Supramolecular Polymerization as a Tool to Reveal the Magnetic Transition Dipole Moment of Heptazines.

Heptazine derivatives have attracted significant interest due to their small S1-T1 gap, which contributes to their unique electronic and optical properties. However, the nature of the lowest excited state remains ambiguous. In the present study, we characterize the lowest optical transition of heptazine by its magnetic transition dipole moment. To measure the magnetic transition dipole moment, the flat heptazine must be chiroptically active, which is difficult to achieve for single heptazine molecules. Therefore, we used supramolecular polymerization as an approach to make homochiral stacks of heptazine derivatives. Upon formation of the supramolecular polymers, the preferred helical stacking of heptazine introduces circular polarization of absorption and fluorescence. The magnetic transition dipole moments for the S1 ← S0 and S1 → S0 are determined to be 0.35 and 0.36 Bohr magneton, respectively. These high values of magnetic transition dipole moments support the intramolecular charge transfer nature of the lowest excited state from nitrogen to carbon in heptazine and further confirm the degeneracy of S1 and T1.

Trade-off between processability and device performance in donor-acceptor semiconductors revealed using discrete siloxane side chains.

Donor-acceptor polymeric semiconductors are crucial for state-of-the-art applications, such as electronic skin mimics. The processability, and thus solubility, of these polymers in benign solvents is critical and can be improved through side chain engineering. Nevertheless, the impact of novel side chains on backbone orientation and emerging device properties often remains to be elucidated. Here, we investigate the influence of elongated linear and branched discrete oligodimethylsiloxane (oDMS) side chains on solubility and device performance. Thereto, diketopyrrolopyrrole-thienothiophene polymers are equipped with various oDMS pendants (PDPPTT-Sin) and subsequently phase separated into lamellar domains. The introduction of a branching point in the siloxane significantly enhanced the solubility of the polymer, as a result of increased backbone distortion. Simultaneously, the charge carrier mobility of the polymers decreased by an order of magnitude upon functionalization with long and/or branched siloxanes. This work unveils the intricate balance between processability and device performance in organic semiconductors, which is key for the development of next-generation electronic devices.

Consequences of Vibrational Strong Coupling on Supramolecular Polymerization of Porphyrins.

Supramolecular polymers display interesting optoelectronic properties and, thus, deploy multiple applications based on their molecular arrangement. However, controlling supramolecular interactions to achieve a desirable molecular organization is not straightforward. Over the past decade, light-matter strong coupling has emerged as a new tool for modifying chemical and material properties. This novel approach has also been shown to alter the morphology of supramolecular organization by coupling the vibrational bands of solute and solvent to the optical modes of a Fabry-Perot cavity (vibrational strong coupling, VSC). Here, we study the effect of VSC on the supramolecular polymerization of chiral zinc-porphyrins (S-Zn) via a cooperative effect. Electronic circular dichroism (ECD) measurements indicate that the elongation temperature (Te) of the supramolecular polymerization is lowered by ∼10 °C under VSC. We have also generalized this effect by exploring other supramolecular systems under strong coupling conditions. The results indicate that the solute-solvent interactions are modified under VSC, which destabilizes the nuclei of the supramolecular polymer at higher temperatures. These findings demonstrate that the VSC can indeed be used as a tool to control the energy landscape of supramolecular polymerization. Furthermore, we use this unique approach to switch between the states formed under ON- and OFF-resonance conditions, achieved by simply tuning the optical cavity in and out of resonance.

Supramolecular polymers form tactoids through liquid-liquid phase separation.

Liquid-liquid phase separation (LLPS) of biopolymers has recently been shown to play a central role in the formation of membraneless organelles with a multitude of biological functions1-3. The interplay between LLPS and macromolecular condensation is part of continuing studies4,5. Synthetic supramolecular polymers are the non-covalent equivalent of macromolecules but they are not reported to undergo LLPS yet. Here we show that continuously growing fibrils, obtained from supramolecular polymerizations of synthetic components, are responsible for phase separation into highly anisotropic aqueous liquid droplets (tactoids) by means of an entropy-driven pathway. The crowding environment, regulated by dextran concentration, affects not only the kinetics of supramolecular polymerizations but also the properties of LLPS, including phase-separation kinetics, morphology, internal order, fluidity and mechanical properties of the final tactoids. In addition, substrate-liquid and liquid-liquid interfaces proved capable of accelerating LLPS of supramolecular polymers, allowing the generation of a myriad of three-dimensional-ordered structures, including highly ordered arrays of micrometre-long tactoids at surfaces. The generality and many possibilities of supramolecular polymerizations to control emerging morphologies are demonstrated with several supramolecular polymers, opening up a new field of matter ranging from highly structured aqueous solutions by means of stabilized LLPS to nanoscopic soft matter.

Tunable emission from H-type supramolecular polymers in optical nanocavities.

H-type supramolecular polymers with preferred helicity and highly efficient emission have been prepared from the self-assembly of chiral tetraphenylene-based monomers. Implementation of the one-dimensional fibers into dielectric nanoparticle arrays allows for a significant reshaping of fluorescence due to weak light-matter coupling.

Solvent-Induced Pathway Complexity of Supramolecular Polymerization Unveiled Using the Hansen Solubility Parameters.

Supramolecular building blocks assembling into helical aggregates are ubiquitous in the current literature, yet the role of solvents in these supramolecular polymerizations often remains elusive. Here, we present a systematic study that quantifies solvent-supramolecular polymer compatibility using the Hansen solubility parameters (δD, δH, and δP). We first studied the solubility space of the supramolecular building block triazine-1,3,5-tribenzenecarboxamide S-T. Due to its amphiphilic nature, a dual-sphere model based on 58 solvents was applied describing the solubility space of the monomeric state (green sphere) and supramolecular polymer state (blue sphere). To our surprise, further in-depth spectroscopic and morphological studies unveiled a distinct solubility region in-between the two spheres giving rise to the formation of higher-order aggregated structures. This phenomenon occurs due to subtle differences in polarity between the solvent and the side chains and highlights the solvent-induced pathway complexity of supramolecular polymerizations. Subsequent variations in concentration and temperature led to the expansion and contraction of both solubility spheres providing two additional features to tune the monomer and supramolecular polymer solubility. Finally, we applied our dual-sphere model on structurally disparate monomers, such as Zn-porphyrin (S-P) and triphenylamine (S-A), demonstrating the generality of the model and the importance of the supramolecular monomer design in connection with the solvent used. This work unravels the solvent-induced pathway complexity of discotic supramolecular building blocks using a parametrized approach in which interactions between the solvent and solute play a crucial role.

The Importance of Effective Ligand Concentration to Direct Epithelial Cell Polarity in Dynamic Hydrogels.

Epithelial cysts and organoids are multicellular hollow structures formed by correctly polarized epithelial cells. Important in steering these cysts from single cells is the dynamic regulation of extracellular matrix presented ligands, and matrix dynamics. Here, control over the effective ligand concentration is introduced, decoupled from bulk and local mechanical properties, in synthetic dynamic supramolecular hydrogels formed through noncovalent crosslinking of supramolecular fibers. Control over the effective ligand concentration is realized by 1) keeping the ligand concentration constant, but changing the concentration of nonfunctionalized molecules or by 2) varying the ligand concentration, while keeping the concentration of non-functionalized molecules constant. The results show that in 2D, the effective ligand concentration within the supramolecular fibers rather than gel stiffness (from 0.1 to 8 kPa) regulates epithelial polarity. In 3D, increasing the effective ligand concentration from 0.5 × 10-3 to 2 × 10-3 m strengthens the effect of increased gel stiffness from 0.1 to 2 kPa, to synergistically yield more correctly polarized cysts. Through integrin manipulation, it is shown that epithelial polarity is regulated by tension-based homeostasis between cells and matrix. The results reveal the effective ligand concentration as influential factor in regulating epithelial polarity and provide insights on engineering of synthetic biomaterials for cell and organoid culture.

Reversible Perspiring Artificial "Fingertips".

Fingertip perspiration is a vital process within human predation, to which the species owes its survival and its biological success. In this paper, the unique human ability of extensive perspiration and controlled friction in self-assembled cholesteric liquid crystals is recreated, mimicking the natural processes that occur in the dermis and epidermis of human skin. This is achieved by inducing porosity in responsive, liquid-bearing material through the controlled-polymerization phase-separation process. The unique topography of human fingerprints is further emulated in the materials by balancing the parallel chirality-induced force and the perpendicular substrate-anchoring force during synthesis. As a result, artificial fingertips are capable of secreting and re-absorbing liquid upon light illumination. By demonstrating the function of the soft material in a tribological aspect, it exhibits a controllable anti-sliding property comparable to human fingertips and subsequently attains a higher degree of biomimicry. This biomimetic fingertip is envisioned being applied in a multitude of fields, ranging from biomedical instruments to interactive, human-like soft robotic devices.

Photo-responsive liquid crystal network-based material with adaptive modulus for haptic application.

Artificially created tactile feedback is in high demand due to fast developments in robotics, remote control in medicine, virtual reality, and smart electronics. Despite significant progress, high-quality haptic feedback devices remain challenging mainly due to the lack of stability and spatiotemporal resolution. In this work, we address these issues by the application of dynamic coatings, based on photo-responsive liquid crystal network (LCN) material. This material adapts upon an external stimulus (UV light with a power intensity of 50-90 mW/cm2) that changes its elastic properties (87% decrease of the modulus for 90 mW/cm2 power intensity of 365 nm UV light). Localized change of adaptive modulus with very high resolution (2 µm) was demonstrated.

Controlling the Processability and Stability of Supramolecular Polymers Using the Interplay of Intra- and Intermolecular Interactions.

Polymer networks crosslinked via non-covalent interactions afford interesting materials for a wide range of applications due to their self-healing capability, recyclability, and tunable material properties. However, when strong non-covalent binding motifs in combination with high crosslink density are used, processing of the materials becomes troublesome because of high viscosities and the formation of insoluble gels. Here, we present an approach to control the processability of grafted polymers containing strong non-covalent interactions by balancing the interplay of intra- and intermolecular hydrogen bonding. A library of copolymers with different degrees of polymerization and content of protected ureido-pyrimidinone-urea (UPy-urea) grafts was prepared. Photo-deprotection in a good solvent like tetrahydrofuran (THF) at low concentrations (≤1 mg mL-1) created intramolecularly assembled nanoparticles. Remarkably, the intrinsic viscosity of these nanoparticle solutions was an order of magnitude lower compared to solutions of the intermolecularly assembled analogues, highlighting the crucial role of intra- versus intermolecular interactions. Due to the strong hydrogen bonds between UPy dimers, the intramolecularly assembled structures were kinetically trapped. As a result, the polymer nanoparticles were readily processed into a bulk material, without causing major changes in the morphology as verified by atomic force microscopy. Subsequent intermolecular crosslinking of the nanoparticle film, by heating to temperatures where the hydrogen-bond exchange becomes fast, resulted in a crosslinked network. The reversibility of the hereby obtained polymer networks was shown by retrieving the intramolecularly assembled nanoparticles via redissolution and sonication of the intermolecularly crosslinked film in THF with a small amount of acid. Our results highlight that the stability and processability of highly supramolecularly crosslinked polymers can be controlled both in solution and in bulk by using the interplay of intra- and intermolecular non-covalent interactions in grafted polymers.

Consequences of Molecular Architecture on the Supramolecular Assembly of Discrete Block Co-oligomers.

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-Si n . In the second, the UPy-UT motif was grafted with discrete oDMS affording grafted UPy-UT- g -Si 7 . 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 -Si 7 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-Si n 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.