Dynamic Covalent Hydrazone Supramolecular Polymers toward Multiresponsive Self-Assembled Nanowire System

Stretchable, Strong, Recyclable Helicide Elastomer Based on Dynamic Covalent Interactions

Current methods for making and disposing synthetic polymers have been widely pursued and are largely unsustainable. As a part of the solution, the reversible nature of dynamic covalent bonds emerges as an extraordinarily diverse and valuable feature in the development of exotic molecules and extended structures. With these bonds, it should be possible to construct recyclable and mechanically interlocked molecular structures using relatively simple precursors with preorganized geometries. A new helicide-based elastomer network is developed here with self-healing, recycling, and degradation features using a similar concept. The best self-healing performance (100%) was noted over 10-20 min, with various H2O, HCl, and NaOH solutions that delivered mechanical properties in the 1-1.4 MPa range. For hydrolytic degradation, the parameters are defined based on the type of binding, the pH of the solutions, and the copolymer network, which endowed a degradation time of approximately 4-11 h for each prepared sample. However, due to the reversible nature of the dynamic bonds, the material showed good recyclable mechanical properties compared to the pristine samples after five consecutive cycles, which meet the requirements of recyclable materials and recyclable packaging.

A novel aggregation-induced enhanced emission aromatic molecule: 2-aminophenylboronic acid dimer

Aggregation-induced enhanced emission (AIEE) molecules have significant applications in optoelectronics, biomedical probes and chemical sensors, and large amounts of AIEE molecules have been reported since the concept of AIEE was proposed. Most aromatic AIEE molecules have complex structures consisting of multiple aromatic rings and/or polycyclic skeletons. In this study, we find that 2-aminophenylboronic acid (2-APBA) with a simple structure is highly emissive in the solid state. Further studies reveal that 2-APBA exists in a dimeric form, and the 2-APBA dimer is a novel AIEE molecule. The underlying AIEE mechanism is that the 2-APBA dimeric units aggregate through intermolecular interactions to produce highly ordered molecular packing without the presence of π–π stacking interactions that would lead to aggregation-caused quenching. Furthermore, the 2-APBA dimer aggregates could reversibly transform into its non-fluorescent monomer form driven by new kinds of dynamic covalent B–N and B–O bonds, illustrating its good potential in molecular recognition, nanogating, chemo/bio-sensing and controlled drug release.

The 2-APBA dimer tending to aggregate into a highly ordered structure is discovered to be AIEE active. Through alternate treatment with CO₂ and N₂, 2-APBA can switch between monomer and dimer aggregates driven by dynamic covalent B–N and B–O bonds.

Tuning the exchange dynamics of boronic acid hydrazones and oximes with pH and redox control

Dynamic bonds continually form and dissociate at equilibrium. Carbonyl compounds with proximal boronic acids, including 2-formylphenylboronic acid (2-FPBA), have been reported to form highly dynamic covalent hydrazone and oxime bonds in physiological conditions, but strategies to tune the dynamics have not yet been reported. Here, we characterize the dynamics of 2-FPBA-derived hydrazones and oximes and account for both the rapid rate of formation (∼102-103 M-1 s-1) and the relatively fast rate of hydrolysis (∼10-4 s-1) at physiological pH. We further show that these substrates undergo exchange with α-nucleophiles, which can be reversibly paused and restarted with pH control. Finally, we show that oxidation of the arylboronic acid effectively abolishes the rapid dynamics, which slows the forward reaction by more than 30 000 times and increases the hydrolytic half-life from 50 minutes to 6 months at physiological pH. These results set the stage to explore these linkages in dynamic combinatorial libraries, reversible bioconjugation, and self-healing materials.

Microcrystal Electron Diffraction Elucidates Water-Specific Polymorphism-Induced Emission Enhancement of Bis-arylacylhydrazone

Aggregation-induced emission (AIE) phenomena have gained intense interest over the last decades because of its importance in solid-state emission. However, the elucidation of a working mechanism is difficult owing to the limited characterization methods on solid-state molecules, further complicated if dynamic structural changes occur. Here, a series of bis-arylacylhydrazones (BAHs) were synthesized, for which their AIE properties are only turned on by the reversible adsorption of water molecules. We used microcrystal electron diffraction (MicroED) to determine the molecular structures of two BAHs directly from bulk powders (without attempting to grow crystals) prepared in the absence or presence of water adsorption. This study reveals the unambiguous characterization of the dependence of crystal packing on the specific cocrystallization with hydrates. The structural analysis demonstrates that water molecules form strong hydrogen bonds with three neighboring BAH-1, resulting in the almost complete planarization and restriction of the intramolecular rotation of the molecule. MicroED plays an important role in providing a decisive clue for the reversible polymorphism changes induced by the adsorption of water molecules, regulating emissive properties.

Additive-free photo-mediated oxidative cyclization of pyridinium acylhydrazones to 1,3,4-oxadiazoles: solid-state conversion in a microporous organic polymer and supramolecular energy-level engineering

We discovered the efficient catalyst-free, photo-mediated oxidative cyclization reaction of bis-p-pyridinium benzoyl hydrazone (BH1) to 2-pyridinium-5-phenyl-1,3,4-oxadiazoles.

Solvent processable and recyclable covalent adaptable organogels based on dynamic trans-esterification chemistry: separation of toluene from azeotropic mixtures

New covalent adaptable networks (CANs) possessing processability and recyclability to monomers are desirable as an alternative to traditional plastics to address plastic waste-related issues.

Photoredox Decarboxylative C(sp3)-N Coupling of α-Diazoacetates with Alkyl N-Hydroxyphthalimide Esters for Diversified Synthesis of Functionalized N-Alkyl Hydrazones

Herein we report a metal-free photocatalytic coupling reaction for the synthesis of structurally and functionally diverse N-alkyl hydrazones from α-diazoacetates and N-alkyl hydroxyphthalimide esters. By employing Rose Bengal as a photocatalyst with yellow LEDs irradiation, over 60 N-alkyl hydrazones were synthesized. Fluorescence quenching analysis and deuterium incorporation experiments reveal that Hantzsch ester serves as both an electron donor and proton source for the reaction. This strategy offers a simple retrosynthetic disconnection for conventionally inaccessible C(sp³)-rich N-alkyl hydrazones.

Enhancing the kinetics of hydrazone exchange processes: an experimental and computational study

Hydrogen-bond acceptors (A) stabilize the transition state, lowering the energy barrier to rapid hydrazone exchange, without need for exogenous catalyst.