Single‐Crystal‐to‐Single‐Crystal Transformation of a Europium(III) Metal–Organic Framework Producing a Multi‐responsive Luminescent Sensor

A sensor with a red‐emission signal is successfully obtained by the solvothermal reaction of Eu³⁺ and heterofunctional ligand bpydbH₂ (4,4′‐(4,4′‐bipyridine‐2,6‐diyl) dibenzoic acid), followed by terminal‐ligand exchange in a single‐crystal‐to‐single‐crystal transformation. As a result of treatments both before and after the metal–organic framework formation, accessible Lewis‐base sites and coordinated water molecules are successfully anchored onto the host material, and they act as signal transmission media for the recognition of analytes at the molecular level. This is the first reported sensor based on a metal–organic framework (MOF) with multi‐responsive optical sensing properties. It is capable of sensing small organic molecules and inorganic ions, and unprecedentedly it can discriminate among the homologues and isomers of aliphatic alcohols as well as detect highly explosive 2,4,6‐trinitrophenol (TNP) in water or in the vapor phase. This work highlights the practical application of luminescent MOFs as sensors, and it paves the way toward other multi‐responsive sensors by demonstrating the incorporation of various functional groups into a single framework.     

Metal–Organic Frameworks with Boronic Acid Suspended and Their Implication for cis‐Diol Moieties Binding

Introduction of accessible boronic acid functionality into metal–organic frameworks (MOFs) might to endow them with desired properties for potential applications in recognition and isolation of cis‐diol containing biomolecules (CDBs). However, no investigation is found to address this topic until now. Herein, Cr‐based MOFs of MIL‐100 (MIL stands for Materials from Institut Lavoisier) integrated with different pendent boronic acid group (MIL‐100‐B) are reported. This new functional material is successfully prepared using a simple metal–ligand–fragment coassembly (MLFC) strategy with isostructure to the parent MIL‐100 as verified by X‐ray diffraction characterization. The integration and content tunability of the boronic acid group in the framework are confirmed by X‐ray photoelectron spectroscopy and ¹¹B NMR. Transmission electron microscopy reveals that MIL‐100‐B can evolve into well‐defined morphology and nanoscale size at optimized boronic acid incorporating level. The obtained MOFs exhibit comparable surface areas and pore volumes with parent MIL‐100 and present exceptional chemical stability in a wide pH range. The inherent boronic acid components in MIL‐100‐B can effectively serve as the recognition units for the cis‐diol moieties and consequently enhance the capture capabilities for CDBs. The exceptional chemical stability, high porosity, and good reusability as well as the intrinsic cis‐diol moieties recognition function prefigure great potential of the current MIL‐100‐B in CDBs purification, sensing, and separation applications.     

Lanthanide–Organic Framework Nanothermometers Prepared by Spray‐Drying

Accurate, noninvasive, and self‐referenced temperature measurements at the submicrometer scale are of great interest, prompted by the ever‐growing demands in the fields of nanotechnology and nanomedicine. The thermal dependence of the phosphor's luminescence provides high detection sensitivity and spatial resolution with short acquisition times in, e.g., biological fluids, strong electromagnetic fields, and fast‐moving objects. Here, it is shown that nanoparticles of [(Tb_0.914Eu_0.086)₂(PDA)₃(H₂O)]·2H₂O (PDA = 1,4‐phenylenediacetic acid), the first lanthanide–organic framework prepared by the spray‐drying method, are excellent nanothermometers operating in the solid state in the 10–325 K range (quantum yield of 0.25 at 370 nm, at room temperature). Intriguingly, this system is the most sensitive cryogenic nanothermometer reported so far, combining high sensitivity (up to 5.96 ± 0.04% K^?1 at 25 K), reproducibility (in excess of 99%), and low‐temperature uncertainty (0.02 K at 25 K).