Polymers with the ability to repair themselves after sustaining damage could extend the lifetimes of materials used in many applications 1 . Most approaches to healable materials require heating the damaged area [2][3][4] . Here we present metallosupramolecular polymers that can be mended through exposure to light. They consist of telechelic, rubbery, low-molecular-mass polymers with ligand end groups that are non-covalently linked through metal-ion binding. On exposure to ultraviolet light, the metal-ligand motifs are electronically excited and the absorbed energy is converted into heat. This causes temporary disengagement of the metal-ligand motifs and a concomitant reversible decrease in the polymers' molecular mass and viscosity 5 , thereby allowing quick and efficient defect healing. Light can be applied locally to a damage site, so objects can in principle be healed under load. We anticipate that this approach to healable materials, based on supramolecular polymers and a light-heat conversion step, can be applied to a wide range of supramolecular materials that use different chemistries.The healing of cracks in amorphous polymers by heating above the glass transition temperature (T g ) involves surface rearrangement and approach of polymer chains, followed by wetting, diffusion and reentanglement of the chains 6 . Because the rates of the final two steps are inversely proportional to the molecular mass, healing is generally slow and inefficient. This problem can be overcome by exploiting thermally reversible, covalent bonds 7,8 or non-covalent supramolecular motifs 5,9,10 that allow the reaction equilibrium to be temporarily shifted to lower-molecular-mass species 11 on exposure to heat. This reduces the viscosity of the material, such that defects can be mended, before the equilibrium is shifted back and the polymer is reformed. Supramolecular polymers that phase separate into physically crosslinked networks (Fig. 1a) should be especially well suited for this purpose, because such morphologies generally bestow the material with high toughness. The supramolecular motifs can disengage in the solid state on exposure to heat or a competitive binding agent 12,13 , causing disassembly into small molecules 14 and viscosity reductions. Reporting a series of supramolecular materials formed by metal-ligand interactions, we demonstrate here that this architecture is an excellent basis for elastomeric materials in which defects can be efficiently repaired. We show that the use of light 15 as a stimulus for the dissociation of supramolecular motifs has distinct advantages over thermally healable systems, including the possibility of exclusively exposing and healing the damaged region.The new polymers are based on a macromonomer comprising a rubbery, amorphous poly(ethylene-co-butylene) core with 2,6-bis(19-methylbenzimidazolyl)pyridine (Mebip) ligands at the termini (Fig. 1b, 3). This design was based on the assumption that the hydrophobic core and the polar metal-ligand motif would phase separate 16 . Metal-Mebip com...

A detailed and systematic investigation of mechanochromic, melt-processed blends between a series of polyethylenes (PE) with crystallinities ranging from 9 to 66% and two excimer-forming, photoluminescent oligo(phenylenevinylene) dyes is described. A dramatic increase in the nucleation rate of dye aggregates, and therewith a decrease in the size of the aggregates, is observed upon grafting long alkyl tails onto the chromophore. The extent of color change observed upon deformation of these materials, and thus the ability of the polymer host to break up dye aggregates upon deformation, is related to the plastic deformation process of PE crystallitess specifically those arranged in a lamellar morphologysand increases with increasing polymer crystallinity, decreasing dye aggregate size, and decreasing rates of deformation.

Mixing and matching: The highly selective detection of chemical‐warfare‐agent mimics can be achieved by judicious combination of carefully designed fluorescent ligands and metal ions. Designed sensor arrays of these multimetal/multiligand systems represent a modular and versatile approach for the detection of organophosphates and other analytes.

Along with biological and nuclear threats, chemical warfare agents are some of the most feared weapons of mass destruction. Compared to nuclear weapons they are relatively easy to access and deploy, which makes them in some aspects a greater threat to national and global security. A particularly hazardous class of chemical warfare agents are the nerve agents. Their rapid and severe effects on human health originate in their ability to block the function of acetylcholinesterase, an enzyme that is vital to the central nervous system. This article outlines recent activities regarding the development of molecular sensors that can visualize the presence of nerve agents (and related pesticides) through changes of their fluorescence properties. Three different sensing principles are discussed: enzyme-based sensors, chemically reactive sensors, and supramolecular sensors. Typical examples are presented for each class and different fluorescent sensors for the detection of chemical warfare agents are summarized and compared.

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The self-assembly polymerization of ditopic macromolecules through metal−ligand binding is an attractive framework for the preparation of high-molecular-weight metallo-supramolecular polymers. This approach was utilized here for the polymerization of a conjugated macromonomer (1) that was derived by functionalizing a low-molecular-weight poly(2,5-dialkoxy-p-phenylene ethynylene) (PPE) core with 2,6-bis(1‘-methylbenzimidazolyl)pyridine (Mebip) ligands on the two terminal positions. To minimize electronic interactions between the PPE moieties and the metal−ligand complexes, nonconjugated hexamethylene spacers were introduced between the PPE and Mebip building blocks. The supramolecular polymerization of macromonomer 1 with equimolar amounts of Zn2+ or Fe2+ resulted in polymers, which exhibit appreciable mechanical properties (loss moduli of [1·Zn(ClO4)2] n and [1·Fe(ClO4)2] n at 25 °C are ca. 450 and 610 MPa, respectively), but on account of their dynamic, reversible nature offer the ease of processing of low-molecular-weight compounds. The optoelectronic properties of these metallopolymers are similar to those of the parent PPE and demonstrate that the functionalities of semiconducting building blocks and coordination chain extenders can be effectively decoupled by a short, nonconjugated spacer.

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The self-assembly polymerization of ditopic monomers via metal–ligand binding is a facile route for the preparation of metallosupramolecular polymers. Here this approach was used for the synthesis of supramolecular poly(p-xylylene)s based on 2,6-bis(1′-methylbenzimidazolyl)pyridine (Mebip) end-capped telechelic oligomers with a p-xylylene core and different metal salts. These polymers can be readily processed from solution and merge the ease of processing of supramolecular materials with the good thermal stability of the p-xylylene core. The nature of the metal cation (Fe2+, Zn2+, La3+) and counteranion (ClO4 –, OTf–, NTf2 –) was systematically varied, and a tetrafunctional supramolecular cross-linker was used to probe how these modifications influence the materials’ properties. Interestingly, and in contrast to other metallosupramolecular polymers, where the nature of the metal salt plays a critical role, only minor property differences were observed for the materials studied. Instead, the properties of the supramolecular poly(p-xylylene)s investigated appear to be primarily governed by the crystalline nature of the telechelic oligomer. We note that minor impurities in the latter can exert a significant influence on the metallosupramolecular polymer’s properties and report a new protocol for the synthesis and purification of Mebip-end-capped p-xylylene telechelic oligomers.