Dynamic Entwined Topology in Helical Covalent Polymers Dictated by Competing Supramolecular Interactions

Naturally occurring polymeric structures often consist of 1D polymer chains intricately folded and entwined through non-covalent bonds, adopting precise topologies crucial for their functionality. The exploration of crystalline 1D polymers through dynamic covalent chemistry (DCvC) and supramolecular interactions represents a novel approach for developing crystalline polymers. This study shows that sub-angstrom differences in the counter-ion size can lead to various helical covalent polymer (HCP) topologies, including a novel metal-coordination HCP (m-HCP) motif. Single-crystal X-ray diffraction (SCXRD) analysis of HCP-Na revealed that double helical pairs are formed by sodium ions coordinating to spiroborate linkages to form rectangular pores. The double helices are interpenetrated by the unreacted diols coordinating sodium ions. The reticulation of the m-HCP structure was demonstrated by the successful synthesis of HCP-K. Finally, ion-exchange studies were conducted to show the interconversion between HCP structures. This research illustrates how seemingly simple modifications, such as changes in counter-ion size, can significantly influence the polymer topology and determine which supramolecular interactions dominate the crystal lattice.

3D Covalent Organic Framework as a Metastable Intermediate in the Formation of a Double-Stranded Helical Covalent Polymer

The design and development of intricate artificial architectures have been pursued for decades. Helical covalent polymer (HCP) was recently reported as an unexpected topology that consists of chiral 1D polymers assembled through weak hydrogen bonds from achiral building blocks. However, many questions remained about the formation, driving force, and the single-handedness observed in each crystal. In this work, we reveal a metastable, racemic, fully covalently cross-linked, 3D covalent organic framework (COF) as an intermediate in the early stage of polymerization, which slowly converts into single-handed HCP double helices through partial fragmentation and self-sorting with the aid of a series of hydrogen bonding. Our work provides an intriguing example where weak noncovalent bonds serve as the determining factor of the overall product structure and facilitate the formation of a sophisticated polymeric architecture.

Dynamic Covalent Self-sorting in Molecular and Polymeric Architectures Enabled by Spiroborate Bond Exchange

Self-sorting is commonly observed in complex reaction systems, which has been utilized to guide the formation of single major by-design molecules. However, most studies have been focused on non-covalent systems, and using self-sorting to achieve covalently bonded architectures is still relatively less explored. In this work, we first demonstrated the dynamic nature of spiroborate linkage and systematically studied the self-sorting behavior observed in the transformation between spiroborate-linked well-defined polymeric and molecular architectures, which are enabled by spiroborate bond exchange. The scrambling between a macrocycle and a 1D helical covalent polymer led to the formation of a molecular cage, whose structures are all unambiguously elucidated by single-crystal X-ray diffraction. The results indicate that the molecular cage is the thermodynamically favored product in this multi-component reaction system. This work represents the first example that a 1D polymeric architecture transforms into a shape-persistent molecular cage, driven by dynamic covalent self-sorting. This study will further guide the design of spiroborate-based materials and open the possibilities for the development of novel complex yet responsive dynamic covalent molecular or polymeric systems.

Cyanurate-Linked Covalent Organic Frameworks Enabled by Dynamic Nucleophilic Aromatic Substitution

We report, for the first time, highly crystalline cyanurate-linked covalent organic frameworks synthesized via dynamic nucleophilic aromatic substitution. The high crystallinity is enabled by the bond exchange reaction (self-correction) between 2,4,6-triphenoxy-1,3,5-triazine and diphenols via reversible S_NAr catalyzed by triazabicyclodecene. The CN-COFs contain flexible backbones that exhibit a unique AA'-stacking due to interlayer hydrogen bonding interactions. The isoreticular expansion study demonstrates the general applicability of this synthetic method. The resulting CN-COFs exhibited good stability, as well as high CO₂/N₂ selectivity.

sp-Carbon Incorporated Conductive Metal-Organic Framework as Photocathode for Photoelectrochemical Hydrogen Generation

Metal-organic frameworks (MOFs) have attracted increasing interest for broad applications in catalysis and gas separation due to their high porosity. However, the insulating feature and the limited active sites hindered MOFs as photocathode active materials for application in photoelectrocatalytic hydrogen generation. Herein, we develop a layered conductive two-dimensional conjugated MOF (2D c-MOF) comprising sp-carbon active sites based on arylene-ethynylene macrocycle ligand via CuO₄ linking, named as Cu₃ HHAE₂ . This sp-carbon 2D c-MOF displays apparent semiconducting behavior and broad light absorption till the near-infrared band (1600 nm). Due to the abundant acetylene units, the Cu₃ HHAE₂ could act as the first case of MOF photocathode for photoelectrochemical (PEC) hydrogen generation and presents a record hydrogen-evolution photocurrent density of ≈260 μA cm^-2 at 0 V vs. reversible hydrogen electrode among the structurally-defined cocatalyst-free organic photocathodes.

Urea-derived graphitic carbon nitride (u-g-C3N4) films with highly enhanced antimicrobial and sporicidal activity

In this manuscript, we describe the fabrication of photoactive biocidal or sporicidal films from urea-derived graphitic carbon nitride (u-g-C₃N₄). Co-deposited films of u-g-C₃N₄ and Escherichia coli O157:H7 (IC₅₀=14.1±0.2mJ) or Staphylococcus aureus (methicillin resistant IC₅₀=33.5±0.2mJ, methicillin sensitive IC₅₀=42.7±0.5mJ) demonstrated significantly enhanced bactericidal behavior upon administration of visible radiation (400nm≤λ≤426nm). In all cases, complete eradication of the microbial sample was realized upon administration of 100mJ of visible radiation, while no antimicrobial activity was observed for non-irradiated samples. In contrast, Bacillus anthracis endospores were more resistant to u-g-C₃N₄ mediated killing with only a ca. 25% reduction in spore viability when treated with a 200mJ dose of visible radiation. Characterization of u-g-C₃N₄ reveals that the improved activity results from enhancements of both the surface area and reduction potential of the material's conduction band edge, coupled with fast injection of charge carriers into localized states and a decline in radiative recombination events. The results of this study demonstrate that g-C₃N₄-based materials offer a viable scaffold for the development of new, visible light driven technologies for controlling potentially pathogenic microorganisms.