Milliseconds Make the Difference in the Far-from-Equilibrium Self-Assembly of Supramolecular Chiral Nanostructures

An Oriented Polymer in a Dynamic Microsolution Pierces Molecular Rings: An Approach toward Polyrotaxane Synthesis under Precise Kinetic Control

In this study, we demonstrated host-guest chemistry under dynamic conditions using a polymer-ring system as a model. We found that a Hagen-Poiseuille flow drives a guest polymer into the cavities of ring hosts repeatedly, in a manner distinct from self-threading under thermodynamic equilibrium. Using poly(ethylene glycol) (PEG) and γ-cyclodextrin (γ-CD) as a representative polymer-ring system, two PEG units were threaded into γ-CD in a head-to-tail fashion, forming extremely long pseudodouble-stranded polyrotaxane (DS-PR) nanofibers. These novel DS-PR structures further assembled hierarchically through facial hydrogen bonding, resulting in micrometer-scale crystalline fibers. We systematically investigated the influence of solution motion on host-guest interactions by varying hydrodynamic parameters (e.g., total flow rate, channel geometry, and channel length) and structural parameters (e.g., polymer length and γ-CD/PEG ratio). Remarkably, the forward end of the PEG chain preferentially pierced the wider rim of the γ-CD. Based on these observations, we devised an active-threading mechanism, wherein the end of the PEG chain pierces multiple rings while satisfying both energetic and steric requirements, with the microflow channel acting as a catalyst to accelerate host-guest interaction. Finally, we explored the possibility of cothreading α- and γ-CD units onto a single PEG chain. Notably, overcoming the classical "lock-and-key" paradigm of host-guest chemistry, the observed "piercing effect" enabled the same PEG chain to thread into two differently sized CDs depending on the α-CD/γ-CD ratio in solution.

Chiroptical Signal Inversion of Peptido-Coassemblies in Confined Parallel-Laminar Microfluidics

Chirality plays a vital role in material properties, and precise control of chiral signals is key to designing functional materials. Supramolecular self-assembly offers an efficient means to integrate chiral building blocks with chromophores, yet controlling the assembly pathway remains challenging due to the complexity of non-covalent interactions. Here, we introduce a continuous parallel-laminar-assisted self-assembly strategy that exploits solvent ordering and solute diffusion in confined environments to regulate chiral signals in multi-component peptide co-assemblies. Notably, six nonpolar amino acids exhibit significantly enhanced chiroptical responses, as confirmed by circular dichroism (CD) and circularly polarized luminescence (CPL) spectroscopy. Intriguingly, Fmoc-Ala and 1-aminopyrene (AP) co-assemblies formed in a microfluidic chip show a reversed chiroptical signal compared to those from batch reactions. Molecular dynamics (MD) simulations and COMSOL modeling suggest that velocity gradients and shear forces in microfluidics induce ordered non-covalent interactions, altering excimer stacking and modulating chiroptical properties. This study presents an effective strategy for controlling chiral optical signals in confined environments, offering an interesting approach for supramolecular chiral transfer and regulation.

Solvent-Free Supramolecular Polymerization for Feather-Like Nanostructured Chiral Fluorescent Polyurethanes with Multimodal Chiroptical Stimuli Responsiveness

Chiral supramolecular polymers with stimuli-responsive circularly polarized luminescence (CPL) are highly desirable for smart flexible optoelectronic devices, but remain rarely reported. Here, a simple solvent-free supramolecular polymerization for preparing chiral polyurethanes is presented by in situ induced self-assembly strategy, using cellulose nanocrystals (CNCs)-based isocyanate prepolymers and macromolecular polyols as precursors, achieving precise control over polymer chain assembly with spot-like arrangement. More importantly, by further incorporating a π-conjugated luminescent dihydroxynaphthalene molecule, CPL-active flexible polyurethane films with feather-like nanostructures are constructed, which promote the ordered arrangement of CNCs-based isocyanate segments due to the increased spatial resistance. The π─H bond network between CNCs and urethane-linked benzene rings drives the self-assembly, enabling higher-level chiral amplification and enhanced fluorescence. Interestingly, the prepared chiral fluorescent polyurethanes display multimodal chiroptical stimuli responsiveness under various stimuli, such as temperature, solvent polarity, pH, and polarized light, due to the sensitivity of the π─H bond network. This work offers new insights into designing solvent-free chiral supramolecular polymers with significant chiroptical potentials.

Heparin binding induced supramolecular chirality into the self-assembly of perylenediimide bolaamphiphile

Chirality is one of the hallmarks of biomolecules. Herein, we utilize heparin, a chiral biomolecule and potent drug, to induce chiral organization into the assembly of an achiral molecule. Polyanionic heparin binds with a dicationic perylenediimide derivative to induce supramolecular helical organization in aqueous medium as well as in a highly competitive cell culture medium.

Investigation of J-Aggregates of 2,3,7,8,12,13,17,18-Octabromo-5,10,15,20-tetrakis(4-sulfonatophenyl) Porphyrin in Aqueous Solutions

The highly distorted water-soluble 2,3,7,8,12,13,17,18-octabromo-5,10,15,20-tetrakis(4-sulfonatophenyl)porphyrin (Br8TPPS44-) is readily protonated under acidic pH, forming the diacid H2Br8TPPS42- and subsequently the zwitterionic H4Br8TPPS4, which eventually evolves into J-aggregates. These latter species exhibit a relevant bathochromic shift with respect to the monomer with a quite sharp band due to motional narrowing. The depolarization ratio measured in resonant light scattering spectra allows estimating a tilt angle of ~20° of the porphyrins in the J-aggregate. The kinetic parameters are obtained by applying a model based on the initial slow nucleation step, leading to a nucleus containing m monomers, followed by fast autocatalytic growth. The kc values for this latter step increase on decreasing the acid concentration and on increasing the porphyrin concentration, with a strong power-law dependence. No spontaneous symmetry breaking or transfer of chirality from chiral inducers is observed. Both Atomic Force Microscopy (AFM) and Dynamic Light Scattering (DLS) point to the presence, in both the solid and solution phases, of globular-shaped aggregates with sizes close to 130 nm. Density functional theory (DFT) calculations performed on simplified models show that (i) upon protonation, the saddled conformation of the porphyrin ring is slightly altered, and a further rotation of the aryl rings occurs, and (ii) the diacid species is more stable than the parent unprotonated porphyrin. Time-dependent DFT analysis allows comparing the UV/Vis spectra for the two species, showing a consistent red shift upon protonation, even if larger than the experimental one. The simulated Raman spectrum agrees with the experimental spectrum acquired on solid samples.

Hierarchically Organized Cocrystal of Tetra-Anionic Porphyrin and Di-Cationic Viologen: Ion Conformations, Supramolecule Interactions, and Porphyrin Arrays

Ionic co-assembly of tetra-anionic porphyrins has been extensively researched in the construction of hierarchically organized architectures with potential application value in organic semiconductors, sunlight catalysts and supramolecular chirality systems. However, such architectures are difficult to grow to a size suitable for single-crystal X-ray diffraction (SCXRD); the lack of single-crystal structures of these architectures leads to challenges in gaining deeper comprehension about that. This study reports a hierarchically organized cocrystal of meso-tetra(4-sulfonato-phenyl)-porphyrin (TSPP^4- ) and N, N'-diethyl-viologen (DEV²⁺ ), wherein wave-like and saddle-like TSPP^4- ions co-aggregate at a stoichiometric ratio of 1 : 2 to form unique porphyrin arrays; the spectrum characteristics and calculated coulombic exciton coupling energy show that these porphyrin arrays are J-aggregates. We prove that the distortion of porphyrin ring of TSPP^4- strongly correlates with the deflection of its phenyl groups. The crystal comprises six different ionic conformations, and the multiplicity of ionic conformation leads to intricate supramolecular interactions.

Chirality transfer from a 3D macro shape to the molecular level by controlling asymmetric secondary flows

Homochirality is a fundamental feature of living systems, and its origin is still an unsolved mystery. Previous investigations showed that external physical forces can bias a spontaneous symmetry breaking process towards deterministic enantioselection. But can the macroscopic shape of a reactor play a role in chiral symmetry breaking processes? Here we show an example of chirality transfer from the chiral shape of a 3D helical channel to the chirality of supramolecular aggregates, with the handedness of the helical channel dictating the direction of enantioselection in the assembly of an achiral molecule. By combining numerical simulations of fluid flow and mass transport with experimental data, we demonstrated that the chiral information is transferred top-down thanks to the interplay between the hydrodynamics of asymmetric secondary flows and the precise spatiotemporal control of reagent concentration fronts. This result shows the possibility of controlling enantioselectively molecular processes at the nanometer scale by modulating the geometry and the operating conditions of fluidic reactors.

External physical forces can bias a spontaneous symmetry breaking process but whether the shape of a reactor plays a role in chiral symmetry breaking processes is an open question. Here, the authors demonstrate chirality transfer from the chiral shape of a 3D helical channel to chiral supramolecular aggregates whereby the handedness of the helical channel dictates the direction of enantioselection.

α-Cyclodextrin-Catalyzed Symmetry Breaking and Precise Regulation of Supramolecular Self-Assembly Handedness with Harata-Kodaka's Rule

Harata-Kodaka's rule predicting the induced chirality of the guest molecules by cyclodextrins has been discovered in the 1970-1990s, yet its ability to control the supramolecular handedness of self-assembled structures has not been sufficiently recognized. Here we show that in a coordinating self-assembly system that is able to form racemic cone shells symmetry breaking occurs if the ligand is prethreaded into α-cyclodextrin prior to metal ion addition, and the handedness of cone shells can be rationally manipulated by creating the two scenarios of the Harata-Kadaka rule through controlling the host-guest dynamics. Since the coordination complexes have strong self-assembling ability, the coordinating ligand would dethread from the cavity of α-cyclodextrin but leaving the induced chirality to the coordinating self-assembly, thus catalyzing symmetry breaking. This work reveals that the dynamic factors such as concentration and molar ratio may play important roles in symmetry breaking at the supramolecular level. The current strategy provides a promising method for the symmetry breaking and manipulation of the handedness of self-assembled materials formed by achiral molecules.

Exploiting Reaction-Diffusion Conditions to Trigger Pathway Complexity in the Growth of a MOF

Coordination polymers (CPs), including metal-organic frameworks (MOFs), are crystalline materials with promising applications in electronics, magnetism, catalysis, and gas storage/separation. However, the mechanisms and pathways underlying their formation remain largely undisclosed. Herein, we demonstrate that diffusion-controlled mixing of reagents at the very early stages of the crystallization process (i.e., within ≈40 ms), achieved by using continuous-flow microfluidic devices, can be used to enable novel crystallization pathways of a prototypical spin-crossover MOF towards its thermodynamic product. In particular, two distinct and unprecedented nucleation-growth pathways were experimentally observed when crystallization was triggered under microfluidic mixing. Full-atom molecular dynamics simulations also confirm the occurrence of these two distinct pathways during crystal growth. In sharp contrast, a crystallization by particle attachment was observed under bulk (turbulent) mixing. These unprecedented results provide a sound basis for understanding the growth of CPs and open up new avenues for the engineering of porous materials by using out-of-equilibrium conditions.

Absolute Asymmetric Catalysis, from Concept to Experiment: A Narrative

The generally accepted hypothesis to explain the origin of biological homochirality (that is to say, the fact that proteinogenic amino acids are left-handed, and carbohydrates right-handed, in all living beings) is to assume, in the course of prebiotic chemical evolution, the appearance of an initial enantiomeric excess in a set of chiral molecular entities by spontaneous mirror-symmetry breaking (SMSB), together with suitable amplification and replication mechanisms that overcome the thermodynamic drive to racemization. However, the achievement of SMSB in chemical reactions taking place in solution requires highly specific reaction networks showing nonlinear dynamics based on enantioselective autocatalysis, and examples of its experimental realization are very rare. On the other hand, emergence of net supramolecular chirality by SMSB in the self-assembly of achiral molecules has been seen to occur in several instances, and the chirality sign of the resulting supramolecular system can be controlled by the action of macroscopic chiral forces. These considerations led us to propose a new mechanism for the generation of net chirality in molecular systems, in which the SMSB takes place in the formation of chiral supramolecular dissipative structures from achiral monomers, leading to asymmetric imbalances in their composition that are subsequently transferred to a standard enantioselective catalytic reaction, dodging in this way the highly limiting requirement of finding suitable reactions in solution that show enantio­selective autocatalysis. We propose the name ‘absolute asymmetric catalysis’ for this approach, in which an achiral monomer is converted into a nonracemic chiral aggregate that is generated with SMSB and that is catalytically active.

Our aim in this Account is to present a step-by-step narrative of the conceptual and experimental development of this hitherto unregarded, but prebiotically plausible, mechanism for the emergence of net chirality in molecular reactions.

1 Introduction: The Origin of Biological Homochirality and Spontaneous Mirror-Symmetry Breaking

2 Experimental Chemical Models for Spontaneous Mirror-Symmetry Breaking: The Soai Reaction and Beyond

3 Spontaneous Mirror-Symmetry Breaking in Supramolecular Chemistry: Plenty of Room at the Top

4 Absolute Asymmetric Catalysis: An Alternative Mechanism for the Emergence of Net Chirality in Molecular Systems

5 Experimental Realization of Top-Down Chirality Transfer to the

Molecular Level

6 Conclusions and Outlook

Directional Supramolecular Polymerization in a Dynamic Microsolution: A Linearly Moving Polymer's End Striking Monomers

Although directional chain reactions are common in nature's self-assembly processes and in covalent polymerizations, it has been challenging to perform such processes in artificial one-dimensional self-assembling systems. In this paper, we describe a system, employing perylene bisimide (PBI) derivatives as monomers, for selectively activating one end of a supramolecular polymer during its growth and, thereby, realizing directional supramolecular polymerization. Upon introduction of a solution containing only a single PBI monomer into the microflow channel, nucleation was induced spontaneously. The dependency of the aggregation efficiency on the flow rate suggested that the shear force facilitated collisions among the monomers to overcome the activation energy required for nucleation. Next, by introducing a solution containing both monomer and polymer, we investigated how the shear force influenced the monomer-polymer interactions. In situ fluorescence spectra and linear dichroism revealed that growth of the polymers was accelerated only when they were oriented under the influence of shear stress. Upon linear motion of the oriented polymer, polymer growth at that single end became predominant relative to the nucleation of freely diffusing monomers. When applying this strategy to a two-monomer system, the second (less active) monomer reacted selectively at the forward-facing terminus of the first polymer, leading to the creation of a diblock copolymer through formation of a molecular heterojunction. This strategy-friction-induced activation of a single end of a polymer-should be applicable more generally to directional supramolecular block copolymerizations of various functional molecules, allowing molecular heterojunctions to be made at desired positions in a polymer.

Microfluidic enhancement of self-assembly systems

Dynamic, kinetically-controlled, self-assembly processes are commonly observed in nature and are capable of creating intricate, functional architectures from simple precursors. However, notably, much of the research into molecular self-assembly has been performed using conventional bulk techniques where the resultant species are dictated by thermodynamic stability to yield relatively simple assemblies. Whereas, the environmental control offered by microfluidic systems offers methods to achieve non-equilibrium reaction conditions capable of increasingly sophisticated self-assembled structures. Alterations to the immediate microenvironment during the assembly of the molecules is possible, providing the basis for kinetically-controlled assembly. This review examines the key mechanism offered by microfluidic systems and the architectures required to access them. The mechanisms include diffusion-led mixing, shear gradient alignment, spatial and temporal confinement, and structural templates in multiphase systems. The works are selected and categorised in terms of the microfluidic approaches taken rather than the chemical constructs which are formed.

Microfluidics for the rapid and controlled preparation of organic nanotubes of bent-core based dendrimers

Recently, bent-core molecules have emerged as excellent building blocks for the obtaining of nanostructures in solvents. Herein, we report the use of a coaxial microfluidic system as a promising tool to control the self-assembly of non-conventional bent-core amphiphiles. Moreover, a TEM study to comprehend the hierarchical self-assembly process in solution was carried out. The proposed tool provides both a cost-effective platform to save hard-to-synthesise reagents and a rapid method to screen a plethora of different parameters, i.e., THF/water ratio, residence time, concentration of the amphiphile, temperature and pH. The experiments allowed to test for the first time the suitability of microfluidics for the self-assembly of bent-core molecules, as well as the study of a range of conditions to control the assembly of different nanostructures in a rapid and controlled manner. Additionally, organic nanostructures were combined with gold nanoparticles to prepare nanocomposites with enhanced properties. Both organic and hybrid nanostructures were also obtained in the solid state. These results may inspire scientists working on supramolecular chemistry and bent-core molecules expanding the scope of microfluidic systems for the self-assembly of other low-molecular-weight compounds.

Tunable Supramolecular Chirogenesis in the Self-Assembling of Amphiphilic Porphyrin Triggered by Chiral Amines

Supramolecular chirality is one of the most important issues in different branches of science and technology, as stereoselective molecular recognition, catalysis, and sensors. In this paper, we report on the self-assembly of amphiphilic porphyrin derivatives possessing a chiral information on the periphery of the macrocycle (i.e., D- or L-proline moieties), in the presence of chiral amines as co-solute, such as chiral benzylamine derivatives. The aggregation process, steered by hydrophobic effect, has been studied in aqueous solvent mixtures by combined spectroscopic and topographic techniques. The results obtained pointed out a dramatic effect of these ligands on the morphology and on the supramolecular chirality of the final self-assembled structures. Scanning electron microscopy topography, as well as fluorescence microscopy studies revealed the formation of rod-like structures of micrometric size, different from the fractal structures formerly observed when the self-assembly process is carried out in the absence of chiral amine co-solutes. On the other hand, comparative experiments with an achiral porphyrin analogue strongly suggested that the presence of the prolinate moiety is mandatory for the achievement of the observed highly organized suprastructures. The results obtained would be of importance for unraveling the intimate mechanisms operating in the selection of the homochirality, and for the preparation of sensitive materials for the detection of chiral analytes, with tunable stereoselectivity and morphology.

Porphyrins Through the Looking Glass: Spectroscopic and Mechanistic Insights in Supramolecular Chirogenesis of New Self-Assembled Porphyrin Derivatives

The solvent driven aggregation of porphyrin derivatives, covalently linked to a L- or D-prolinate enantiomer, results in the stereospecific formation of species featuring remarkable supramolecular chirality, as a consequence of reading and amplification of the stereochemical information stored in the proline-appended group. Spectroscopic, kinetic, and topographic SEM studies gave important information on the aggregation processes, and on the structures of the final chiral architectures. The results obtained may be the seeds for the construction of stereoselective sensors aiming at the detection, for example, of novel emergent pollutants from agrochemical, food, and pharmaceutical industry.

Morphology control in metallosupramolecular assemblies through solvent-induced steric demand

Controlling the supramolecular self-assembly of π-conjugated systems into defined morphologies is a prerequisite for the preparation of functional materials. In recent years, the development of sophisticated sample preparation protocols and modulation of various experimental conditions (solvent, concentration, temperature, etc.) have enabled precise control over aggregation pathways of different types of monomer units. A common method to achieve pathway control consists in the combination of two miscible solvents in defined proportions - a "poor" and "good" solvent. However, the role of solvents of opposed polarity in the self-assembly of a given building block still remains an open question. Herein, we unravel the effect of aggregation-inducing solvent systems of opposed polarity (aqueous vs. non-polar media) on the supramolecular assembly of a new bolaamphiphilic Pt(ii) complex. A number of experimental methods show a comparable molecular packing in both media driven by a synergy of solvophobic, aromatic and weak hydrogen-bonding interactions. However, morphological analysis of the respective aggregates in aqueous and non-polar media reveals a restricted aggregate growth in aqueous media into spherical nanoparticles and a non-restricted 2D-nanosheet formation in non-polar media. These findings are attributed to a considerably more efficient solvation and, in turn, increased steric demand of the hydrophilic chains in aqueous media than in nonpolar media, which can be explained by the entrapment of water molecules in the hydrophilic aggregate shell via hydrogen bonds. Our findings reveal that the different solvation of peripheral solubilizing groups in solvents of opposed polarity is an efficient method for morphology control in self-assembly.

Competing Roles of Two Kinds of Ligand during Nonclassical Crystallization of Pillared-Layer Metal-Organic Frameworks Elucidated Using Microfluidic Systems

To diversify metal-organic frameworks (MOFs), multi-component MOFs constructed from more than two kinds of bridging ligand have been actively investigated due to the high degree of design freedom afforded by the combination of multiple ligands. Predicting the synthesis conditions for such MOFs requires an understanding of the crystallization mechanism, which has so far remained elusive. In this context, microflow systems are efficient tools for capturing non-equilibrium states as they facilitate precise and efficient mixing with reaction times that correspond to the distance from the mixing point, thus enabling reliable control of non-equilibrium crystallization processes. Herein, we prepared coordination polymers with pillared-layer structures and observed the intermediates in the syntheses with an in-situ measurement system that combines microflow reaction with UV/Vis and X-ray absorption fine-structure spectroscopies, thereby enabling their rapid nucleation to be monitored. Based on the results, a three-step nonclassical nucleation mechanism involving two kinds of intermediate is proposed.

Microfluidic out-of-equilibrium control of molecular nanotubes

The bottom-up fabrication of functional nanosystems for light-harvesting applications and excitonic devices often relies on molecular self-assembly. Gaining access to the intermediate species involved in self-assembly would provide valuable insights into the pathways via which the final architecture has evolved, yet difficult to achieve due to their intrinsically short-lived nature. Here, we employ a lab-on-a-chip approach as a means to obtain in situ control of the structural complexity of an artificial light-harvesting complex: molecular double-walled nanotubes. Rapid and stable dissolution of the outer wall was realized via microfluidic mixing thereby rendering the thermodynamically unstable inner tubes accessible to spectroscopy. By measurement of the linear dichroism and time-resolved photoluminescence of both double-walled nanotubes and isolated inner tubes we show that the optical (excitonic) properties of the inner tube are remarkably robust to such drastic perturbation of the system's supramolecular structure as removal of the outer wall. The developed platform is readily extendable to a broad range of practical applications such as e.g. self-assembling systems and molecular photonics devices.

Interplay between structural hierarchy and exciton diffusion in artificial light harvesting

Unraveling the nature of energy transport in multi-chromophoric photosynthetic complexes is essential to extract valuable design blueprints for light-harvesting applications. Long-range exciton transport in such systems is facilitated by a combination of delocalized excitation wavefunctions (excitons) and exciton diffusion. The unambiguous identification of the exciton transport is intrinsically challenging due to the system's sheer complexity. Here we address this challenge by employing a spectroscopic lab-on-a-chip approach: ultrafast coherent two-dimensional spectroscopy and microfluidics working in tandem with theoretical modeling. We show that at low excitation fluences, the outer layer acts as an exciton antenna supplying excitons to the inner tube, while under high excitation fluences the former converts its functionality into an exciton annihilator which depletes the exciton population prior to any exciton transfer. Our findings shed light on the excitonic trajectories across different sub-units of a multi-layered artificial light-harvesting complex and underpin their great potential for directional excitation energy transport.

Steering the Self-Assembly Outcome of a Single NDI Monomer into Three Morphologically Distinct Supramolecular Assemblies, with Concomitant Change in Supramolecular Polymerization Mechanism

Noncovalent self-assembly creates an effective route to highly sophisticated supramolecular polymers with tunable properties. However, the outcome of this assembly process is highly dependent on external conditions. In this work, a monomeric naphthalene diimide (NDI), designed to allow solubility in a wide range of solvents, can assemble into three distinct noncovalent supramolecular species depending on solvent composition and temperature. Namely, while the self-assembly in chlorinated solvents yields relatively short, hydrogen-bonded nanotubes, the reduction of solvent polarity changes the assembly outcome, yielding π-π stacking polymers, which can further bundle into a more complex aggregate. The obtained polymers differ not only in their global morphology but-more strikingly-also in the thermodynamics and kinetics of their supramolecular self-assembly, involving isodesmic or two-stage cooperative assembly with kinetic hysteresis, respectively. Ultimately, three distinct assembly states can be accessed in a single experiment.

In Situ Photophysical Characterization of π-Conjugated Oligopeptides Assembled via Continuous Flow Processing

Bioinspired materials have been developed with the aim of harnessing natural self-assembly for precisely engineered functionality. Microfluidics is poised to play a key role in the directed assembly of advanced materials with ordered nano and mesoscale features. More importantly, there is a strong need for understanding the kinetics of continuous assembly processes. In this work, we describe a continuous microfluidic system for the assembly and alignment of synthetic oligopeptides with π-conjugated cores using a three-dimensional (3D) flow focusing of inlet reactant streams. This system facilitates in situ confocal fluorescence microscopy and in situ fluorescence lifetime imaging microscopy (FLIM), which can be used in unprecedented capacity to characterize the integrity of peptides during the assembly process. To achieve continuous assembly, we integrate chevron patterns in the ceiling and floor of the microdevice to generate a 3D-focused sheath flow of the reactant peptide. Consequently, the peptide stream is directed toward an acidic triggering stream in a cross-slot geometry which mediates assembly into higher-order fiber-like structures. Using this approach, the focused peptide stream is assembled using a planar extensional flow, which ensures high degrees of microstructural alignment within the assembled material. We demonstrate the efficacy of this approach using three different synthetic oligopeptides, and in all cases, we observe the efficient and continuous assembly of oligopeptides. In addition, finite element simulations are used to guide device design and to validate 3D focusing. Overall, this approach presents an efficient and effective method for the continuous assembly and alignment of ordered materials using microfluidics.

A Competing Hydrogen Bonding Pattern to Yield a Thermo-Thickening Supramolecular Polymer

Introduction of competing interactions in the design of a supramolecular polymer (SP) creates pathway complexity. Ester-bis-ureas contain both a strong bis-urea sticker that is responsible for the build-up of long rod-like objects by hydrogen bonding and ester groups that can interfere with this main pattern in a subtle way. Spectroscopic (FTIR and CD), calorimetric (DSC), and scattering (SANS) techniques show that such ester-bis-ureas self-assemble into three competing rod-like SPs. The previously unreported low-temperature SP is stabilized by hydrogen bonds between the interfering ester groups and the urea moieties. It also features a weak macroscopic alignment of the rods. The other structures form isotropic dispersions of rods stabilized by the more classical urea-urea hydrogen bonding pattern. The transition from the low-temperature structure to the next occurs reversibly by heating and is accompanied by an increase in viscosity, a rare feature for solutions in hydrocarbons.

Symmetry Breaking in Self-Assembled Nanoassemblies

The origin of biological homochirality, e.g., life selects the L-amino acids and D-sugar as molecular component, still remains a big mystery. It is suggested that mirror symmetry breaking plays an important role. Recent researches show that symmetry breaking can also occur at a supramolecular level, where the non-covalent bond was crucial. In these systems, equal or unequal amount of the enantiomeric nanoassemblies could be formed from achiral molecules. In this paper, we presented a brief overview regarding the symmetry breaking from dispersed system to gels, solids, and at interfaces. Then we discuss the rational manipulation of supramolecular chirality on how to induce and control the homochirality in the self-assembly system. Those physical control methods, such as Viedma ripening, hydrodynamic macro- and micro-vortex, superchiral light, and the combination of these technologies, are specifically discussed. It is hoped that the symmetry breaking at a supramolecular level could provide useful insights into the understanding of natural homochirality and further designing as well as controlling of functional chiral materials.

Metallogels: Availability, Applicability, and Advanceability

Introducing metal components into gel matrices provides an effective strategy to develop soft materials with advantageous properties such as: optical activity, conductivity, magnetic response activity, self-healing activity, catalytic activity, etc. In this context, a thorough overview of application-oriented metallogels is provided. Considering that many well-established metallogels start from serendipitous discoveries, insights into the structure-gelation relationship will offer a profound impact on the development of metallogels. Initially, design strategies for discovering new metallogels are discussed, then the advanced applications of metallogels are summarized. Finally, perspectives regarding the design of metallogels, the potential applications of metallogels and their derivative materials are briefly proposed.

A General Approach for Fluid Patterning and Application in Fabricating Microdevices

Engineering the fluid interface such as the gas-liquid interface is of great significance for solvent processing applications including functional material assembly, inkjet printing, and high-performance device fabrication. However, precisely controlling the fluid interface remains a great challenge owing to its flexibility and fluidity. Here, a general method to manipulate the fluid interface for fluid patterning using micropillars in the microchannel is reported. The principle of fluid patterning for immiscible fluid pairs including air, water, and oils is proposed. This understanding enables the preparation of programmable multiphase fluid patterns and assembly of multilayer functional materials to fabricate micro-optoelectronic devices. This general strategy of fluid patterning provides a promising platform to study the fundamental processes occurring on the fluid interface, and benefits applications in many subjects, such as microfluidics, microbiology, chemical analysis and detection, material synthesis and assembly, device fabrication, etc.

Molecular Synchronization Enhances Molecular Interactions: An Explanatory Note of Pressure Effects

In this study, we investigated a unique aspect of the supramolecular polymerization of tetrakis (4-sulfonatophenyl) porphyrin (TPPS), a self-assembling porphyrin, under non-equilibrium conditions by subtracting the effects of back-pressure on its polymerization. We focused on the enhanced self-assembly abilities of TPPS under a process of rapid proton diffusion in a microflow channel. Rapid protonation caused synchronization of many sets of protonation/deprotonation equilibria on the molecular scale, leading to the production of many sets of growing suparmolecular spices. Pressure effects in the microflow channel, which could potentially promote self-assembly of TPPS, were negligible, becoming predominant only when the system was in the synchronized state.

Control over the emerging chirality in supramolecular gels and solutions by chiral microvortices in milliseconds

The origin of homochirality in life is a fundamental mystery. Symmetry breaking and subsequent amplification of chiral bias are regarded as one of the underlying mechanisms. However, the selection and control of initial chiral bias in a spontaneous mirror symmetry breaking process remains a great challenge. Here we show experimental evidences that laminar chiral microvortices generated within asymmetric microchambers can lead to a hydrodynamic selection of initial chiral bias of supramolecular systems composed of exclusively achiral molecules within milliseconds. The self-assembled nuclei with the chirality sign affected by the shear force of enantiomorphic microvortices are subsequently amplified into almost absolutely chirality-controlled supramolecular gels or nanotubes. In contrast, turbulent vortices in stirring cuvettes fail to select the chirality of supramolecular gels. This study reveals that a laminar chiral microflow can induce enantioselection far from equilibrium, and provides an insight on the origin of natural homochirality.

Symmetry breaking and chiral amplification are fundamental principles in chemistry and biology but the control of initial chiral bias remains a great challenge. Here the authors show that chiral microvortices can lead to a selection of initial chiral bias of supramolecular systems composed of achiral molecules.

Self-assembled materials and supramolecular chemistry within microfluidic environments: from common thermodynamic states to non-equilibrium structures

Self-assembly is a crucial component in the bottom-up fabrication of hierarchical supramolecular structures and advanced functional materials. Control has traditionally relied on the use of encoded building blocks bearing suitable moieties for recognition and interaction, with targeting of the thermodynamic equilibrium state. On the other hand, nature leverages the control of reaction-diffusion processes to create hierarchically organized materials with surprisingly complex biological functions. Indeed, under non-equilibrium conditions (kinetic control), the spatio-temporal command of chemical gradients and reactant mixing during self-assembly (the creation of non-uniform chemical environments for example) can strongly affect the outcome of the self-assembly process. This directly enables a precise control over material properties and functions. In this tutorial review, we show how the unique physical conditions offered by microfluidic technologies can be advantageously used to control the self-assembly of materials and of supramolecular aggregates in solution, making possible the isolation of intermediate states and unprecedented non-equilibrium structures, as well as the emergence of novel functions. Selected examples from the literature will be used to confirm that microfluidic devices are an invaluable toolbox technology for unveiling, understanding and steering self-assembly pathways to desired structures, properties and functions, as well as advanced processing tools for device fabrication and integration.

Biomimetic temporal self-assembly via fuel-driven controlled supramolecular polymerization

Temporal control of supramolecular assemblies to modulate the structural and transient characteristics of synthetic nanostructures is an active field of research within supramolecular chemistry. Molecular designs to attain temporal control have often taken inspiration from biological assemblies. One such assembly in Nature which has been studied extensively, for its well-defined structure and programmable self-assembly, is the ATP-driven seeded self-assembly of actin. Here we show, in a synthetic manifestation of actin self-assembly, an ATP-selective and ATP-fuelled, controlled supramolecular polymerization of a phosphate receptor functionalised monomer. It undergoes fuel-driven nucleation and seeded growth that provide length control and narrow dispersity of the resultant assemblies. Furthermore, coupling via ATP-hydrolysing enzymes yielded its transient characteristics. These results will usher investigations into synthetic analogues of important biological self-assembly motifs and will prove to be a significant advancement toward biomimetic temporally programmed materials.

Chiral signs of TPPS co-assemblies with chiral gelators: role of molecular and supramolecular chirality

A dianionic tetrakis(4-sulfonatophenyl)porphyrin (TPPS) self-assembled into J-aggregates when it co-assembled with a chiral cationic amphiphile via supramolecular gelation. The chiral signs of TPPS J aggregates followed the supramolecular chirality of amphiphilic assemblies rather than the molecular chirality of the amphiphile.

Drug-Loaded Supramolecular Gels Prepared in a Microfluidic Platform: Distinctive Rheology and Delivery through Controlled Far-from-Equilibrium Mixing

It is shown here that controlled mixing of a gelator, drug, solvent, and antisolvent in a microfluidic channel leads to faster setting gels and more robust materials with longer release profiles than the physical gels of the same composition obtained using random mixing in solution. The system is similar to a related gelator system we had studied previously, but we were unable to apply the same gelling procedure because of the instability of the colloid caused by the small structural modification (length of the alkyl chain in the bis-imidazolium head group). This situation holds true for the gels formed with varying compositions and under different conditions (gelator/drug ratio, solvent proportion, and flow rates), with the most significant differences being the improved gel rheology and slower drug release rates. Very importantly, the gels (based on a previously unexplored system) have a higher water content ratio (water/EtOH 4:1) than others in the family, making their medicinal application more attractive. The gels were characterized by a variety of microscopy techniques, X-ray diffraction and infrared spectroscopy, and rheology. Salts of the antiinflammatory drugs ibuprofen and indomethacin were successfully incorporated into the gels. The diffraction experiments indicate that these composite gels with relatively short alkyl chains in the gelator component contrast to previous systems, in that they exhibit structural order and the presence of crystalline areas of the drug molecule implying partial phase separation (even though these drug crystallites are not discernible by microscopy). Furthermore, the release study with the gel incorporating ibuprofenate showed promising results that indicate a possible drug delivery vehicle application for this and related systems.

Non-equilibrium supramolecular polymerization

Supramolecular polymerization has been traditionally focused on the thermodynamic equilibrium state, where one-dimensional assemblies reside at the global minimum of the Gibbs free energy. The pathway and rate to reach the equilibrium state are irrelevant, and the resulting assemblies remain unchanged over time. In the past decade, the focus has shifted to kinetically trapped (non-dissipative non-equilibrium) structures that heavily depend on the method of preparation (i.e., pathway complexity), and where the assembly rates are of key importance. Kinetic models have greatly improved our understanding of competing pathways, and shown how to steer supramolecular polymerization in the desired direction (i.e., pathway selection). The most recent innovation in the field relies on energy or mass input that is dissipated to keep the system away from the thermodynamic equilibrium (or from other non-dissipative states). This tutorial review aims to provide the reader with a set of tools to identify different types of self-assembled states that have been explored so far. In particular, we aim to clarify the often unclear use of the term "non-equilibrium self-assembly" by subdividing systems into dissipative, and non-dissipative non-equilibrium states. Examples are given for each of the states, with a focus on non-dissipative non-equilibrium states found in one-dimensional supramolecular polymerization.

Discrimination of supramolecular chirality using a protein nanopore

Supramolecular chirality may emerge from self-assembly processes to yield architectures that differ only in the topological arrangement of their constituent parts. Since the properties of the resulting enantiomeric assemblies are identical, purification and characterisation can be challenging. Here, we have examined the hypothesis that the intrinsic chirality of a protein nanopore can be exploited to detect supramolecular chirality. Transient blockages in the ion current flowing through a single membrane-spanning α-haemolysin nanopore were shown to discriminate between M4L6 tetrahedral coordination cages of opposing chiralities. The single-molecule nature of the approach facilitated direct access to the rates of association and dissociation with the nanopore, which allowed the concentrations of the enantiomeric supramolecular assemblies to be determined in situ. Thus, we have established that a protein nanopore can be used to discriminate the chiral topologies of supramolecular assemblies, even when they are too large to fully enter the nanopore.

Spatial control of chirality in supramolecular aggregates

Chirality is one of the most intriguing properties of matter related to a molecule’s lack of mirror symmetry. The transmission of chirality from the molecular level up to the macroscopic scale has major implications in life sciences but it is also relevant for many chemical applications ranging from catalysis to spintronic. These technological applications require an accurate control of morphology, homogeneity and chiral handedness of thin films and nanostructures. We demonstrate a simple approach to specifically transfer chirality to the model supramolecular system of J aggregates of the protonated form of tetrakis(4-sulfonatophenyl)-porphyrin by utilizing a soft lithography technique. This approach successfully allows the fabrication of an ordered distribution of sub-micrometric structures in precise and controllable positions with programmed chirality, providing a fundamental breakthrough toward the exploitation of chiral supramolecular aggregates in technological applications, such as sensors, non-linear optics and spintronic.

Chiral Supramolecular Gels with Lanthanide Ions: Correlation between Luminescence and Helical Pitch

We report the correlation between the fluorescence intensity and the helical pitch of supramolecular hydrogels with Tb(III) and Eu(III) as well as their inkjet printing patterning as an application. The luminescent gels, which exhibited three different emissions of red, green, and blue, could be prepared without and with Eu(III) and Tb(III). The luminescence intensity of supramolecular gels (gel-Tb and gel-Eu) composed of Tb(III) and Eu(III) was ca. 3-fold larger than that of the sol (1+Tb(III) or 1+Eu(III)), which was attributed to large tilting angles between molecules. By AFM observations, these gels showed well-defined right-handed helical nanofibers formed by coordination bonds in which the helical pitch lengths were strongly dependent on the concentrations of lanthanide ions. In particular, the large luminescence intensity of gel-Tb exhibited a smaller helical pitch length than that of gel-1 due to relatively weak π-π stacking with large tilting angles between molecules. The luminescence intensities were enhanced linearly with increasing concentrations of lanthanide ions. This is the first example of the correlation between the helical pitch length and the luminescence intensity of supramolecular materials. The coordination bonding in supramolecular hydrogels had a strong influence on rheological properties. We also developed a water-compatible inkjet printing system to generate luminescent supramolecular gels on A4-sized paper. The images of a logo and the text were composed of three different emissions and were well-printed on A4 sized paper coated with gel-1.

Reversible and irreversible emergence of chiroptical signals in J-aggregates of achiral 4-sulfonatophenyl substituted porphyrins: intrinsic chirality vs. chiral ordering in the solution

Different origins of the reversible and irreversible emergence of chiroptical signals in the title J-aggregates.

Tuning the structure of 1,3,5-benzene tricarboxamide self-assemblies through stereochemistry

A heterochiral BTA monomer forms long rods in cyclohexane whilst its homochiral analogue assembles into dimers.