Closed-Loop Recycling of Vinylogous Urethane Vitrimers.

Devising energy-efficient strategies for the depolymerization of plastics and the recovery of their structural components in high yield and purity is key to a circular plastics economy. Here, we report a case study in which we demonstrate that vinylogous urethane (VU) vitrimers synthesized from bis-polyethylene glycol acetoacetates (aPEG) and tris(2-aminoethyl)amine can be degraded by water at moderate temperature with almost quantitative recovery (≈98 %) of aPEG. The rate of depolymerization can be controlled by the temperature, amount of water, molecular weight of aPEG, and composition of the starting material. These last two parameters also allow one to tailor the mechanical properties of the final materials, and this was used to access soft, tough, and brittle vitrimers, respectively. The straightforward preparation and depolymerization of the aPEG-based VU vitrimers are interesting elements for the design of polymer materials with enhanced closed-loop recycling characteristics.

An electrolyte additive for the improved high voltage performance of LiNi0.5Mn1.5O4 (LNMO) cathodes in Li-ion batteries.

High-voltage cathode materials are important for the implementation of high-energy-density Li-ion batteries. However, with increasing cut-off voltages, interfacial instabilities between electrodes and the electrolyte limit their commercial development. This study addresses this issue by proposing a new electrolyte additive, (3-aminopropyl)triethoxysilane (APTS). APTS stabilises the interface between the LiNi0.5Mn1.5O4 (LNMO) cathode and the electrolyte in LNMO‖Li half-cells due to its multifunctional character. The amino groups in APTS facilitate the formation of a robust protective cathode layer. Its silane groups improve layer stability by neutralising the electrolyte's detrimental hydrogen fluoride and water. Electrochemical measurements reveal that the addition of 0.5 wt% APTS significantly improves the long-term cycling stability of LNMO‖Li half-cells at room temperature and 55 °C. APTS-addition to the electrolyte delivers excellent capacity retention of 92% after 350 cycles at room temperature and 71% after 300 cycles at 55 °C (1C) contrasting with the much lower performances of the additive-free electrolyte. The addition of a 0.5 wt% (3-glycidyloxypropyl)trimethoxysilane (GLYMO) additive, which contains only the siloxane group, but lacks the amine group, displayed a capacity retention of 73% after 350 cycles at room temperature but degraded significantly upon cycling at 55 °C.

Computational design of anisotropic nanocomposite actuators.

This paper presents a theoretical investigation of the design of a new actuator type made of anisotropic colloidal particles grafted with stimuli-responsive polymer chains. These artificial muscles combine the osmotic actuation principle of stimuli-responsive hydrogels with the structural alignment of colloidal liquid crystals to achieve directional motion. The solubility of the stimuli-responsive polymer in the neutral state, its degree of polymerization, the salt concentration, and the grafting density of the polymer chains on the surface of the colloidal particles are investigated and identified as important for actuator performance and tunability. The computational results suggest that the proposed mechanically active material matches or exceeds the performances of natural muscles and provide the guidelines for the realization of artificial muscles with predetermined actuation properties.

Chemical Upcycling of Conventional Polyureas into Dynamic Covalent Poly(aminoketoenamide)s.

The chemical upcycling of polymers is an emerging strategy to transform post-consumer waste into higher-value chemicals and materials. However, on account of the high stability of the chemical bonds that constitute their main chains, the chemical modification of many polymers proves to be difficult. Here, we report a versatile approach for the upcycling of linear and cross-linked polyureas, which are widely used because of their high chemical stability. The treatment of these polymers or their composites with acetylacetone affords di-vinylogous amide-terminated compounds in good yield. These products can be reacted with aromatic isocyanates, and the resulting aminoketoenamide bonds are highly dynamic at elevated temperatures. We show here that this conversion scheme can be exploited for the preparation of dynamic covalent poly(aminoketoenamide) networks, which are healable and reprocessable through thermal treatment without any catalyst.

Supramolecular Stability of Benzene-1,3,5-tricarboxamide Supramolecular Polymers in Biological Media: Beyond the Stability-Responsiveness Trade-off.

Supramolecular assemblies have been gaining attention in recent years in the field of drug delivery because of their unique formulation possibilities and adaptive behavior. Their non-covalent nature allows for their self-assembly formulation and responsiveness to stimuli, an appealing feature to trigger a therapeutic action with spatiotemporal control. However, facing in vivo conditions is very challenging for non-covalent structures. Dilution and proteins in blood can have a direct impact on self-assembly, destabilizing the supramolecules and leading to a premature and uncontrolled cargo release. To rationalize this behavior, we designed three monomers exhibiting distinct hydrophobic cores that self-assemble into photo-responsive fibers. We estimated their stability-responsiveness trade-off in vitro, finding two well-separated regimes. These are low-robustness regime, in which the system equilibrates quickly and responds readily to stimuli, and high-robustness regime, in which the system equilibrates slowly and is quite insensitive to stimuli. We probed the performance of both regimes in a complex environment using Förster resonance energy transfer (FRET). Interestingly, the stability-responsiveness trade-off defines perfectly the extent of disassembly caused by dilution but not the one caused by protein interaction. This identifies a disconnection between intrinsic supramolecular robustness and supramolecular stability in the biological environment, strongly influenced by the disassembly pathway upon protein interaction. These findings shed light on the key features to address for supramolecular stability in the biological environment.

Polyaromatic cores for the exfoliation of popular 2D materials.

Two-dimensional (2D) nanomaterials have attracted interest from the scientific community due to their unique properties. The production of these materials has been carried out by diverse methodologies, the liquid phase exfoliation being the most promising one due to its simplicity and potential scalability. The use of several stabilizers allows to obtain dispersions of these 2D nanomaterials in solvents with low boiling points. Herein we describe a general exfoliation method for different 2D materials employing a biphasic water/dichloromethane system and two different (poly)aromatic hydrocarbons (PAHs). This method allows us to obtain dispersions of the exfoliated 2D materials with high concentrations in the organic solvent. Due to the low boiling point of dichloromethane, and therefore its easy removal, the obtained dispersions can be employed as additives for different composites. We corroborate that the exfoliation efficiency is improved due to the π-π and van der Waals interactions between the PAHs and the layers of the 2D materials.

Tuning the donor-acceptor interactions in phase-segregated block molecules.

The assembly of donor-acceptor molecules via charge transfer (CT) interactions gives rise to highly ordered nanomaterials with appealing electronic properties. Here, we present the synthesis and bulk co-assembly of pyrene (Pyr) and naphthalenediimide (NDI) functionalized oligodimethylsiloxanes (oDMS) of discrete length. We tune the donor-acceptor interactions by connecting the pyrene and NDI to the same oligomer, forming a heterotelechelic block molecule (NDI-oDMSPyr), and to two separate oligomers, giving Pyr and NDI homotelechelic block molecules (Pyr-oDMS and NDI-oDMS). Liquid crystalline materials are obtained for binary mixtures of Pyr-oDMS and NDI-oDMS, while crystallization of the CT dimers occurred for the heterotelechelic NDI-oDMS-Pyr block molecule. The synergy between crystallization and phase-segregation coupled with the discrete length of the oDMS units allows for perfect order and sharp interfaces between the insulating siloxane and CT layers composed of crystalline CT dimers. We were able to tune the lamellar domain spacing and donor-acceptor CT interactions by applying pressures up to 6 GPa on the material, making the system promising for soft-material nanotechnologies. These results demonstrate the importance of the molecular design to tune the CT interactions and stability of a CT material.

Heterolytic Bond Cleavage in a Scissile Triarylmethane Mechanophore.

Covalent mechanophores display the cleavage of a weak covalent bond when a sufficiently high mechanical force is applied. Three different covalent bond breaking mechanisms have been documented thus far, including concerted, homolytic, and heterolytic scission. Motifs that display heterolytic cleavage typically separate according to non-scissile reaction pathways that afford zwitterions. Here, we report a new mechanochromic triarylmethane mechanophore, which dissociates according to a scissile heterolytic pathway and displays a pronounced mechanochromic response. The mechanophore was equipped with two styrenylic handles that allowed its incorporation as a cross-linker into poly(N,N-dimethylacrylamide) and poly(methyl acrylate-co-2-hydroxyethyl acrylate) networks. These materials are originally colorless, but compression or tensile deformation renders the materials colored. By combining tensile testing and in situ transmittance measurements, we show that this effect is related to scissile cleavage leading to colored triarylmethane carbocations.

Tuning of Morphology by Chirality in Self-Assembled Structures of Bis(Urea) Amphiphiles in Water.

We present the synthesis and self-assembly of a chiral bis(urea) amphiphile and show that chirality offers a remarkable level of control towards different morphologies. Upon self-assembly in water, the molecular-scale chiral information is translated to the mesoscopic level. Both enantiomers of the amphiphile self-assemble into chiral twisted ribbons with opposite handedness, as supported by Cryo-TEM and circular dichroism (CD) measurements. The system presents thermo-responsive aggregation behavior and combined transmittance measurements, temperature-dependent UV, CD, TEM, and micro-differential scanning calorimetry (DSC) show that a ribbon-to-vesicles transition occurs upon heating. Remarkably, chirality allows easy control of morphology as the self-assembly into distinct aggregates can be tuned by varying the enantiomeric excess of the amphiphile, giving access to flat sheets, helical ribbons, and twisted ribbons.

Stepwise Adsorption of Alkoxy-Pyrene Derivatives onto a Lamellar, Non-Porous Naphthalenediimide-Template on HOPG.

The development of new strategies for the preparation of multicomponent supramolecular assemblies is a major challenge on the road to complex functional molecular systems. Here we present the use of a non-porous self-assembled monolayer from uC33 -NDI-uC33 , a naphthalenediimide symmetrically functionalized with unsaturated 33 carbon-atom-chains, to prepare bicomponent supramolecular surface systems with a series of alkoxy-pyrene (PyrOR) derivatives at the liquid/HOPG interface. While previous attempts at directly depositing many of these PyrOR units at the liquid/HOPG interface failed, the multicomponent approach through the uC33 -NDI-uC33 template enabled control over molecular interactions and facilitated adsorption. The PyrOR deposition restructured the initial uC33 -NDI-uC33 monolayer, causing an expansion in two dimensions to accommodate the guests. As far as we know, this represents the first example of a non-porous or non-metal complex-bearing monolayer that allows the stepwise formation of multicomponent supramolecular architectures on surfaces.

Discordant Supramolecular Fibres Reversibly Depolymerised by Temperature and Light.

Synthetic stimuli responsive supramolecular polymers attract increasing interest for their ability to mimic the unique properties of natural assemblies. Here we focus on the well-studied benzene-1,3,5-tricarboxamide (BTA) motif, and substitute it with two (S)-3,7-dimethyloctyl groups and an azobenzene photoswitch. We demonstrate the UV (λ=365 nm) induced depolymerisation of the helical hydrogen-bonded polymers in methylcyclohexane (MCH) through circular dichroism and UV-vis spectroscopy in dilute solution (15 µm), and NMR and iPAINT super-resolution microscopy in concentrated solution (300 µm). The superstructure can be regenerated after thermal depolymerization, whilst repeated depolymerisation can be reversed without degradation by irradiating at λ=455 nm. Molecular dynamics simulations show that the most energetically favourable configuration for these polymers in MCH is a left-handed helical network of hydrogen-bonds between the BTA cores surrounded by two right-handed helices of azobenzenes. The responsiveness to two orthogonal triggers across a broad concentration range holds promise for use in, for example, photo-responsive gelation.

Molecular motor-functionalized porphyrin macrocycles.

Molecular motors and switches change conformation under the influence of an external stimulus, e.g. light. They can be incorporated into functional systems, allowing the construction of adaptive materials and switchable catalysts. Here, we present two molecular motor-functionalized porphyrin macrocycles for future photo-switchable catalysis. They display helical, planar and point chirality, and are diastereomers, which differ in the relative orientation of the motor and macrocyclic components. Fluorescence, UV-vis, and 1H NMR experiments reveal that the motor-functionalized macrocycles can bind and thread different variants of viologen guests, including a one-side blocked polymeric one of 30 repeat units. The latter feature indicates that the motor systems can find the open end of a polymer chain, thread on it, and move along the chain to eventually bind at the viologen trap, opening possibilities for catalytic writing on single polymer chains via chemical routes.

Combinatorial Selection Among Geometrical Isomers of Discrete Long-Carbon-Chain Naphthalenediimides Induces Local Order at the Liquid/Solid Interface.

We report two families of naphthalenediimides (NDIs) symmetrically functionalized with discrete carbon chains comprising up to 55 carbon atoms (Cn-NDI-Cn, n = 39, 44, 50, and 55) and their self-assembly at the 1-phenyloctane/highly oriented pyrolytic graphite interface (1-PO/HOPG interface). The compounds differ by the presence or absence of two or three internal double bonds in the carbon chains (unsaturated and saturated Cn-NDI-Cn, respectively). Combinatorial distributions of geometrical isomers displaying either the E- or Z-configuration at each double bond are obtained for the unsaturated compounds. Analysis of the self-assembled monolayers of equally long unsaturated and saturated Cn-NDI-Cn by scanning tunneling microscopy (STM) reveal that all Cn-NDI-Cn tend to form lamellar systems featuring alternating areas of aromatic cores and carbon chains. Extended chain lengths are found to significantly increase disorder in the self-assembled monolayers due to misalignments and enhanced strength of interchain interactions. This phenomenon is antagonized by the local order-inducing effect of the internal double bonds: unsaturated Cn-NDI-Cn give qualitatively more ordered self-assembled monolayers compared to their saturated counterparts. The use of combinatorial distributions of unsaturated Cn-NDI-Cn geometrical isomers does not represent a limitation to achieve local order in the self-assembled monolayers. The self-assembly process operates a combinatorial search and selects the geometrical isomer(s) affording the most thermodynamically stable pattern, highlighting the adaptive character of the system. Finally, the antagonistic interplay between the extended carbon chain lengths and the presence of internal double bonds brings to the discovery of the lamellar "phase C" morphology for unsaturated Cn-NDI-Cn with n ≥ 50.

Synthesis of Core-Modified Third-Generation Light-Driven Molecular Motors.

The synthesis and characterization of a series of light-driven third-generation molecular motors featuring various structural modifications at the central aromatic core are presented. We explore a number of substitution patterns, such as 1,2-dimethoxybenzene, naphthyl, 1,2-dichlorobenzene, 1,1':2',1″-terphenyl, 4,4″-dimethoxy-1,1':2',1″-terphenyl, and 1,2-dicarbomethoxybenzene, considered essential for designing future responsive systems. In many cases, the synthetic routes for both synthetic intermediates and motors reported here are modular, allowing for their post-functionalization. The structural modifications introduced in the core of the motors result in improved solubility and a bathochromic shift of the absorption maxima. These features, in combination with a structural design that presents remote functionalization of the stator with respect to the fluorene rotors, make these novel motors particularly promising as light-responsive actuators in covalent and supramolecular materials.

An Azobenzene-Based Single-Component Supramolecular Polymer Responsive to Multiple Stimuli in Water.

One of the most appealing features of supramolecular assemblies is their ability to respond to external stimuli due to their noncovalent nature. This provides the opportunity to gain control over their size, morphology, and chemical properties and is key toward some of their applications. However, the design of supramolecular systems able to respond to multiple stimuli in a controlled fashion is still challenging. Here we report the synthesis and characterization of a novel discotic molecule, which self-assembles in water into a single-component supramolecular polymer that responds to multiple independent stimuli. The building block of such an assembly is a C3-symmetric monomer, consisting of a benzene-1,3,5-tricarboxamide core conjugated to a series of natural and non-natural functional amino acids. This design allows the use of rapid and efficient solid-phase synthesis methods and the modular implementation of different functionalities. The discotic monomer incorporates a hydrophobic azobenzene moiety, an octaethylene glycol chain, and a C-terminal lysine. Each of these blocks was chosen for two reasons: to drive the self-assembly in water by a combination of H-bonding and hydrophobicity and to impart specific responsiveness. With a combination of microscopy and spectroscopy techniques, we demonstrate self-assembly in water and responsiveness to temperature, light, pH, and ionic strength. This work shows the potential to integrate independent mechanisms for controlling self-assembly in a single-component supramolecular polymer by the rational monomer design and paves the way toward the use of multiresponsive systems in water.

Engineering Long-Range Order in Supramolecular Assemblies on Surfaces: The Paramount Role of Internal Double Bonds in Discrete Long-Chain Naphthalenediimides.

Achieving long-range order with surface-supported supramolecular assemblies is one of the pressing challenges in the prospering field of non-covalent surface functionalization. Having access to defect-free on-surface molecular assemblies will pave the way for various nanotechnology applications. Here we report the synthesis of two libraries of naphthalenediimides (NDIs) symmetrically functionalized with long aliphatic chains (C28 and C33) and their self-assembly at the 1-phenyloctane/highly oriented pyrolytic graphite (1-PO/HOPG) interface. The two NDI libraries differ by the presence/absence of an internal double bond in each aliphatic chain (unsaturated and saturated compounds, respectively). All molecules assemble into lamellar arrangements, with the NDI cores lying flat and forming 1D rows on the surface, while the carbon chains separate the 1D rows from each other. Importantly, the presence of the unsaturation plays a dominant role in the arrangement of the aliphatic chains, as it exclusively favors interdigitation. The fully saturated tails, instead, self-assemble into a combination of either interdigitated or non-interdigitated diagonal arrangements. This difference in packing is spectacularly amplified at the whole surface level and results in almost defect-free self-assembled monolayers for the unsaturated compounds. In contrast, the monolayers of the saturated counterparts are globally disordered, even though they locally preserve the lamellar arrangements. The experimental observations are supported by computational studies and are rationalized in terms of stronger van der Waals interactions in the case of the unsaturated compounds. Our investigation reveals the paramount role played by internal double bonds on the self-assembly of discrete large molecules at the liquid/solid interface.

Selenoamides modulate dipole-dipole interactions in hydrogen bonded supramolecular polymers of 1,3,5-substituted benzenes.

We report the synthesis and self-assembly behavior of a chiral C3-symmetrical benzene-tricarboselenoamide. The introduction of the selenoamide moiety enhances the dipolar character of the supramolecular interaction and confers a remarkable thermal stability to the supramolecular polymers obtained.

Tandem catalysis in multicomponent solvent-free biofluids.

Enzymes are widely employed to reduce the environmental impact of chemical industries as biocatalysts improve productivity and offer high selectively under mild reaction conditions in a diverse range of chemical transformations. The poor stability of biomacromolecules under reaction conditions is often a critical bottleneck to their application. Protein engineering or immobilization onto solid substrates may remedy this limitation but, unfortunately, this is often at the expense of catalytic potency or substrate specificity. In this work, we show that the combinatorial approach of chemical modification and supramolecular nanoencapsulation can endow mechanistically diverse enzymes with apparent extremophilic behavior. A protein-polymer surfactant core-shell architecture facilitates construction of increasingly complex biofluids from individual biosynthetic components, each of which retain biological activity at hydration levels almost two orders of magnitude below solvation. The herein constructed multifunctional biofluids operate in tandem up to 150 °C and in the total absence of solvent under apparent diffusional mass-transport limitation. The biosynthetic promotion of extremophilic traits for enzymes with diverse catalytic motions and chemical functions highlights the extraordinary capacity for a viscous surfactant milieu to replace both hydration and bulk waters.

Resistive switching in an organic supramolecular semiconducting ferroelectric.

The combination of switchable dipolar side groups and the semiconducting core of the newly synthetized C3-symmetric benzotrithiophene molecule (BTTTA) leads to an ordered columnar material showing continuous tunability from injection- to bulk-limited conductivity modulation.

Directing the Solid-State Organization of Racemates via Structural Mutation and Solution-State Assembly Processes.

Chirality plays a central role in biomolecular recognition and pharmacological activity of drugs and can even lead to new functions such as spin filters. Although there have been significant advances in understanding and controlling the helical organization of enantiopure synthetic molecular systems, rationally dictating the assembly of mixtures of enantiomer (including racemates) is nontrivial. Here we demonstrate that a subtle change in molecular structure coupled with the understanding of assembly processes of enantiomers and racemates, in both dilute solution and concentrated gels, acts as a stepping stone to rationally control the organization in the solid-state. We have studied trans-1,2-disubstituted cyclohexanes as model systems with carboxamide, thioamide, and their combination as functional groups. On comparing the gelation propensity of individual enantiomers and racemates, we find that racemates of carboxamide, thioamide, and their combination adopt self-sorting, coassembly, and mixed organization, respectively. Remarkably, these modes of assembly of racemates were also retained in solid-state. These results point out that studying the solution-phase assembly is a key link for connecting molecular structure with the assembly in the solid-state, even for racemates.