A Multimodal Ratiometric Luminescent Thermometer Based on a Single-Dysprosium Metal-Organic Framework

Bifunctional Lanthanide MOFs with Phosphorus Ligands: Selective Luminescent Detection of Borides and CO2 Conversion

There is an increasing demand for the development of lanthanide metal-organic frameworks and derived multifunctional materials. The functional properties of such compounds are influenced by the arrangement of various Lewis basic sites or structural configurations of the ligands. In this study, a series of isostructural Ln-MOFs containing a phosphine-dicarboxylate ligand, [Ln(HL)(L)(DMF)]·DMF (where H2L = 5-(diphenylphosphanyl)isophthalic acid, Ln = Tb3+ (1), Eu3+ (2), Gd3+ (3), Ce3+ (4), and Nd3+ (5)), was synthesized under solvothermal conditions and characterized in detail. Among the obtained compounds, Tb-MOF 1 demonstrated excellent luminescent properties with a high quantum yield (90.45%) and considerable lifetime (1266 μs). Furthermore, 1 acts as a unique luminescent Ln sensor for 4-formylphenylboronic acid and 9-[3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl]carbazole, exhibiting low detection limits of 1.38 and 3.62 mM, respectively. Additionally, Nd-MOF 5 acts as an efficient catalyst for coupling carbon dioxide to epoxy compounds, resulting in high conversion rates (up to 96%). This study further extends the growing family of Ln-MOFs and provides insights for preparing multifunctional materials through the modification of organic ligands with specific functional groups.

Weak Coupling Strategy to Construct High-Performance Sm/Tb-Doped Lanthanide Coordination Polymer Luminescent Sensor for D2O Detection

Accurate measurement of the purity and content of heavy water is of great concern in nuclear energy, the chemical industry, and biomedicine. Since the physical and chemical properties of D2O and H2O are very similar, achieving luminescent detection is challenging. Due to the difference in the vibrational frequency of the O-D and the O-H bonds, the quenching efficiency of the excited state of Ln3+ is different, which leads to a significant difference in the optical properties of Ln3+. Based on this theory, we composed a weak coupling strategy to strengthen the luminescence difference of Ln3+. Then, we demonstrated the weak coupling effect and how to improve detection performance by analyzing L1-Eu0.14Tb0.86(C22H20Eu0.14Tb0.86N3O10) and L1-Sm0.45Tb0.55(C22H20Sm0.45Tb0.55N3O10). The structure and performance of the two sensors were characterized in detail. A series of heavy water detection luminescence sensing experiments show that L1-Sm0.45Tb0.55 and L1-Eu0.14Tb0.86 can not only qualitatively distinguish D2O and H2O with the naked eye but also quantitatively detect any concentration of H2O in D2O. The prepared composite films L1-Sm0.45Tb0.55@PMMA and L1-Eu0.14Tb0.86@PMMA have practical application value. The application of Sm/Tb-doped lanthanide coordination polymers for detecting the H2O content in D2O has not been reported.

Strategy of Constructing Ratio-Dependent Coordination Polymer probes and Their Film Application with a Smart Phone for Detection of Lomefloxacin Hydrochloride and Sodium Salicylate

Lomefloxacin hydrochloride (LMFX) and sodium salicylate (SS) are important targets for real-time detection due to their widespread uses in daily life; accurate and portable monitoring of LMFX and SS is crucial for human health concerns accordingly. Developing a precise and smart platform for determination of the above analytes remains a significant challenge. Herein, a high-sensitivity platform incorporating a luminescence electrospinning film, self-designed smart-phone app, and portable 3D printing device has been developed to identify LMFX and SS. In this work, two heterometallic coordination polymers with two-dimensional layer structures have been synthesized based on 2,2'-oxidiacetic acid ligand (H2oda), namely, [LnPb(oda)2(CH3COO)]n [Ln = Eu (IMU-1); Tb (IMU-2)]. IMU-1 and IMU-2 were ratio-dependent luminescence probes, which could selectively and sensitively sense with LMFX and SS, respectively. Additionally, the synthesized electrospinning films incorporating IMU-1 and IMU-2 were employed to identify LMFX and SS. Both films could rapidly photograph and color-capture through a portable 3D printing device, along with a self-designed smart-phone app that enabled convenient and quick determination of the concentrations of the above analytes. Remarkably, the mechanism exploration indicated that electron transfer from ligands to analytes affected the antenna effect and further utilized the intrinsic luminescence of analytes along with the luminescence quenching of Ln3+ ions. Furthermore, a strategy for constructing ratio-based fluorescent probes by exploiting the luminescence of analytes and Ln3+ ions in host coordination polymers is proposed. This work provides a new insight by combining luminescence probes, portable devices, and a smart-phone app for real-time detection of drugs and food additives.

A mixed Ce/Eu metal-organic framework for ratiometric detection of Al3+ ion

As a heavy metal ion, excessive aluminum ions pose a serious threat to human health and the ecological environment. Developing a simple, efficient, and fast detection method to detect the content of aluminum ions is of great significance, especially for ensuring human health and ecological safety. Herein, the mixed rare earth metal-organic framework (Ce0.74Eu0.26TPTC and Ce0.62Eu0.38TPTC) were prepared based on simple ligand 1,1':4',1″-Terphenyl-2',4,4″,5'-tetracarboxylic acid (H4TPTC). The Ce0.74Eu0.26TPTC and Ce0.62Eu0.38TPTC have dual luminescence centers, which can be used as ratio fluorescent probes to detect Al3+ ions, making the detection results more accurate and reliable. Therefore, this work can promote the further development of rare earth-based MOFs in the detection of heavy metal ions.

Design and application of dual-emission metal-organic framework-based ratiometric fluorescence sensors

Metal-organic frameworks (MOFs) are novel inorganic-organic hybridized crystals with a wide range of applications. In the last twenty years, fluorescence sensing based on MOFs has attracted much attention. MOFs can exhibit luminescence from metal nodes, ligands or introduced guests, which provides an excellent fluorescence response in sensing. However, single-signal emitting MOFs are susceptible to interference from concentration, environment, and excitation intensity, resulting in poor accuracy. To overcome the shortcomings, dual-emission MOF-based ratiometric fluorescence sensors have been proposed and rapidly developed. In this review, we first introduce the luminescence mechanisms, synthetic methods, and detection mechanisms of dual-emission MOFs, highlight the strategies for constructing ratiometric fluorescence sensors based on dual-emission MOFs, and classify them into three categories: intrinsic dual-emission and single-emission MOFs with luminescent guests, and non-emission MOFs with other luminescent materials. Then, we summarize the recent advances in dual-emission MOF-based ratiometric fluorescence sensors in various analytical industries. Finally, we discuss the current challenges and prospects for the future development of these sensors.

AIE Ligand-Based Luminescent Ln-MOFs for Rapid and Selective Sensing of Tetracycline

The design of highly stable and dual-emission lanthanide metal-organic frameworks (Ln-MOFs) is promising for practical chemical sensor applications. Rational design and synthesis of photoresponsive organic ligands provide a feasible approach to achieving highly fluorescent dual-emission Ln-MOFs. In this study, a tetraphenylpyrazine-based AIE ligand, H4L, was synthesized and combined with lanthanide ions (including Sm3+, Eu3+, Gd3+, and Tb3+) to fabricate a series of Ln-MOFs named Ln-L. The single-crystal analysis revealed that all Ln-L belonged to the tetragonal space group P4212 and featured a 2-fold interpenetrated 3D structure. Leveraging rational design, Eu-L exhibited a sensitive response to tetracycline, making it a promising fluorescence sensor for tetracycline detection. The experiments demonstrated that Eu-L could rapidly and quantitatively detect tetracycline and its analogs within 30 s. The lowest detection limits for tetracycline, oxytetracycline, and chlortetracycline were 0.43, 0.92, and 0.81 μM, respectively. Additionally, the probe displayed excellent reusability and exceptional selectivity. A plausible sensing mechanism was proposed, supported by both experimental and theoretical analyses. Furthermore, the study discovered that on-site and real-time determination of TCs in aqueous solutions could be achieved by using luminescence test papers and composite films derived from Eu-L.

Engineering of metal-organic frameworks (MOFs) for thermometry

Metal-organic frameworks (MOFs ) are excellent candidates for use in chemistry, material sciences and engineering thanks to their interesting qualitative features and potential applications. Quite interestingly, the luminescence of MOFs can be engineered by regulation of the ligand design, metal ion selection and encapsulation of guest molecules within the MOF cavity. Temperature is a very crucial physical parameter and the market share of temperature sensors is rapidly expanding with technology and medicinal advancement. Among the wide variety of available temperature sensors, recently MOFs have emerged as potential temperature sensors with the capacity to precisely measure the temperature. Lanthanide-based thermometry has advantages because of its ratiometric response ability, high quantum yield and photostability, and therefore lanthanide-based MOFs were initially focused on to construct MOF thermometers. As science and technology have gradually changed, it has been observed that with the inclusion of dye, quantum dots, etc. within the MOF cavity, it is possible to develop MOF-based thermometry. This review consolidates the recent advances of MOF-based ratiometric thermometers and their mechanism of energy transfer for determining the temperature (thermal sensitivity and temperature uncertainty). In addition, some fundamental points are also discussed, such as concepts for guiding the design of MOF ratiometric thermometers, thermometric performance and tuning the properties of MOF thermometers.