Nitric Oxide (NO) as a Reagent for Topochemical Framework Transformation and Controlled NO Release in Covalent Organic Frameworks.

Covalent organic frameworks (COFs) have emerged as versatile platforms for the separation and storage of hazardous gases. Simultaneously, the synthetic toolbox to tackle the "COF trilemma" has been diversified to include topochemical linkage transformations and post-synthetic stabilization strategies. Herein, we converge these themes and reveal the unique potential of nitric oxide (NO) as a new reagent for the scalable gas-phase transformation of COFs. Using physisorption and solid-state nuclear magnetic resonance spectroscopy on 15N-enriched COFs, we study the gas uptake capacity and selectivity of NO adsorption and unravel the interactions of NO with COFs. Our study reveals the clean deamination of terminal amine groups on the particle surfaces by NO, exemplifying a unique surface passivation strategy for COFs. We further describe the formation of a NONOate linkage by the reaction of NO with an amine-linked COF, which shows controlled release of NO under physiological conditions. NONOate-COFs thus show promise as tunable NO delivery platforms for bioregulatory NO release in biomedical applications.

Direct and Linker-Exchange Alcohol-Assisted Hydrothermal Synthesis of Imide-Linked Covalent Organic Frameworks.

Covalent organic frameworks (COFs) are an extensively studied class of porous materials, which distinguish themselves from other porous polymers in their crystallinity and high degree of modularity, enabling a wide range of applications. However, the established synthetic protocols for the synthesis of stable and crystalline COFs, such as imide-linked COFs, often requires the use of high boiling solvents and toxic catalysts, making their synthesis expensive and environmentally harmful. Herein, we report a new environmentally friendly strategy-an alcohol-assisted hydrothermal polymerization approach (aaHTP) for the synthesis of a wide range of crystalline and porous imide-linked COFs. This method allows us to gain access to new COFs and to avoid toxic solvents by up to 90% through substituting commonly used organic solvent mixtures with water and small amounts of n-alcohols without being restricted to water-soluble linker molecules. Additionally, we use the aaHTP to demonstrate an eco-friendly COF-to-COF transformation of an imine-linked COF into a novel imide-linked COF via linkage replacement, inaccessible using published reaction conditions.

Ionothermal Synthesis of Imide-Linked Covalent Organic Frameworks.

Covalent organic frameworks (COFs) are an extensively studied class of porous materials, which distinguish themselves from other porous polymers in their crystallinity and high degree of modularity, enabling a wide range of applications. COFs are most commonly synthesized solvothermally, which is often a time-consuming process and restricted to well-soluble precursor molecules. Synthesis of polyimide-linked COFs (PI-COFs) is further complicated by the poor reversibility of the ring-closing reaction under solvothermal conditions. Herein, we report the ionothermal synthesis of crystalline and porous PI-COFs in zinc chloride and eutectic salt mixtures. This synthesis does not require soluble precursors and the reaction time is significantly reduced as compared to standard solvothermal synthesis methods. In addition to applying the synthesis to previously reported imide COFs, a new perylene-based COF was also synthesized, which could not be obtained by the classical solvothermal route. In situ high-temperature XRPD analysis hints to the formation of precursor-salt adducts as crystalline intermediates, which then react with each other to form the COF.

In†Situ Generation of Electrolyte inside Pyridine-Based Covalent Triazine Frameworks for Direct Supercapacitor Integration.

The synthesis of porous electrode materials is often linked with the generation of waste that results from extensive purification steps and low mass yield. In contrast to porous carbons, covalent triazine frameworks (CTFs) display modular properties on a molecular basis through appropriate choice of the monomer. Herein, the synthesis of a new pyridine-based CTF material is showcased. The porosity and nitrogen-doping are tuned by a careful choice of the reaction temperature. An in-depth structural characterization by using Ar physisorption, X-ray photoelectron spectroscopy, and Raman spectroscopy was conducted to give a rational explanation of the material properties. Without any purification, the samples were applied as symmetrical supercapacitors and showed a specific capacitance of 141 F g-1 . Residual ZnCl2 , which acted formerly as the porogen, was used directly as the electrolyte salt. Upon the addition of water, ZnCl2 was dissolved to form the aqueous electrolyte in situ. Thereby, extensive and time-consuming washing steps could be circumvented.