Unravelling denaturation, temperature and cosolvent-driven chiroptical switching in peptide self-assembly with switchable piezoelectric responses

Herein, we explore the intricate pathway complexity, focusing on the dynamic interplay between kinetic and thermodynamic states, during the supramolecular self-assembly of peptides. We uncover a multiresponsive chiroptical switching phenomenon influenced by temperature, denaturation and content of cosolvent in peptide self-assembly through pathway complexity (kinetic vs. thermodynamic state). Particularly noteworthy is the observation of chiroptical switching during the denaturation process, marking an unprecedented phenomenon in the literature. Furthermore, the variation in cosolvent contents produces notable chiroptical switching effects, emphasizing their infrequent incidence. Such chiroptical switching yields switchable piezoresponsive peptide-based nanomaterials, demonstrating the potential for dynamic control over material properties. In essence, our work pioneers the ability to control piezoresponsive behavior by transforming nanostructures from kinetic to thermodynamic states through pathway complexity. This approach provides new insights and opportunities for tailoring material properties in self-assembled systems.

Gold Nanoclusters Whose Photoluminescent Properties are Dynamically Tunable by Modulating the Assembly Pathway Complexity

Modulating the assembly pathway is an indispensable strategy for optimizing the performance of optical materials. However, implementing this strategy is nontrivial for metal nanocluster building blocks, due to the limited functional modification of nanoclusters and complexity of their emission mechanism. In this report, we demonstrate that a gold nanocluster modified by 4,6-diamino-2-pyrimidinethiol (DPT-AuNCs) self-assembles into two distinct aggregation structures in methanol (MeOH)/water mixed solvent, thus exhibiting pathway complexity. Kinetic studies show that DPT-AuNCs firstly assembles into non-luminescent nanofibers (kinetically controlled), which further transforms into strongly luminescent microflowers (thermodynamically controlled). In-depth analysis of the assembly mechanism reveals that the transformation of aggregation structures involves the disassembly of nanofibers and a subsequent nucleation-growth process. Temperature-dependent photoluminescence (PL) spectroscopy and infrared (IR) measurements reveal that inter-cluster hydrogen bonding bridged by solvent molecules and C-H⋅⋅⋅π interaction are the key factors for emission enhancement. The photoluminescent property of DPT-AuNCs can be controlled by varying the cosolvent in water, enabling DPT-AuNCs to distinguish different kind of alcohols, particularly the isomerism n-propanol (NPA) and isopropanol (IPA). Additionally, the addition of seeds effectively regulate the assembly kinetics of DPT-AuNCs. This study advances our understanding of assembly pathways and improves the luminescent performance of nanoclusters (NCs).

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.

Noncovalent Catalyst-cum-Inhibitor Directed Supramolecular Pathway Selection and Asymmetry Amplification by Aggregate Cross-Nucleation

The key to any controlled supramolecular polymerization (CSP) process lies in controlling the nucleation step, which is typically achieved by sequestering monomers in a kinetically trapped state. However, kinetic traps that are shallow cannot prevent spontaneous nucleation, thus limiting the applicability of the CSP in such systems. We use a molecular additive to overcome this limitation by modifying the energy landscape of a competitive self-assembly process and increasing the kinetic stability of an otherwise short-lived trap state. The additive achieves this by simultaneously catalyzing OFF-pathway nucleation and inhibiting ON-pathway aggregation. In the process, it guides the molecular assembly exclusively toward the OFF-pathway aggregate analogue. The mechanisms of OFF-pathway catalysis and ON-pathway inhibition are elucidated. By specifically targeting the nucleation step, it was possible to achieve pathway selection at an extremely low additive-to-monomer ratio of 1:100. The generality of our approach is also demonstrated for other related molecular systems. Finally, removing the additive triggers the cross-nucleation of the ON-pathway aggregate on the surface of a less stable, OFF-pathway aggregate analogue. The resultant supramolecular polymer not only exhibits a more uniform morphology but more importantly, a marked improvement in the structural order that leads to an amplification of chiral asymmetry and a high absorption dissymmetry factor (gAbs) of ∼0.05.

Seed-Induced Living Two-Dimensional (2D) Supramolecular Polymerization in Water: Implications on Protein Adsorption and Enzyme Inhibition

In biological systems, programmable supramolecular frameworks characterized by coordinated directional non-covalent interactions are widespread. However, only a small number of reports involve pure water-based dynamic supramolecular assembly of artificial π-amphiphiles, primarily due to the formidable challenge of counteracting the strong hydrophobic dominance of the π-surface in water, leading to undesired kinetic traps. This study reveals the pathway complexity in hydrogen-bonding-mediated supramolecular polymerization of an amide-functionalized naphthalene monoimide (NMI) building block with a hydrophilic oligo-oxyethylene (OE) wedge. O-NMI-2 initially produced entropically driven, collapsed spherical particles in water (Agg-1); however, over a span of 72 h, these metastable Agg-1 gradually transformed into two-dimensional (2D) nanosheets (Agg-2), favoured by both entropy and enthalpy contributions. The intricate self-assembly pathways in O-NMI-2 enable us to explore seed-induced living supramolecular polymerization (LSP) in water for controlled synthesis of monolayered 2D assemblies. Furthermore, we demonstrated the nonspecific surface adsorption of a model enzyme, serine protease α-Chymotrypsin (α-ChT), and consequently the enzyme activity, which could be regulated by controlling the morphological transformation of O-NMI-2 from Agg-1 to Agg-2. We delve into the thermodynamic aspects of such shape-dependent protein-surface interactions and unravel the impact of seed-induced LSP on temporally controlling the catalytic activity of α-ChT.

Control of Kinetic Pathways toward Supramolecular Chiral Polymorphs for Tunable Circularly Polarized Luminescence

An amphiphilic aza-BODIPY dye (S)-1 bearing two chiral hydrophilic side chains with S-stereogenic centers was synthesized. This dye exhibited kinetic-controlled self-assembly pathways and supramolecular chiral polymorphism properties in MeOH/H2O (9/1, v/v) mixed solvent. The (S)-1 monomers first aggregated into a kinetic controlled, off-pathway species Agg. A, which was spontaneously transformed into an on-pathway metastable aggregate (Agg. B) and subsequently into the thermodynamic Agg. C. The three aggregate polymorphs of dye (S)-1 displayed distinct optical properties and nanomorphologies. In particular, chiral J-aggregation characteristics were observed for both Agg. B and Agg. C, such as Davydov-split absorption bands (Agg. B), extremely sharp and intense J-band with large bathochromic shift (Agg. C), non-diminished fluorescence upon aggregation, as well as strong bisignated Cotton effects. Moreover, the AFM and TEM studies revealed that Agg. A had the morphology of nanoparticle while fibril or rod-like helical nanostructures with left-handedness were observed respectively for Agg. B and Agg. C. By controlling the kinetic transformation process from Agg. B to Agg. C, thin films consisting of Agg. B and Agg. C with different ratios were prepared, which displayed tunable CPL with emission maxima at 788-805 nm and g-factors between -4.2×10-2 and -5.1×10-2.

Two-Dimensional Living Supramolecular Polymerization: Improvement in Edge Roughness of Supramolecular Nanosheets by Using a Dummy Monomer

Supramolecular polymers are formed through nucleation (i. e., initiation) and polymerization processes, and kinetic control over the nucleation process has recently led to the realization of living supramolecular polymerization. Changing the viewpoint, herein we focus on controlling the polymerization process, which we expect to pave the way to further developments in controlled supramolecular polymerization. In our previous study, two-dimensional living supramolecular polymerization was used to produce supramolecular nanosheets with a controlled area; however, these had rough edges. In this study, the growth of the nanosheets was controlled by using a 'dummy' monomer to produce supramolecular nanosheets with smoothed edges.

Supramolecular Polymerization of a Pyrene-Substituted Diamide and Its Ensemble of Kinetically Trapped Configurations

The prevalence of kinetically accessible states in supramolecular polymerization pathways has been exploited to control the growth of the polymer and thereby to obtain niche morphologies. Yet, these pathways themselves are not easily amenable for experimental delineation but could potentially be understood through molecular dynamics (MD) simulations. Herein, we report an extensive investigation of the self-assembly of pyrene-substituted diamide (PDA) monomers in solution, conducted using atomistic MD simulations and advanced sampling methods. We characterize such kinetic and thermodynamic states as well as the transition pathways and free energy barriers between them. PDA forms a dimeric segment with the N- to C-termini vectors of the diamide moieties arranged either in parallel or anti-parallel fashion. This characteristic, combined with the molecule's torsional flexibility and pyrene-solvent interactions, presents an ensemble of molecular configurations contributing to the kinetic state in the polymerization pathway. While this ensemble primarily comprises short oligomers containing a mix of anti-parallel and parallel dimeric segments, the thermodynamic state of the assembly is a right-handed polymer featuring parallel ones only. Our work thus offers an approach by which the landscape of any specific supramolecular polymerization can be deconstructed.

Distinct seed topologies enable comparison of elongation and secondary nucleation pathways in seeded supramolecular polymerization

The influence of seed topologies on seeded supramolecular polymerization was examined using helicoidal and toroidal supramolecular polymer seeds. The addition of these seeds to a supersaturated solution of monomers led to distinct nucleation-growth kinetics, which were attributed to the significant difference between the elongation from helicoid termini and secondary nucleation catalyzed by the toroid surface.

Impact of sample history and solvent effects on pathway control in the supramolecular polymerisation of Au(i)-metallopeptide amphiphiles

We investigate the kinetics of the supramolecular polymerisation of an Au(i)-metallopeptide amphiphile that assembles into exceptionally long and rigid nanofibers. We developed a precise preparation protocol to measure the concentration dependent assembly kinetics which elucidated a nucleation-elongation dominated supramolecular polymerisation process. We show striking differences in the assembly behavior and morphology in aqueous media, even at organic solvent contents as low as 1 vol%, compared to pure buffer.

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.

Thermoreversible Polymorph Transitions in Supramolecular Polymers of Hydrogen-Bonded Squaramides

Hydrogen-bonded squaramide (SQ) supramolecular polymers exhibit uncommon thermoreversible polymorph transitions between particle- and fiber-like nanostructures. SQs 1-3, with different steric bulk, self-assemble in solution into particles (AggI) upon cooling to 298 K, and SQs 1 and 2, with only one dendronic group, show a reversible transformation into fibers (AggII) by further decreasing the temperature to 288 K. Nano-DSC and UV/Vis studies on SQ 1 reveal a concentration-dependent transition temperature and ΔH for the AggI-to-AggII conversion, while the kinetic studies on SQ 2 indicate the on-pathway nature of the polymorph transition. Spectroscopic and theoretical studies reveal that these transitions are triggered by the molecular reorganization of the SQ units changing from slipped to head-to-tail hydrogen bonding patterns. This work unveils the thermodynamic and kinetic aspects of reversible polymorph transitions that are of interest to develop stimuli-responsive systems.

Density-tunable pathway complexity in a minimalistic self-assembly model

An open challenge in self-assembly is learning how to design systems that can be conditionally guided towards different target structures depending on externally-controlled conditions. Using a theoretical and numerical approach, here we discuss a minimalistic self-assembly model that can be steered towards different types of ordered constructs at the equilibrium by solely tuning a facile selection parameter, namely the density of building blocks. Metadynamics and Langevin dynamics simulations allow us to explore the behavior of the system in and out of equilibrium conditions. We show that the density-driven tunability is encoded in the pathway complexity of the system, and specifically in the competition between two different main self-assembly routes. A comprehensive set of simulations provides insight into key factors allowing to make one self-assembling pathway prevailing on the other (or vice versa), determining the selection of the final self-assembled products. We formulate and validate a practical criterion for checking whether a specific molecular design is predisposed for such density-driven tunability of the products, thus offering a new, broader perspective to realize and harness this facile extrinsic control of conditional self-assembly.

Controlling the length of porphyrin supramolecular polymers via coupled equilibria and dilution-induced supramolecular polymerization

Multi-component systems often display convoluted behavior, pathway complexity and coupled equilibria. In recent years, several ways to control complex systems by manipulating the subtle balances of interaction energies between the individual components have been explored and thereby shifting the equilibrium between different aggregate states. Here we show the enantioselective chain-capping and dilution-induced supramolecular polymerization with a Zn²⁺-porphyrin-based supramolecular system when going from long, highly cooperative supramolecular polymers to short, disordered aggregates by adding a monotopic Mn³⁺-porphyrin monomer. When mixing the zinc and manganese centered monomers, the Mn³⁺-porphyrins act as chain-cappers for Zn²⁺-porphyrin supramolecular polymers, effectively hindering growth of the copolymer and reducing the length. Upon dilution, the interaction between chain-capper and monomers weakens as the equilibria shift and long supramolecular polymers form again. This dynamic modulation of aggregate morphology and length is achieved through enantioselectivity in the aggregation pathways and concentration-sensitive equilibria. All-atom and coarse-grained molecular simulations provide further insights into the mixing of the species and their exchange dynamics. Our combined experimental and theoretical approach allows for precise control of molecular self-assembly and chiral discrimination in complex systems.

A novel pathway and seeded polymerizations of aggregates at the thermodynamic state for an amido-anthraquinone compound

The rationally designed monomer 1 underwent supramolecular polymerization to form aggregates via a novel pathway in which the intramolecular H-bond remained intact.

Luminescence property switching in 1D supramolecular polymerization of organic donor–π-acceptor chromophores

The naphthalene monoimide building block endows with amide functionality undergoes supramolecular polymerization in a J type fashion in a particular co-solvent composition. This leads to luminescent property switching as a result of PET effect.

Externally Regulated Specific Molecular Recognition Driven Pathway Selectivity in Supramolecular Polymerization

This article reveals 4-dimethylaminopyridine (DMAP) regulated pathway selectivity in the supramolecular polymerization of a naphthalene-diimide derivative (NDI-1), appended with a carboxylic acid group. In decane, NDI-1 produces ill-defined aggregate (Agg-1) due to different H-bonding motifs of the -COOH group. With one mole equivalent DMAP, the NDI-1/DMAP complex introduces new nucleation condition and exhibits a cooperative supramolecular polymerization producing J-aggregated fibrillar nanostructure (Agg-2). With 10 % DMAP and fast cooling (10 K/min), similar nucleation and open chain H-bonding with the free monomer in an anti-parallel arrangement produces identical J-aggregate (Agg-2a). With 2.5 % DMAP and slow cooling (1 K/min), a distinct nucleation and supramolecular polymerization pathway emerge leading to the thermodynamically controlled Agg-3 with face-to-face stacking and 2D-morphology. Slow cooling with 5-10 % DMAP produces a mixture of Agg-2a and Agg-3. Computational modelling studies provide valuable insights into the internal order and the pathway complexity.

Solute-Solvent Interactions in Modern Physical Organic Chemistry: Supramolecular Polymers as a Muse

Interactions between solvents and solutes are a cornerstone of physical organic chemistry and have been the subject of investigations over the last century. In recent years, a renewed interest in fundamental aspects of solute-solvent interactions has been sparked in the field of supramolecular chemistry in general and that of supramolecular polymers in particular. Although solvent effects in supramolecular chemistry have been recognized for a long time, the unique opportunities that supramolecular polymers offer to gain insight into solute-solvent interactions have become clear relatively recently. The multiple interactions that hold the supramolecular polymeric structure together are similar in strength to those between solute and solvent. The cooperativity found in ordered supramolecular polymers leads to the possibility of amplifying these solute-solvent effects and will shed light on extremely subtle solvation phenomena. As a result, many exciting effects of solute-solvent interactions in modern physical organic chemistry can be studied using supramolecular polymers. Our aim is to put the recent progress into a historical context and provide avenues toward a more comprehensive understanding of solvents in multicomponent supramolecular systems.

Control of self-assembly pathways toward conglomerate and racemic supramolecular polymers

Homo- and heterochiral aggregation during crystallization of organic molecules has significance both for fundamental questions related to the origin of life as well as for the separation of homochiral compounds from their racemates in industrial processes. Herein, we analyse these phenomena at the lowest level of hierarchy – that is the self-assembly of a racemic mixture of (R,R)- and (S,S)-PBI into 1D supramolecular polymers. By a combination of UV/vis and NMR spectroscopy as well as atomic force microscopy, we demonstrate that homochiral aggregation of the racemic mixture leads to the formation of two types of supramolecular conglomerates under kinetic control, while under thermodynamic control heterochiral aggregation is preferred, affording a racemic supramolecular polymer. FT-IR spectroscopy and quantum-chemical calculations reveal unique packing arrangements and hydrogen-bonding patterns within these supramolecular polymers. Time-, concentration- and temperature-dependent UV/vis experiments provide further insights into the kinetic and thermodynamic control of the conglomerate and racemic supramolecular polymer formation.

Homo- and heterochiral aggregation is a process of interest to prebiotic and chiral separation chemistry. Here, the authors analyze the self-assembly of a racemic mixture into 1D supramolecular polymers and find homochiral aggregation into conglomerates under kinetic control, while under thermodynamic control a racemic polymer is formed.

Transient dormant monomer states for supramolecular polymers with low dispersity

Temporally controlled cooperative and living supramolecular polymerization by the buffered release of monomers has been recently introduced as an important concept towards obtaining monodisperse and multicomponent self-assembled materials. In synthetic, dynamic supramolecular polymers, this requires efficient design strategies for the dormant, inactive states of the monomers to kinetically retard the otherwise spontaneous nucleation process. However, a generalized design principle for the dormant monomer states to expand the scope of precision supramolecular polymers has not been established yet, due to the enormous differences in the mechanism, energetic parameters of self-assembly and monomer exchange dynamics of the diverse class of supramolecular polymers. Here we report the concept of transient dormant states of monomers generated by redox reactions as a predictive general design to achieve monodisperse supramolecular polymers of electronically active, chromophoric or donor-acceptor, monomers. The concept has been demonstrated with charge-transfer supramolecular polymers with an alternating donor-acceptor sequence.

Monodisperse and well-defined self-assembled materials can be obtained by fuel-driven temporally controlled supramolecular polymerization via the buffered release of monomers. Here the authors show that a redox-responsive transient dormant state of monomer generated by redox reaction can lead to supramolecular polymers with low dispersity.

Revealing the Influences of Solvent Boiling Point and Alkyl Chains on the Adlayer Crystallinity of Furan-Diketopyrrolopyrrole-Thienylene Copolymer at Molecular Level

Crystallinity of the polymer poly(3,6-difuran-2-yl-2,5-di(2-octyldodecyl)-pyrrolo[3,4-c]pyrrole-1,4-dione-altthieylenevinylene) (PDVF) adlayers casted from low-boiling-point (L-bp), medium-bp (M-bp), and high-bp (H-bp) solvents was investigated through scanning tunneling microscopy (STM) and analyzed by the assistance of Hansen solubility parameter (HSP) theory and molecular dynamics (MD) simulations. Crystallinity of the PDVF adlayers increases evidently from the L- to H-bp solvents. Also, the solvent with an alkyl chain such as ethylbenzene (EB) facilitates in improving the crystallinity than the one without an alkyl chain such as chlorobenzene (CB) if the solvent bp is present in the same group. The HSP space discloses that EB is a marginal solvent for PDVF in contrast to CB. Quasi-isolate PDVF in the EB solution revealed by MD simulations facilitates the formation of crystallized domains through surface assembling mechanism. However, in CB, interconnected PDVF molecules through intermolecular overlapping tend to generate amorphous structures through direct deposition of the preformed structures in solution.

Controlled supramolecular polymerization of π-systems

Externally-initiated controlled supramolecular polymerization of the kinetically trapped aggregated state in a chain growth mechanism can produce well-defined living supramolecular polymers and copolymers.

Synergistic repulsive interactions trigger pathway complexity

We demonstrate the impact of synergistic repulsive interactions on pathway complexity in aqueous media.

Heterogeneous photocatalytic performances of CO2 reduction based on the [Emim]BF4 + TEOA + H2O system

The photochemical reduction of CO2 was studied in a 1-ethyl-3-methylimidazolium tetrafluoroborate, triethanolamine and water ([Emim]BF4 + TEOA + H2O) system under visible light irradiation. The integration of CdS and the Co-bpy complex, which acted as a photocatalyst and cocatalyst, respectively, was employed as an efficient catalytic system for the CO2-to-CO conversion. The utilization of [Emim]BF4 and water took advantage of their green properties. The amount of CO production showed that the test medium containing 10 vol% H2O was favourable for the catalytic performance of the CO2 reduction. In order to further study the factors that influenced the current system, the physical and spectroscopy properties were characterized by altering the composition ratio of the ingredients. Relevant parameters, including the viscosity, conductivity, solubility and coordination, were adjusted using the ratio of the H2O/[Emim]BF4 addition, resulting in a different catalytic performance. All of these attempts led to an optimal reaction condition for the CO2 reduction process.

Exploiting Coordination Isomerism for Controlled Self-Assembly

We exploited the inherent geometrical isomerism of a PtII complex as a new tool to control supramolecular assembly processes. UV irradiation and careful selection of solvent, temperature, and concentration leads to tunable coordination isomerism, which in turn allows fully reversible switching between two distinct aggregate species (1D fibers↔2D lamellae) with different photoresponsive behavior. Our findings not only broaden the scope of coordination isomerism, but also open up exciting possibilities for the development of novel stimuli-responsive nanomaterials.

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.

Tandem Interplay of the Host-Guest Interaction and Photoresponsive Supramolecular Polymerization to 1D and 2D Functional Peptide Materials

Peptide 1 with an Aβ42 amyloid nucleating core and a photodimerizable 4-methylcoumarin moiety at its N terminus demonstrates the step-wise self-assembly in water to form nanoparticles, with eventual transformation into 1D nanofibers. Addition of γ-cyclodextrin to 1 with subsequent irradiation with UV light at 320 nm resulted in morphological conversion to free-standing 2D nanosheets mediated by the host-guest interaction. Mechanical agitation of the 1D and 2D nanostructures led to seeds with narrow polydispersity indices, which by mediation of seeded supramolecular polymerization found seamless control over the dimensions of the nanostructures. Such structural and temporal control to differentiate the pathway was exploited to tune the mechanical strength of hierarchical hydrogel materials. Finally, the dimensional characteristics of the positively charged peptide fibers and sheets were envisaged as excellent exfoliating agents for inorganic hybrid materials, for example, MoS₂.

Supramolecular Block Copolymers by Seeded Living Polymerization of Perylene Bisimides

Living covalent polymerization has been a subject of intense research for many decades and has culminated in the synthesis of a large variety of block copolymers (BCPs) with structural and functional diversity. In contrast, the research on supramolecular BCPs is still in its infancy and their generation by living processes remains a challenge. Here we report the formation of supramolecular block copolymers by two-component seeded living polymerization of properly designed perylene bisimides (PBIs) under precise kinetic control. Our detailed studies on thermodynamically and kinetically controlled supramolecular polymerization of three investigated PBIs, which contain hydrogen-bonding amide side groups in imide position and chlorine, methoxy, or methylthio substituents in 1,7 bay-positions, revealed that these PBIs form kinetically metastable H-aggregates, which can be transformed into the thermodynamically favored J-aggregates by seed-induced living polymerization. We show here that copolymerization of kinetically trapped states of one PBI with seeds of another PBI leads to the formation of supramolecular block copolymers by chain-growth process from the seed termini as confirmed by UV/vis spectroscopy and atomic force microscopy (AFM). This work demonstrates for the first time the formation of triblock supramolecular polymer architectures with A-B-A and B-A-B block pattern by alternate two-component seeded polymerization in a living manner.

Pathway Control in Cooperative vs. Anti-Cooperative Supramolecular Polymers

Controlling the nanoscale morphology in assemblies of π-conjugated molecules is key to developing supramolecular functional materials. Here, we report an unsymmetrically substituted amphiphilic Pt^II complex 1 that shows unique self-assembly behavior in nonpolar media, providing two competing anti-cooperative and cooperative pathways with distinct molecular arrangement (long- vs. medium-slipped, respectively) and nanoscale morphology (discs vs. fibers, respectively). With a thermodynamic model, we unravel the competition between the anti-cooperative and cooperative pathways: buffering of monomers into small-sized, anti-cooperative species affects the formation of elongated assemblies, which might open up new strategies for pathway control in self-assembly. Our findings reveal that side-chain immiscibility is an efficient method to control anti-cooperative assemblies and pathway complexity in general.

Living supramolecular polymerization based on reversible deactivation of a monomer by using a 'dummy' monomer

New method of living supramolecular polymerization is demonstrated. Spontaneous nucleation of a reactive monomer is suppressed by using a ‘dummy’ monomer. Addition of seeds can initiate supramolecular polymerization in a chain-growth manner.

Although living supramolecular polymerization (LSP) has recently been realized, the scope of the monomer structures applicable to the existing methods is still limited. For instance, a monomer that spontaneously nucleates itself cannot be processed in a manner consistent with LSP. Herein, we report a new method for such a “reactive” monomer. We use a ‘dummy’ monomer which has a similar structure to the reactive monomer but is incapable of one-dimensional supramolecular polymerization. We show that in the presence of the dummy monomer, the reactive monomer is kinetically trapped in the dormant state. In this way, spontaneous nucleation of the reactive monomer is retarded; yet, addition of seeds of a supramolecular polymer can initiate the supramolecular polymerization in a chain growth manner. As a result, we obtain the supramolecular polymer of the reactive monomer with a controlled length, which is otherwise thermodynamically inaccessible. We believe that this concept will expand the scope of LSP for the synthesis of other functional supramolecular polymers, and thus lead to a variety of applications.

Seeded Polymerization of an Amide-Functionalized Diketopyrrolopyrrole Dye in Aqueous Media

The self-assembly of an amide-functionalized dithienyldiketopyrrolopyrrole (DPP) dye in aqueous media was achieved through seed-initiated supramolecular polymerization. Temperature- and time-dependent studies showed that the spontaneous polymerization of the DPP derivative was temporally delayed upon cooling the monomer solution in a methanol/water mixture. Theoretical calculations revealed that an amide-functionalized DPP derivative adopts an energetically favorable folded conformation in the presence of water molecules due to hydration. This conformational change is most likely responsible for the trapping of monomers in the initial stage of the cooperative supramolecular polymerization in aqueous media. However, the monomeric species can selectively interact with externally added fragmented aggregates as seeds through concerted π-stacking and hydrogen-bonding interactions. Consequently, the time course of the supramolecular polymerization and the morphology of the aggregated state can be controlled, and one-dimensional fibers that exhibit a J-aggregate-like bathochromically shifted absorption band can be obtained.

Modulation of side chain crystallinity in alternating copolymers

A remarkable enhancement in crystalline melting temperature (T_m) was observed in a series of fatty acids and mPEG containing alternating copolymers with the lone increase in mPEG chain lengths.

Pathway driven self-assembly and living supramolecular polymerization in an amyloid-inspired peptide amphiphile

Temperature dependent stepwise self-assembly and seeded supramolecular polymerization of a peptide amphiphile form metastable nanoparticles to single nanofibers or twisted bundles, to render a mechanically tunable hydrogel.