Macromolecular Design Strategies for Preventing Active‐Material Crossover in Non‐Aqueous All‐Organic Redox‐Flow Batteries

Intermittent energy sources, including solar and wind, require scalable, low‐cost, multi‐hour energy storage solutions in order to be effectively incorporated into the grid. All‐Organic non‐aqueous redox‐flow batteries offer a solution, but suffer from rapid capacity fade and low Coulombic efficiency due to the high permeability of redox‐active species across the battery's membrane. Here we show that active‐species crossover is arrested by scaling the membrane's pore size to molecular dimensions and in turn increasing the size of the active material above the membrane's pore‐size exclusion limit. When oligomeric redox‐active organics (RAOs) were paired with microporous polymer membranes, the rate of active‐material crossover was reduced more than 9000‐fold compared to traditional separators at minimal cost to ionic conductivity. This corresponds to an absolute rate of RAO crossover of less than 3 μmol cm⁻² day⁻¹ (for a 1.0 m concentration gradient), which exceeds performance targets recently set forth by the battery industry. This strategy was generalizable to both high and low‐potential RAOs in a variety of non‐aqueous electrolytes, highlighting the versatility of macromolecular design in implementing next‐generation redox‐flow batteries.     

Photoresponsive Circular Supramolecular Polymers: A Topological Trap and Photoinduced Ring‐Opening Elongation

Topological features of one‐dimensional macromolecular chains govern the properties and functionality of natural and synthetic polymers. To address this issue in supramolecular polymers, we synthesized two topologically distinct supramolecular polymers with intrinsic curvature, circular and helically folded nanofibers, from azobenzene‐functionalized supramolecular rosettes. When a mixture of circular and helically folded nanofibers was exposed to UV light, selective unfolding of the latter open‐ended supramolecular polymers was observed as a result of the curvature‐impairing internal force produced by the trans‐to‐cis photoisomerization of the azobenzene. This distinct sensitivity suggests that the topological features of supramolecular polymers define their mechanical stability. Furthermore, the exposure of circular supramolecular polymers in more polar media to UV irradiation resulted in ring opening followed by chain elongation, thus demonstrating that the circular supramolecular polymer can function as a topological kinetic trap.     

Backbone‐Degradable Polymers Prepared by Chemical Vapor Deposition

Polymers prepared by chemical vapor deposition (CVD) polymerization have found broad acceptance in research and industrial applications. However, their intrinsic lack of degradability has limited wider applicability in many areas, such as biomedical devices or regenerative medicine. Herein, we demonstrate, for the first time, a backbone‐degradable polymer directly synthesized via CVD. The CVD co‐polymerization of [2.2]para ‐cyclophanes with cyclic ketene acetals, specifically 5,6‐benzo‐2‐methylene‐1,3‐dioxepane (BMDO), results in well‐defined, hydrolytically degradable polymers, as confirmed by FTIR spectroscopy and ellipsometry. The degradation kinetics are dependent on the ratio of ketene acetals to [2.2]para ‐cyclophanes as well as the hydrophobicity of the films. These coatings address an unmet need in the biomedical polymer field, as they provide access to a wide range of reactive polymer coatings that combine interfacial multifunctionality with degradability.     

Synthesis of Responsive Two‐Dimensional Polymers via Self‐Assembled DNA Networks

Despite a growing interest in two‐dimensional polymers, their rational synthesis remains a challenge. The solution‐phase synthesis of a two‐dimensional polymer is reported. A DNA‐based monomer self‐assembles into a supramolecular network, which is further converted into the covalently linked two‐dimensional polymer by anthracene dimerization. The polymers appear as uniform monolayers, as shown by AFM and TEM imaging. Furthermore, they exhibit a pronounced solvent responsivity. The results demonstrate the value of DNA‐controlled self‐assembly for the formation of two‐dimensional polymers in solution.     

Tight Xenon Confinement in a Crystalline Sandwich‐like Hydrogen‐Bonded Dimeric Capsule of a Cyclic Peptide

A cyclic hexapeptide with three pyridyl moieties connected to its backbone forms a hydrogen‐bonded dimer, which tightly encapsulates a single xenon atom, like a pearl in its shell. The dimer imprints its shape and symmetry to the captured xenon atom, as demonstrated by ¹²⁹Xe NMR spectroscopy, single‐crystal X‐ray diffraction, and computational studies. The dimers self‐assemble hierarchically into tubular structures to form a porous supramolecular architecture, whose cavities are filled by small molecules and gases.     

One‐Pot Synthesis of Cyclopropane‐Fused Cyclic Amidines: An Oxidative Carbanion Cyclization

A novel and efficient one‐pot method has been developed for the synthesis of cyclopropane‐fused bicyclic amidines on the basis of a CuBr₂‐mediated oxidative cyclization of carbanions. The usefulness of this unique multicomponent strategy has been demonstrated by the use of a wide variety of substrates to furnish novel cyclopropane‐containing amidines with a quaternary center in very good yields. This ketenimine‐based approach provides straightforward access to biologically active and pharmaceutically important 3‐azabicyclo[n .1.0]alkane frameworks under mild conditions. The synthetic power of this methodology is exemplified in the concise synthesis of the pharmaceutically important antidepressant drug candidate GSK1360707 and key intermediates for the synthesis of amitifadine, bicifadine, and narlaprevir.