Photopatterning of fluorescent host-guest carriers through pore activation of metal-organic framework single crystals

Erasable Photopatterning of Stilbene-Based Metal-Organic Framework Films

The development of photosensitive materials for erasable photopatterning is of significant interest in anti-counterfeiting and information storage applications. Herein two kinds of stilbene-based metal-organic framework (MOF) films with layer by layer method for studying photopatterning is reported. The resulting 2D Zn₂ (sdc)₂ MOF film (sdc = 4,4'-stilbenedicarboxylate) exhibits excellent photosensitive features with a very short photoconversion time (<35 s) while the 3D MOF Zn₄ O(sdc)₆ film does not have the property due to the fact that only parallel and short distance arrangement of olefin groups in the adjacent MOF layers can trigger [2+2] photocycloaddition. Furthermore, the Zn₂ (sdc)₂ film indicates obvious reversible fluorescent photoswitch behavior between yellow and blue fluorescence emission, which can achieve high-efficient, erasable photopatterning with various sizes (ca. 20 microns to decimeter). This study not only develops a new kind of photosensitive crystalline network film but also provides erasable photopatterning from macroscopic to microscopic in optical applications.

A photoprogrammable electronic nose with switchable selectivity for VOCs using MOF films

Advanced analytical applications require smart materials and sensor systems that are able to adapt or be configured to specific tasks. Based on reversible photochemistry in nanoporous materials, we present a sensor array with a selectivity that is reversibly controlled by light irradiation. The active material of the sensor array, or electronic nose (e-nose), is based on metal-organic frameworks (MOFs) with photoresponsive fluorinated azobenzene groups that can be optically switched between their trans and cis state. By irradiation with light of different wavelengths, the trans-cis ratio can be modulated. Here we use four trans-cis values as defined states and employ a four-channel quartz-crystal microbalance for gravimetrically monitoring the molecular uptake by the MOF films. We apply the photoprogrammable e-nose to the sensing of different volatile organic compounds (VOCs) and analyze the sensor array data with simple machine-learning algorithms. When the sensor array is in a state with all sensors either in the same trans- or cis-rich state, cross-sensitivity between the analytes occurs and the classification accuracy is not ideal. Remarkably, the VOC molecules between which the sensor array shows cross-sensitivity vary by switching the entire sensor array from trans to cis. By selectively programming the e-nose with light of different colors, each sensor exhibits a different isomer ratio and thus a different VOC affinity, based on the polarity difference between the trans- and cis-azobenzenes. In such photoprogrammed state, the cross-sensitivity is reduced and the selectivity is enhanced, so that the e-nose can perfectly identify the tested VOCs. This work demonstrates for the first time the potential of photoswitchable and thus optically configurable materials as active sensing material in an e-nose for intelligent molecular sensing. The concept is not limited to QCM-based azobenzene-MOF sensors and can also be applied to diverse sensing materials and photoswitches.

Directional asymmetry over multiple length scales in reticular porous materials

In nature and synthetic materials, asymmetry is a useful tool to create complex and functional systems constructed from a limited number of building blocks. Reticular chemistry has allowed the synthesis of a wide range of discrete and extended structures, from which modularity permits the controlled assembly of their constituents to generate asymmetric configurations of pores or architectures. In this perspective, we present the different strategies to impart directional asymmetry over nano/meso/macroscopic length scales in porous materials and the resulting novel properties and applications.

Design strategies for the controlled assembly of discrete and extended reticular materials with asymmetric configurations of pores or architectures.

Core–shell metal–macrocycle framework (MMF): spatially selective dye inclusion through core-to-shell anisotropic transport along crystalline 1D-channels connected by epitaxial growth

Core–shell porous metal–macrocycle frameworks were fabricated via an epitaxial growth procedure to observe core-to-shell anisotropic transport of a dye.

Rising Up: Hierarchical Metal-Organic Frameworks in Experiments and Simulations

Controlled synthesis across several length scales, ranging from discrete molecular building blocks to size- and morphology-controlled nanoparticles to 2D sheets and thin films and finally to 3D architectures, is an advanced and highly active research field within both the metal-organic framework (MOF) domain and the overall material science community. Along with synthetic progress, theoretical simulations of MOF structures and properties have shown tremendous progress in both accuracy and system size. Further advancements in the field of hierarchically structured MOF materials will allow the optimization of their performance; however, this optimization requires a deep understanding of the different synthesis and processing techniques and an enhanced implementation of material modeling. Such modeling approaches will allow us to select and synthesize the highest-performing structures in a targeted rational manner. Here, recent progress in the synthesis of hierarchically structured MOFs and multiscale modeling and associated simulation techniques is presented, along with a brief overview of the challenges and future perspectives associated with a simulation-based approach toward the development of advanced hierarchically structured MOF materials.

Host–guest energetic materials constructed by incorporating oxidizing gas molecules into an organic lattice cavity toward achieving highly-energetic and low-sensitivity performance

Powerful oxidizer N₂O was incorporated into an organic lattice cavity through aeration crystallization, and smart host–guest energetic materials with highly-energetic and low-sensitivity performance were obtained.

Disassembly of Hydrophobic Photosensitizer by Biodegradable Zeolitic Imidazolate Framework-8 for Photodynamic Cancer Therapy

Photodynamic therapy (PDT), an alternative to conventional cancer therapeutics, has gained increasing attention for its noninvasive advantage and simultaneous fluorescence imaging property. PDT is a tripartite process that functions in the simultaneous presence of a photosensitizer (PS), light, and available oxygen molecules. However, many highly efficient PSs are hydrophobic and highly tend to self-aggregate in aqueous solution, leading to quick quenching of the PDT effect. Here we construct zeolitic imidazolate framework-8 (ZIF-8) containing water-insoluble photosensitizer zinc(II) phthalocyanine (ZnPc), a typical hydrophobic PS, by one-step coprecipitation process, named as ZnPc@ZIF-8. The micropores of ZIF-8 act as molecular cages to separate and maintain hydrophobic ZnPc in the monomeric state and protect it against self-aggregation, which enables the encapsulated ZnPc to generate cytotoxic singlet oxygen (¹O₂) under light irradiation (650 nm) in aqueous condition. The formed nanosystem of ZnPc@ZIF-8 can be endocytosed by cancer cells and exhibits red fluorescent emission with excellent photodynamic activity for cancer treatment in vitro. In addition, ZnPc@ZIF-8 is acid-sensitive and would completely degrade after PDT, which can be monitored by the self-quenching of fluorescence emission of ZnPc. This work paves a facile way for resolving the problem of solubility and bioavailability of hydrophobic PS by utilizing metal-organic frameworks as nanocarriers.