Multielectron‐Transfer‐based Rechargeable Energy Storage of Two‐Dimensional Coordination Frameworks with Non‐Innocent Ligands

The metallically conductive bis(diimino)nickel framework (NiDI), an emerging class of metal–organic framework (MOF) analogues consisting of two‐dimensional (2D) coordination networks, was found to have an energy storage principle that uses both cation and anion insertion. This principle gives high energy led by a multielectron transfer reaction: Its specific capacity is one of the highest among MOF‐based cathode materials in rechargeable energy storage devices, with stable cycling performance up to 300 cycles. This mechanism was studied by a wide spectrum of electrochemical techniques combined with density‐functional calculations. This work shows that a rationally designed material system of conductive 2D coordination networks can be promising electrode materials for many types of energy devices.     

A Novel Bat‐Shaped Dicyanomethylene‐4H‐pyran‐Functionalized Naphthalimide for Highly Efficient Solution‐Processed Multilevel Memory Devices

Small‐molecule‐based multilevel memory devices have attracted increasing attention because of their advantages, such as super‐high storage density, fast reading speed, light weight, low energy consumption, and shock resistance. However, the fabrication of small‐molecule‐based devices always requires expensive vacuum‐deposition techniques or high temperatures for spin‐coating. Herein, through rational tailoring of a previous molecule, DPCNCANA (4,4′‐(6,6′‐bis(2‐octyl‐1,3‐dioxo‐2,3‐dihydro‐1H‐benzo[de]isoquinolin‐6‐yl)‐9H,9′H‐[3,3′‐bicarbazole]‐9,9′‐diyl)dibenzonitrile), a novel bat‐shaped A‐D‐A‐type (A‐D‐A=acceptor–donor–acceptor) symmetric framework has been successfully synthesized and can be dissolved in common solvents at room temperature. Additionally, it has a low‐energy bandgap and dense intramolecular stacking in the film state. The solution‐processed memory devices exhibited high‐performance nonvolatile multilevel data‐storage properties with low switching threshold voltages of about −1.3 and −2.7 V, which is beneficial for low power consumption. Our result should prompt the study of highly efficient solution‐processed multilevel memory devices in the field of organic electronics.     

Solid‐State Molecular Nanomagnet Inclusion into a Magnetic Metal–Organic Framework: Interplay of the Magnetic Properties

Single‐ion magnets (SIMs) are the smallest possible magnetic devices and are a controllable, bottom‐up approach to nanoscale magnetism with potential applications in quantum computing and high‐density information storage. In this work, we take advantage of the promising, but yet insufficiently explored, solid‐state chemistry of metal–organic frameworks (MOFs) to report the single‐crystal to single‐crystal inclusion of such molecular nanomagnets within the pores of a magnetic MOF. The resulting host–guest supramolecular aggregate is used as a playground in the first in‐depth study on the interplay between the internal magnetic field created by the long‐range magnetic ordering of the structured MOF and the slow magnetic relaxation of the SIM.     

Thermoplastic Membranes Incorporating Semiconductive Metal–Organic Frameworks: An Advance on Flexible X‐ray Detectors

Semiconductive metal–organic frameworks (MOFs) have emerged in applications such as chemical sensors, electrocatalysts, energy storage materials, and electronic devices. However, examples of semiconductive MOFs within flexible electronics have not been reported. We present flexible X‐ray detectors prepared by thermoplastic dispersal of a semiconductive MOF ( SCU‐13 ) through a commercially available polymer, poly(vinylidene fluoride). The flexible detectors exhibit efficient X‐ray‐to‐electric current conversion with enhanced charge‐carrier mobility and low trap density compared to pelleted devices. A high X‐ray detection sensitivity of 65.86 μCGy_air^?1 cm^?2 was achieved, which outperforms other pelleted devices and commercial flexible X‐ray detectors. We demonstrate that the MOF‐based flexible detectors can be operated at multiple bending angles without a deterioration in detection performance. As a proof‐of‐concept, an X‐ray phase contrast under bending conditions was constructed using a 5×5 pixelated MOF‐based imager.     

A Solvent‐Free Hot‐Pressing Method for Preparing Metal–Organic‐Framework Coatings

Metal–organic frameworks (MOFs), with their well‐defined pores and rich structural diversity and functionality, have drawn a great deal of attention from across the scientific community. However, industrial applications are hampered by their intrinsic fragility and poor processability. Stable and resilient MOF devices with tunable flexibility are highly desirable. Herein, we present a solvent‐ and binder‐free approach for producing stable MOF coatings by a unique hot‐pressing (HoP) method, in which temperature and pressure are applied simultaneously to facilitate the rapid growth of MOF nanocrystals onto desired substrates. This strategy was proven to be applicable to carboxylate‐based, imidazolate‐based, and mixed‐metal MOFs. We further successfully obtained superhydrophobic and “Janus” MOF films through layer‐by‐layer pressing. This HoP method can be scaled up in the form of roll‐to‐roll production and may push MOFs into unexplored industrial applications.     

Hollow Multi‐Shelled Structure with Metal–Organic‐Framework‐Derived Coatings for Enhanced Lithium Storage

Herein, we present heterogeneous hollow multi‐shelled structures (HoMSs) prepared by exploiting the properties of the metal–organic framework (MOFs) casing. Through accurately controlling the transformation of MOF layer into different heterogeneous casings, we can precisely design HoMSs of SnO₂@Fe₂O₃(MOF) and SnO₂@FeO_x‐C(MOF), which not only retain properties of the original SnO₂‐HoMSs, but also structural information from the MOFs. Tested as anode materials in LIBs, SnO₂@Fe₂O₃ (MOF)‐HoMSs demonstrate superior lithium‐storage capacity and cycling stability to the original SnO₂‐HoMSs, which can be attributed to the topological features from the MOF casing. Making a sharp contrast to the electrodes of SnO₂@Fe₂O₃ (particle)‐HoMSs fabricated by hydrothermal method, the capacity retention after 100 cycles for the SnO₂@Fe₂O₃ (MOF)‐HoMSs is about eight times higher than that of the SnO₂@Fe₂O₃ (particle)‐HoMS.     

Storage of Electrical Information in Metal–Organic‐Framework Memristors

Single crystals of a cyclodextrin‐based metal–organic framework (MOF) infused with an ionic electrolyte and flanked by silver electrodes act as memristors. They can be electrically switched between low and high conductivity states that persist even in the absence of an applied voltage. In this way, these small blocks of nanoporous sugar function as a non‐volatile RRAM memory elements that can be repeatedly read, erased, and re‐written. These properties derive from ionic current within the MOF and the deposition of nanometer‐thin passivating layers at the anode flanking the MOF crystal. The observed phenomena are crucially dependent on the sub‐nanometer widths of the channels in the MOF, allowing the passage of only smaller ions. Conversely, with the electrolyte present but no MOF, there are no memristance or memory effects.     

Crystal Dynamics in Multi‐stimuli‐Responsive Entangled Metal–Organic Frameworks

An understanding of solid‐state crystal dynamics or flexibility in metal–organic frameworks (MOFs) showing multiple structural changes is highly demanding for the design of materials with potential applications in sensing and recognition. However, entangled MOFs showing such flexible behavior pose a great challenge in terms of extracting information on their dynamics because of their poor single‐crystallinity. In this article, detailed experimental studies on a twofold entangled MOF ( f‐MOF‐1) are reported, which unveil its structural response toward external stimuli such as temperature, pressure, and guest molecules. The crystallographic study shows multiple structural changes in f‐MOF‐1 , by which the 3 D net deforms and slides upon guest removal. Two distinct desolvated phases, that is, f‐MOF‐1 a and f‐MOF‐1 b , could be isolated; the former is a metastable one and transformable to the latter phase upon heating. The two phases show different gated CO₂ adsorption profiles. DFT‐based calculations provide an insight into the selective and gated adsorption behavior with CO₂ of f‐MOF‐1 b . The gate‐opening threshold pressure of CO₂ adsorption can be tuned strategically by changing the chemical functionality of the linker from ethanylene (?CH₂?CH₂?) in f‐MOF‐1 to an azo (?N=N?) functionality in an analogous MOF, f‐MOF‐2 . The modulation of functionality has an indirect influence on the gate‐opening pressure owing to the difference in inter‐net interaction. The framework of f‐MOF‐1 is highly responsive toward CO₂ gas molecules, and these results are supported by DFT calculations.     

Towards Highly‐Efficient Phototriggered Data Storage by Utilizing a Diketopyrrolopyrrole‐Based Photoelectronic Small Molecule

A cooperative photoelectrical strategy is proposed for effectively modulating the performance of a multilevel data‐storage device. By taking advantage of organic photoelectronic molecules as storage media, the fabricated device exhibited enhanced working parameters under the action of both optical and electrical inputs. In cooperation with UV light, the operating voltages of the memory device were decreased, which was beneficial for low energy consumption. Moreover, the ON/OFF current ratio was more tunable and facilitated high‐resolution multilevel storage. Compared with previous methods that focused on tuning the storage media, this study provides an easy approach for optimizing organic devices through multiple physical channels. More importantly, this method holds promise for integrating multiple functionalities into high‐density data‐storage devices.     

Hydrangea‐like NiCo‐based Bimetal‐organic Frameworks,and their Pros and Cons as Supercapacitor Electrode Materials in Aqueous Electrolytes

Hydrangea‐like NiCo‐based bimetal‐organic frameworks (NiCo‐MOF) are synthesized in DMF‐EtOH solution via a solvothermal method, using 4,4′‐biphenyldicarboxylic acid as a ligand. NiCo‐MOF having a highest capacity of 1056.6 F · g^–1 at 0.5 A · g^–1 and 457.7 F · g^–1 even at 10 A · g^–1 is achieved at a Ni/Co/BPDC molar ratio of 1:1:1, a temperature of 170 °C and a reaction time of 12 hours. It exhibits secondary 3D microsphere structures assembled by primary 2D nanosheet structures, good crystalline structure and good thermal stability below 350 °C in air. All the electrochemical data show that NiCo‐MOF has the pros and cons as supercapacitor electrode materials in aqueous electrolytes. On the one hand, NiCo‐MOF has a high capacity even at a high current density, low internal resistance, charge‐transfer resistance and ion diffusion impendence, owing to the ordered coordination structure, 2D nanosheet structure and 3D assembled microsphere structure of NiCo‐MOF. On the other hand, the cycling stability and rate capability are not ideal enough due to the hydrolysis of coordination bonds in aqueous electrolytes, especially, in alkaline solution. The good dispersion and high electrochemical activity of metal ions bring a high capacity for NiCo‐MOF, but they result in the poor stability of NiCo‐MOF. In the future work, finding a suitable organic electrolyte is an effective way to enhance the cycling stability of NiCo‐MOF as well as deriving more stable skeleton materials from NiCo‐MOF.     

Density Functional Theory Study of Hydrogen Adsorption in a Ti‐Decorated Mg‐Based Metal–Organic Framework‐74

The Ti‐binding energy and hydrogen adsorption energy of a Ti‐decorated Mg‐based metal–organic framework‐74 (Mg‐MOF‐74) were evaluated by using first‐principles calculations. Our results revealed that only three Ti adsorption sites were found to be stable. The adsorption site near the metal oxide unit is the most stable. To investigate the hydrogen‐adsorption properties of Ti‐functionalized Mg‐MOF‐74, the hydrogen‐binding energy was determined. For the most stable Ti adsorption site, we found that the hydrogen adsorption energy ranged from 0.26 to 0.48 eV H₂^?1. This is within the desirable range for practical hydrogen‐storage applications. Moreover, the hydrogen capacity was determined by using ab initio molecular dynamics simulations. Our results revealed that the hydrogen uptake by Ti‐decorated Mg‐MOF‐74 at temperatures of 77, 150, and 298 K and ambient pressure were 1.81, 1.74, and 1.29 H₂ wt %, respectively.     

Resistance Controllability in Alkynylgold(III) Complex‐Based Resistive Memory for Flash‐Type Storage Applications

Owing to the demands of state‐of‐the‐art information technologies that are suitable for vast data storage, the necessity for organic memory device (OMD) materials is highlighted. However, OMDs based on metal complexes are limited to several types of transition‐metal complex systems containing nitrogen‐donor ligands. Herein, attempts are made to introduce novel alkynylgold(III) materials into memory devices with superior performance. In this respect, an alkynyl‐containing coumarin gold(III) complex, [(C₁₉N₅H₁₁)Au−C≡C−C₉H₅O], has been synthesized and integrated into a sandwiched Al/[(C₁₉N₅H₁₁)Au−C≡C−C₉H₅O]/indium tin oxide device. By precisely controlling the compliance current (I _cc), the devices show different switching characteristics from flash‐type binary resistance switching (I _cc≤10⁻³ A) to WORM‐type (WORM=write once read many times) ternary resistance switching (I _cc=10⁻² A). This work explores electrical gold(III) complex based memories for potential use in organic electronics.     

Conductance Photoswitching of Metal–Organic Frameworks with Embedded Spiropyran

Conductive metal–organic frameworks (MOFs) as well as smart, stimuli‐responsive MOF materials have attracted considerable attention with respect to advanced applications in energy harvesting and storage as well as in signal processing. Here, the conductance of MOF films of type UiO‐67 with embedded photoswitchable nitro‐substituted spiropyrans was investigated. Under UV irradiation, the spiropyran (SP) reversibly isomerizes to the open merocyanine (MC) form, a zwitterionic molecule with an extended conjugated π‐system. The light‐induced SP–MC isomerization allows for remote control over the conductance of the SP@UiO‐67 MOF film, and the conductance can be increased by one order of magnitude. This research has the potential to contribute to the development of a new generation of photoelectronic devices based on smart hybrid materials.     

Direct Fabrication of Free‐Standing MOF Superstructures with Desired Shapes by Micro‐Confined Interfacial Synthesis

Recently, metal–organic frameworks (MOFs) with multifunctional pore chemistry have been intensively investigated for positioning the desired morphology at specific locations onto substrates for manufacturing devices. Herein, we develop a micro‐confined interfacial synthesis (MIS) approach for fabrication of a variety of free‐standing MOF superstructures with desired shapes. This approach for engineering MOFs provides three key features: 1) in situ synthesis of various free‐standing MOF superstructures with controlled compositions, shape, and thickness using a mold membrane; 2) adding magnetic functionality into MOF superstructures by loading with Fe₃O₄ nanoparticles; 3) transferring the synthesized MOF superstructural array on to flat or curved surface of various substrates. The MIS route with versatile potential opens the door for a number of new perspectives in various applications.     

MOF‐Derived Double‐Layer Hollow Nanoparticles with Oxygen Generation Ability for Multimodal Imaging‐Guided Sonodynamic Therapy

The high reactive oxygen species (ROS) generation ability and simple construction of sonosensitizer systems remain challenging in sonodynamic therapy against the hypoxic tumor. In this work, we rationally prepared MOF‐derived double‐layer hollow manganese silicate nanoparticle (DHMS) with highly effective ROS yield under ultrasound irradiation for multimodal imaging‐guided sonodynamic therapy (SDT). The presence of Mn in DHMS increased ROS generation efficiency because it could be oxidized by holes to improve the electron–hole separation. Moreover, DHMS could produce oxygen in the tumor microenvironment, which helps overcome the hypoxia of the solid tumor and thus enhance the treatment efficiency. In vivo experiments demonstrated efficient tumor inhibition in DHMS‐mediated SDT guided by ultrasound and magnetic resonance imaging. This work presents a MOF‐derived nanoparticle with sonosensitive and oxygen generating ability, which provides a promising strategy for tumor hypoxia in SDT.     

An Efficient Visible and Near‐Infrared (NIR) Emitting SmIII Metal–Organic Framework (Sm‐MOF) Sensitized by Excited‐State Intramolecular Proton Transfer (ESIPT) Ligand

We report herein an unprecedented example of a luminescent Sm^III metal–organic framework (Sm‐MOF), in which both the visible and near‐infrared (NIR) emissions of Sm³⁺ ions are able to be sensitized by an excited‐state intramolecular proton transfer (ESIPT) ligand. Due to the solvent‐mediated interchange between enol and keto excited states of the ligand and subsequent energy transfer rate to Sm³⁺ ions, the luminescent decay lifetime of the Sm‐MOF can be tuned in different solvent‐grinding systems.     

A Catalase‐Like Metal‐Organic Framework Nanohybrid for O2‐Evolving Synergistic Chemoradiotherapy

Tumor hypoxia, the “Achilles’ heel” of current cancer therapies, is indispensable to drug resistance and poor therapeutic outcomes especially for radiotherapy. Here we propose an in situ catalytic oxygenation strategy in tumor using porphyrinic metal‐organic framework (MOF)‐gold nanoparticles (AuNPs) nanohybrid as a therapeutic platform to achieve O₂‐evolving chemoradiotherapy. The AuNPs decorated on the surface of MOF effectively stabilize the nanocomposite and serve as radiosensitizers, whereas the MOF scaffold acts as a container to encapsulate chemotherapeutic drug doxorubicin. In vitro and in vivo studies verify that the catalase‐like nanohybrid significantly enhances the radiotherapy effect, alleviating tumor hypoxia and achieving synergistic anticancer efficacy. This hybrid nanomaterial remarkably suppresses the tumor growth with minimized systemic toxicity, opening new horizons for the next generation of theranostic nanomedicines.     

In Situ Formation of Frustrated Lewis Pairs in a Water‐Tolerant Metal‐Organic Framework for the Transformation of CO2

Frustrated Lewis pairs (FLPs) consist of sterically hindered Lewis acids and Lewis bases, which provide high catalytic activity towards non‐metal‐mediated activation of “inert” small molecules, including CO₂ among others. One critical issue of homogeneous FLPs, however, is their instability upon recycling, leading to catalytic deactivation. Herein, we provide a solution to this issue by incorporating a bulky Lewis acid‐functionalized ligand into a water‐tolerant metal‐organic framework (MOF), named SION‐105 , and employing Lewis basic diamine substrates for the in situ formation of FLPs within the MOF. Using CO₂ as a C1‐feedstock, this combination allows for the efficient transformation of a variety of diamine substrates into benzimidazoles. SION‐105 can be easily recycled by washing with MeOH and reused multiple times without losing its identity and catalytic activity, highlighting the advantage of the MOF approach in FLP chemistry.     

A Conjugated Polymer Containing Arylazopyrazole Units in the Side Chains for Field‐Effect Transistors Optically Tunable by Near Infra‐Red Light

Optically tunable field‐effect transistors (FETs) with near infra‐red (NIR) light show promising applications in various areas. Now, arylazopyrazole groups are incorporated in the side chains of a semiconducting donor–acceptor (D‐A) polymer. The cis–trans interconversion of the arylazopyrazole can be controlled by 980 nm and 808 nm NIR light irradiation, by utilizing NaYF₄:Yb,Tm upconversion nanoparticles and the photothermal effect of conjugated D‐A polymers, respectively. This reversible transformation affects the interchain packing of the polymer thin film, which in turn reversibly tunes the semiconducting properties of the FETs by the successive 980 nm and 808 nm light irradiation. The resultant FETs display fast response to NIR light, good resistance to photofatigue, and stability in storage for up to 120 days. These unique features will be useful in future memory and bioelectronic wearable devices.     

Metal–Organic Framework (MOF)‐Derived Nanoporous Carbon Materials

Metal–organic framework (MOF)‐derived nanoporous carbon materials have attracted significant interest due to their advantages of controllable porosity, good thermal/chemical stability, high electrical conductivity, catalytic activity, easy modification with other elements and materials, etc. Thus, MOF‐derived carbons have been used in numerous applications, such as environmental remediations, energy storage systems (i.e. batteries, supercapacitors), and catalysts. To date, many strategies have been developed to enhance the properties and performance of MOF‐derived carbons. Herein, we introduce and summarize recent important approaches for advanced MOF‐derived carbon structures with a focus on precursor control, heteroatom doping, shape/orientation control, and hybridization with other functional materials.