force microscope (AFM) measurements of molec...

Self-assembly of amphiphilic linear diblock rod-coil molecules by hydrogen bond and π-π stacking interactions

Aromatic amphiphilic molecules (1) consisting of three biphenyl groups linked together with ether bonds as a rigid rod segment and poly(ethylene oxide) with the number of repeating units of 17 as a coil segment were synthesized, and their self-assembly behavior in the bulk state and aqueous solution was investigated. In bulk, molecules 1 self-assembled into 1-D lamellar structure in the solid state or smectic A phase in the liquid crystalline phase via the cooperative effects of π-π stacking, micro-phase separation and hydrogen bond interactions. In dilute aqueous solutions, molecules 1 were observed to self-assemble into cylindrical micelles owned uniform diameter and length of hundreds of nanometers.

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.

Three‐dimensional crystalline supramolecular nanostructures from self‐assembly of rod–coil molecules incorporating lateral carboxyl group in the middle of the rod segment

AbstractWe report the synthesis and self‐assembling behaviour of coil–rod–coil molecules 1a–1c and 2a–2c, which incorporate lateral carboxyl or ester groups in the middle of the rod segment. The self‐assembling behaviour of these molecules was investigated in the bulk using differential scanning calorimetry, polarised optical microscopy and small‐angle X‐ray scattering. Our results reveal that hydrogen bonds strongly influence the self‐assembling behaviour of rod‐like building blocks. Molecules 1a–1c, which incorporate carboxyl groups in the middle of rod segments, self‐assemble into two‐dimensional (2‐D) columnar, three‐dimensional (3‐D) body‐centred tetragonal and 3‐D hexagonal close‐packed assemblies in the crystalline state. However, molecules 2a–2c, which contain ester groups in the centre of rod segments, self‐assemble into unexpected lamellar, hexagonal perforated lamellar and 2‐D columnar nanostructures in the bulk, indicating that hydrogen bonds impede intermolecular stacking in this rod–coil system. © 2015 Society of Chemical Industry