Future of Supramolecular Copolymers Unveiled by Reflecting on Covalent Copolymerization

Mapping in situ the assembly and dynamics in aqueous supramolecular polymers

Supramolecular polymers, bonded through directional non-covalent interactions, closely mimic dynamic behaviors of biological nanofibers. However, the complexity of assembly pathways makes it highly challenging to unravel the nature of supramolecular dynamics in aqueous environments. Here we introduce a precise combinatorial titration methodology to probe in situ the assembly of peptide amphiphiles (PAs). This approach reveals a binary assembly mechanism governed by equilibrium between spheroidal micelles and β-sheet polymers. Weakening hydrogen bonding shifts the equilibrium towards micelles and decreases the internal structural order of filamentous polymers, promoting supramolecular dynamics. Extending this methodology to two-component copolymerization systems, we find a surprising tendency to form blocky nanostructures with reduced internal phase separation as the mismatch in peptide sequence decreases. Interestingly, while well-mixed copolymers acquire different dynamics, mismatched ones retain the characteristic supramolecular motion of their homopolymer counterparts. These critical insights into supramolecular dynamics offer strategies to tailor the dynamic functions of supramolecular nanomaterials.

Elucidating the Boundary of Intercalation vs Sequestration in Supramolecular Polymers by Retrosynthetic Design Toward the Construction of Complex Supramolecular Systems

Controlled social self-sorting by intercalation can offer distinct properties at the supramolecular level that go beyond the sum of its parts. Likewise, controlling narcissistic self-sorting by sequestration can induce unique system properties. In contrast, the interface between the two cases has hitherto remained underexplored, and clear design rules remain elusive. Herein it is demonstrated that by fine-tuning the molecular similarity of supramolecular synthons, intricate control over concerted supramolecular equilibria can be achieved. By reducing the molecular similarity, a former intercalator can be tuned to become a strong or weak sequestrator. Understanding these roles in binary mixtures allows to rationalize more complex tertiary systems. Consequently, the influence of an uncommon dual sequestration mechanism is revealed. Further, an unprecedented hybrid mechanism between supramolecular intercalation and sequestration can be demonstrated. We are hopeful that the results presented herein will contribute to the development and understanding of concerted processes in complex supramolecular systems.

Redox-Controlled, Sequential Self-Sorting of Supramolecular Assemblies in Model Protocells

Self-sorting of cellular components is essential for maintaining order and function in living systems, enabling complex processes to operate seamlessly. Emulating such self-sorting in synthetic self-assembly, however, has conventionally relied on structural or chirality mismatches of monomers yielding self-sorted systems under thermodynamic conditions. In contrast, reaction-coupled, kinetically controlled self-assembly, ubiquitous in biological systems, is critical for achieving spatiotemporal characteristics. Extending this principle to temporally self-sorted synthetic assemblies is key to developing multi-component biomimetic systems. Herein, we present a strategy towards this direction, to achieve sequential self-sorting of supramolecular assemblies through differences in the chemical-reactivity of monomers, coupled to redox-reactions. This approach exploits the distinct redox potentials of monomers to achieve precise temporal-control over self-sorting, while inherent structural mismatches among monomers ensure the kinetic stability of self-sorted state. Reduction reactions transiently disrupt their assemblies into dormant inactive monomeric states, while subsequent kinetically controlled reassembly occurs via reversible oxidation reactions. Finally, utilizing this sequential self-sorting, we aim to mimic multicomponent cellular self-organization by demonstrating the kinetically controlled growth of self-sorted structures in the presence of model protocells, using lipid vesicles as compartments. Although spatial-distribution remains non-selective, the dormant monomeric states facilitate monomer encapsulation and the unprecedented stepwise-formation of self-sorted assemblies within model protocells.

Supramolecular Polymers for Drug Delivery

Supramolecular polymers are constructed through highly reversible and directionally specific non-covalent interactions between monomer units. This unique feature enables supramolecular polymers to undergo controlled structural reconfiguration and functional transformation in response to external stimuli, imparting them with high environmental responsiveness and self-healing properties. In particular, supramolecular polymers exhibit several specific advantages compared to conventional polymers, such as inherent degradability, the ease of preparation and the incorporation of functional units, and smart responsiveness to various biological stimuli. These characters make supramolecular polymers promising candidates for intelligent drug delivery systems in complex biological environments. In this review, we comprehensively summarize the latest developments and representative achievements of supramolecular polymers in drug delivery fields, focusing primarily on the design and synthesis, the properties and functionalities, and the practical applications of supramolecular polymers in small molecule drug delivery, gene therapy, and protein delivery. Finally, we highlight future research directions, focusing on multifunctionality, adaptability, and personalized therapy. We focus on recent studies that address key challenges in the field, providing rational polymer design, important properties, functionality, and understanding delivery strategies. These developments are expected to advance supramolecular polymers as new platforms of intelligent drug delivery systems, offering innovative solutions for the treatment of complex diseases.

Interfacing Flexible Design and Social Self-Sorting Enables Comprehensive Control over Photophysical and Self-Assembly Properties of Supramolecular Polymers

Supramolecular self-assembly offers an intriguing approach to construct microarchitectures, which combine properties of their molecular constituents with dynamic supramolecular features. Control over intermolecular interactions and their resulting properties can sometimes be achieved by targeted design. However, it is often unfeasible to transfer the insights gained from a specific supramolecular synthon to another chromophore without tedious synthetic work guided by trial and error. Herein we demonstrate how a flexible molecular design approach enables access to a diverse library of photophysical properties, which can be further diversified by social self-sorting strategies using a second supramolecular building block as a modulator. By intercalation into the supramolecular polymer the modulator can disrupt interchromophore interactions and modulate the ensembles emissive properties across the visible color space by simply adjusting the ratio between the two building blocks. Furthermore, by combining a chromophore appended synthon with a different morphology than the modulator the mesoscopic size distribution of the coassemblies can be modified to resemble either of its constituents. Crucially, this moldability is not only achievable for systems under thermodynamic control, but can be also employed to tune photophysical properties and thermal stability profiles of kinetically controlled states. Finally, the thermodynamic stability of the modulated polymers can be adjusted by varying the amount of solubilizing alkyl chains in the ensemble. This peripheral stabilization approach does not affect the engineered photophysical or supramolecular properties. Our results demonstrate how flexible molecular design enriched by a supramolecular modulator can offer access to a wide variety of photophysical properties and enable unique fine-tuning of various supramolecular properties.

Ion Mobility Mass Spectrometry to Probe Sequences in Supramolecular Copolymers

The analysis of the microstructure of supramolecular copolymers is difficult because of their dynamic character. Here, benzene-1,3,5-tricarboxamide (BTA) co-assemblies are analysed by ion mobility - mass spectrometry (IM-MS) to reveal the presence of various sequences. For example, the IM-MS mobilogram for hexamers composed of 4 units from a first monomer and 2 units from a second monomer is a broad distribution due to the presence of 9 possible isomeric sequences, which can be sorted out based on calculated collision cross-sections. This approach gives unprecedented information on supramolecular copolymer sequences.

Helical-Sense Matching Facilitates Supramolecular Copolymerization of Helical-Chiral Pillar[5]arenes

Supramolecular polymerization using two-dimensional π-conjugated chiral monomers has been mainly demonstrated because the supramolecular polymerization can be controlled by stereocommunication through π-π stacking between the two-dimensional chiral monomers. We herein report supramolecular copolymerization utilizing three-dimensional pentahedrons with twisted helical chirality through different combinations of helical-chiral acidic and basic pillar[5]arenes as comonomers. In this case, helical-sense matching is key to facilitating the supramolecular copolymerization. Based on the unique helical chirality of the three-dimensional pillared structure of the pillar[5]arenes and alternate ion-pairing interactions between acidic and basic groups on their bilateral rims, the homochiral helical-sense matching system forms kinetically stable nanowire-shaped supramolecular copolymers, generating the supramolecular gel in high concentrations. At elevated temperatures, the nanowire structure undergoes a transformation into thermodynamically stable nanoparticles, resulting in a gel-to-sol transition. This process can be hindered by introducing linear guest molecules, which prohibit the unit swing of pillar[5]arenes and stabilize the nanowires and supramolecular gel. By tailoring the enantiomeric ratio (e.r.) values of the chiral combinations, the helical-sense-dependent gel-to-sol transition was realized, specifically by decreasing the e.r. values. Because of helical-sense mismatching, the heterochiral system generates short, branched nanowires and presents as a turbid solution. These distinct differences reveal that the helical-sense matching between three-dimensional chiral pillar[5]arene comonomers is important for supramolecular copolymerization.

Investigating the self-assembly of 2NapFF and ureido-pyrimidinone multicomponent systems for cell culture

Low molecular weight gels are formed via the self-assembly of small molecules into fibrous structures. In the case of hydrogels, these networks entrap large volumes of water, yielding soft materials. Such gels tend to have weak mechanical properties and a high permeability for cells, making them particularly appealing for regenerative medicine applications. Ureido-pyrimidinone (UPy) supramolecular gelators are self-assembling systems that have demonstrated excellent capabilities as biomaterials. Here, we combine UPy-gelators with another low molecular weight gelator, the functionalized dipeptide 2NapFF. We have successfully characterized these multicomponent systems on a molecular and bulk scale. The addition of 2NapFF to a crosslinked UPy hydrogel significantly increased hydrogel stiffness from 30 Pa to 1300 Pa. Small-angle X-ray scattering was used to probe the underlying structures of the systems and showed that the mixed UPy and 2NapFF systems resemble the scattering data produced by the pristine UPy systems. However, when a bifunctional UPy-crosslinker was added, the scattering was close to that of the 2NapFF only samples. The results suggest that the crosslinker significantly influences the assembly of the low molecular weight gelators. Finally, we analysed the biocompatibility of the systems using fibroblast cells and found that the cells tended to spread more effectively when the crosslinking species was incorporated. Our results emphasise the need for thorough characterisation at multiple length scales to finely control material properties, which is particularly important for developing novel biomaterials.

Shape-tunable two-dimensional assemblies from chromophore-conjugated crystallizable poly(L-lactides) with chain-length-dependent photophysical properties

This work reports temperature-dependent shape-changeable two-dimensional (2D) nanostructures by crystallization-driven self-assembly (CDSA) from a chromophore-conjugated poly(L-lactide) (PLLA) homopolymer (PTZ-P1) that contained a polar dye, phenothiazine (PTZ), at the chain-end of the crystallizable PLLA. The CDSA of PTZ-P1 in a polar solvent, isopropanol (iPrOH), by an uncontrolled heating-cooling process, majorly generates lozenge-shaped 2D platelets via chain-folding-mediated crystallization of the PLLA core, leading to the display of the phenothiazines on the 2D surface that confers colloidal stability and orange-emitting luminescent properties to the crystal lamellae. Isothermal crystallization at 60 °C causes a morphological change in PTZ-P1 platelets from lozenge to truncated-lozenge to perfect hexagon under different annealing times, while no shape change was noticed in the structurally similar PTZ-P2 polymer with a longer PLLA chain under similar conditions. This study unveils the complex link between the 2D platelet morphologies and degree of polymerization (DP) of PLLA and the corona-forming dye character. Further, the co-assembly potential of PTZ-P1 with hydrophobic pyrene-terminated PLLAs of varying chain lengths (PY-P1, PY-P2, and PY-P3) was examined, as these two dyes could form a Förster Resonance Energy Transfer (FRET) pair on the 2D surface. The impact of the length of the crystallizable PLLA on the photophysical properties of the surface-occupied chromophores revealed crucial insights into interchromophoric interactions on the platelet surface. A reduction in the propensity for π-stacking with increasing chain-folding in longer PLLAs is manifested in the chain-length-dependent FRET efficiencies and excimer emission lifetimes within the resultant monolayered 2D assemblies. The unconventional "butterfly-shaped" molecular architecture of the tested phenothiazine, combined with its varied functional features and polar character, adds a distinctive dimension to the underdeveloped field of CDSA of chromophore-conjugated poly(L-lactides), opening future avenues for the development of advanced nanostructured biodegradable 2D materials with programmable morphology and optical functions.

Metallosupramolecular Multiblock Copolymers of Lanthanide Complexes by Seeded Living Polymerization

Supramolecular block copolymers, derived via seeded living polymerization, are increasingly recognized for their rich structural and functional diversity, marking them as cutting-edge materials. The use of metal complexes in supramolecular block copolymerization not only offers a broad range of block copolymers through the structural similarity in the coordination geometry of the central metal ion but also controls spectroscopic properties, such as emission wavelength, emission strength, and fluorescence lifetime. However, the exploration of metallosupramolecular multiblock copolymerization based on metal complexes remains quite limited. In this work, we present a pioneering synthesis of metallosupramolecular multiblock copolymers utilizing Eu3+ and Tb3+ complexes as building blocks. This is achieved through the strategic manipulation of nonequilibrium self-assemblies via a living supramolecular polymerization approach. Our comprehensive exploration of both thermodynamically and kinetically regulated metallosupramolecular polymerizations, centered around Eu3+ and Tb3+ complexes with bisterpyridine-modified ligands containing R-alanine units and a long alkyl group, has highlighted intriguing behaviors. The monomeric [R-L1Eu(NO3)3] complex generates a spherical structure as the kinetic product. In contrast, the monomeric [R-L1Eu2(NO3)6] complex generates fiber aggregates as a thermodynamic product through intermolecular interactions such as π-π stacking, hydrophobic interaction, and H-bonds. Utilizing the Eu3+ complex, we successfully conducted seed-induced living polymerization of the monomeric building unit under kinetically regulated conditions. This yielded a metallosupramolecular polymer of precisely controlled length with minimal polydispersity. Moreover, by copolymerizing the kinetically confined Tb3+ complex state ("A" species) with a seed derived from the Eu3+ complex ("B" species), we were able to fabricate metallosupramolecular tri- and pentablock copolymers with A-B-A, and B-A-B-A-B types, respectively, through a seed-end chain-growth mechanism.

Increasing Dimensionality in Self-Assembly: Toward Two-Dimensional Supramolecular Polymers

Different approaches to achieve 2D supramolecular polymers, as an alternative to the covalent bottom-up approaches reported for the preparation of 2D materials, are reviewed. The significance of the operation of weak non-covalent forces to induce a lateral growth of a number of self-assembling units is collected. The examples of both thermodynamically and kinetically controlled formation of 2D supramolecular polymers showed in this review demonstrate the utility of this strategy to achieve new 2D materials with biased morphologies (nanosheets, scrolls, porous surfaces) and showing elegant applications like chiral recognition, enantioselective uptake or asymmetric organic transformations. Furthermore, elaborated techniques like seeded or living supramolecular polymerizations have been demonstrated to give rise to complex 2D nanostructures.

Enzymatic Reaction-Coupled, Cooperative Supramolecular Polymerization

Nature employs sophisticated mechanisms to precisely regulate self-assembly and functions within biological systems, exemplified by the formation of cytoskeletal filaments. Various enzymatic reactions and auxiliary proteins couple with the self-assembly process, meticulously regulating the length and functions of resulting macromolecular structures. In this context, we present a bioinspired, reaction-coupled approach for the controlled supramolecular polymerization in synthetic systems. To achieve this, we employ an enzymatic reaction that interfaces with the adenosine triphosphate (ATP)-templated supramolecular polymerization of naphthalene diimide monomers (NSG). Notably, the enzymatic production of ATP (template) plays a pivotal role in facilitating reaction-controlled, cooperative growth of the NSG monomers. This growth process, in turn, provides positive feedback to the enzymatic production of ATP, creating an ideal reaction-coupled assembly process. The success of this approach is further evident in the living-growth characteristic observed during seeding experiments, marking this method as the pioneering instance where reaction-coupled self-assembly precisely controls the growth kinetics and structural aspects of supramolecular polymers in a predictive manner, akin to biological systems.

Electronically and geometrically complementary perylenediimides for kinetically controlled supramolecular copolymers

The synthesis of 3,4,9,10-benzo[d,e]isoquinolino[1,8-g,h]quinoline-tetracarboxylic diimide (BQQDI) 1 endowed with peripheral trialkoxybenzamide fragments is reported and its self-assembling features investigated. The peripheral benzamide moieties generate metastable monomeric species that afford a kinetically controlled supramolecular polymerization. The electron-withdrawing character of 1 in comparison with previously reported PDIs 2, together with the similar geometry, makes this dye an optimal candidate to perform seeded supramolecular copolymerization yielding four different supramolecular block copolymers. Whilst heteropolymers poly-1-co-2a, poly-2a-co-1 and poly-1-co-2b present an H-type arrangement of the monomeric units, heteropolymer poly-2b-co-1, prepared by seeding the chiral, metastable monomers of 2b with achiral seeds of 1, produces chiral, J-type aggregates. Interestingly, the monosignated CD signal of pristine poly-2b changes to a bisignated CD signal most probably due to the formation of columnar domains around the seeds of 1 which implies the blocky nature of the supramolecular copolymers formed.

Self-assembled π-conjugated chromophores: preparation of one- and two-dimensional nanostructures and their use in photocatalysis

Photocatalytic systems have attracted research interest as a clean approach to generate energy from abundant sunlight. In this context, developing efficient and robust photocatalytic structures is crucial. Recently, self-assembled organic chromophores have entered the stage as alternatives to both molecular systems and (in)organic semiconductors. Nanostructures made of self-assembled π-conjugated dyes offer, on the one hand, molecular customizability to tune their optoelectronic properties and activities and on the other hand, provide benefits from heterogeneous catalysis that include ease of separation, recyclability and improved photophysical properties. In this contribution, we present recent achievements in constructing supramolecular photocatalytic systems made of chromophores for applications in water splitting, H2O2 evolution, CO2 reduction, or environmental remediation. We discuss strategies that can be used to prepare ordered photocatalytic systems with an emphasis on the effect of packing between the dyes and the resulting photocatalytic activity. We further showcase supramolecular strategies that allow interfacing the organic nanostructures with co-catalysts, molecules, polymers, and (in)organic materials. The principles discussed here are the foundation for the utilization of these self-assembled materials in photocatalysis.

Controlled Supramolecular Polymerization via Bioinspired, Liquid-Liquid Phase Separation of Monomers

Dynamic supramolecular assemblies, driven by noncovalent interactions, pervade the biological realm. In the synthetic domain, their counterparts, supramolecular polymers, endowed with remarkable self-repair and adaptive traits, are often realized through bioinspired designs. Recently, controlled supramolecular polymerization strategies have emerged, drawing inspiration from protein self-assembly. A burgeoning area of research involves mimicking the liquid-liquid phase separation (LLPS) observed in proteins to create coacervate droplets and recognizing their significance in cellular organization and diverse functions. Herein, we introduce a novel perspective on synthetic coacervates, extending beyond their established role in synthetic biology as dynamic, membraneless phases to enable structural control in synthetic supramolecular polymers. Drawing parallels with the cooperative growth of amyloid fibrils through LLPS, we present metastable coacervate droplets as dormant monomer phases for controlled supramolecular polymerization. This is achieved via a π-conjugated monomer design that combines structural characteristics for both coacervation through its terminal ionic groups and one-dimensional growth via a π-conjugated core. This design leads to a unique temporal LLPS, resulting in a metastable coacervate phase, which subsequently undergoes one-dimensional growth via nucleation within the droplets. In-depth spectroscopic and microscopic characterization provides insights into the temporal evolution of disordered and ordered phases. Furthermore, to modulate the kinetics of liquid-to-solid transformation and to achieve precise control over the structural characteristics of the resulting supramolecular polymers, we invoke seeding in the droplets, showcasing living growth characteristics. Our work thus opens up new avenues in the exciting field of supramolecular polymerization, offering general design principles and controlled synthesis of precision self-assembled structures in confined environments.

Strategies for Synthesizing Supramolecular Block Copolymers

Over the past decade, controlled supramolecular polymerization has been extensively studied and gradually shifted to supramolecular block copolymerization. Supramolecular block copolymers (BCPs) are considered the holy grail for developing supramolecular materials with new functionalities due to their fascinating structures and ability to introduce diverse functions. From a thermodynamic view to kinetic aspects, great progress has been made in the synthetic strategies of BCPs in the past few years. This Concept summarizes various strategies to realize supramolecular block copolymerization. The focus is on providing researchers with a methodological basis for achieving heterogeneous nucleation-elongation.

Supramolecular copolymerization of hydrophobic and hydrophilic monomers in liquid crystalline media

In the case of covalent polymers, immiscible polymers can be integrated by covalently linking them together, but such a strategy is not possible in supramolecular polymers. Here we report the supramolecular copolymerization of two porphyrin-based monomers, C10P2H and TEGPCu with side chains bearing cyanobiphenyl (CB) groups at the ends of hydrophobic alkyl or hydrophilic tetraethylene glycol chains, respectively. These monomers undergo self-sorting supramolecular polymerization in highly diluted solutions ([monomer] = 3.4 × 10-9 mol% (2.0 × 10-8 mol L-1)) in nonpolar media due to the incompatibility of the side chains. Surprisingly, these monomers undergo supramolecular copolymerization under high concentration conditions ([monomer] = 7.7 mol%) in the medium of 4-cyano-4'-pentyloxybiphenyl (5OCB) to form a columnar liquid crystalline phase under thermodynamic conditions, where the individual columns are composed of supramolecular block copolymers. The combination of CB ends of both monomers and the 5OCB medium is essential for the two monomers to form an integrated structure in a condensed system without phase separation.

Frustrated π-stacking

The properties of functional materials based on organic π-conjugated systems are governed extensively by intermolecular interactions between π-molecules. To establish clear relationships between supramolecular structures and functional properties, it is essential to attain structurally well-defined π-stacks, particularly in solution, as this enables the collection of valuable spectroscopic data. However, precise control and fine-tuning of π-stacks pose significant challenges due to the weak and bidirectional nature of π-π stacking interactions. This article introduces the concept of "frustrated π-stacking," strategically balancing attractive (π-π interaction) and repulsive (steric hindrance) forces in self-assembly to exert control over the sizes, sequences of π-stacks, and slip-stacked structures. These research efforts contribute to a deeper understanding of the correlation between π-stacks and their properties, thereby providing useful insights for the development of molecular materials with the desired performance.

Therapeutic Supramolecular Polymers: Designs and Applications

The self-assembly of low-molecular-weight building motifs into supramolecular polymers has unlocked a new realm of materials with distinct properties and tremendous potential for advancing medical practices. Leveraging the reversible and dynamic nature of non-covalent interactions, these supramolecular polymers exhibit inherent responsiveness to their microenvironment, physiological cues, and biomolecular signals, making them uniquely suited for diverse biomedical applications. In this review, we intend to explore the principles of design, synthesis methodologies, and strategic developments that underlie the creation of supramolecular polymers as carriers for therapeutics, contributing to the treatment and prevention of a spectrum of human diseases. We delve into the principles underlying monomer design, emphasizing the pivotal role of non-covalent interactions, directionality, and reversibility. Moreover, we explore the intricate balance between thermodynamics and kinetics in supramolecular polymerization, illuminating strategies for achieving controlled sizes and distributions. Categorically, we examine their exciting biomedical applications: individual polymers as discrete carriers for therapeutics, delving into their interactions with cells, and in vivo dynamics; and supramolecular polymeric hydrogels as injectable depots, with a focus on their roles in cancer immunotherapy, sustained drug release, and regenerative medicine. As the field continues to burgeon, harnessing the unique attributes of therapeutic supramolecular polymers holds the promise of transformative impacts across the biomedical landscape.

Living Self-Assembly of Metastable and Stable Two-Dimensional Platelets from a Single Small Molecule

This study reports the design of a donor-acceptor (D-A) molecule with two fluorene units on each side of a benzothiadiazole moiety, which allows multiple intermolecular interactions to compete with one another so as to induce the evolution of the metastable 2D platelets to the stable 2D platelets during the self-assembly of the D-A molecule. Importantly, the living seeded self-assembly of metastable and stable 2D structures with precisely controlled sizes can be conveniently achieved using an appropriate supersaturated level of a solution of the D-A molecule as the seeded growth medium that can temporarily hold the almost-proceeding spontaneous nucleation from competing with the seeded growth. The stable 2D platelets with smaller area sizes exhibit higher sensitivity to gaseous dimethyl sulfide, illustrating that the novel living self-assembly method provides more available functional structures with controlled sizes for practical applications. The key finding of this study is that the new living methodology is separated into two independent processes: the elaborate molecular design for various crystalline structures as seeds and the application of a supersaturated solution with appropriate levels as the growth medium to grow the uniform structures with controlled sizes; this would make convenient and possible the living seeded self-assembly of rich 1D, 2D, and 3D architectures.

Three-Component Multiblock 1D Supramolecular Copolymers of Ir(III) Complexes with Controllable Sequences

Multicomponent supramolecular block copolymers (BCPs) have attracted much attention due to their potential functionalities, but examples of three-component supramolecular BCPs are rare. Herein, we report the synthesis of three-component multiblock 1D supramolecular copolymers of Ir(III) complexes 1-3 by a sequential seeded supramolecular polymerization approach. Precise control over the kinetically trapped species via the pathway complexity of the monomers is the key to the successful synthesis of BCPs with up to 9 blocks. Furthermore, 5-block BCPs with different sequences could be synthesized by changing the addition order of the kinetic species during a sequentially seeded process. The corresponding heterogeneous nucleation-elongation process has been confirmed by the UV/Vis absorption spectra, and each segment of the multiblock copolymers could be characterized by both TEM and SEM. Interestingly, the energy transfer leads to weakened emission of 1-terminated and enhanced emission of 3-terminated BCPs. This study will be an important step in advancing the synthesis and properties of three-component BCPs.

Ferrocene: an exotic building block for supramolecular assemblies

Ferrocene (Fc), a classical organometallic complex, has found potential applications in ligand design, catalysis, and analytical, biological, medicinal and materials chemistry. In recent years, the use of Fc as a building block in supramolecular chemistry has emerged. The molecular shape, size, and hydrophobicity of Fc make it an ideal guest for a variety of macrocyclic host molecules to form stable host-guest complexes. The vertical distance (3.3 Å) between two cyclopentadienyl rings and molecular "ball bearing" property in Fc support the formation of intramolecular π-π stacking, H-bonding and metallophilic interactions between two appropriate substituents in 1,n'-disubstituted ferrocenes. Along with these molecular features, the rigidity along with rotational flexibility, redox reversibility and oxidation-triggered tunable hydrophobicity of Fc have led to its use as an exotic building block for the development of a wide range of supramolecular assemblies such as smart molecular receptors, intricate metal-organic assemblies, supramolecular polymers, and gels including out-of-equilibrium assemblies and metal nanoparticle assemblies. This review highlights the concepts behind the design and development of these assemblies, where the Fc unit has a direct and defined role in their formation and function. The use of Fc in supramolecular assembly is still a relatively young field and set to be the subject of increasing research interest towards the development of fascinating supramolecular structures with tailored properties and programmable functions towards applications in materials and biological sciences.

Cascade Energy Transfer and White-Light Emission in Chirality-Controlled Crystallization-Driven Two-Dimensional Co-assemblies from Donor and Acceptor Dye-Conjugated Polylactides

Achieving predictable and programmable two-dimensional (2D) structures with specific functions from exclusively organic soft materials remains a scientific challenge. This article unravels stereocomplex crystallization-driven self-assembly as a facile method for producing thermally robust discrete 2D-platelets of diamond shape from biodegradable semicrystalline polylactide (PLA) scaffolds. The method involves co-assembling two PLA stereoisomers, namely, PY-PDLA and NMI-PLLA, which form stereocomplex (SC)-crystals in isopropanol. By conjugating a well-known Förster resonance energy transfer (FRET) donor and acceptor dye, namely, pyrene (PY) and naphthalene monoimide (NMI), respectively, to the chain termini of these two interacting stereoisomers, a thermally robust FRET process can be stimulated from the 2D array of the co-assembled dyes on the thermally resilient SC-PLA crystal surfaces. Uniquely, by decorating the surface of the SC-PLA crystals with an externally immobilized guest dye, Rhodamine-B, similar diamond-shaped structures could be produced that exhibit pure white-light emission through a surface-induced two-step cascade energy transfer process. The FRET response in these systems displays remarkable dependence on the intrinsic crystalline packing, which could be modulated by the chirality of the co-assembling PLA chains. This is supported by comparing the properties of similar 2D platelets generated from two homochiral PLLAs (PY-PLLA and NMI-PLLA) labeled with the same FRET pair.

Thermo-/Mechano-Chromic Chiral Coordination Dimer: Formation of Switchable and Metastable Discrete Structure through Chiral Self-Sorting

Although strong chiral self-sorting often emerges in extended covalent or supramolecular polymers, the phenomenon is generally weak in discrete assemblies (e.g., dimers and oligomers) of small molecules due to the lack of a cooperative growth mechanism. Consequently, chiral self-sorting has been overlooked in the design of switchable and metastable discrete supramolecular structures. Here, we report a butyl-benzo[h]quinoline-based iridium(III) complex (Bu-Ir) with helical chirality at its metal center, which forms preferentially a homochiral dimer and exhibits thermo-/mechano-chromism based on a monomer-dimer transformation. While a five-coordinate monomer is formed in a racemic or an enantiopure Bu-Ir solution at 25 °C, a six-coordinate homochiral dimer complex is formed almost exclusively at low temperatures, with a higher degree of dimerization in enantiopure Bu-Ir solution. Estimation of apparent dimerization binding constants (K) and thermodynamic parameters (ΔH and ΔS) based on variable temperature ultraviolet-visible (UV-vis) and 1H NMR spectra reveals a strong preference for homochiral dimerization (largest known value for the coordination complex, Khomo/Khetero > 50). Notably, crystals of the homochiral dimer are metastable, undergoing a distinct color change upon grinding (from yellow to red) due to mechanical cleavage of coordination bonds (i.e., a dimer to monomer transformation). A comparison with control compounds having different substituents (proton, methyl, isopropyl, and phenyl groups) reveals that Bu-Ir dimerization involves both strong homochiral self-sorting preference and connected thermo-/mechano-chromic behavior, which is based on matched propeller-shaped chirality and subtle steric repulsion between alkyl substituents that render the homochiral dimer switchable and metastable. These findings provide substantial insights into the emergence of dynamic functionality based on the rational design of discrete chiral assemblies.

A Coformer Approach for Supramolecular Polymerization at High Concentrations

Insolubility of functional molecules caused by polymorphism sometimes poses limitations for their solution-based processing. Such a situation can also occur in the preparation processes of supramolecular polymers formed in a solution. An effective strategy to address this issue is to prepare amorphous solid states by introducing a "coformer" molecule capable of inhibiting the formation of an insoluble polymorph through co-aggregation. Herein, inspired by the coformer approach, we demonstrated a solubility enhancement of a barbiturate π-conjugated compound that can supramolecularly polymerize through six-membered hydrogen-bonded rosettes. Our newly synthesized supramolecular coformer molecule features a sterically demanding methyl group in the π-conjugated unit of the parent molecule. Although the parent molecule exhibits low solubility in nonpolar solvents due to the formation of a crystalline polymorph comprising a tape-like hydrogen-bonded array prior to the supramolecular polymerization, mixing with the coformer compound enhanced the solubility by inhibiting mesoscopic organization of the tapes. The two monomers were then co-polymerized into desired helicoidal supramolecular polymers through the formation of heteromeric rosettes.

Impact of subtle intermolecular interactions on the structure and dynamics of multicomponent supramolecular polymers

Multicomponent supramolecular polymers offer versatile dynamic and functional properties; however, the influence of the monomer chemical structures on their structure-dynamics-function relationship remains unclear. In this study, we investigated the subtle variations in monomer interactions using one monomer and its two dopant derivatives, with functionalization away from the self-assembling core. We systematically investigated their multicomponent supramolecular polymers using a combination of spectroscopy and super-resolution microscopy. Our results highlight the significant impact of the supplementary intermolecular interactions, resulting from the functional motifs located away from the core and present in small quantities, on the microstructure and dynamics. Thus, a comprehensive approach, combining spectroscopy, microscopy, and well-designed experiments, is essential for assessing multicomponent supramolecular polymers. These findings have implications for the rational design of functional multicomponent supramolecular materials.

Chiral supramolecular polymers

As an active branch within the field of supramolecular polymers, chiral supramolecular polymers (SPs) are an excellent benchmark to generate helical structures that can clarify the origin of homochirality in Nature or help determine new exciting functionalities of organic materials. Herein, we highlight the most utilized strategies to build up chiral SPs by using chiral monomeric units or external stimuli. Selected examples of transfer of asymmetry, in which the point or axial chirality contained by the monomeric units is efficiently transferred to the supramolecular scaffold yielding enantioenriched helical structures, will be presented. The importance of the thermodynamics and kinetics associated with those processes is stressed, especially the influence that parameters such as the helix reversal and mismatch penalties exert on the achievement of amplification of asymmetry in co-assembled systems will also be considered. Remarkable examples of breaking symmetry, in which chiral supramolecular polymers can be attained from achiral self-assembling units by applying external stimuli like stirring, solvent or light, are highlighted. Finally, the specific and promising applications of chiral supramolecular polymers are presented with recent relevant examples.

Controlling the Morphological Features, Aspect Ratio and Emission Patterns of Supramolecular Copolymers by Restricted Dimensional Growth

One of the bottlenecks associated with supramolecular polymerization of functional π-systems is the spontaneous assembly of monomers leading to one- or two-dimensional (1D or 2D) polymers without control over chain length and optical properties. In the case of supramolecular copolymerization of monomers that are structurally too diverse, preferential self-sorting occurs unless they are closely interacting donor-acceptor pairs. Herein, it is established that the spontaneous 1D polymerization of a phenyleneethynylene (PE) derivative and the 2D polymerization of a Bodipy derivative (BODIPY) can be controlled by copolymerizing them in different ratios, leading to unusual spindle-shaped structures with controlled aspect ratio, as evident by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and confocal laser scanning microscopy (CLSM) studies. For example, when the content of BODIPY is 50 % in the BODIPY-PE mixture, the 1D polymerization of PE is significantly restricted to form elongated spindle-like structures having an aspect ratio of 4-6. The addition of 75 % of BODIPY to PE resulted in circular spindles having an aspect ratio of 1-2.5, thereby completely restricting the 1D polymerization of PE monomers. Moreover, the resultant supramolecular copolymers exhibited morphology and aspect ratio dependent emission features as observed by the time-resolved emission studies.

Supramolecular alternating copolymers with highly efficient fluorescence resonance energy transfer

This article reports alternating supramolecular copolymerization of two naphthalene-diimide (NDI)-derived building blocks (NDI-1 and NDI-2) under thermodynamic control. Both monomers contain a central NDI chromophore, attached to a hydrocarbon-chain and a carboxylic-acid group. The NDI core in NDI-2 is symmetrically substituted with two butane-thiol groups, which makes it distinct from NDI-1. In decane, a 1 : 1 mixture of NDI-1 and NDI-2 shows spontaneous gelation and a typical fibrillar network, unlike the behavior of either of the components individually. The solvent-dependent UV/vis spectrum of the mixed sample in decane shows bathochromically shifted sharp absorption bands and a sharp emission band (holds a mirror-image relationship) with a significantly small Stokes shift compared to those in CHCl3, indicating J-aggregation. In contrast, the aggregated spectra of the individual monomers show broad structureless features, suggesting ill-defined aggregates. Cooling curves derived from the temperature-dependent UV/vis spectroscopy studies revealed early nucleation and a signature of well-defined cooperative polymerization for the mixed sample, unlike either of the individual components. Molecular dynamics simulations predicted the greatest dimer formation tendency for the NDI-1 + NDI-2 (1 : 1), followed by pure NDI-1 and NDI-2. Theoretical studies further revealed a partial positive charge in the NDI ring of NDI-1 when compared to NDI-2, promoting the alternating stacking propensity, which is also favored by the steric factor as NDI-2 is core-substituted with alkyl thiols. Such theoretical predictions fully corroborate with the experimental results showing 1 : 1 stoichiometry (from Job's plot) of the two monomers, indicating alternate stacking sequences in the H-bonded (syn-syn catemer type) supramolecular copolymer. Such alternating supramolecular copolymers showed highly efficient (>93%) fluorescence resonance energy transfer (FRET).

Supramolecular Block Copolymers from Tricarboxamides. Biasing Co-assembly by the Incorporation of Pyridine Rings

The synthesis of a series of triangular-shaped tricarboxamides endowed with three picoline or nicotine units (compounds 2 and 3, respectively) or just one nicotine unit (compound 4) is reported, and their self-assembling features investigated. The pyridine rings make compounds 2-4 electronically complementary with our previously reported oligo(phenylene ethynylene)tricarboxamides (OPE-TA) 1 to form supramolecular copolymers. C3 -symmetric tricarboxamide 2 forms highly stable intramolecular five-membered pseudocycles that impede its supramolecular polymerization into poly-2 and the co-assembly with 1 to yield copolymer poly-1-co-2. On the other hand, C3 -symmetric tricarboxamide 3 readily forms poly-3 with great stability but unable to form helical supramolecular polymers despite the presence of the peripheral chiral side chains. The copolymer poly-1-co-3 can only be obtained by a previous complete disassembly of the constitutive homopolymers in CHCl3 . Helical poly-1-co-3 arises in a process involving the transfer of the helicity from racemic poly-1 to poly-3, and the amplification of asymmetry from chiral poly-3 to poly-1. Importantly, C2v -symmetric 4, endowed with only one nicotinamide moiety and three chiral side chains, self-assembles into a P-type helical supramolecular polymer (poly-4) in a thermodynamically controlled cooperative process. The combination of poly-1 and poly-4 generates chiral supramolecular copolymer poly-1-co-4, whose blocky microstructure has been investigated by applying the previously reported supramolecular copolymerization model.

Multistep, site-selective noncovalent synthesis of two-dimensional block supramolecular polymers

Although the principles of noncovalent bonding are well understood and form the basis for the syntheses of many intricate supramolecular structures, supramolecular noncovalent synthesis cannot yet achieve the levels of precision and complexity that are attainable in organic and/or macromolecular covalent synthesis. Here we show the stepwise synthesis of block supramolecular polymers from metal-porphyrin derivatives (in which the metal centre is Zn, Cu or Ni) functionalized with fluorinated alkyl chains. These monomers first undergo a one-dimensional supramolecular polymerization and cyclization process to form a toroidal structure. Subsequently, successive secondary nucleation, elongation and cyclization steps result in two-dimensional assemblies with concentric toroidal morphologies. The site selectivity endowed by the fluorinated chains, reminiscent of regioselectivity in covalent synthesis, enables the precise control of the compositions and sequences of the supramolecular structures, as demonstrated by the synthesis of several triblock supramolecular terpolymers.

Dynamic Control over Hierarchically Dendritic Architectures of Simple Heterogenous Monomers by Living Supramolecular Assembly

The successful preparation of supramolecular block copolymers (SBCPs) by living supramolecular assembly technology requires two kinetic systems in which both the seed (nucleus) and heterogenous monomer providers are in non-equilibrium. However, employing simple monomers to construct the SBCPs via this technology is almost impossible because the low spontaneous nucleation barrier of simple molecules prevents the formation of kinetic states. Here, with the help of confinement from layered double hydroxide (LDH), various simple monomers successfully form living supramolecular co-assemblies (LSCA). LDH overcomes a considerable energy barrier to obtain living seeds to support the growth of the inactivated second monomer. The ordered LDH topology is sequentially mapped to the seed, second monomer, and binding sites. Thus, the multidirectional binding sites are endowed with the ability to branch, making the branch length of dendritic LSCA reach its maximum value of 3.5 cm so far. The strategy of universality will guide exploration into the development of multi-function and multi-topology advanced supramolecular co-assemblies.

Multi-chiral materials comprising metallosupramolecular and covalent helical polymers containing five axial motifs within a helix

Supramolecular and covalent polymers share multiple structural effects such as communication mechanisms among monomer repeating units, which are related to their axial helical structure. Herein, a unique multi-helical material combining information from both metallosupramolecular and covalent helical polymers is presented. In this system, the helical structure described by the poly(acetylene) (PA) backbone (cis-cisoidal, cis-transoidal) guides the pendant groups in a fashion where a tilting degree emerges between a pendant and the adjacent ones. As a result, a multi-chiral material is formed comprising four or five axial motifs when the polyene skeleton adopts either a cis-transoidal or cis-cisoidal configuration: the two coaxial helices-internal and external-and the two or three chiral axial motifs described by the bispyridyldichlorido Pt^II complex array. These results show that complex multi-chiral materials can be obtained by polymerizing appropriate monomers that combine both point chirality and the ability to generate chiral supramolecular assemblies.

Hierarchical Composite Self-Sorted Supramolecular Gel Noodles

Multicomponent supramolecular systems can be used to achieve different properties and new behaviors compared to their corresponding single component systems. Here, a two-component system is used, showing that a non-gelling component modifies the assembly of the gelling component, allowing access to co-assembled structures that cannot be formed from the gelling component alone. The systems are characterized across multiple length scales, from the molecular level by NMR and CD spectroscopy to the microstructure level by SANS and finally to the material level using nanoindentation and rheology. By exploiting the enhanced mechanical properties achieved through addition of the second component, multicomponent noodles are formed with superior mechanical properties to those formed by the single-component system. Furthermore, the non-gelling component can be triggered to crystallize within the multicomponent noodles, allowing the preparation of new types of hierarchical composite noodles.

Pathway Complexity in Supramolecular Copolymerization and Blocky Star Copolymers by a Hetero-Seeding Effect

This study unravels the intricate kinetic and thermodynamic pathways involved in the supramolecular copolymerization of the two chiral dipolar naphthalene monoimide (NMI) building blocks (O-NMI and S-NMI), differing merely by a single heteroatom (oxygen vs sulfur). O-NMI exhibits distinct supramolecular polymerization features as compared to S-NMI in terms of its pathway complexity, hierarchical organization, and chiroptical properties. Two distinct self-assembly pathways in O-NMI occur due to the interplay between the competing dipolar interactions among the NMI chromophores and amide-amide hydrogen (H)-bonding that engenders distinct nanotapes and helical fibers, from its antiparallel and parallel stacking modes, respectively. In contrast, the propensity of S-NMI to form only a stable spherical assembly is ascribed to its much stronger amide-amide H-bonding, which outperforms other competing interactions. Under the thermodynamic route, an equimolar mixture of the two monomers generates a temporally controlled chiral statistical supramolecular copolymer that autocatalytically evolves from an initially formed metastable spherical heterostructure. In contrast, the sequence-controlled addition of the two monomers leads to the kinetically driven hetero-seeded block copolymerization. The ability to trap O-NMI in a metastable state allows its secondary nucleation from the surface of the thermodynamically stable S-NMI spherical "seed", which leads to the core-multiarmed "star" copolymer with reversibly and temporally controllable length of the growing O-NMI "arms" from the S-NMI "core". Unlike the one-dimensional self-assembly of O-NMI and its random co-assembly with S-NMI, which are both chiral, unprecedentedly, the preferred helical bias of the nucleating O-NMI fibers is completely inhibited by the absence of stereoregularity of the S-NMI "seed" in the "star" topology.

Controlled Self-assembly of Gold(I) Complexes by Multiple Kinetic Aggregation States with Nonlinear Optical and Waveguide Properties

Introduction of multiple kinetic aggregation states (Aggs) into the self-assembly pathway could bring complexity and flexibility to the self-assemblies, which is difficult to realize due to the delicate equilibria established among different Aggs bonded by weak noncovalent interactions. Here, we describe a series of chiral and achiral d¹⁰ Au^I bis(N-heterocyclic carbene, NHC) complexes, and the achiral complex could undergo self-assembly with multiple kinetic Aggs. Generation of multiple kinetic Aggs was realized by applying chiral or achiral seeds exhibiting large differences in elongation temperatures for their respective cooperative self-assembly processes. We further showed that the chiral Au^I self-assemblies having non-centrosymmetric packing forms exhibit nonlinear optical response of second harmonic generation (SHG), while the SHG signal is absent in the achiral analogue. The crystalline achiral Au^I self-assemblies could function as optical waveguides with strong emission polarization.

Bioinspired crowding directs supramolecular polymerisation

Crowding effects are crucial to maintaining functionality in biological systems, but little is known about their role in analogous artificial counterparts. Within the growing field of supramolecular polymer science, crowding effects have hitherto remained underappreciated. Herein, we show that crowding effects exhibit strong and distinct control over the kinetics, accessible pathways and final outcomes of supramolecular polymerisation processes. In the presence of a pre-formed supramolecular polymer as crowding agent, a model supramolecular polymer dramatically changes its self-assembly behaviour and undergoes a morphological transformation from bundled fibres into flower-like hierarchical assemblies, despite no co-assembly taking place. Notably, this new pathway can only be accessed in crowded environments and when the crowding agent exhibits a one-dimensional morphology. These results allow accessing diverse morphologies and properties in supramolecular polymers and pave the way towards a better understanding of high-precision self-assembly in nature.

Optical Signal Modulation in Photonic Waveguiding Heteroarchitectures with Continuously Variable Visible-To-Near-Infrared Emission Color

Photonic circuit systems based on optical waveguiding heteroarchitectures have attracted considerable interest owing to their potential to overcome the speed limitation in electronic circuits by modulating the optical signal at the micro- or nanoscale. However, controlling the parameters, including the wavelength and polarization of the light outcoupling, as well as the sequence among different building blocks, remains a key issue. Herein, supramolecular heteroarchitectures made by phosphorescent organometallic complexes of Pt, Pd, Cu, and Au are applied as photonic logic gates that show continuously variable emission colors from 475 to 810 nm, low waveguide losses down to 0.0077 dB µm^-1 , and remarkable excitation-light polarization-dependent photoluminescence with anisotropy ratios up to 0.68. The sequences among Pt, Pd, Au, and Cu building blocks in the heteroarchitectures are controlled by living supramolecular polymerization or crystallization-driven self-assembly synthetic approaches. The results indicate the prospects for using organometallic complexes and supramolecular synthetic approaches to prepare photonic circuit systems with tunable emission color and controllable sequences among different blocks that achieve modulation of the optical signal in the visible-to-near-infrared spectral region.

Kinetically Programming Copolymerization-like Coassembly of Multicomponent Nanoparticles with DNA

Programmable coassembly of multicomponent nanoparticles (NPs) into heterostructures has the capability to build upon nanostructured metamaterials with enhanced complexity and diversity. However, a general understanding of how to manipulate the sequence-defined heterostructures using straightforward concepts and quantitatively predict the coassembly process remains unreached. Drawing inspiration from the synthetic concepts of molecular block copolymers is extremely beneficial to achieve controllable coassembly of NPs and access mesoscale structuring mechanisms. We herein report a general paradigm of kinetic pathway guidance for the controllable coassembly of bivalent DNA-functionalized NPs into regular block-copolymer-like heterostructures via the stepwise polymerization strategy. By quantifying the coassembly kinetics and structural statistics, it is demonstrated that the coassembly of multicomponent NPs, through directing the specific pathways of prepolymer intermediates, follows the step-growth copolymerization mechanism. Meanwhile, a quantitative model is developed to predict the growth kinetics and outcomes of heterostructures, all controlled by the designed elements of the coassembly system. Furthermore, the stepwise polymerization strategy can be generalized to build upon a great variety of regular nanopolymers with complex architectures, such as multiblock terpolymers and ladder copolymers. Our theoretical and simulation results provide fundamental insights on quantitative predictions of the coassembly kinetics and coassembled outcomes, which can aid in realizing a diverse set of supramolecular DNA materials by the rational design of kinetic pathways.

Time-Resolved Atomistic Imaging and Statistical Analysis of Daptomycin Oligomers with and without Calcium Ions

Daptomycin (DP) is effective against multiple drug-resistant Gram-positive pathogens because of its distinct mechanism of action. An accepted mechanism includes Ca²⁺-triggered aggregation of the DP molecule to form oligomers. DP and its oligomers have so far defied structural analysis at a molecular level. We studied the ability of DP molecule to aggregate by itself in water, the effects of Ca²⁺ ions to promote the aggregation, and the connectivity of the DP molecules in the oligomers by the combined use of dynamic light scattering in water and atomic-resolution cinematographic imaging of DP molecules captured on a carbon nanotube on which the DP molecule is installed as a fishhook. We found that the DP molecule aggregates weakly into dimers, trimers, and tetramers in water, and strongly in the presence of calcium ions, and that the tetramer is the largest oligomer in homogeneous aqueous solution. The dimer remains as the major species, and we propose a face-to-face stacked structure based on dynamic imaging using millisecond and angstrom resolution transmission electron microscopy. The tetramer in its cyclic form is the largest oligomer observed, while the trimer forms in its linear form. The study has shown that the DP molecule has an intrinsic property of forming tetramers in water, which is enhanced by the presence of calcium ions. Such experimental structural information will serve as a platform for future drug design. The data also illustrate the utility of cinematographic recording for the study of self-organization processes.

Harmonizing Topological Features of Self-Assembled Fibers by Rosette-Mediated Random Supramolecular Copolymerization and Self-Sorting of Monomers by Photo-Cross-Linking

Random copolymerization is an effective approach to synthesize the desired polymers by harmonizing distinct properties of different monomers. For supramolecular polymers in which monomer binding is inherently dynamic, it is difficult to achieve random copolymerization of monomers with distinct molecular structures and properties due to an enthalpic advantage upon self-recognition (self-sorting). Herein, we demonstrate an example of thermodynamically controlled random supramolecular copolymerization of two monomers functionalized with barbituric acid via the formation of six-membered hydrogen-bonded rosette intermediates to exhibit structural harmonization of the two main-chain motifs, i.e., intrinsically curved and linear motifs. One monomer based on naphthalene chromophore exclusively forms toroidal fibers, whereas another one bearing additional photoreactive diacetylene moiety affords linearly elongated fibers. Supramolecular copolymerization of the two monomers is achieved by cooling hot monomer mixtures in a nonpolar solvent, which results in the formation of thermodynamically stable spirally folded yet elongated fibers. Atomic force microscopic observations and theoretical simulations of the experimental data obtained by absorption spectroscopy reveal the homopolymerization of the diacetylene-functionalized monomer in the high-temperature region, followed by the incorporation of the naphthalene monomer in the medium-temperature region to form supramolecular copolymers with random monomer sequence. Finally, we demonstrate that the random copolymerization process can be switched to a narcissistically self-sorting one by deactivating monomer exchange through the photo-cross-linking of the diacetylene-functionalized monomers.

Supramolecular copolymerization through self-correction of non-polymerizable transient intermediates

Kinetic control over structures and functions of complex assembly systems has aroused widespread interest. Understanding the complex pathway and transient intermediates is helpful to decipher how multiple components evolve into complex assemblies. However, for supramolecular polymerizations, thorough and quantitative kinetic analysis is often overlooked. Challenges remain in collecting the information of structure and content of transient intermediates in situ with high temporal and spatial resolution. Here, the unsolved evolution mechanism of a classical self-sorting supramolecular copolymerization system was addressed by employing multidimensional NMR techniques coupled with a microfluidic technique. Unexpected complex pathways were revealed and quantitatively analyzed. A counterintuitive pathway involving polymerization through the 'error-correction' of non-polymerizable transient intermediates was identified. Moreover, a 'non-classical' step-growth polymerization process controlled by the self-sorting mechanism was unraveled based on the kinetic study. Realizing the existence of transient intermediates during self-sorting can encourage the exploitation of this strategy to construct kinetic steady state assembly systems. Moreover, the strategy of coupling a microfluidic technique with various characterization techniques can provide a kinetic analysis toolkit for versatile assembly systems. The combined approach of coupling thermodynamic and kinetic analyses is indispensable for understanding the assembly mechanisms, the rules of emergence, and the engineering of complex assembly systems.

Chirality-Controlled Supramolecular Donor-Acceptor Copolymerization with Distinct Energy Transfer Efficiency

Chirality delivers substantial value to the field of supramolecular polymers, not only serving as a probe to monitor the dynamic assembly process but providing access to chiroptical materials. The current study demonstrates that, for supramolecular donor-acceptor copolymers, their comonomer organization modes can be greatly influenced by stereocommunication at the molecular level. The enantiopure N-[(1R or 1S)-phenylethyl]benzamides are incorporated into two structurally similar comonomers, locating between the π-aromatic diethynylacene core and the alkyl chain peripheries. Parallel arrangement of the stereogenic methyl units brings steric hindrance between the homochiral comonomers, which is relieved for the heterochiral comonomers due to the adoption of staggered arrangement. It consequently steers randomly mixed organization for the homochiral supramolecular copolymers within the nanofibers. In comparison, the heterochiral counterparts form nanoparticles in an alternate donor-acceptor organization manner. The variation of comonomer arrangement modes gives rise to distinct energy transfer efficiency at the supramolecular level. Overall, the elaborate manipulation of stereogenic centers in the comonomer structures exerts significant impacts on the characteristics of supramolecular copolymers, which could be useful for chiral sensing, recognition, and optoelectronic applications.

Chain Assembly Kinetics from Magnetic Colloidal Spheres

Magnetic colloidal chains are a microrobotic system with promising applications due to their versatility, biocompatibility, and ease of manipulation under magnetic fields. Their synthesis involves kinetic pathways that control chain quality, length, and flexibility, a process performed by first aligning superparamagnetic particles under a one-dimensional magnetic field and then chemically linking them using a four-armed maleimide-functionalized poly(ethylene glycol). Here, we systematically vary the concentration of the poly(ethylene glycol) linkers, the reaction temperature, and the magnetic field strength to study their impact on the physical properties of synthesized chains, including the chain length distribution, reaction temperature, and bending modulus. We find that this chain fabrication process resembles step-growth polymerization and can be accurately described by the Flory-Schulz model. Under optimized experimental conditions, we have successfully synthesized long flexible colloidal chains with a bending modulus, which is 4 orders of magnitude smaller than previous studies. Such flexible and long chains can be folded entirely into concentric rings and helices with multiple turns, demonstrating the potential for investigating the actuation, assembly, and folding behaviors of these colloidal polymer analogues.

Catalytic One-Handed Helix Induction and Subsequent Static Memory of Poly(biphenylylacetylene)s Assisted by a Small Amount of Carboxy Groups Introduced at the Pendants

A dynamically racemic helical copolymer composed of an achiral biphenylylacetylene (BPA) bearing methoxymethoxy groups at the 2,2'-positions and 1 mol % of an achiral BPA carrying 2-carboxy-2'-methoxymethoxy groups at the biphenyl pendants was found to fold into an excess one-handed helix with significant amplification of the helicity in the presence of a small amount of optically active amines. The induced macromolecular helicity was retained ("memorized") after removal of the chiral amines. The copolymer had a significant sensitivity for detecting the chirality of chiral amines with a sensitivity more than 10000-fold higher than that of the corresponding homopolymers with no carboxy group, thus showing Cotton effects even in the presence of a 0.01 equiv of an optically active amine. The effects of the substituents at the 4'-position of the biphenyl pendants of the copolymers and the structures of the chiral amines on the macromolecular helicity induction were also investigated.

Supramolecular Polymerization of a Photo-Fluttering Chiral Monomer: A Temporarily Suspendable Chain Growth by Light

Using a photochemically fluttering thiophene-fused cyclooctatetraene derivative (COT) as a nonplanar chiral monomer, we have succeeded in remotely suspending the supramolecular polymerization in a temporal manner by a completely new strategy. The COT monomer with an 8π electron core adopts a saddle shape in the ground state and flutters 5.8 × 10³ times faster upon photoirradiation than in the dark as a result of the stabilized planar conformation by the excited-state aromaticity (Baird aromaticity). Detailed investigation revealed that without photoirradiation the rate constant of the fluttering motion is 1/560 times smaller than that of the chain elongation, indicating that the fluttering of COT does not affect the chain elongation in the dark. In contrast, under photoirradiation (365 nm), the fluttering of COT is at least 11 times more rapid than the chain elongation, thereby suppressing the elongation event. The rapid fluttering of COT to suspend the chain elongation is not accompanied by a decrease in active monomer concentration, leading to depolymerization.

Supramolecular Biomaterials in the Netherlands

Synthetically designed biomaterials strive to recapitulate and mimic the complex environment of natural systems. Using natural materials as a guide, the ability to create high performance biomaterials that control cell fate, and support the next generation of cell and tissue-based therapeutics, is starting to emerge. Supramolecular chemistry takes inspiration from the wealth of non-covalent interactions found in natural materials that are inherently complex, and using the skills of synthetic and polymer chemistry, recreates simple systems to imitate their features. Within the past decade, supramolecular biomaterials have shown utility in tissue engineering and the progress predicts a bright future. On this 30th anniversary of the Netherlands Biomaterials and Tissue Engineering society, we will briefly recount the state of supramolecular biomaterials in the Dutch academic and industrial research and development context. This review will provide the background, recent advances, industrial successes and challenges, as well as future directions of the field, as we see it. Throughout this work, we notice the intricate interplay between simplicity and complexity in creating more advanced solutions. We hope that the interplay and juxtaposition between these two forces can propel the field forward.

Bottom-up supramolecular assembly in two dimensions

The self-assembly of molecules in two dimensions (2D) is gathering attention from all disciplines across the chemical sciences. Attracted by the interesting properties of two-dimensional inorganic analogues, monomers of different chemical natures are being explored for the assembly of dynamic 2D systems. Although many important discoveries have been already achieved, great challenges are still to be addressed in this field. Hierarchical multicomponent assembly, directional non-covalent growth and internal structural control are a just a few of the examples that will be discussed in this perspective about the exciting present and the bright future of two-dimensional supramolecular assemblies.

The self-assembly of molecules in two dimensions (2D) is gathering attention from all disciplines across the chemical sciences. This perspective discusses the main strategies to direct the supramolecular self-assembly of organic monomers in 2D.

Vapor-Phase Living Assembly of π-Conjugated Organic Semiconductors

In contrast to well-studied amphiphilic block copolymers (BCPs) and π-stacked dyes, living assembly of hydrophobic π-conjugated materials has not yet been explored to date. Using a microspacing physical vapor transport (PVT) technique, the prefabricated microrods of organic semiconductors involving 9,10-dicyanoanthracene (DCA, A) or its binary alloy (B) can act as seeds to initiate living homoepitaxial growth from their ends, giving elongated microrods with controlled length. Red-green-red tricolor fluorescent microrod heterostructures with low dispersity are further realized by living heteroepitaxial growth of B microrod blocks on A seed microrod tips. Upon varying the growth sequence of each block, reverse triblock microrods are also accessible. Such a seed-induced living growth is applicable to triblock microrod heterostructures of more binary combinations as well as even more complex penta- and hepta-block heterostructures comprising A and B. By virtue of a convenient vapor-phase growth method, the present work demonstrates the generality of living assembly of π-conjugated materials.