The widespread contamination of water by emerging contaminants (ECs) demands the development of efficient remediation technologies. Although advanced oxidation processes reliant on reactive oxygen species (ROS) show promise, they typically depend on energy- or reagent-intensive activation methods. Here, we introduce a linker steric hindrance-induced defect engineering (LSH-DE) strategy for metal–organic frameworks, which enables catalytic ROS generation using molecular oxygen (O2) as a benign terminal oxidant at ambient temperature and pressure. By systematically modulating the steric bulk of organic linkers, we precisely create missing-linker defects and direct the formation of oxygen vacancy (Vo) in robust Ce-UiO-66 during a rapid 15 min synthesis. Spectroscopic and computational analyses confirm that these oxygen vacancies promote O2 adsorption and activation to yield superoxide radicals (•O2–). The optimized catalyst, Ce-UiO-66-(CH3)2, demonstrates superior activity in degrading ubiquitous ECs without requiring external energy inputs or chemical mediators. Furthermore, integration of Ce-UiO-66-(CH3)2 into a membrane-based recirculating flow-through system enabled sustained water treatment, maintaining >90% BPA removal over 48 h with a high water permeance of 101.5 L m–2 h–1 bar–1. This work presents a general and sustainable approach for designing catalytic defects in MOFs, advancing the development of green, next-generation water purification technologies.
Abstract Carbon dots (CDs) have emerged as scalable, metal-free photocatalysts, but their use as conjugate organo-photocatalysts for enantioselective chemistry remains unexplored. Here, we covalently anchor a chiral imidazolidinone organocatalyst to amorphous, citric acid-derived CDs, giving a colloidal conjugate that acts as both photosensitizer and enantiodetermining component. This chiral CD material promotes the asymmetric radical α-alkylation of aldehydes in up to 84% yield and 93% e.e. Its semihomogeneous nature enables catalyst recovery by precipitation and reuse over five cycles with only minor loss in yield and e.e. The well-dispersed conjugate is also compatible with continuous photoflow, where Bayesian optimization in only 10 experiments enabled a gram-scale reaction in 80% yield and 91% e.e. This work establishes chiral conjugate CDs as a practical, recoverable platform for sustainable asymmetric photocatalysis.
Chromium-catalyzed asymmetric Nozaki–Hiyama–Kishi (NHK) reaction is a powerful tool for constructing synthetically valuable enantioenriched homoallylic alcohols and allenols. However, catalytic asymmetric NHK-type coupling of allylic or propargylic C–O electrophiles remains largely underdeveloped. Herein, we report a photomediated chromium-catalyzed deoxygenative coupling of activated allylic and propargylic alcohols with aldehydes, enabling the synthesis of a variety of chiral homoallylic alcohols with wide structural diversity and allenols. The reactions were performed under mild conditions, and a wide range of synthetically useful functional groups was found to be well tolerated. Importantly, this method provides a straightforward way for the construction of homoallylic alcohols bearing a chiral quaternary carbon center with high ee and dr. Furthermore, stereodivergent access to all four homoallylic alcohol stereoisomers is realized through orthogonal combinations of Z/E-configured allylic alcohols and R/S-configured ligands. Combined experimental and computational mechanistic studies provided insight into the key catalytic intermediate and the origin of stereocontrol.
Molecular solar thermal (MOST) energy storage compounds capture solar photon energy in the strained chemical bonds of metastable photoisomers and release it on demand as heat, yet simultaneously achieving visible-light absorption and high energy storage density has remained a persistent challenge. Here we introduce 9-aryl acridine N-oxides as MOST compounds based on visible-light-driven dearomative ring expansion. Irradiation at 470 nm, near the solar irradiance maximum at 482 nm, quantitatively converts these compounds to metastable 1,2-oxazepines, which thermally revert to the parent N-oxides and discharge the stored energy. The system achieves energy storage densities of up to 0.54 MJ/kg, comparable to Dewar anthracenes, while absorbing substantially more red-shifted light and offering nearly 3 orders of magnitude longer storage lifetimes of up to 1.4 years in the solid state. The thermal half-lives of the 1,2-oxazepines are tunable through para-substitution on the aryl ring and solvation, enabling up to a 1,300-fold reduction in half-life. Crucially, the 9-aryl substituent biases the transient oxaziridine intermediate toward selective reversion to the N-oxide over competing decomposition pathways, overcoming the limitations of other acridine N-oxides reported to date. This work establishes light-induced ring expansion as an effective strategy for MOST and expands the scope of viable MOST compounds.
Biomarker-specific molecular imaging is vital in precision medicine. However, a fundamental challenge of most molecular imaging methods is the difficulty of distinguishing specific molecular signal from nonspecific signal arising from the distribution of the molecular probe. This is even more pronounced in metabolically active organs such as the kidney and liver where the probe may concentrate prior to elimination. As a result, almost all molecular imaging relies on delayed imaging to achieve specificity, but this constrains clinical throughput and impedes rapid assessment of the diseased organ. Here, we report a magnetic resonance (MR) probe, Fe(II)-IAFP2, which combines 3 drivers of relaxivity enhancement to decouple disease specificity from probe distribution. Fe(II)-IAFP2 is MR-silent in its Fe(II) state, producing negligible MR signal even at high concentrations. In inflammatory, fibrogenic microenvironments common to many diseases, rapid oxidation to Fe(III) activates MR enhancement, while reversible aldehyde-mediated binding to remodeled extracellular matrix further amplifies relaxivity and promotes retention at the site of tissue injury. This dual activation–retention mechanism enables robust signal generation within minutes of administration. In mouse models of renal and liver fibrogenesis, Fe(II)-IAFP2 generated disease-associated MR contrast within minutes after intravenous administration. Together, this work demonstrates an effective strategy for rapid, activity-based molecular MR imaging through the combination of pathological activation and complementary tissue retention.
