Integration of Fluorescent Functionality into Pressure-Amplifying Metal-Organic Frameworks

Phenothiazine-dioxide-based Cu-MOFs: preserving porosity through the incorporation of substituents into organic linkers

Metal-organic frameworks (MOFs) with high porosity usually suffer from problems associated with pore collapse upon activation. Preserving the porosity can thus be considered an important subject to be resolved with regard to the application of MOFs as industrial materials. Herein, we report the preservation of the porosity of phenothiazine-dioxide-based Cu-MOFs via the incorporation of substituents into the organic linkers.

Probing the Limits of Mechanical Stability of the Mesoporous Metal-Organic Framework DUT-76(Cu) by Hydrocarbon Physisorption

The mechanical robustness of MOFs is crucial in most adsorption-related applications. Herein, we investigated the interaction of the mesoporous metal-organic framework DUT-76(Cu) with various C1-C4 hydrocarbons at their boiling points. During adsorption, the pore structure partially collapsed into an amorphous phase while retaining a residual porosity. We employed a combination of multicycle physisorption experiments using different hydrocarbons (methane, ethane, ethylene, propane, propylene, n-butane, and 1,3-butadiene) along with X-ray diffraction, scanning electron microscopy, and total scattering to examine this transition. This methodology allowed us to gain a comprehensive understanding of the effects on the crystal structure, local structure, and macroscopic behavior of the material. Furthermore, we identified specific correlations among the chain length, number of double bonds, and adsorption/desorption cycle stability, which are influenced by adsorption-induced stress. These multicycle adsorption experiments served as semiquantitative tools for assessing the mechanical stability of mesoporous frameworks.

Negative gas adsorption transitions and pressure amplification phenomena in porous frameworks

Nanoporous solids offer a wide range of functionalities for industrial, environmental, and energy applications. However, only a limited number of porous materials are responsive, i.e. the nanopore dynamically alters its size and shape in response to external stimuli such as temperature, pressure, light or the presence of specific molecular stimuli adsorbed inside the voids deforming the framework. Adsorption-induced structural deformation of porous solids can result in unique counterintuitive phenomena. Negative gas adsorption (NGA) is such a phenomenon which describes the spontaneous release of gas from an "overloaded" nanoporous solid via adsorption-induced structural contraction leading to total pressure amplification (PA) in a closed system. Such pressure amplifying materials may open new avenues for pneumatic system engineering, robotics, damping, or micromechanical actuators. In this review we illustrate the discovery of NGA in DUT-49, a mesoporous metal-organic framework (MOF), and the subsequent examination of conditions for its observation leading to a rationalization of the phenomenon. We outline the development of decisive experimental and theoretical methods required to establish the mechanism of NGA and derive key criteria for observing NGA in other porous solids. We demonstrate the application of these design principles in a series of DUT-49-related model compounds of which several also exhibit NGA. Furthermore, we provide an outlook towards applying NGA as a pressure amplification material and discuss possibilities to discover novel NGA materials and other counterintuitive adsorption phenomena in porous solids in the future.

Reticular Synthesis of Flexible Rare-Earth Metal-Organic Frameworks: Control of Structural Dynamics and Sorption Properties Through Ligand Functionalization

An exciting direction in metal-organic frameworks involves the design and synthesis of flexible structures which can reversibly adapt their structure when triggered by external stimuli. Controlling the extent and nature of response in such solids is critical in order to develop custom dynamic materials for advanced applications. Towards this, it is highly important to expand the diversity of existing flexible MOFs, generating novel materials and gain an in-depth understanding of the associated dynamic phenomena, eventually unlocking key structure-property relationships. In the present work, we successfully utilized reticular chemistry for the construction of two novel series of highly crystalline, flexible rare-earth MOFs, RE-thc-MOF-2 and RE-teb-MOF-1. Extensive single-crystal to single-crystal structural analyses coupled with detailed gas and vapor sorption studies, shed light onto the unique responsive behavior. The development of these series is related to the reported RE-thc-MOF-1 solids which were found to display a unique continuous breathing and gas-trapping property. The synthesis of RE-thc-MOF-2 and RE-teb-MOF-1 materials represents an important milestone as they provide important insights into the key factors that control the responsive properties of this fascinating family of flexible materials and demonstrates that it is possible to control their dynamic behavior and the associated gas and vapor sorption properties.

Directionally In Situ Self-Assembled Iridium(III)-Polyimine Complex-Encapsulated Metal-Organic Framework Two-Dimensional Nanosheet Electrode To Boost Electrochemiluminescence Sensing

Manufacturing electrochemiluminescence (ECL) electrodes to detect analytes with high performance in the aqueous phase for water-insoluble metal complexes is a great challenge. Here, a directional self-assembling avenue for in situ fabricating iridium(III)-polyimine complex-encapsulated metal-organic framework (MOF) two-dimensional electrode Hf-MOF/Ir2PD/APS/ITO is developed. The electrode displayed bright red ECL emission with high stability in the aqueous phase and specific adsorption toward ssDNA against dsDNA and mNs. That is to say, a "high-performance and multifunctional ECL electrode" is presented and explored for sensitive detection of acetamiprid (Ace) with a limit of detection of 0.0025 nM, where Ace-aptamer recognition-switched Exonuclease III-mediated digestion to make large numbers of Fc-labeled ssDNA transform into Fc-mNs. Furthermore, the proposed method was triumphantly employed to monitor the change in the residual concentration of Ace in pakchoi. This work breaks through the bottleneck of metal complex-based ECL emission in organic solvents and provides a novel strategy to develop high-performance ECL sensors.

A light-operated dual-mode method for neuroblastoma diagnosis based on a Tb-MOF: from biometabolite detection to logic devices

Tb-DBA can not only serve as a light-operated dual-mechanism driven platform to detect VMA (an early pathological feature of neuroblastoma), but can also produce a different fluorescence response to epinephrine (EP, the metabolic precursor of VMA).