A Miniaturized Linear pH Sensor Based on a Highly Photoluminescent Self-Assembled Europium(III) Metal-Organic Framework

Second-Sphere Interaction Promoted Turn-On Fluorescence for Selective Sensing of Organic Amines in a TbIII -based Macrocyclic Framework

Guided by a second-sphere interaction strategy, we fabricated a Tb(III)-based metal-organic framework (MMCF-4) for turn-on sensing of methyl amine with ultra-low detection limit and high turn-on efficiency. MMCF-4 features lanthanide nodes shielded in a nonacoordinate geometry along with secondary coordination spheres that are densely populated with H-bond interacting sites. Nonradiative routes were inhibited by binding-induced rigidification of the ligand on the second coordination sphere, resulting in luminescence amplification. Such remote interacting mechanism involved in the turn-on sensing event was confirmed by single-crystal X-ray diffraction and molecular dynamic simulation studies. The design of both primary and secondary coordination spheres of Tb(III) enabled the first turn-on sensing of organic amines in aqueous conditions. Our work suggests a promising strategy for high-performance turn-on sensing for Ln-MOFs and luminous materials driven by other metal chromophores.

Recent Advances in Small Molecule-Based Intracellular pH Probes

Intracellular pH plays an important role in many biological and pathological processes. Small-molecule based pH probes are found to be the most effective for pH sensing because of ease of preparation, high sensitivity, and quick response. They have many advantages such as small perturbation to the functions of the target, functional adaptability, cellular component-specific localization, etc. The present review highlights the flurry of recent activity in the development of such probes. The probes are categorized based on the type of fluorophore used like quinoline, coumarin, BODIPY, rhodamine, indolium, naphthalimide, etc., and their analytical performance is discussed.

pH response of a hydroxyl-functionalized luminescent metal–organic framework based phosphor

The ligand sensitized Tb³⁺ centered emission of Tb-doped Y-based hydroxyl functionalized MOFs has been utilized for pH sensing in the visible range.

Chemical Detection Using a Metal-Organic Framework Single Crystal Coupled to an Optical Fiber

The quantitative detection and real-time monitoring of target chemicals in the liquid phase are made possible by combining the tailored adsorption properties of metal-organic framework (MOF) material and the precise measuring capabilities of an optical fiber (OF) Fabry-Pérot interferometer (FPI) device. As the single-crystal MOF host adsorbs target analyte guests from the environment, its dielectric properties change causing the reflection spectrum derived from the FPI device to shift. A single crystal of HKUST-1 was attached to the end-face of an OF to form the sensor OF∪MOF (∪, union). The sensor's response curve was accurately measured using low concentrations of the target analyte nitrobenzene, an explosive simulant. Additionally, the uptake rate of nitrobenzene into the MOF single crystal was characterized. The experimental results show that the sensor achieved quantitative and real-time adsorption measurements of a target analyte.

Chiral Sensing Using Circularly Polarized Luminescence of Bis(phenanthroline dicarboxylic acid) EuIII Complex Induced by Allosteric-type Interaction with Amino Acid Molecules

[Eu(pda)₂ ]^- and [Eu(bda)₂ ]^- (pda=1,10-phenanthroline-2, 9-dicarboxylic acid; bda=2,2' bipyridine 5,5'-dicarboxylic acid) have an achiral D_2d structure in crystals. These complexes exhibit circularly polarized luminescence (CPL) in water containing chiral amino acids. In this work, induced CPL of [Eu(pda)₂ ]^- and [Eu(bda)₂ ]^- in water solutions containing a mixture of d- and l- amino acids were examined. Plots of g_lum values of the induced CPL as a function of mol-fraction of l- and d- arginine reveal that [Eu(pda)₂ ]^- favors homo-association ([Eu(pda)₂ ]^- -(l-arginine)₂ or [Eu(pda)₂ ]^- -(d-arginine)₂ ) over hetero-association {[Eu(pda)₂ ]^- -(l-arginine)⋅(d-arginine)}. This suggests that association of an arginine molecule induces a structural change in [Eu(pda)₂ ]^- to promote chiral selective association to another arginine, i.e., homo-allosteric association. On the other hand, the system of [Eu(pda)₂ ]^- with histidine favors hetero-allosteric association over homo-association. No allosteric effect is recognized in CPL from [Eu(bda)₂ ]^- .

Lanthanide Organic Framework Luminescent Thermometers

Metal-organic frameworks (MOFs) are excellent platforms for engineering luminescence properties as their building blocks, metal ions, linkers, and guest ions or molecules, are all potential sources of light emission. Temperature is one of the most important physical properties affecting the dynamics and viability of natural and engineered systems. Because the luminescence of certain lanthanide-bearing MOFs changes considerably with temperature, in the last few years, these materials have been explored as optical thermometers, especially in temperature sensing based on the intensity ratios of two separate electronic transitions. This review discusses the main concepts and ideas assisting the design of such ratiometric thermometers, and identifies the main challenges presented to this nascent field: develop nanothermometers for bio-applications and nanomedicine; understand the energy transfer mechanisms determining the thermal sensitivity; achieve effective primary thermometers; realize multifunctional nanothermometers; integrate Ln³⁺ -based thermometers in commercial products.

Chemical Sensors Based on Metal-Organic Frameworks

Metal-organic frameworks (MOFs) as chemical sensors have developed rapidly in recent years. There have been many papers concerning this field and interest is still growing. The reason is that the specific merits of MOFs can be utilized to enhance sensitivity and selectivity by various energy/charge transfers occurring among different ligands, ligand, and metal centers, such as from ligands to metal centers or metal centers to ligands, as well as from MOF skeletons to guest species. This review intends to provide an update on recent progress in various applications of different MOF-based sensors on the basis of their luminescent and electrochemical responses towards small molecules, gas molecules, ions (cations and anions), pH, humidity, temperature, and biomolecules. MOF-based sensors function by utilizing different mechanisms, including luminescent responses of "turn-on" and "turn-off", as well as electrochemical responses.

One-pot synthesis of hydrazono-sulfonamide adducts using Cu(BTC) MOF catalyst and their remarkable AIEE properties: unprecedented copper(ii)-catalyzed generation of ketenimine

One pot & simple operation; short reaction time; no column purification; very less catalyst loading; scalable.