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The desire to construct complex molecular systems is driven by the need for technological (r)evolution and our intrinsic curiosity to comprehend the origin of life. Supramolecular chemists tackle this challenge by combining covalent and noncovalent reactions leading to multicomponent systems with emerging complexity. However, this synthetic strategy often coincides with difficult preparation protocols and a narrow window of suitable conditions. Here, we report on unsuspected observations of our group that highlight the impact of subtle “irregularities” on supramolecular systems. Based on the effects of pathway complexity, minute amounts of water in organic solvents or small impurities in the supramolecular building block, we discuss potential pitfalls in the study of complex systems. This article is intended to draw attention to often overlooked details and to initiate an open discussion on the importance of reporting experimental details to increase reproducibility in supramolecular chemistry.

International audience; During the XIXth century, France has been the theater of many discoveries in stereochemistry thanks to prestigious physicists, chemists, and crystallographers. Among them, Louis Pasteur is certainly the father of molecular chirality (the so-called molecular dissymmetry), and because of the exceptionally favored conditions of his famous discovery on the resolution of tartrates, his findings have often been attributed to serendipity. But let us not forget that "in the fields of observation, chance only favors the prepared minds."

Materials with highly ordered nanoscale structures can translate molecular processes to macroscopic function. Here we report on the photo-controlled organization of achiral alternating copolymers composed of discrete length blocks showing well-defined sub-10 nm morphologies. These alternating copolymers consist of main-chain azobenzene building blocks alternating with discrete oDMS blocks of various precise lengths. Remarkably, we demonstrate the imprinting of a stable helical molecular arrangement in spin-casted thin films by irradiation with circularly polarized light, without chiral dopant or plasticizer required. By following the out-of-equilibrium photo-switching process over irradiation time, the mechanism of molecular reorganization is unraveled and rationalized with the nature of the morphology. Linear photo-organization is preferentially reached with flexible and symmetric cylindrical structures while helical photo-organization is most easily obtained with robust but rotatable lamella structures. These findings suggest that precision in the synthesis and assembly of alternating copolymers can lead to complete control over molecular organization and main-chain motion.

The correlation between molecular structure and mechanism of supramolecular polymerizations is a topic of great interest, with a special focus on the pathway complexity of porphyrin assemblies. Their cooperative polymerization typically yields highly ordered, long 1D polymers and is driven by a combination of π‐stacking due to solvophobic effects and hydrogen bonding interactions. Subtle changes in molecular structure, however, have significant influence on the cooperativity factor and yield different aggregate types (J‐ versus H‐aggregates) of different lengths. In this study, the influence of amide connectivity on the self‐assembly behavior of porphyrin‐based supramolecular monomers was investigated. While in nonpolar solvents, C=O centered monomers readily assemble into helical supramolecular polymers via a cooperative mechanism, their NH centered counterparts form short, non‐helical J‐type aggregates via an isodesmic pathway. A combination of spectroscopy and density functional theory modelling sheds light on the molecular origins causing this stunning difference in assembly properties and demonstrates the importance of molecular connectivity in the design of supramolecular systems. Finally, their mutual interference in copolymerization experiments is presented., Amide connectivity in the molecular design of porphyrin supramolecular monomers strongly impacts the assembly behavior in nonpolar solvents. While C=O centered monomers aggregate cooperatively into long, 1D supramolecular fibers, their NH‐centered counterparts only form isodesmic J‐aggregates. With a combination of spectroscopy and density functional modelling, the authors shed light on the molecular origins of these differences in properties.

The radionuclide thorium-229 features an isomer with an exceptionally low excitation energy that enables direct laser manipulation of nuclear states. It constitutes one of the leading candidates for use in next-generation optical clocks$^{1–3}$. This nuclear clock will be a unique tool for precise tests of fundamental physics$^{4–9}$. Whereas indirect experimental evidence for the existence of such an extraordinary nuclear state is substantially older$^{10}$, the proof of existence has been delivered only recently by observing the isomer’s electron conversion decay$^{11}$. The isomer’s excitation energy, nuclear spin and electromagnetic moments, the electron conversion lifetime and a refined energy of the isomer have been measured$^{12–16}$. In spite of recent progress, the isomer’s radiative decay, a key ingredient for the development of a nuclear clock, remained unobserved. Here, we report the detection of the radiative decay of this low-energy isomer in thorium-229 ($^{229m}$Th). By performing vacuum-ultraviolet spectroscopy of $^{229m}$Th incorporated into large-bandgap CaF$_{2}$ and MgF$_{2}$ crystals at the ISOLDE facility at CERN, photons of 8.338(24) eV are measured, in agreement with recent measurements$^{14–16}$ and the uncertainty is decreased by a factor of seven. The half-life of $^{229m}$Th embedded in MgF$_{2}$ is determined to be 670(102) s. The observation of the radiative decay in a large-bandgap crystal has important consequences for the design of a future nuclear clock and the improved uncertainty of the energy eases the search for direct laser excitation of the atomic nucleus. The nucleus of the radioisotope thorium-229 (${}^{229}$Th) features an isomer with an exceptionally low excitation energy that enables direct laser manipulation of nuclear states. For this reason, it is a leading candidate for use in next-generation optical clocks. This nuclear clock will be a unique tool, amongst others, for tests of fundamental physics. While first indirect experimental evidence for the existence of such an extraordinary nuclear state is significantly older, the proof of existence has been delivered only recently by observing the isomer's electron conversion decay and its hyperfine structure in a laser spectroscopy study, revealing information on the isomer's excitation energy, nuclear spin and electromagnetic moments. Further studies reported the electron conversion lifetime and refined the isomer's energy. In spite of recent progress, the isomer's radiative decay, a key ingredient for the development of a nuclear clock, remained unobserved. In this Letter, we report the detection of the radiative decay of this low-energy isomer in thorium-229 (${}^{229\mathrm{m}}$Th). By performing vacuum-ultraviolet spectroscopy of ${}^{229\mathrm{m}}$Th incorporated into large-bandgap CaF${}_2$ and MgF${}_2$ crystals at the ISOLDE facility at CERN, the photon vacuum wavelength of the isomer's decay is measured as 148.71(42) nm, corresponding to an excitation energy of 8.338(24) eV. This value is in agreement with recent measurements, and decreases the uncertainty by a factor of seven. The half-life of ${}^{229\mathrm{m}}$Th embedded in MgF${}_2$ is determined to be 670(102) s. The observation of the radiative decay in a large-bandgap crystal has important consequences for the design of a future nuclear clock and the improved uncertainty of the energy eases the search for direct laser excitation of the atomic nucleus.

Controlling the reciprocity between chemical reactivity and supramolecular structure is a topic of great interest in the emergence of molecular complexity. In this work, we investigate the effect of a covalent reaction as a trigger to depolymerize a supramolecular assembly. We focus on the impact of an in situ thiol–ene reaction on the (co)polymerization of three derivatives of benzene-1,3,5-tricarboxamide (BTA) monomers functionalized with cysteine, hexylcysteine, and alkyl side chains: Cys-BTA, HexCys-BTA, and a-BTA. Long supramolecular polymers of Cys-BTA can be depolymerized into short dimeric aggregates of HexCys-BTAvia the in situ thiol–ene reaction. Analysis of the system by time-resolved spectroscopy and light scattering unravels the fast dynamicity of the structures and the mechanism of depolymerization. Moreover, by intercalating the reactive Cys-BTA monomer into an unreactive inert polymer, the in situ thiol–ene reaction transforms the intercalator into a sequestrator and induces the depolymerization of the unreactive polymer. This work shows that the implementation of reactivity into supramolecular assemblies enables temporal control of depolymerization processes, which can bring us one step closer to understanding the interplay between non-covalent and covalent chemistry., We report on the controlled depolymerization of supramolecular 1D polymers into well-defined dimers triggered by a covalent reaction on the side chains of the monomer.

Efficient fragmentation of catalyst particles during the polymerization of olefins is a necessary process to maintain catalyst activity and obtain discrete polymer particles with ideal density and morphology. Collecting experimental evidence on the fragmentation process is essential for a fundamental understanding of this phenomenon. However, visualizing the very early onset of fragmentation within catalyst particles has been proven challenging. This study investigates the development of fragmentation at different reaction conditions in an industrial SiO2-supported metallocene catalyst of the type Zr/MAO/SiO2 (MAO = methylaluminoxane) early-stage of ethylene polymerization, i.e., in the range 1–20 g polyethylene per g catalyst. Focused ion beam-scanning electron microscopy was employed to visualize particle cross-sections with high 2-D resolution (i.e., a few tens of nm), showing that ethylene polymerization starts at two main fronts: one at the outer surface and one at the walls of the macropores within the particle. The relative rate of polymerization at these fronts was assessed by estimating the extent of polyethylene, catalyst, and macroporosity within each cross-section via image segmentation. When polymerization at these fronts proceeds at similar rates, fragmentation is extensive and a combination of both layer-by-layer and bi-sectioning modes; conversely, an imbalance between the two due to unideal reaction conditions, non-homogeneous active site distribution, or insufficient macroporosity leads to a sub-optimal fragmentation. This methodology revealed a detailed understanding of catalyst fragmentation for this commercial catalyst. However, it can be applied to a broader range of polymerization catalysts and parameters, amplifying the knowledge on such an intricated phenomenon.

How to control the self-assembly of complex molecular systems is unknown. Yet, these complex molecular systems are fundamental for advances in material and biomedical sciences. A step forward is to transform one-step self-assembly into multistep synthesis involving covalent and noncovalent reactions. Key to this approach is to explore the chemical space at the frontiers of advanced covalent synthesis and supramolecular chemistry. Herein, we describe a selection of such reported cases and provide a guide for current limitations and insights for future directions. This outlook is meant to trigger collaborations between synthetic organic and supramolecular chemists, to expand the repertoire of organic syntheses working with supramolecular assemblies and thereby join forces to achieve stepwise emergence of molecular complexity in supramolecular systems., We discuss the state-of-the-art, current limitations, and future directions of the synthesis of complex molecular systems using a combination of covalent and noncovalent reaction steps.

Supramolecular block copolymers composed of discrete blocks have promising properties for nanotechnology resulting from their ability to combine well-defined morphologies with good bulk material properties. Here, we present the impact of a well-defined siloxane block in either the main-chain or present as pendant grafts on the properties of supramolecular block copolymers that form ordered nanostructures with sub-5 nm domains. For this, two types of supramolecular block copolymers were synthesized based on the ureidopyrimidinone-urethane (UPy-UT) motif. In the first, oligodimethylsiloxanes (oDMS) of discrete length were end-capped with the UPy-UT motif, affording main-chain UPy-UT-Sin. In the second, the UPy-UT motif was grafted with discrete oDMS affording grafted UPy-UT-g-Si7. For the two systems, the compositions are similar; only the molecular architecture differs. In both cases, crystallization of the UPy-UT block is in synergy with phase segregation of the oDMS, resulting in the formation of lamellar morphologies. The grafted UPy-UT-g-Si7 can form long-range ordered lamellae, resulting in the formation of micrometer-sized 2D sheets of supramolecular polymers which show brittle properties. In contrast, UPy-UT-Sin forms a ductile material. As the compositions of both BCOs are similar, the differences in morphology and mechanical properties are a direct consequence of the molecular architecture. These results showcase how molecular design of the building block capable of forming block copolymers translates into controlled nanostructures and material properties as a result of the supramolecular nature of the interactions.

This work investigates the use of blast loadings and inverse modeling for the identification of the strain rate hardening model parameters of fibre reinforced polymers. An experimental setup allowing the generation of known and predictable blast waves, leading to repeatable dynamic response in composite plates and the measurement of the displacement and strain fields, is developed. The dynamic response of the plates is measured by means of high-speed cameras and a 3D digital image correlation technique. A suitable numerical model that is able to reproduce the experimental conditions and predict the blast response of the plates is developed. Finally, the experimental measurements and the numerical calculation are combined through an inverse method in order to identify the strain rate hardening model parameters of the tensile and shear strengths of glass fibre reinforced epoxy.

Supramolecular systems are intrinsically dynamic and sensitive to changes in molecular structure and external conditions. Because of these unique properties, strategies to control polymer length, composition, comonomer sequence, and morphology have to be developed for sufficient control over supramolecular copolymerizations. We designed photoresponsive, mono acyl hydrazone functionalized benzene-1,3,5-tricarboxamide (m-BTA) monomers that play a dual role in the coassembly with achiral alkyl BTAs (a-BTA). In the E isomer form, the chiral m-BTA monomers intercalate into stacks of a-BTA and dictate the chirality of the helices. Photoisomerization to the Z isomer transforms the intercalator into a chain capper, allowing dynamic shortening of chain length in the supramolecular aggregates. We combine optical spectroscopy and light-scattering experiments with theoretical modeling to show the reversible decrease in length when switching from the E to Z isomer of m-BTA in the copolymer with inert a-BTA. With a mass-balance thermodynamic model, we gain additional insights into the composition of copolymers and length distributions of the species over a broad range of concentrations and mixing ratios of a-BTA/m-BTA. Moreover, the model was used to predict the impact of an additive (chain capper and intercalator) on the chain length over a range of concentrations, showing a remarkable amplification of efficiency at high concentrations. By employing a stimuli-responsive comonomer in a mostly inert polymer, we can cooperatively amplify the effect of the switching and obtain photocontrol of polymer length. Moreover, this dynamic decrease in chain length causes a macroscopic gel-to-sol phase transformation of the copolymer gel, although 99.4% of the organogel is inert to the light stimulus.

The interest in Be as an impurity in GaN stems from the challenge to understand why GaN can be doped p type with Mg, while this does not work for Be. While theory has actually predicted an acceptor level for Be that is shallower than Mg, it was also argued that Be is not a suitable acceptor because its am-photeric nature, i.e. its tendency to occupy substitutional Ga as well as interstitial sites, would be considerably more pronounced than for Mg and hence lead to self-compensation. Using the emission channeling technique at the ISOLDE/CERN facility, we determined the lattice location of 11Be (t1/2 = 13.8 s) in different doping types of GaN as a function of implantation temperature. We find within an accuracy of 0.08 Å that the location of interstitial Be is the one predicted by theory. The room temperature interstitial fraction of 11Be was correlated with the GaN doping type, being highest (up to ~80%) in p type and lowest in n-GaN, thus giving direct evidence for the amphoteric character of Be. We find that interstitial 11Be fractions are generally much higher than for Mg, which confirms that indeed self-compensation should be consid-erably more pronounced for Be. With rising implantation temperature, an increasing conversion of interstitial to substitutional Be is observed, involving at least two clearly identifiable steps at 50–150 °C and 350–500 °C. This suggests that the migration of interstitial Be may be subject to two different activation ener-gies.

The combination of covalent and non-covalent synthesis is omnipresent in nature and potentially enables access to new materials. Yet, the fundamental principles that govern such a synthesis are barely understood. Here, we demonstrate how even simple reaction mixtures behave surprisingly complex when covalent reactions are coupled to self-assembly processes. Specifically, we study the reaction behavior of a system in which the in situ formation of discotic benzene-1,3,5-tricarboxamide (BTA) monomers is linked to an intertwined non-covalent reaction network including self-assembly into helical BTA polymers. This system shows an unexpected phase-separation behavior in which an interplay of reactant/product concentrations, side-products and solvent purity determines the system composition. We envision that these insights can bring us one step closer to how to design the synthesis of systems in a combined covalent/non-covalent fashion.

The influence of a patterned substrate on obliquely deposited, exchange biased Co/CoO films was studied. It was found that substrates decorated with nanoparticle patterns provide the option to manipulate the orientation of the magnetic easy axis in obliquely deposited thin films. The complementary methods of SQUID magnetometry and polarized neutron reflectometry were used to disentangle the different contributions to the magnetic hysteresis of such complex magnetic systems.

Control over molecular motion is facilitated in materials with highly ordered nanoscale structures. Here we report on the fabrication of cholesteric liquid-crystal networks by circularly polarized light irradiation, without the need for chiral dopant or plasticizer. The polymer network is obtained by photopolymerization of a smectic achiral diacrylate mesogen consisting of an azobenzene core and discrete oligodimethylsiloxane tails. The synchronous helical photoalignment and photopolymerization originate from the cooperative movement of the mesogens ordered in well-defined responsive structures, together with the flexibility of the oligodimethylsiloxane blocks. The resulting thin films show excellent thermal stability and light-induced memory features with reversible responses. Additionally, we demonstrate the fabrication of photo-patterned films of liquid-crystal networks with opposite helical senses. These findings provide a new method to make light-controllable chiroptical materials with exciting applications in optics and photonics.