Molecular knots remain difficult to produce using the current synthetic methods of chemistry because of their topological complexity. We report here the near-quantitative self-assembly of a trefoil knot from a naphthalenediimide-based aqueous disulfide dynamic combinatorial library. The formation of the knot appears to be driven by the hydrophobic effect and leads to a structure in which the aromatic components are buried while the hydrophilic carboxylate groups remain exposed to the solvent. Moreover, the building block chirality constrains the topological conformation of the knot and results in its stereoselective synthesis. This work demonstrates that the hydrophobic effect provides a powerful strategy to direct the synthesis of entwined architectures.

A classic paradigm of soft and extensible polymer materials is the difficulty of combining reversible elasticity with high fracture toughness, in particular for moduli above 1 MPa. Our recent discovery of multiple network acrylic elastomers opened a pathway to obtain precisely such a combination. We show here that they can be seen as true molecular composites with a well-cross-linked network acting as a percolating filler embedded in an extensible matrix, so that the stress-strain curves of a family of molecular composite materials made with different volume fractions of the same cross-linked network can be renormalized into a master curve. For low volume fractions (<3%) of cross-linked network, we demonstrate with mechanoluminescence experiments that the elastomer undergoes a strong localized softening due to scission of covalent bonds followed by a stable necking process, a phenomenon never observed before in elastomers. The quantification of the emitted luminescence shows that the damage in the material occurs in two steps, with a first step where random bond breakage occurs in the material accompanied by a moderate level of dissipated energy and a second step where a moderate level of more localized bond scission leads to a much larger level of dissipated energy. This combined use of mechanical macroscopic testing and molecular bond scission data provides unprecedented insight on how tough soft materials can damage and fail.

• A submitted manuscript is the version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal.If the publication is distributed under the terms of Article 25fa of the Dutch Copyright Act, indicated by the "Taverne" license above, please follow below link for the End User Agreement: Strain-induced light emission from mechanoluminescent cross-linkers in silica-filled poly(dimethylsiloxane) demonstrated that covalent bond scission contributes significantly to irreversible stress-softening upon the initial extension, known as the Mullins effect. The crosslinkers contained dioxetanes that emit light upon force-induced bond scission. The filled elastomer emitted light in cyclic uniaxial tension, but only on exceeding the previous maximum strain. The amount of light increased with hysteresis energy in a power law of exponent 2.0, demonstrating that covalent bond scission became increasingly important in the strain regime studied. Below ~100-120 % strain, corresponding to an energy absorption of (0.082 ± 0.012) J cm -3 , mechanoluminescence was not detectable. Calibration of the light intensity indicated that by 190 % strain, less than 0.1% of the dioxetane moieties break. Small but significant amounts of 2 light were emitted upon unloading, suggesting a complex stress transfer to the dioxetanes mediated by the fillers. Pre-strained material emitted light on straining perpendicularly, but not parallel to the original tensile direction, demonstrating that covalent bond scission is highly anisotropic. These findings show that the scission of even a small number of covalent bonds plays a discernible role in the Mullins effect in filled silicone elastomers. Such mechanisms may be active in other types of filled elastomers.

A chemiluminescent mechanophore, bis(adamantyl-1,2-dioxetane), is used to investigate the covalent bond scission resulting from the sorption of chloroform by glassy poly(methyl methacrylate) (PMMA) networks. Bis(adamantyl)-1,2-dioxetane units incorporated as cross-linkers underwent mechanoluminescent scission, demonstrating that solvent ingress caused covalent bond scission. At higher cross-linking densities, the light emission took the form of hundreds of discrete bursts, widely varying in intensity, with each burst composed of 107–109 photons. Camera imaging indicated a relatively slow propagation of bursts through the material and permitted analysis of the spatial correlation between the discrete bond-breaking events. The implications of these observations for the mechanism of sorption and fracture are discussed.

of color in these materials has fascinated scientists for centuries, with early breakthroughs in understanding these phenomena made by Hooke, Newton [6] and Lord Rayleigh. [7] Another type of structural color arises from surface plasmon resonance, i.e., the resonant coupling between light and metallic nanostructures, which craftspeople have used since the Bronze age to impart color to ceramics and glass. [8,9] Over the past 30 years, fabricating structurally colored materials has been greatly facilitated by the rapid development of lithography-based technologies and directed self-assembly methodologies, which permit precise control of structural ordering at the nano-and microscale. Photonic and plasmonic materials can now be used to control and manipulate the flow of light in a plethora of colorful applications in the modern world, ranging from microoptical components [10] and lasing materials [11,12] to household products, such as nontoxic and photostable pigments for paints and cosmetics. [13-15] Artificial, structurally colored materials have been made predominantly from hard, rigid components. Their colors are stable as long as the nanostructure remains intact, but the application of excessive forces to these relatively brittle structures typically leads to an irreversible structural change and thus a change or loss of color. By contrast, many natural photonic coloration strategies are dynamic and responsive, such as in chameleons, [16] cephalopods, [17-20] tetra fish, [21] and the tortoise beetle. [22] For example, chameleon skin contains photonic arrays of high-refractive-index guanine nanocrystals that are embedded in a softer, low-refractive-index cytoplasmic matrix. [16] The reversible deformation of such composite structures enables the animal to reflect wavelengths of light in a spatially and spectrally selective manner for dazzling camouflage displays. Recent progress in synthetic approaches toward precisely ordered soft nanostructures has opened up a new class of structurally colored materials that also respond dynamically and reversibly to stimuli, such as pH, heat, light, and deformation. The design of responsive photonic structures has often been informed and inspired by natural coloration strategies. [3,23-25] To mimic natural materials and access responsive structural color, polymers are frequently employed as a component on account of their mechanical (low moduli and optionally elastic behavior) and optical (high transparency, low refractive Mechanochromic effects in structurally colored materials are the result of deformation-induced changes to their ordered nanostructures. Polymeric materials which respond in this way to deformation offer an attractive combination of characteristics, including continuous strain sensing, high strain resolution, and a wide strain-sensing range. Such materials are potentially useful for a wide range of applications, which extend from pressure-sensing bandages to anti-counterfeiting devices. Focusing on the materials design aspects, recent developments in this fi...