Developing Luminescent Ratiometric Thermometers Based on a Covalent Organic Framework (COF)

Heavy-Atom-Free Covalent Organic Frameworks for Organic Room-Temperature Phosphorescence via Förster and Dexter Energy Transfer Mechanism

Covalent organic frameworks (COFs), with their accessible nanoscale porosity, selectable building blocks, and precisely engineered topology, offer unique benefits in the design of room-temperature phosphorescent (RTP) materials. However, their potential has been limited by phosphorescence quenching caused by interlayer π-π stacking interactions. This paper presents a novel strategy to enhance RTP in heavy-atom-free COFs by employing a donor-acceptor (D-A) system that leverages the Förster resonance energy transfer (FRET) and Dexter energy transfer (DET) mechanisms. Among the materials investigated, the best-performing COF exhibits a phosphorescence lifetime of 4.35 ms at room temperature. Spectral analysis, structural analysis, and theoretical calculations indicate the presence of intralayer FRET processes as well as interlayer DET processes within the D-A COF system. Potential anti-counterfeiting applications are explored by exploiting the unique phosphorescent properties of these materials. Additionally, the inherent permanent porosity of COFs presents new opportunities for future development and application. This strategy offers many promising prospects for advancing the RTP technology in COF materials and broadens their potential applications in various fields.

Ionic Covalent Organic Framework as a Dual Functional Sensor for Temperature and Humidity

Visual sensing of humidity and temperature by solids plays an important role in the everyday life and in industrial processes. Due to their hydrophobic nature, most covalent organic framework (COF) sensors often exhibit poor optical response when exposed to moisture. To overcome this challenge, the optical response is set out to improve, to moisture by incorporating H-bonding ionic functionalities into the COF network. A highly sensitive COF, consisting of guanidinium and diformylpyridine linkers (TG-DFP), capable of detecting changes in temperature and moisture content is fabricated. The hydrophilic nature of the framework enables enhanced water uptake, allowing the trapped water molecules to form a large number of hydrogen bonds. Despite the presence of non-emissive building blocks, the H-bonds restrict internal bond rotation within the COF, leading to reversible fluorescence and solid-state optical hydrochromism in response to relative humidity and temperature.

One-Pot Synthesis of a Mixed-Valent Copper(I/II)-Coordinated Covalent Organic Framework Induced by γ-Ray Radiation

Metal-anchored covalent organic frameworks (COFs), as a class of significant derivatives of COFs, are widely used as heterogeneous catalysts in diverse chemical reactions. However, they are typically synthesized via post-treatment strategies, which often lead to the decline of COF crystallinity, decrease of porous properties, instability in catalytic performances, generation of additional chemical waste, and consumption of excess time and energy. In this work, we demonstrate an approach to construct a metal-functionalized COF via a one-pot method induced by γ-ray radiation. Specifically, copper-coordinated COF was in situ synthesized by irradiating a mixture of monomers and copper salt under ambient conditions. Interestingly, the initial Cu2+ ions were reduced to Cu+ ions by the radiation-generated reducing species, affording a unique mixed-valent copper(I/II)-coordinated COF. Additionally, the copper-coordinated COF displayed enhanced crystallinity and porous properties compared to those of the parent COF, displaying an opposite trend to the postsynthetic method. Notably, the introduced copper on the COF skeleton endowed the parent COF with catalytic ability. The resulting copper-coordinated COF exhibited remarkable catalytic performances in the reduction of 4-nitrophenol to 4-aminophenol and maintained almost unchanged catalytic performance after five catalytic cycles.

Covalent organic frameworks-based materials for antibiotics fluorescence detection

Antibiotics play a vital role in safeguarding people's health since most bacterial infection can be efficiently controlled and cured by treating with suitable antibiotics. However, excessive use of antibiotics in husbandry and aquaculture leaded to the pollution of eco-environment. Thus, it is important to develop simple facile methods and effective functional materials for quick on-site analysis of antibiotics. Covalent organic frameworks (COFs), as a kind of porous crystalline covalent bond linked polymers, have demonstrated its power in multiple fields. Herein, we will discuss COFs-based materials utilized as antibiotics sensors with fluorescence method. For each sensor, we will mainly discuss the mechanism for antibiotics recognition, the preparation, characterization and fluorescence sensing performance of specific antibiotics. The mechanism to illustrate the interaction between sensors and antibiotics analytes would also be stressed.

Engineering Covalent Organic Frameworks Toward Advanced Zinc-Based Batteries

Zinc-based batteries (ZBBs) have demonstrated considerable potential among secondary batteries, attributing to their advantages including good safety, environmental friendliness, and high energy density. However, ZBBs still suffer from issues such as the formation of zinc dendrites, occurrence of side reactions, retardation of reaction kinetics, and shuttle effects, posing a great challenge for practical applications. As promising porous materials, covalent organic frameworks (COFs) and their derivatives have rigid skeletons, ordered structures, and permanent porosity, which endow them with great potential for application in ZBBs. This review, therefore, provides a systematic overview detailing on COFs structure pertaining to electrochemical performance of ZBBs, following an in depth discussion of the challenges faced by ZBBs, which includes dendrites and side reactions at the anode, as well as dissolution, structural change, slow kinetics, and shuttle effect at the cathode. Then, the structural advantages of COF-correlated materials and their roles in various ZBBs are highlighted. Finally, the challenges of COF-correlated materials in ZBBs are outlined and an outlook on the future development of COF-correlated materials for ZBBs is provided. The review would serve as a valuable reference for further research into the utilization of COF-correlated materials in ZBBs.

Radiation-Assisted Assembly of a Highly Dispersed Nanomolybdenum-Functionalized Covalent Organic Framework

Two-dimensional covalent organic frameworks (2D COFs), featuring a large surface area and 1D pore structure, serve as promising scaffolds for anchoring functional guest compounds, which can significantly enhance their performance and thus expand their potential applications. Postsynthetic strategy for COFs functionalization is versatile but challenging because of their tedious procedure with high time and energy consumption, generation of excess reaction waste, and damage to COF crystallinity. We report in this work a general strategy for the synthesis of inorganic nanocompound-functionalized COF composites in a one-pot way. Specifically, a high-crystallinity nanoscale molybdenum compound is successfully introduced into a COF skeleton with high dispersion in situ during the crystallization process of the COF induced by gamma ray radiation under ambient conditions. The obtained COF@Mo composites exhibit remarkable sorption performance for methylene blue and many other organic dyes in aqueous solution with the advantages of ultrarapid uptake dynamics and high removal efficiency.

Ratiometric dual-emitting thermometers based on rhodamine B dye-incorporated (nano) curcumin periodic mesoporous organosilicas for bioapplications

This study explores the potential of combining periodic mesoporous organosilicas (PMOs) with a fluorescent dye to develop a ratiometric thermometry system with enhanced stability, sensitivity, and biocompatibility. PMOs, ordered porous materials known for their stability and versatility, serve as an ideal platform. Curcumin, a natural polyphenol and fluorescent dye, is incorporated into PMOs to develop curcumin-functionalized PMOs (C-PMO) and curcumin-pyrazole-functionalized PMOs (CP-PMO) via hydrolysis and co-condensation. These PMOs exhibit temperature-dependent fluorescence properties. The next step involves encapsulating rhodamine B (RhB) dye within the PMO pores to create dual-emitting PMO@dye nanocomposites, followed by a lipid bilayer (LB) coating to enhance biocompatibility and dye retention. Remarkably, within the physiological temperature range, C-PMO@RhB@LB and CP-PMO@RhB@LB demonstrate noteworthy maximum relative sensitivity (Sr) values of up to 1.69 and 2.60% K-1, respectively. This approach offers versatile means to create various ratiometric thermometers by incorporating different fluorescent dyes, holding promise for future temperature sensing applications.

Construction of a Zn(II)-Eu(III) Nanoring with Temperature-Dependent Luminescence for the Qualitative and Quantitative Detection of Neopterin as an Inflammatory Marker

A nine-metal Zn(II)-Eu(III) nanoring 1 with a diameter of about 2.3 nm was constructed by the use of a long-chain Schiff base ligand. It shows a luminescence response to neopterin (Neo) through the enhancement of lanthanide emission with high selectivity and sensitivity, which can be used to quantitatively analyze the concentrations of Neo in fetal calf serum and urine. The luminescence sensing of 1 to Neo is temperature-dependent, and it displays more obvious response behavior at lower temperatures. Filter paper strips bearing 1 can be used to qualitatively detect Neo by the color change from chartreuse to red under a UV lamp. The limit of detection is as low as 3.77 × 10-2 nM.

Europium(III) Functionalized Covalent Organic Framework as Sensitive and Selective Fluorescent Switch for Detection of Uranium

Uranium poses severe health risks due to its radioactivity and chemical toxicity if released into the environment. Therefore, there is an urgent demand to develop sensing materials in situ monitoring of uranium with high sensitivity and stability. In this work, a fluorescent Eu3+-TFPB-Bpy is synthesized by grafting Eu3+ cation onto TFPB-Bpy covalent organic framework (COF) synthesized through Schiff base condensation of monomers 1,3,5-tris(4-formylphenyl)benzene (TFPB) and 5,5'-diamino-2,2'-bipyridine (Bpy). The fluorescence of Eu3+-TFPB-Bpy is enhanced compared with that of TFPB-Bpy, which is originated from the intramolecular rotations of building blocks limited by the bipyridine units of TFPB-Bpy coordinated with Eu3+. More significantly, Eu3+-TFPB-Bpy is a highly efficient probe for sensing UO22+ in aqueous solution with the luminescence intensity efficiently amplified by complexation of UO22+ with Eu3+. The turn-on sensing capability was derived from the resonance energy transfer occurring from UO22+ to the Eu3+-TFPB-Bpy. The developed probe displayed desirable linear range from 5 nM to 5 μM with good selectivity and rapid response time (2 s) for UO22+ in mining wastewater. This strategy provides a vivid illustration for designing luminescence lanthanide COF hybrid materials with applications in environmental monitoring.

Orthogonal Postsynthetic Copolymerization of Hydrogen-Bonded Organic Frameworks into a PolyHOF Membrane

Hydrogen-bonded organic frameworks (HOFs) have shown promise in various fields; however, the construction of HOF/polymer hybrid membranes that can maintain both structural and functional integrity remains challenging. In this study, we here fabricated a new HOF (HOF-50) with reserved polymerizable allyl group via charge-assisted H-bonds between the carboxylate anion and amidinium, and subsequently copolymerized the HOF with monomers to construct a covalently bonded HOF/polymer hybrid (polyHOF) membrane. The resulting polyHOF membrane not only exhibits customizable mechanical properties and extreme stability, but also shows an exceptional ratiometric luminescent temperature-sensing function with very high sensitivity and visibility even when the lanthanide content is two orders of magnitude lower than that of the reported mixed-lanthanide metal-organic frameworks (MOFs) and lanthanide-doped covalent organic frameworks (COFs). This orthogonal postsynthesis copolymerization strategy may provide a general approach for preparing covalently connected HOF/polymer hybrid membranes for diverse applications.

Intensity and lifetime ratiometric luminescent thermometer based on a Tb(III) coordination polymer

A three-dimensional terbium(III) coordination polymer of formula [Tb(bttb)0.5(2,5-pzdc)0.5]n (1) [H4bttb = 1,2,4,5-tetrakis(4'-carboxyphenyl)benzene and H2-2,5-pzdc = 2,5-pyrazinedicarboxylic acid] was obtained under hydrothermal conditions. The bttb4- tetraanion in 1 adopts the bridging and chelating-bridging pseudo-oxo coordination modes while the 2,5-pzdc2- dianion exhibits a rather unusual bis-bidentate bridging pseudo-oxo coordination mode, both ligands being responsible for the stiffness of the resulting 3D structure. Solid-state photoluminescent measurements illustrate that 1 exhibits remarkable green luminescence emission, the most intense band occurring in the region of 550 nm (5D4 → 7F5) with lifetimes at the millisecond scale. Thermometric performances of 1 reveal a maximum relative sensitivity (Sm) of 0.76% K-1 at 295 K (δT = 0.05 K), constituting a TbIII ratiometric solid luminescent thermometer over the physiological temperature range. Variable-temperature static (dc) magnetic susceptibility measurements for 1 in the temperature range 2.0-300 K show the expected behavior for the depopulation of the splitted mJ levels of the 7F7 ground state of the magnetically anisotropic terbium(III) ion plus a weak antiferromagnetic interaction through the carboxylate bridges. No significant out-of-phase magnetic susceptibility signals were observed for 1 in the temperature range 2.0-10.0 K, either in the absence or presence of a static dc magnetic field.

Composition Control in Molecular Cluster-Aggregates: A Toolbox for Optical Output Tunability via Energy Transfer Pathways

Composition control is a powerful tool for obtaining high-performance lanthanide (Ln) luminescent materials with adjustable optical outputs. This strategy is well-established for hierarchically structured nanoparticles, but it is rarely applied to molecular compounds due to the limited number of metal centers within a single unit. In this work, we present a series of molecular cluster-aggregates (MCAs) with an icosanuclear core {Ln2Eu2Tb16} (Ln = Ce, Pr, Nd, Sm, Gd, Dy, Ho, Er, Tm, and Yb) in which we explore composition control, akin to nanoparticles, to modulate the optical output. More specifically, we target to understand how the presence of a third LnIII doping ion would impact the well-known TbIII → EuIII energy transfer and the ratiometric optical thermometry performance based on the TbIII/EuIII pair. Photophysical properties at room and at varying temperatures were investigated. Based on experimental data and well-established intrinsic features, such as spin-orbit coupling strength and LnIII 4f energy levels' structure, we discuss the possible luminescent processes present in each MCA and provide insight into qualitative trends that can be rationally correlated throughout the series.

Spotlight on Luminescence Thermometry: Basics, Challenges, and Cutting-Edge Applications

Luminescence (nano)thermometry is a remote sensing technique that relies on the temperature dependency of the luminescence features (e.g., bandshape, peak energy or intensity, and excited state lifetimes and risetimes) of a phosphor to measure temperature. This technique provides precise thermal readouts with superior spatial resolution in short acquisition times. Although luminescence thermometry is just starting to become a more mature subject, it exhibits enormous potential in several areas, e.g., optoelectronics, photonics, micro- and nanofluidics, and nanomedicine. This work reviews the latest trends in the field, including the establishment of a comprehensive theoretical background and standardized practices. The reliability, repeatability, and reproducibility of the technique are also discussed, along with the use of multiparametric analysis and artificial-intelligence algorithms to enhance thermal readouts. In addition, examples are provided to underscore the challenges that luminescence thermometry faces, alongside the need for a continuous search and design of new materials, experimental techniques, and analysis procedures to improve the competitiveness, accessibility, and popularity of the technology.

Luminescent Single-Molecule Magnets as Dual Magneto-Optical Molecular Thermometers

Luminescent thermometry allows the remote detection of the temperature and holds great potential in future technological applications in which conventional systems could not operate. Complementary approaches to measuring the temperature aiming to enhance the thermal sensitivity would however represent a decisive step forward. For the first time, we demonstrate the proof-of-concept that luminescence thermometry could be associated with a complementary temperature readout related to a different property. Namely, we propose to take advantage of the temperature dependence of both magnetic (canonical susceptibility and relaxation time) and luminescence features (emission intensity) found in Single-Molecule Magnets (SMM) to develop original dual magneto-optical molecular thermometers to conciliate high-performance SMM and Boltzmann-type luminescence thermometry. We highlight this integrative approach to concurrent luminescent and magnetic thermometry using an air-stable benchmark SMM [Dy(bbpen)Cl] (H2 bbpen=N,N'-bis(2-hydroxybenzyl)-N,N'-bis(2-methylpyridyl)ethyl-enediamine)) exhibiting Dy3+ luminescence. The synergy between multiparametric magneto-optical readouts and multiple linear regression makes possible a 10-fold improvement in the relative thermal sensitivity of the thermometer over the whole temperature range, compared with the values obtained with the single optical or magnetic devices.

Lanthanide Functionalized Covalent Organic Frameworks Hybrid Materials for Luminescence Responsive Chemical Sensing

Covalent organic frameworks (COFs) possess several unique features of structural and functional chemistry, together with other modular photophysical performance, which make them candidates for luminescence responsive chemical sensing. Lanthanide (Ln3+ ) functionalized COFs hybrid materials still keep the parent COFs' virtues and also embody the abundant multiple luminescence response with both COFs and Ln3+ ions or other guest species. In this review, the summary is highlighted on the lanthanide functionalized COFs hybrid materials and their relevant systems for luminescence responsive chemical sensing. It is subdivided into five sections involving the three main topics. Firstly, the basic knowledges of COFs materials related to the luminescence responsive chemical sensing are introduced (including three sections), involving the chemistry, application and post-synthetic modification (PSM) of COFs, the luminescence and luminescence responsive chemical sensing, and the luminescence responsive chemical sensing of non-lanthanide functionalized COFs hybrids materials. Secondly, the systematic progresses are outlined on the lanthanide functionalized COFs hybrid materials in luminescence responsive chemical sensing, which is the emphasis for this review. Finally, the conclusion and prospect are given.

Turning 3D Covalent Organic Frameworks into Luminescent Ratiometric Temperature Sensors

In this study, we report hybrid crystalline lanthanide-containing 3D covalent organic framework (Ln@3D COF) materials that are suitable for temperature sensing applications. Different routes to obtain these hybrid materials were tested and compared for material quality and thermometric properties. In the first approach, a bipyridine-containing 3D COF (Bipy COF) was grafted with a range of visible emitting lanthanide (Eu3+, Tb3+, Dy3+, and Eu3+/Tb3+) β-diketonate complexes. In the second approach, a novel nanocomposite material was prepared by embedding NaYF4:Er,Yb nanoparticles on the surface of a nonfunctionalized 3D COF (COF-300). To the best of our knowledge, the luminescent materials developed here are the first 3D COFs to be tested as ratiometric temperature sensors. In fact, for the Bipy COF, two different types of thermometers were tested (the Eu3+/Tb3+ system and a rare Dy3+ system), with both showing excellent temperature sensing properties. The reported NaYF4:Er,Yb/COF-300 nanocomposite material combines upconverting nanoparticles with 3D COFs, similar to previously reported metal organic framework (MOF) nanocomposite materials; however, this type of hybrid material has not yet been explored for COFs. As such, our findings open a new pathway toward potential multifunctional materials that can combine thermometry with other modalities, such as catalysis or drug delivery, in just one nanocomposite material.

Hydrophobicity Tailoring of Ferric Covalent Organic Framework/MXene Nanosheets for High-Efficiency Nitrogen Electroreduction to Ammonia

Electrocatalytic nitrogen reduction reaction (NRR) represents a promising sustainable approach for NH3 synthesis. However, the poor NRR performance of electrocatalysts is a great challenge at this stage, mainly owing to their low activity and the competitive hydrogen evolution reaction (HER). Herein, 2D ferric covalent organic framework/MXene (COF-Fe/MXene) nanosheets with controllable hydrophobic behaviors are successfully prepared via a multiple-in-one synthetic strategy. The boosting hydrophobicity of COF-Fe/MXene can effectively repel water molecules to inhibit the HER for enhanced NRR performances. By virtue of the ultrathin nanostructure, well-defined single Fe sites, nitrogen enrichment effect, and high hydrophobicity, the 1H,1H,2H,2H-perfluorodecanethiol modified COF-Fe/MXene hybrid shows a NH3 yield of 41.8 µg h-1 mgcat. -1 and a Faradaic efficiency of 43.1% at -0.5 V versus RHE in a 0.1 m Na2 SO4 water solution, which are vastly superior to the known Fe-based catalysts and even to the noble metal catalysts. This work provides a universal strategy to design and synthesis of non-precious metal electrocatalysts for high-efficiency N2 reduction to NH3 .

Stacking Lanthanide-MOF Thin Films to Yield Highly Sensitive Optical Thermometers

Easy-to-integrate, remote read-out thermometers with fast response are of huge interest in numerous application fields. In the context of optical read-out devices, sensors based on the emission of lanthanides (Eu(III), Tb(III)) are particularly promising. Here, by using a layer-by-layer (LbL) approach in the liquid-phase epitaxy process, a series of continuous, low-thickness lanthanide-MIL-103 SURMOFs were fabricated to yield highly sensitive thermometers with optical readout. These Ln-SURMOFs exhibit remarkable temperature-sensing photoluminescence behavior, which can be read out using the naked eye. High transmittance is realized as well by precisely controlling the film thickness and the quality of these Ln-SURMOF thermometers. Moreover, we demonstrate that the thermal sensitivity can be improved in the temperature regime above 120 K, by controlling the energy transfer between Tb(III) and Eu(III). This performance is achieved by employing a sophisticated supramolecular architecture, namely MOF-on-MOF heteroepitaxy.

Design of Smartphone-Assisted Point-of-Care Platform for Colorimetric Sensing of Uric Acid via Visible Light-Induced Oxidase-Like Activity of Covalent Organic Framework

Monitoring of uric acid (UA) levels in biological samples is of great significance for human health, while the development of a simple and effective method for the precise determination of UA content is still challenging. In the present study, a two-dimensional (2D) imine-linked crystalline pyridine-based covalent organic framework (TpBpy COF) was synthesized using 2,4,6-triformylphloroglucinol (Tp) and [2,2'-bipyridine]-5,5'-diamine (Bpy) as precursors via Schiff-base condensation reactions and was characterized with scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS), Powder X-ray diffraction (PXRD), Fourier transform infrared (FT-IR) spectroscopy, and Brunauer-Emmett-Teller (BET) assays. The as-synthesized TpBpy COF exhibited excellent visible light-induced oxidase-like activity, ascribed to the generation of superoxide radicals (O₂^•-) by photo-generated electron transfer. TpBpy COF could efficiently oxidase the colorless substrate 3,3',5,5'-tetramethylbenzydine (TMB) into blue oxidized TMB (oxTMB) under visible light irradiation. Based on the color fade of the TpBpy COF + TMB system by UA, a colorimetric procedure was developed for UA determination with a detection limit of 1.7 μmol L^-1. Moreover, a smartphone-based sensing platform was also constructed for instrument-free and on-site detection of UA with a sensitive detection limit of 3.1 μmol L^-1. The developed sensing system was adopted for UA determination in human urine and serum samples with satisfactory recoveries (96.6-107.8%), suggesting the potential practical application of the TpBpy COF-based sensor for UA detection in biological samples.

Water-Soluble Cationic Eu3+-Metallopolymer with High Quantum Yield and Sensitivity for Intracellular Temperature Sensing

Lanthanide-based (Ln³⁺) luminescent materials are ideal candidates for use in fluorescence intracellular temperature sensing. However, it remains a great challenge to obtain a Ln³⁺-ratiometric fluorescence thermometer with high sensitivity and quantum yield in an aqueous environment. Herein, a cationic Eu³⁺-metallopolymer was synthesized via the coordination of Eu(TTA)₃·2H₂O with an AIE active amphipathic polymer backbone that contains APTMA ((3-acrylamidopropyl) trimethylammonium) and NIPAM (N-isopropylacrylamide) units, which can self-assemble into nanoparticles in water solution with APTMA and NIPAM as the hydrophilic shell. This polymer exhibited highly efficient dual-emissive white-light emission (Φ = 34.3%). Particularly, when the temperature rises, the NIPAM units will transform from hydrophilic to hydrophobic in the spherical core of the nanoparticle, while the VTPE units are moved from inside the nanoparticle to the shell, activating its nonradiative transition channel and thereby decreasing its energy transfer to Eu³⁺ centers, endowing the Eu³⁺-metallopolymer with an extremely high temperature sensing sensitivity within the physiological temperature range. Finally, the real-time monitoring of the intracellular temperature variation is further conducted.

Multi-color fluorescence sensing platform for visual determination of norfloxacin based on a terbium (Ш) functionalized covalent organic framework

Sensitive and visual determination of fluoroquinolone antibiotics (FQs) is of great significance since their abuse and inappropriate handling can be problematic. Herein, we propose a lanthanide covalent organic framework fluorescence sensing system (Tb@COF-Ru) with visualization capability to determine the FQs level, where Tb@COF was employed as the sensing probe, while the red-emitting Ru(bpy)₃²⁺ serves as a constant red fluorescent background. With increasing norfloxacin concentration, the green fluorescence of Tb³⁺ is gradually enhanced, finally realizing the multicolor fluorescence change from red to green. With a smartphone for RGB analysis, visual monitoring and quantitative analysis were realized without any sophisticated instrument. Limits of detection for the fluorescence quantitative and visual mode for norfloxacin were 0.33 nM and 7.3 μM, respectively. This method was rapid (1 min) and visualized, providing a simple analysis of various food matrices (honey, milk, egg and beef) and water samples for trace FQs.

Fully-Conjugated Covalent Organic Frameworks with Two Metal Sites for Oxygen Electrocatalysis and Zn-Air Battery

Covalent organic frameworks (COFs) are a promising alternative toward catalysis, due to the unique framework structure and the excellent chemical stability. However, the scarcity of unsaturated metal sites and the low conductivity have constrained the advancement of these materials for catalysis of electrochemical reactions. Exploring next-generation conductive metal-covalent organic frameworks (M-COFs) with extra metal active sites is crucial for improving their catalytic activity. Herein, a novel fully-conjugated M-COFs (Co-PorBpy-Co) with two types of metal sites is proposed and achieved by solvothermal method in the presence of carbon nanotube (CNT). The electrocatalyst constructed by the Co-PorBpy-Co exhibits excellent oxygen reduction reaction (ORR) activity (E1/2 = 0.84 V vs RHE, n = 3.86), superior to most COFs-based catalysts. Theoretical result shows the CoN2 sites are extremely active for ORR, and Co-PorBpy-Co exhibits excellent conductivity for electron transfer. The Zn-air battery constructed by Co-PorBpy-Co/CNT manifests excellent power density (159.4 mW cm-2 ) and great cycling stability, surpassing that of 20 wt% Pt/C catalyst. This work not only proposes a novel design concept for electrocatalysts, but establishes a mechanism platform for single-metal atom electrocatalysis and synergistic effect.

A sweat-responsive covalent organic framework film for material-based liveness detection and sweat pore analysis

Covalent organic frameworks have shown considerable application potential and exceptional properties in the construction of stimulus-responsive materials. Here, we designed a sweat-responsive covalent organic framework film for material-based fingerprint liveness detection. When exposed to human sweat, the COF_TPDA-TFPy film can transform from yellow to red. The COF_TPDA-TFPy film, when touched by living fingers, can produce the naked-eye-identified fingerprint pattern through the sweat-induced color change, while artificial fake fingerprints cannot. This technique, which we named material-based liveness detection, can thus intuitively discern living fingers from fake fingerprints with a 100% accuracy rate. Additionally, the distribution of sweat pores on human skin can also be collected and analyzed by shortening the contact time. By merely washing them with ethanol, all the samples can be utilized again. This work inventively accomplished material-based liveness detection and naked-eye-identified sweat pore analysis and highlighted their potential for use in clinical research and personal identification.

Imine-Linked Covalent Organic Framework Modulates Oxidative Stress in Alzheimer's Disease

Oxidative stress due to Cu²⁺-triggered aggregation of β-amyloid protein (Aβ) and reactive oxygen species (ROS) overexpression in the brain is an important hallmark of early stages of Alzheimer's disease (AD) pathogenesis. The ideal modulator for improving the oxidative stress microenvironment in AD brains should take both Cu²⁺ and ROS into consideration, which has been rarely reported. Here, a combined therapeutic strategy was achieved by co-encapsulating superoxide dismutase (SOD) and catalase (CAT) in imine-linked covalent organic frameworks (COFs), which were modified with peptide KLVFF (T5). The nanocomposite SC@COF-T5 exhibited an oxidative stress eradicating ability through ROS elimination and Cu²⁺ chelation, combined with the inhibition of Aβ42 monomer aggregation and disaggregation of Aβ42 fibrils. In vivo experiments indicated that SC@COF-T5 with a high blood-brain barrier (BBB) penetration efficiency was effective to reduce Aβ deposition, expression of pro-inflammatory cytokines, ROS levels, and neurologic damage in AD model mice, consequently rescuing memory deficits of AD mice. This work not only confirms the feasibility and merits of the therapeutic strategy regarding multiple targets for treatment of early AD pathogenesis but also opens up a novel direction for imine-linked COFs in biomedical applications.

Reticular Synthesis of One-Dimensional Covalent Organic Frameworks with 4-c sql Topology for Enhanced Fluorescence Emission

Covalent organic frameworks (COFs) have been extensively investigated due to their unique structure, porosity, and functionality. However, at the topological level, COFs remain as two-dimensional (2D) or three-dimensional (3D) structures, while COFs with one-dimensional (1D) topology have not been systematically explored. In this work, we proposed a synthetic strategy for the construction of 1D-COFs based on non-linear edges and suitable high-symmetry vertices. Compared with their 2D-COFs counterparts, the 1D-COFs with AIEgens located at the vertex of the frame exhibited enhanced fluorescence. The density functional theory (DFT) calculations revealed that the dimensional-induced rotation restriction (DIRR) effect could spontaneously introduce additional non-covalent interactions between the strip frames, which could substantially diminish non-radiative transitions. This work also provides protocols for the design of 1D-COFs and a guidance scheme for the synthesis of emitting COFs.

2D Conductive Covalent Organic Frameworks with Abundant Carbonyl Groups for Electrochemical Sensing

Due to their permanent porosity, robust chemical stability, and tunable structure, covalent organic frameworks (COFs) are very attractive in the application of energy storage, catalysis, sorption, and sensing. However, the very low conductivity of COFs severely restricts their application in electrochemical sensing. Here, an aza-fused π-conjugated COFs with abundant carbonyl groups (COF1) was synthesized and deployed as electrode materials in electrochemical sensing for the first time. The current response of the acetylcholinesterase biosensor based on COF1 increases three times when compared to the electrode without COF1. The effects of carbonyl groups on signal enhancement were proved in depth by a series of characterization and comparison experiments with the prepared COF2 without carbonyl groups. The results demonstrated that exposed carbonyl active sites of COF1 can promote the effective immobilization and bioactivity preserving of enzyme molecules and contribute to the enrichment of analytes. Together with the good conductivity of COF1 derived from a fully extended 2D aromatized π-conjugated system, all of which improve the biosensor performance. The COF1-based biosensor exhibited fast response speed, high sensitivity, good selectivity and practicability, and robust stability for organophosphorus pesticide detection and proved to be a promising tool for the rapid and onsite detection of organophosphorus pesticides in the environment.

Cu-α-diimine Compounds Encapsulated in Porous Materials as Catalysts for Electrophilic Amination of Aromatic C-H Bonds

Electrophilic amination has emerged as a more environmentally benign approach to construct arene C-N bonds. However, heterogeneous catalysts remain largely unexplored in this area, even though their use could facilitate product purification and catalyst recovery. Here we investigate strategies to heterogenize a Cu(2,2'-bipyridine) catalyst for the amination of arenes lacking a directing group with hydroxylamine-O-sulfonic acid (HOSA). Besides immobilization of Cu on a metal-organic framework (MOF) or covalent organic framework (COF) with embedded 2,2'-bipyridines, a ship-in-a-bottle approach was followed in which the Cu complex is encapsulated in the pores of a zeolite. Recyclability and hot centrifugation tests show that zeolite Beta-entrapped Cu^II(2,2'-bipyridine) is superior in terms of stability. With N-methylmorpholine as a weakly coordinating, weak base, simple arenes, such as mesitylene, could be aminated with yields up to 59%, corresponding to a catalyst TON of 24. The zeolite could be used in three consecutive runs without a decrease in activity. Characterization of the catalyst by EPR and XAS showed that the active catalytic complex consisted of a site-isolated Cu^II species with one 2,2'-bipyridine ligand.

Dual-mode vehicles with simultaneous thermometry and drug release properties based on hollow Y2O3:Er,Yb and Y2O2SO4:Er,Yb spheres

Employing luminescence thermometry in the biomedical field is undeniably appealing as many health conditions are accompanied by temperature changes. In this work, we show our ongoing efforts and results at designing novel vehicles for dual-mode thermometry and pH-dependent drug release based on hollow spheres. Hereby for that purpose, we exploit the hollow Y2O3 and Y2O2SO4 host materials. These two inorganic hollow phosphors were investigated and showed to have excellent upconversion Er3+-Yb3+ luminescence properties and could be effectively used as optical temperature sensors in the physiological temperature range when induced by near-infrared CW light (975 nm). Further, doxorubicin was exploited as a model anti-cancer drug to monitor the pH-dependent drug release of these materials showing that they can be used for simultaneous thermometry and drug delivery applications.

Complexing Eu3+/Tb3+ in a Nanoscale Postmodified Zr-MOF toward Temperature-Modulated Multispectrum Chromism

In recent years, extensive research has been directed toward the successful preparation of nanoscale luminescent thermometers with high sensitivities operative in a broad temperature range. To achieve this goal, we have devised a unique design and facile multistep synthesis of Zr-ctpy-NMOF@Tb_xEu_y compounds by confining Ln-complexes (Ln = Eu³⁺/Tb³⁺) into a robust nanoscale Zr-NMOF (MOF-808) via postsynthetic modification. Covalent grafting of 4-(4'-carboxyphenyl)-2,2':6,2″terpyridine ligand (ctpy) with a high triplet state energy and corresponding immobilization of bimetallic Ln³⁺ ions resulted in yellow light-emitting Zr-ctpy-NMOF@Tb_1.66Eu_0.14 to achieve a sensitivity of 5.2% K^-1 (thermal uncertainty dT < 1 K) operative over a broad temperature range of 25-400 K. To defeat the odds related to the detection of minute temperature changes using luminescent materials, we prepared a white light-emitting Zr-ctpy-NMOF@Tb_1.4Eu_0.31 that showed temperature-modulated multispectrum chromism where the color drastically changes from green (at 25 K, Q.Y.: 20.21%) to yellowish-green (at 200 K, Q.Y.: 23.13%) to white (at 300 K, Q.Y.: 26.4%) to orange (at 350 K, Q.Y.: 26.93%) and finally red (at 400 K, Q.Y.: 28.2%) with a high energy transfer efficiency of 49.8%, which is further supported by electron-phonon coupling.

Metalated covalent organic frameworks: from synthetic strategies to diverse applications

Covalent organic frameworks (COFs) are a class of organic crystalline porous materials discovered in the early 21st century that have become an attractive class of emerging materials due to their high crystallinity, intrinsic porosity, structural regularity, diverse functionality, design flexibility, and outstanding stability. However, many chemical and physical properties strongly depend on the presence of metal ions in materials for advanced applications, but metal-free COFs do not have these properties and are therefore excluded from such applications. Metalated COFs formed by combining COFs with metal ions, while retaining the advantages of COFs, have additional intriguing properties and applications, and have attracted considerable attention over the past decade. This review presents all aspects of metalated COFs, from synthetic strategies to various applications, in the hope of promoting the continued development of this young field.

Functionalized luminescent covalent organic frameworks hybrid material as smart nose for the diagnosis of Huanglongbing

Quantitative identification of several volatile organic compounds (VOCs) associated with the same disease provides a strong guarantee of the accurate analysis of the disease. Designing a single luminescent material to interact differently with multiple analytes can generate response patterns with remarkable diversity. Here, a highly green luminescent imine-based 2D COF (TtDFP) is designed and synthesized. TtDFP has ultrasensitive detection performance for trace water in organic solvent. Constructing a ratiometric fluorescence sensor can improve sensitivity for detecting analytes. To contrast the fluorescence signals of Eu³⁺ and COFs in sensing assays, a simple postsynthetic modification (PSM) method is used to introduce Eu³⁺ into TtDFP. The obtained red luminescent hybrid material Eu³⁺@TtDFP EVA film can be a fluorescent nose capable of "sniffing out" and quantifying VOCs (GA and PhA) associated with Huanglongbing (HLB, a devastating disease of citrus) at ppb levels. This work provides a technique of developing functionalized COF hybrid material to facilitate the distinction of various VOCs, which can also be extended to monitor the levels of other VOCs relevant to human health.

Effective Photosensitization in Excited-State Equilibrium: Brilliant Luminescence of TbIII Coordination Polymers Through Ancillary Ligand Modifications

Molecular photosensitizers provide efficient light-absorbing abilities for photo-functional materials. Herein, effective photosensitization in excited-state equilibrium is demonstrated using five Tb^III coordination polymers. The coordination polymers are composed of Tb^III ions (emission center), hexafluoroacetylacetonato (photosensitizer ligands), and phosphine oxide-based bridges (ancillary ligands). The two types of ligand combinations induces a rigid coordination structure via intermolecular interactions, resulting in high thermal stability (with decomposition temperatures above 300 °C). Excited-triplet-state lifetimes of photosensitizer ligands (τ=120-1320 μs) are strongly dependent on the structure of the ancillary ligands. The photosensitizer with a long excited-triplet-state lifetime (τ≥1120 μs) controls the excited state equilibrium between the photosensitizer and Tb^III , allowing the construction of Tb^III coordination polymer with high Tb^III emission quantum yield (≥70 %).

Preparation of cationic hierarchical porous covalent organic frameworks for rapid and effective enrichment of perfluorinated substances in dairy products

Perfluorinated substances (PFASs) are harmful pollutants that have environmental persistence and high bioaccumulation. Effective sample pretreatment must be performed to detect trace or even ultra-trace PFASs in actual samples because of their extremely low contents in complex samples. In this study, a cationic hierarchical porous covalent organic frameworks (C-H-COF) were customized via a template-assisted strategy using polystyrene spheres (PS) as sacrificial materials and a post-synthetic modification method. C-H-COF showed good adsorption selectivity for PFASs owing to the dual effects of the full utilization of the internal adsorption sites and electrostatic interaction. The key role of electrostatic attraction in the extraction of PFASs using C-H-COF was further proven by density functional theory (DFT) calculations. The maximum adsorption capacity of the C-H-COF for perfluorooctanoic acid (PFOA) was 400 mg·g⁻¹, which was superior to that of microporous COFs (M-COF) and hierarchical porous COFs without cationic functionalization (H-COF). Accordingly, an analytical method for sensitively detecting five PFASs was established by employing C-H-COF as a dispersive solid phase extraction (DSPE) adsorbent combined with ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS), and the limits of detection were 0.011‒0.29 ng·L⁻¹. Moreover, the hierarchical porous structure of the C-H-COF accelerated the mass transfer of analytes so that the extraction process could be completed within 10 min. This method was employed to analyze PFASs in dairy products, in which the ultra-trace levels of analytes were quickly determined with spiked recoveries of 80.1‒112.6%. This work not only provides a rational synthetic strategy for novel ionic hierarchical porous COFs but also helps to expand the application of COFs in sample pretreatment.

The postsynthetic renaissance of luminescent lanthanide ions on crystalline porous organic framework materials

A series of crystalline porous organic framework materials (CPOFs), such as metal-organic frameworks (MOFs), covalent organic frameworks (COFs) and hydrogen bonded organic frameworks (HOFs) have received extensive attentions due to...

Fluorescence Thermometer: Intermediation of the Fontal Temperature and Light

The rapid advance of thermal materials and fluorescence spectroscopy has extensively promoted micro-scale fluorescence thermometry development in recent years. Based on the advantages of fast response, high sensitivity, simple operation,...

An imine-linked covalent organic framework for renewable and sensitive determination of antibiotic

Lanthanide-functionalized porous organic materials have been the promising candidates in the chemical and biological sensing. Considering the superior thermal and solvent stability of covalent organic frameworks (COFs), the development of lanthanide ions-functionalized COFs based sensing platform is meaningful, while remains to be a challenge. In this work, a new imine-linked COF which provides suitable coordination sites for Tb³⁺ was constructed via the Schiff base reaction between P-phenylenediamine (Pda) and 2,6-Diformylpyridine (Dfp). Benefiting from its high signal-to-noise, the COF@Tb shows excellent ability to determinate ciprofloxacin (CIP) with a detection limit of 3.01 nM. The measurement can maintain good stability in the presence of potential interference or in actual sample. Being washed with ethanol after each measurement, COF@Tb can be recycled for five times. This work provides a novel alternative strategy for efficient construction of lanthanide-grafted COFs and may promote the development of porous organic materials based chemical sensing.

Porous polyelectrolyte frameworks: synthesis, post-ionization and advanced applications

Porous organic polymers (POPs), which feature high surface areas, robust skeletons, tunable pores, adjustable functionality and versatile applicability, have constituted a designable platform to develop advanced organic materials. Endowing polyelectrolytes with the distinct characteristics of POPs will attract mounting interest as the structural diversity of polyelectrolytes will bring the new hope of intriguing applications and potential benefits. In this review, the striking progress in ionized POPs (i-POPs) has been systematically summarized with regard to their synthetic strategies and applications. In the synthesis of i-POPs, we illustrate the representative ionic building blocks and charged functional groups capable of constructing the polyelectrolyte frameworks. The synthetic methods, including direct synthesis and post-modification, are detailed for the i-POPs with amorphous or crystalline structures, respectively. Subsequently, we outline the distinctive performances of i-POPs in adsorption, separation, catalysis, sensing, ion conduction and biomedical applications. The survey concerns the interplay between the surface chemistry, ionic interaction and pore confinement that cooperatively promote the performance of i-POPs. Finally, we conclude with the remaining challenges and promising opportunities for the on-going development of i-POPs.

One ion to catch them all: Targeted high-precision Boltzmann thermometry over a wide temperature range with Gd3

Ratiometric luminescence thermometry with trivalent lanthanide ions and their 4fn energy levels is an emerging technique for non-invasive remote temperature sensing with high spatial and temporal resolution. Conventional ratiometric luminescence thermometry often relies on thermal coupling between two closely lying energy levels governed by Boltzmann's law. Despite its simplicity, Boltzmann thermometry with two excited levels allows precise temperature sensing, but only within a limited temperature range. While low temperatures slow down the nonradiative transitions required to generate a measurable population in the higher excitation level, temperatures that are too high favour equalized populations of the two excited levels, at the expense of low relative thermal sensitivity. In this work, we extend the concept of Boltzmann thermometry to more than two excited levels and provide quantitative guidelines that link the choice of energy gaps between multiple excited states to the performance in different temperature windows. By this approach, it is possible to retain the high relative sensitivity and precision of the temperature measurement over a wide temperature range within the same system. We demonstrate this concept using YAl3(BO3)4 (YAB):Pr3+, Gd3+ with an excited 6PJ crystal field and spin-orbit split levels of Gd3+ in the UV range to avoid a thermal black body background even at the highest temperatures. This phosphor is easily excitable with inexpensive and powerful blue LEDs at 450 nm. Zero-background luminescence thermometry is realized by using blue-to-UV energy transfer upconversion with the Pr3+-Gd3+ couple upon excitation in the visible range. This method allows us to cover a temperature window between 30 and 800 K.

Facile preparation of core-shell magnetic organic covalent framework via self-polymerization of two-in-one strategy as a magnetic solid-phase extraction adsorbent for determination of Rhodamine B in food samples

The monomer of two-in-one molecular design strategy (i.e., A₂B₂ type monomer) 1,6-bis(4-formylphenyl)-3,8-bis((4-aminophenyl) ethynyl)) pyrene (BFBAEPy) was self-polymerized and coated on the modified Fe₃O₄ surface to synthesize a magnetic covalent organic framework (Fe₃O₄@COF) nanocomposite with a core-shell structure. Before high-performance liquid chromatography with ultraviolet detection (HPLC-UV) determination, Fe₃O₄@COF was used as a magnetic solid-phase extraction (MSPE) adsorbent to enrich Rhodamine B (RhB) illegally added to Chili powder and Chinese prickly ash. It had a large specific surface area and suitable pore size, which promoted the efficient adsorption of RhB dye and eliminated the interference of the matrix. Several key parameters affecting the extraction recovery rate were investigated, including adsorption capacity, adsorption time, pH, ionic strength, elution solvent, elution volume and elution time. Under the best optimized conditions, within the linear detection range of 0.05-5 µg/mL for RhB with the limit of detection (LOD) was 0.0038 µg/mL, excellent linearity (correlation coefficient R²=0.9997), and good repeatability (relative standard deviations RSD%< 3.8%), satisfactory extraction recovery rate (91.7%-97.5%). Therefore, the application of the established method to the detection of RhB in food samples has bright prospects.

Upconverting Er3+-Yb3+ Inorganic/Covalent Organic Framework Core-Shell Nanoplatforms for Simultaneous Catalysis and Nanothermometry

Lanthanide-based luminescent nanoparticles that are thermally responsive can be used to probe temperature changes at a nanoscale regime. However, materials that can work as both a nanothermometer and a catalyst are limited. Herein, we show that covalent organic frameworks (COFs), which is an emerging class of porous crystalline materials, can be grown around lanthanide nanoparticles to create unique core-shell nanostructures. In this way, the COF (shell) supports copper metal ions as catalytic sites and simultaneously lanthanide nanoparticles (β-NaLuF₄:Gd,Er,Yb-core) locally measure the temperature during the catalytic reaction. Moreover, β-NaLuF₄:Gd,Er,Yb nanoparticles are upconverting materials and hence can be excited at longer wavelengths (975 nm), which do not affect the catalysis substrates or the COF. As a proof-of-principle, a three-component addition reaction of benzaldehyde, indole, and malononitrile was studied. The local temperature was probed using luminescence nanothermometry during the catalytic reaction.

Turn-On Photocatalysis: Creating Lone-Pair Donor-Acceptor Bonds in Organic Photosensitizer to Enhance Intersystem Crossing

There is growing interest in developing triplet photosensitizers in terms of implementing photochemical strategies in synthetic chemistry. However, synthesis of stable triplet organic photosensitizers is nontrivial and often requires the use of heavy atoms. Herein, an alternative strategy is demonstrated to enhance the triplet generation efficiency by implanting lone-pair donor-acceptor bonds in the conjugated covalent organic frameworks (COFs). This powerful method is validated using COFs that host triazine, a moiety that has been extensively investigated in photocatalysis. Spectroscopic analysis and theoretical calculations reveal substantial improvements in the photoabsorptivity and triple-state photogeneration efficiency, consistent with catalytic tests concerning industrially relevant sulfide oxidation. These systems represent a promising addition to the rapidly increasing arsenal of synthetic photocatalytic systems.

Single-Metallic Thermoresponsive Coordination Network as a Dual-Parametric Luminescent Thermometer

The single-metallic coordination networks (CNs), simultaneously exhibiting temperature-dependent lifetime (TDLT) and emission band shift (TDEBS), are desirable for application in luminescent thermometers with high accuracy and reliability in a large temperature range. Nonetheless, up to date, there are no reports on such kinds of materials due to the lack of in-depth understanding of the origin of TDLT and TDEBS at a molecule level, being critical for exploiting a universal approach to design a dual-parametric CN phosphorescent thermometer (CN-PT). Herein, we have constructed a thermoresponsive CN [Cu₂(L1)Br₂]_∞ (IAM21-1, L1 = N¹,N⁶-di(pyridin-3-yl)adipamide) via a flexible-ligand-implanted strategy. The TDLT and TDEBS properties of IAM21-1 enable it to be applied as a single-metallic dual-parametric CN-PT in 50-500 K, which is the widest temperature range reported so far. The combination of structure analysis and DFT calculations demonstrates that the redshift of the emission band upon the decreasing temperature originates from the reversible skeleton-shrinkage-triggered narrower band gap. This work has unveiled the origin of TDLT and TDEBS properties and proposed an efficient strategy for designing dual-parametric CN-PTs.

Ionic Covalent-Organic Framework Nanozyme as Effective Cascade Catalyst against Bacterial Wound Infection

The increasing resistance risks of conventional antibiotic abuse and the formed biofilm on the surface of wounds have been demonstrated to be the main problems for bacteria-caused infections and unsuccessful wound healing. Treatment by reactive oxygen species, such as the commercial H₂ O₂ , is a feasible way to solve those problems, but limits in its lower efficiency. Herein, an ionic covalent-organic framework-based nanozyme (GFeF) with self-promoting antibacterial effect and good biocompatibility has been developed as glucose-triggered cascade catalyst against bacterial wound infection. Besides the efficient conversion of glucose to hydrogen peroxide, the produced gluconic acid by loading glucose oxidase can supply a compatible catalytic environment to substantially improve the peroxidase activity for generating more toxic hydroxyl radicals. Meanwhile, the adhesion between the positively charged GFeF and the bacterial membrane can greatly enhance the healing effects. This glucose-triggered cascade strategy can reduce the harmful side effects by indirectly producing H₂ O₂ , potentially used in the wound healing of diabetic patients.

The design of dual-switch fluorescence intensity ratio thermometry with high sensitivity and thermochromism based on a combination strategy of intervalence charge transfer and up-conversion fluorescence thermal enhancement

Currently, the temperature sensing performances of inorganic photoluminescence materials based on fluorescence intensity ratio technology have become a research hotspot in the optical thermometry field due to their non-contact sensing, fast response and high stability. However, several problems have obstructed the development of optical temperature sensing materials, including low sensitivity and narrow temperature measurement ranges. In view of the above dilemma, a new optical thermometer La2Mo3O12:Yb3+,Pr3+ designed based on the combination strategy of intervalence charge transfer and up-conversion fluorescence thermal enhancement was developed. Under excitation at 450 nm, the thermometer can work in a range from 298 to 648 K and the relative sensitivity reaches as high as 2.000% K-1 at 648 K. Under excitation at 980 nm, the thermometer can sense temperature with a wide range from 298 to 748 K and the relative sensitivity reaches as high as 4.325% K-1 at 598 K. A dual-switch optical temperature sensing material with high-sensitivity and a wide temperature measurement range has been successfully developed. Our research design strategies will give inspiration to the research on multi-switch temperature sensing materials with high sensitivity and a wide temperature measurement range.

Crystalline Porous Materials for Nonlinear Optics

Crystalline porous materials have been extensively explored for wide applications in many fields including nonlinear optics (NLO) for frequency doubling, two-photon absorption/emission, optical limiting effect, photoelectric conversion, and biological imaging. The structural diversity and flexibility of the crystalline porous materials such as the metal-organic frameworks, covalent organic frameworks, and polyoxometalates provide numerous opportunities to orderly organize the dipolar chromophores and to systemically modify the type and concentration of these dipolar chromophores in the confined spaces, which are highly desirable for NLO. Here, the recent advances in the crystalline porous NLO materials are discussed. The second-order NLO of crystalline porous materials have been mainly devoted to the chiral and achiral structures, while the third-order NLO crystalline porous materials have been categorized into pure organic and hybrid organic/inorganic materials. Some representative properties and applications of these crystalline porous materials in the NLO regime are highlighted. The future perspective of challenges as well as the potential research directions of crystalline porous materials have been also proposed.