A Luminescent Metal-Organic Framework Thermometer with Intrinsic Dual Emission from Organic Lumophores

Nanozyme-induced deep learning-assisted smartphone integrated colorimetric and fluorometric dual-mode for detection of tetracycline analogs

In this work, a colorimetric and fluorescent dual-mode probe controlled by NH2-MIL-88 B (Fe, Ni) nanozymes was developed to visually detect tetracycline antibiotics (TCs) residues quantitatively, as well as accurately distinguish the four most widely used tetracycline analogs (tetracycline (TC), chrycline (CTC), oxytetracycline (OTC), and doxycycline (DC)). Colorless substrate 3,3',5,5'-tetramethylbenzidine (TMB) may be oxidized to blue oxidized TMB by the Fe Fenton reaction, which was catalyzed by the NH2-MIL-88 B (Fe, Ni) nanozyme with POD-like activity. The colorimetric detection system allows TCs to interact with NH2-MIL-88 B (Fe, Ni). This inhibits the production of ·OH, weakens the oxidation process of TMB, and ultimately lightens the blue color in the system by blocking the electron transfer between NH2-MIL-88 B (Fe, Ni) and H2O2. Furthermore, TCs can interact with NH2-MIL-88 B (Fe, Ni) as a result of the internal filtering effect, which causes the fluorescence intensity to decrease as TCs concentration increases. Additionally, a portable instrument that combines a smartphone sensing platform with colorimetric and fluorescent signals was created for the quick, visual quantitative detection of TCs. The colorimetric and fluorescent dual-mode nano platform enables color change, with detection limits (LODs) of 0.182 μM and 0.0668 μM for the spectrometer and smartphone sensor, respectively, based on the inhibition of fluorescence and enzyme-like activities by TCs. Overall, the colorimetric and fluorescence dual-mode sensor has good stability, high specificity, and an efficient way to eliminate false-positive issues associated with a single detection mode.

Luminescence Thermometry Beyond the Biological Realm

As the field of luminescence thermometry has matured, practical applications of luminescence thermometry techniques have grown in both frequency and scope. Due to the biocompatibility of most luminescent thermometers, many of these applications fall within the realm of biology. However, luminescence thermometry is increasingly employed beyond the biological realm, with expanding applications in areas such as thermal characterization of microelectronics, catalysis, and plasmonics. Here, we review the motivations, methodologies, and advances linked to nonbiological applications of luminescence thermometry. We begin with a brief overview of luminescence thermometry probes and techniques, focusing on those most commonly used for nonbiological applications. We then address measurement capabilities that are particularly relevant for these applications and provide a detailed survey of results across various application categories. Throughout the review, we highlight measurement challenges and requirements that are distinct from those of biological applications. Finally, we discuss emerging areas and future directions that present opportunities for continued research.

Fluorescence Thermometers Involving Two Ranges of Temperature: Coordination Polymer and DMSP Embedding

The measurement of temperature is indispensable in the fields of life, science, and industry. Fluorescence thermometers are attractive to researchers because of their advantages such as noncontact, high sensitivity, fast response, and excellent anti-interference. Here, a new coordination polymer (HNU-76) was synthesized by assembling Zn2+ with the H3TCA ligand, a fluorescent molecule with an AIE behavior, which can be used as a fluorescence thermometer. At 100-210 K, the fluorescence intensity ratio of HNU-76 versus temperature conforms to an Arrhenius-type decay relationship (R2 = 0.997), which can be the candidate for low-temperature sensing. In order to increase the sensing range, 4-[4-(dimethylamino)styryl] pyndine (DMSP) was successfully embedded on HNU-76, obtaining HNU-76⊃DMSP. The fluorescence intensity of HNU-76⊃DMSP conforms to an Arrhenius-type decay relationship (R2 = 0.997) at 270-360 K versus temperature. HNU-76 can be used for fluorescence detection at low temperatures, due to the DMSP loading, and HNU-76⊃DMSP can serve as the temperature thermometer in a range of temperatures common. Both materials show good cyclability and have the potential to be used in fluorescence thermometers.

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

The design of high-performance luminescent MOF thermometers with multi-operation modes has been long sought but remains a formidable challenge. In this work, for the first time, we present a multimodal luminescent ratiometric thermometer based on the single-lanthanide metal-organic framework (MOF) DyTPTC-2Me (H₄TPTC-2Me = 2',5'-dimethyl-[1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid). It not only has the characteristic luminescence of Dy³⁺ in which the atomic transitions from the ⁴I_15/2 and ⁴F_9/2 states (thermally coupled energy levels, TCELs) are included but also emits ligand fluorescence due to the efficient energy back-transfer of Dy³⁺ to the ligand, thus allowing accurate non-invasive determination of temperature by different modes. In particular, the TCEL-based emissions of the Dy³⁺ ions give ideal signals for measuring the temperature in the 303-423 K range. The emissions of the ligand and Dy³⁺ (⁴F_9/2 → ⁶H_13/2) are used for temperature sensing in the range of 423 to 503 K. Both two modes feature promising thermometric performance, including high relative sensitivity, high temperature resolution, and excellent repeatability. Their combination is thus beneficial to achieve more accurate temperature detection over a broad temperature range, which can broaden the application scope of the ratiometric luminescent thermometers.

Multi-Emission from Single Metal-Organic Frameworks under Single Excitation

Multi-emission materials have come to prominent attention ascribed to their extended applications other than single-emission ones. General and robust design strategies of a single matrix with multi-emission under single excitation are urgently required. Metal-organic frameworks (MOFs) are porous materials prepared with organic ligands and metal nodes. The variety of metal nodes and ligands makes MOFs with great superiority as multi-emission matrices. Guest species encapsulated into the channels or pores of MOFs are the additional emission sites for multi-emission. In this review, multi-emission MOFs according to the different excitation sites are summarized and classified. The emission mechanisms are discussed, such as antenna effect, excited-state intramolecular proton transfer (ESIPT) and tautomerism for dual-emission. The factors that affect the emissions are revealed, including ligand-metal energy transfer and host-guest interaction, etc. Multi-emission MOFs could be predictably designed and prepared, once the emissive factors are controlled rationally in combination with the different multi-emission mechanisms. Correspondingly, new and practical applications are realized, including but not limited to ratiometric/multi-target sensing and bioimaging, white light-emitting diodes, and anti-counterfeiting. The design strategies of multi-emission MOFs and their extensive applications are reviewed. The results will shed light on other multi-emission systems to develop the structure-derived functionality and applications.

Recent Progress in Metal-Organic Framework Based Fluorescent Sensors for Hazardous Materials Detection

Population growth and industrial development have exacerbated environmental pollution of both land and aquatic environments with toxic and harmful materials. Luminescence-based chemical sensors crafted for specific hazardous substances operate on host-guest interactions, leading to the detection of target molecules down to the nanomolar range. Particularly, the luminescence-based sensors constructed on the basis of metal-organic frameworks (MOFs) are of increasing interest, as they can not only compensate for the shortcomings of traditional detection techniques, but also can provide more sensitive detection for analytes. Recent years have seen MOFs-based fluorescent sensors show outstanding advantages in the field of hazardous substance identification and detection. Here, we critically discuss the application of MOFs for the detection of a broad scope of hazardous substances, including hazardous gases, heavy metal ions, radioactive ions, antibiotics, pesticides, nitro-explosives, and some harmful solvents as well as luminous and sensing mechanisms of MOF-based fluorescent sensors. The outlook and several crucial issues of this area are also discussed, with the expectation that it may help arouse widespread attention on exploring fluorescent MOFs (LMOFs) in potential sensing applications.

A photoluminescent thermometer made from a thermoresponsive tetranuclear gold complex and phosphor N630

Reaction of [(3-bdppmapy)(AuCl)₂] with NaHmba (3-bdppmapy = N,N'-bis-(diphenylphosphanylmethyl-3-aminopytidine, H₂mba = 2-mercaptobenzoic acid) resulted in a new tetranuclear Au/P/S complex [(3-bdppmapy)₂(AuHmba)₃(AuCl)] (1). Upon excitation at 370 nm, 1 exhibited solid state, room temperature, green fluorescent emission (QY = 4.7%, τ = 2.58 ns) which was significantly enanced at lower temperatures due to strengthening of the Au-Au interaction. Different ratios of 1 with phosphor N630 in PMMA were used to make thermochromic photoluminescent films and fibres that could be fabricated into an optical thermometer sensitive over temperature ranges 80-300 K and 300-370 K.

Diverse physical functionalities of rare-earth hexacyanidometallate frameworks and their molecular analogues

The combination of rare-earth metal complexes and hexacyanidometallates of transition metals is a fruitful pathway for achieving functional materials exhibiting a wide scope of mechanical, magnetic, optical, and electrochemical properties.

Metal-Organic Frameworks with Multiple Luminescence Emissions: Designs and Applications

Emissive species are powerful for luminescent detection with high sensitivity and simple procedure and for light-emitting diode (LED) lighting because of their high efficiency, long lifetime, and low energy consumption. Here we propose the concept of multiple luminescence emissions from a single matrix or species under single-wavelength excitation. Multiemission not only realizes the high sensitivity of luminescence sensing but also possesses the capacity of self-reference for environment-free interferences. The color change is also convenient for visible detection. In multiemission species, every emissive center responds to a specific analyte to improve the efficiency for multiple-target detection. Multiemission also extends the applications to anticounterfeiting, colorful LEDs, and information storage. To date, it is still challenging to combine more than one type of emissive center in a single matrix or species. Obtaining multiemission under single-wavelength excitation also needs exquisite design. Metal-organic frameworks (MOFs) are porous hybrid assemblies prepared with metal ions and organic ligands. Metal nodes and ligands with large π-conjugated systems have the potential for the construction of luminescent MOFs. Abundant and diverse precursors provide the possibility to prepare MOFs with multiple luminescence emissions. The pores or channels of MOFs also act as hosts to encapsulate luminescent guest species as additional emissive sites. In this Account, we propose the concept of multiple-luminescence MOFs (ML-MOFs) and summarize the recent research progress on their designs, constructions, and applications reported by our group and others. ML-MOFs are MOFs that possess more than one emissive center under single-wavelength excitation. Six different kinds of construction strategies of ML-MOFs are introduced: (1) multiemission from both metal nodes and ligands in single MOFs; (2) use of mixed-metal nodes as multiemission centers in single MOFs; (3) combination of different emissive MOFs as a whole to achieve multiemission application; (4) host-guest emissions from emissive MOFs after encapsulation of luminescent guest species; (5) organization of different emissive ligands in a single MOF for multiemission; and (6) use of single ligands exhibiting dual emission to prepare ML-MOFs. We also discuss the mechanisms that realize multiple emissions from MOFs under single-wavelength excitation, such as the antenna effect and excited-state intramolecular proton transfer. The applications of ratiometric sensing, LED lighting, anticounterfeiting, and information storage are summarized. With this Account, we hope to spark new ideas and to inspire new endeavors in the design and construction of ML-MOFs, especially with postsynthetic techniques such as postsynthetic modification, postsynthetic exchange, and postsynthetic deprotection, to promote the applications of MOFs in sensing, lighting, information storage, and others.

Thermo-responsive light-emitting metal complexes and related materials

This review discusses the fundamentals and design strategies for the development of thermo-responsive metal–ligand coordination materials and the applications of these materials in temperature sensing, bioimaging, information security, etc.

Multicenter Metal-Organic Framework-Based Ratiometric Fluorescent Sensors

Metal-organic frameworks (MOFs) with multiple emission centers are newly emerging as ratiometric sensors owing to their high sensitivity and high selectivity toward a wide range of targeted functional species. Energy transfer between the light-absorbing group and emission centers and between different emission centers is the key to rationally design and synthesize MOF-based ratiometric sensors. A good match between the energy levels of the light-absorbing groups and emission centers is the prerequisite for MOF-based sensors to exhibit multiple emissions, and a good match of the MOF-based sensors and those of the targeted species can increase the sensitivity and selectivity, but this match is highly challenging to obtain via synthesis. MOFs with multiple emission centers can be produced by functionalizing MOFs with multiple lanthanide centers, organic luminophores, dyes, carbon dots, and other such emissive groups. In this progress report, recent advances in the strategies for synthesizing MOFs with multiple emission centers and their applications for ratiometric sensing of solution conditions, including the pH value, and ion, organic molecule, and biomolecule concentrations, are summarized, as are the related sensing mechanisms.

Design and properties of multiple-emitter luminescent metal–organic frameworks

This feature article reviews the design strategies by which multiple different emission sources could be combined for creating multi-emitter luminescent metal–organic frameworks (LMOFs).

A new type of composite MOFs based on high-valent Sb(v)-based units and cuprous-halide clusters

An unusual high-valent Sb(v)-based unit [SbL₂]^- (L = 2-(hydroxymethyl)-2-(pyridin-4-yl)-1,3-propanediol) was developed for the first time to combine with various cuprous-halide clusters for the construction of a brand-new class of heterometallic MOFs. This work not only promotes the limited development of Sb-based MOFs, but also provides a practical strategy for developing new types of composite materials.

Amino-Functionalized Al-MOF for Fluorescent Detection of Tetracyclines in Milk

A fluorescent method for detection of tetracyclines (TCs) in milk was developed by using the NH₂-MIL-53(Al) nanosensor synthesized via a one-pot hydrothermal method. The nanosensor had a crystalline nanoplates structure with rich groups of -NH₂ and -COOH. The -NH₂/-COOH of NH₂-MIL-53(Al) reacted with the -CO-/-OH of TCs to form a complex. The electron of -NH₂/-COOH from the NH₂-BDC ligand transferred to the -CO-/-OH of TCs. -NH₂ of the NH₂-MIL-53(Al) interacted with the -CO-/-OH of TCs by hydrogen bonding. The quenching efficiency of the inner filter effect (IFE) was calculated to contribute 57-89%. The synergistic effect of photoinduced electron transfer (PET) and IFE account for fluorescence quenching. TCs were quantitatively detected in milk samples with recoveries of 85.15-112.13%; the results were in great accordance with high-performance liquid chromatography (HPLC) ( P > 0.05), confirming the NH₂-MIL-53(Al) nanosensor has potential applicability for the detection of TCs in food matrix.

A robust wave-like silver–thiolate chain based metal–organic network: synthesis, structure and luminescence

A wave-like silver–thiolate chain based metal–organic network has been prepared via facile one-pot synthesis, and shows ultra-stability and intense luminescence.

Photoluminescence modulation of an atomically precise silver(i)-thiolate cluster via site-specific surface engineering

A series of pyridyl ligand functionalized silver-thiolate nanoclusters with an identical cuboctahedron Ag12 core were prepared through site-specific surface engineering and fully characterized. Their wide-range photoluminescence modulation was systematically studied.

Inherently Eu2+ /Eu3+ Codoped Sc2 O3 Nanoparticles as High-Performance Nanothermometers

Luminescent nanothermometers have shown competitive superiority for contactless and noninvasive temperature probing especially at the nanoscale. Herein, we report the inherently Eu²⁺ /Eu³⁺ codoped Sc₂ O₃ nanoparticles synthesized via a one-step and controllable thermolysis reaction where Eu³⁺ is in-situ reduced to Eu²⁺ by oleylamine. The stable luminescence emission of Eu³⁺ as internal standard and the sensitive response of Eu²⁺ emission to temperature as probe comprise a perfect ratiometric nanothermometer with wide-range temperature probing (77-267 K), high repeatability (>99.94%), and high relative sensitivity (3.06% K^-1 at 267 K). The in situ reduction of Eu³⁺ to Eu²⁺ ensures both uniform distribution in the crystal lattice and simultaneous response upon light excitation of Eu²⁺ /Eu³⁺ . To widen this concept, Tb³⁺ is codoped as additional internal reference for tunable temperature probing range.

Solid-State Carbon Dots with Red Fluorescence and Efficient Construction of Dual-Fluorescence Morphologies

Stable solid-state red fluorescence from organosilane-functionalized carbon dots (CDs) with sizes around 3 nm is reported for the first time. Meanwhile, a novel method is also first reported for the efficient construction of dual-fluorescence morphologies. The quantum yield of these solid-state CDs and their aqueous solution is 9.60 and 50.7%, respectively. The fluorescence lifetime is 4.82 ns for solid-state CDs, and 15.57 ns for their aqueous solution. These CDs are detailedly studied how they can exhibit obvious photoluminescence overcoming the self-quenching in solid state. Luminescent materials are constructed with dual fluorescence based on as-prepared single emissive CDs (red emission) and nonfluorescence media (starch, Al₂ O₃ , and RnOCH₃ COONa), with the characteristic peaks located at nearly 440 and 600 nm. Tunable photoluminescence can be successfully achieved by tuning the mass ratio of CDs to solid matrix (such as starch). These constructed dual-fluorescence CDs/starch composites can also be applied in white light-emitting diodes with UV chips (395 nm), and oxygen sensing.

Anion-templated nanosized silver clusters protected by mixed thiolate and diphosphine

S^2-, MoO₄^2-, and Mo₆O₂₂^8- were successfully employed as templates in the formation of six high-symmetry polynuclear silver clusters as exemplified in the single-crystal X-ray structures of [S@Ag₁₈(^tBuC₆H₄S)₁₆(dppp)₄]·DMF·5CH₃CN·3CH₃OH (1), [MoO₄@Ag₂₄(MeC₆H₄S)₁₂(dppm)₆(MoO₄)₄]·2BF₄·C₂H₅NO (2), [MoO₄@Ag₂₄(MeC₆H₄S)₁₂(dppm)₆(MoO₄)₄]·2CF₃SO₃ (3), [MoO₄@Ag₂₄(MeC₆H₄S)₁₂(dppf)₆(MoO₄)₄]·2CF₃SO₃ (4), [MoO₄@Ag₂₄(MeC₆H₄S)₁₂(dppb)₆(MoO₄)₄]·2CF₃SO₃ (5) and [Mo₆O₂₂@Ag₄₆(^tBuC₆H₄S)₃₂(dppm)₄(CH₃CN)₈]·6CF₃SO₃ (6) (dppp = 1,3-bis(diphenylphosphino)propane, dppm = bis(diphenylphosphino)methane, dppf = 1,1'-bis(diphenylphosphino)ferrocene and dppb = 1,4-bis(diphenylphosphino)butane). Cluster 1 is a S^2--centered octadecanuclear banana-shaped molecule. Clusters 2-5 have similar structures consisting of a tetrahedron of a MoO₄^2- core and four MoO₄^2- where three silver atoms cap each face and a pair sits on each edge, giving tetraicosanuclear ball-shaped molecules. Although different diphosphine ligands and silver salts were used in the syntheses, 2-5 contain a common building cluster unit with similar geometry and nuclearity. With (Bu₄N)₂Mo₆O₁₉ as a template, a giant 46-silver-atom cluster encapsulates an in situ modified Mo₆O₂₂^8- unit. The nuclearity and geometry depend on the size and shape of the templates. High-resolution electrospray mass spectrometry (HR-ESI-MS) analyses of 4 indicate its exceptionally high stability in acetonitrile. The solid-state luminescence of 1 as a function of the temperature exhibits thermochromism from red to yellow due to the different intensities of the two bands. This work established a new strategy for the construction of polynuclear silver clusters using an anionic template and mixed S- and P-donor ligands where a promising approach for building novel dual emissive materials is unraveled.

Metal–organic frameworks: functional luminescent and photonic materials for sensing applications

This review summarizes the diverse routes to derive sensing applications from suitably functionalized and crystal-engineered metal–organic framework (MOF) materials, either by fluorometric responses, or based on photonic crystal-based signal transduction.

Intrinsic triple-emitting 2D copper thiolate coordination polymer as a ratiometric thermometer working over 400 K range

A new lamellar, [Cu(p-SPhCO₂Me)]_n, coordination polymer exhibits intrinsic triple emission with great potential as optical thermometer working over 400 K range and up to 500 K.

Through-space Förster-type energy transfer in isostructural zirconium and hafnium-based metal–organic layers

Identical energy transfer rates in isostructural Zr and Hf metal–organic layers revealed dominant through-space energy transfer over the through-bond one.

Moisture-Stable Zn(II) Metal-Organic Framework as a Multifunctional Platform for Highly Efficient CO2 Capture and Nitro Pollutant Vapor Detection

A moisture-stable three-dimensional (3D) metal-organic framework (MOF), {(Me2NH2)[Zn2(bpydb)2(ATZ)](DMA)(NMF)2}n (1, where bpydb = 4,4'-(4,4'-bipyridine-2,6-diyl)dibenzoate, ATZ = deprotonated 5-aminotetrazole, DMA = N,N-dimethylacetamide, and NMF = N-methylformamide), with uncoordinated N-donor sites and charged framework skeleton was fabricated. This MOF exhibits interesting structural dynamic upon CO2 sorption at 195 K and high CO2/N2 (127) and CO2/CH4 (131) sorption selectivity at 298 K and 1 bar. Particularly, its CO2/CH4 selectivity is among the highest MOFs for selective CO2 separation. The results of Grand Canonical Monte Carlo (GCMC) simulation indicate that the polar framework contributes to the strong framework-CO2 binding at zero loading, and the tetrazole pillar contributes to the high CO2 uptake capacity at high loading. Furthermore, the solvent-responsive luminescent properties of 1 indicate that it could be utilized as a fluorescent sensor to detect trace amounts of nitrobenzene in both solvent and vapor systems.

A dye encapsulated terbium-based metal–organic framework for ratiometric temperature sensing

A ratiometric and colorimetric thermometer with high sensitivity and significant color change from 50 to 300 K has been developed by encapsulating the luminescent dye 7-diethylamino-4-methylcoumarin (C460) into the channels of a terbium-based MOFTbTATAB.