Photoresponsive Metal Organic Frameworks Research Articles

Rational design of Bacteria-Targeted and Photo-Responsive MOF gel with antibacterial and anti-inflammatory function for infected wound healing

Damaged skin is prone to recurrent bacterial infections, which hinder proper wound healing and exacerbate inflammation. Urgent attention is required to devise versatile dressings possessing antibacterial and anti-inflammatory attributes to facilitate wound recovery. In this study, we engineered a photo-responsive metal–organic frameworks (MOFs) gel, targeting bacteria, and endowed it with antibacterial and anti-inflammatory effects to address infected wound healing. On the one hand, the anionic MOF was choose to support cationic natural drug Berberine (BBR) to achieve slow release of anti-inflammatory drugs. On the other hand, the incorporation of Ag nanoparticles onto MOFs not only facilitates the generation of reactive oxygen species (ROS) via photocatalysis under visible light but also furnishes sites for boric acid group attachment to target bacteria and expedites ROS transfer. The resultant MOFs@Ag-B@BBR exhibited potent photodynamic antibacterial activity against Staphylococcus aureus and MRSA at a low concentration of 37.5 µg mL−1, surpassing the efficacy of most reported MOFs-based nano-antimicrobials. Upon application of the MOFs@Ag-B@BBR composite hydrogel to infected wounds, the released BBR, in conjunction with photodynamic antibacterial action, significantly mitigated inflammatory responses and fostered wound healing. This study provides a widely applicable approach for rational design of MOFs materials with enhance antibacterial and anti-inflammatory functions.

Time-Resolved Spectroscopy for Dynamic Investigation of Photoresponsive Metal-Organic Frameworks.

Photoresponsive MOFs with precise and adjustable reticular structures are attractive for light conversion applications. Uncovering the photoinduced carrier dynamics lays the essential foundation for the further development and optimization of the MOF material. With the application of time-resolved spectroscopy, photophysical processes including excimer formation, energy transfer/migration, and charge transfer/separation have been widely investigated. However, the identification of distinct photophysical processes in real experimental MOF spectra still remains difficult due to the spectral and dynamic complexity of MOFs. In this Perspective, we summarize the typical spectral features of these photophysical processes and the related analysis methods for dynamic studies performed by time-resolved photoluminescence (TR-PL) and transient absorption (TA) spectroscopy. Based on the recent understanding of excited-state properties of photoresponsive MOFs and the discussion of challenges and future outlooks, this Perspective aims to provide convenience for MOF kinetic analysis and contribute to the further development of photoresponsive MOF material.

Photoresponsive metal-organic framework with combined photodynamic therapy and hypoxia-activated chemotherapy for the targeted treatment of rheumatoid arthritis

Activated M1-type macrophages, which produce inflammatory factors that exacerbate rheumatoid arthritis (RA), represent crucial target cells for inhibiting the disease process. In this study, we developed a novel photoresponsive targeted drug delivery system (TPNPs-HA) that can effectively deliver the hypoxia-activated prodrug tirapazamine (TPZ) specifically to activated macrophages. After administration, this metal-organic framework, PCN-224, constructed uing the photosensitizer porphyrin, exhibits the ability to generate excessive toxic reactive oxygen species (ROS) when exposed to near-infrared light. Additionally, the oxygen-consumed hypoxic environment further activates the chemotherapeutic effect of TPZ, thus creating a synergistic combination of photodynamic therapy (PDT) and hypoxia-activated chemotherapy (HaCT) to promote the elimination of activated M1-type macrophages. The results highlight the significantly potential of this photoresponsive nano-delivery system in providing substantial relief for RA. Furthermore, these findings support its effectiveness in inhibiting the disease process of RA, thereby offering new possibilities for the development of precise and accurate strategies for RA.

Highly selective photoreduction of CO2 catalyzed by the encapsulated heterometallic-substituted polyoxometalate into a photo-responsive metal-organic framework

The highly selective photoreduction of CO2 into valuable chemical fuels such as CO has been considered as an effective strategy to address modern energy and environmental issues. In this work, we have adopted the well-established impregnation approach to construct a P2W15Ni3{Re(CO)3}3 @NU-1000 composite by incorporating heterometallic-substituted P2W15Ni3{Re(CO)3}3 polyoxometalate (POM) into the pores of metal-organic framework (NU-1000) host. Upon light irradiation, the resulting P2W15Ni3{Re(CO)3}3@NU-1000 composite can effectively photocatalyze CO2 reduction, obtaining a CO production of 28982 μmol g−1 with 93.5% selectivity during 10-h photocatalysis. The catalytic system exhibits great long-term recyclability and stability for at least four successive recycles. The proposed photocatalytic mechanism was confirmed by a series of photochemical and spectroscopic analyses.

Photo-responsive metal–organic frameworks – design strategies and emerging applications in photocatalysis and adsorption

The emergence of light-responsive metal–organic frameworks represents an opportunity for stimuli responsive platform design for environmental applications.

Coumarin-functionalized metal-organic frameworks: adsorbents with photo-responsive active sites for adsorptive desulfurization.

Photo-responsive metal-organic frameworks (PMOFs) have great potential in on-demand controllable adsorption processes under distinct light conditions, which is challenging to realize by conventional adsorbents with static frameworks and properties. Here, we report a new type of adsorbent with photo-responsive active sites for adsorptive desulfurization. Coumarin monomers were incorporated in MIL-101(Cr) to construct the photo-responsive adsorbents by coordinating with unsaturated chromium sites. Trigged by UV light (>310 nm), coumarin monomers undergo dimerization to a cyclobutane structure, which forms a conjugation effect with π electrons on the aromatic ring of the sulfur compound, leading to remarkably increased uptake of 4,6-dimethyldibenzothiophene (4,6-DMDBT). Coumarin dimers can transform back to monomers under irradiation of 254 nm UV light, corresponding to decreased adsorption of 4,6-DMDBT. The change in adsorption amount between PMOF and the coumarin monomers and dimers is up to 62.8%. The present study might open up an avenue for the fabrication of adsorbents with on-demand active sites for various applications.

Advances and Application Prospect on Photoresponsive Metal-organic Frameworks

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Application of photo-responsive metal-organic framework in cancer therapy and bioimaging

Metal-organic frameworks (MOFs) are a class of hybrid porous crystalline materials that are assembled with metal ions/clusters and organic linkers. The fungibility of organic ligands and metal centers endow MOFs that are easy to design and synthesize. Based on their unique structure, multifarious MOFs with diverse functionalities have recently been widely applied in various research areas. Particularly striking is the application of photo-responsive MOFs in biological sensing and imaging. Notably, the photoelectronic properties make photo-responsive MOFs an ideal platform for cancer phototherapy. Moreover, ultrahigh porosities and tunable pore sizes allow MOFs to load anticancer drugs, further enhancing the antitumor efficiency. In this review, the categories and developing strategies of MOFs are briefly introduced. The application fields of MOFs in bioimaging, such as up-conversion fluorescence imaging, single/two-photon fluorescence bioimaging, magnetic resonance imaging, etc., are summarized. The working mechanism of MOFs in photo-responsive, photothermal therapy (PTT), and photodynamic therapy (PDT) are expounded. Examples of using MOFs for cancer treatment, including PTT, PDT, chemotherapy, and radiotherapy, are also demonstrated. Lastly, current limitations, challenges, and future perspectives for bioimaging and cancer treatment of MOFs are discussed. We believe that the versatile MOF will bring the dawn to the next generation of cancer treatment.

Fe/Mn Bimetal-Doped ZIF-8-Coated Luminescent Nanoparticles with Up/Downconversion Dual-Mode Emission for Tumor Self-Enhanced NIR-II Imaging and Catalytic Therapy.

ZIF-8, as an important photoresponsive metal-organic framework (MOF), holds great promise in the field of cancer theranostics owing to its versatile physiochemical properties. However, its photocatalytic anticancer application is still restricted because of the wide bandgap and specific response to ultraviolet light. Herein, we developed lanthanide-doped nanoparticles (LDNPs) coated with Fe/Mn bimetal-doped ZIF-8 (LDNPs@Fe/Mn-ZIF-8) for second near-infrared (NIR-II) imaging-guided synergistic photodynamic/chemodynamic therapy (PDT/CDT). The LDNPs were synthesized by encapsulating an optimal Yb3+/Ce3+-doped active shell on the NaErF4:Tm core to achieve dual-mode red upconversion (UC) and NIR-II downconversion (DC) emission upon NIR laser irradiation. At the optimal doping concentration, the UC and DC NIR-II emission intensities of LDNPs were increased 30.2- and 13.2-fold above those of core nanoparticles, which endowed LDNPs@Fe/Mn-ZIF-8 with an outstanding capability to carry out UC-mediated PDT and NIR-II optical imaging. In addition, the dual doping of Fe2+/Mn2+ markedly decreased the bandgap of the ZIF-8 photosensitizer from 5.1 to 1.7 eV, expanding the excitation threshold of ZIF-8 to the visible light region (∼650 nm), which enabled Fe/Mn-ZIF-8 to be efficiently excited by UC photons to achieve photocatalytic-driven PDT. Furthermore, Fe2+/Mn2+ ions could be responsively released in the tumor microenvironment through degradation of Fe/Mn-ZIF-8, thereby producing hydroxyl radicals (·OH) by Fenton/Fenton-like reactions to realize CDT. Meanwhile, the degradation of Fe/Mn-ZIF-8 endowed the nanosystems with tumor self-enhanced NIR-II imaging function, providing precise guidance for CDT/PDT.

Photoresponsive Metal-Organic Frameworks as Adjustable Scaffolds in Reticular Chemistry.

The easy and remote switching of light makes this stimulus an ideal candidate for a large number of applications, among which the preparation of photoresponsive materials stands out. The interest of several scientists in this area in order to achieve improved functionalities has increase parallel to the growth of the structural complexity of these materials. Thus, metal-organic frameworks (MOFs) turned out to be ideal scaffolds for light-responsive ligands. This review is focused on the integration of photoresponsive organic ligands inside MOF crystalline arrays to prepare enhanced functional materials. Besides the summary of the preparation, properties and applications of these materials, an overview of the future outlook of this research area is provided.

Pebax-based membrane filled with photo-responsive Azo@NH2-MIL-53 nanoparticles for efficient SO2/N2 separation

The preparation of mixed matrix membranes (MMMs) using metal–organic framework (MOF) as fillers is one of the simple and effective methods to improve the gas permeability and selectivity of membranes, and it has an attractive prospect to achieve controllable gas separation process. Herein, NH2-MIL-53 nanoparticles are synthesized by hydrothermal method and modified by aminoazobenzene (Azo) by decompression loading technology. The multifunctional Azo@NH2-MIL-53 nanoparticles are incorporated into the Pebax matrix to fabricate MMMs for efficient and controllable SO2 separation. Pebax/Azo@NH2-MIL-53–20% membrane exhibits the maximum SO2 permeability of 2570 Barrer with a SO2/N2 selectivity of 717 and the separation process of SO2/N2 has dynamic photo-responsive characteristics under different light conditions, which is attributed to the incorporation of the Azo@NH2-MIL-53. First, the NH2-MIL-53 nanoparticles with high specific surface area of 637 m2.g−1 and pore size of 1.50 nm are introduced into MMMs to construct rich SO2 transport channels, increasing the diffusivity selectivity. Second, the inherent –NH2 groups and introduced -N = N- groups in Azo@NH2-MIL-53 increase the affinity of SO2, enhancing the solubility selectivity. Third, by artificially changing the light conditions to accurately control the conformation of Azo and the pore structure of NH2-MIL-53 is changed, which significantly changes the SO2 adsorption capacity of NH2-MIL-53. Due to light is available in abundance in the form of sunlight, the mixed matrix membrane coupled with photo-responsive MOF can achieve more efficient and energy-saving gas separation process.

Trans-Cis Kinetic Study of Azobenzene-4,4'-dicarboxylic Acid and Aluminium and Zirconium Based Azobenzene-4,4'-dicarboxylate MOFs.

Metal organic frameworks (MOFs) are porous hybrid crystalline materials that consist of organic linkers coordinated to metal centres. The trans–cis isomerisation kinetics of the azobenzene-4,4′-dicarboxylic acid (AZB(COOH)2) precursor, as well as the Al3+ (Al-AZB)- and Zr4+ (Zr-AZB)-based MOFs with azobenzene-4,4′-dicarboxylate linkers, are presented. The photo-isomerization in the MOFs originates from singly bound azobenzene moieties on the surface of the MOF. The type of solvent used had a slight effect on the rate of isomerization and half-life, while the band gap energies were not significantly affected by the solvents. Photo-responsive MOFs can be classified as smart materials with possible applications in sensing, drug delivery, magnetism, and molecular recognition. In this study, the MOFs were applied in the dye adsorption of congo red (CR) in contaminated water. For both MOFs, the UV-irradiated cis isomer exhibited a slightly higher CR uptake than the ambient-light exposed trans isomer. Al-AZB displayed a dye adsorption capacity of over 95% for both the UV-irradiated and ambient light samples. The ambient light exposed Zr-AZB, and the UV irradiated Zr-AZB had 39.1% and 44.6% dye removal, respectively.

Fabrication and characterization of photo-responsive metal–organic framework membrane for gas sensing using planar optical waveguide sensor

A facile, novel fabrication approach using UV light irradiation was proposed to fabricate a photo-responsive metal–organic framework (PR-MOF-1, [Zn2-(bdc)2-(dpNDI)]n, where bdc = benzene-1,4-dicarboxylic acid; dpNDI = N,N′-di(4-pyridyl)-1,4,5,8-naphthalenetetracarboxy diimide) membrane. The morphology of the PR-MOF-1 framework evolved from a honeycomb porous structure to a densified ladder-layered structure after 60 min of UV-light illumination. The as-grown film was optically transparent and exhibited a greater sensing response to ethylenediamine (EDA) gas in the presence of interfering substances such as ammonia and dimethylamine as well as benzene, toluene, xylene, and styrene gases, as measured using an asymmetric planar optical waveguide gas sensor. When the EDA gas molecule was adsorbed on the surface of the membrane, charge transfer between them preferably occurred, leading to a change in the membrane surface conformation. As an ideal sensing material for EDA gas detection, the PR-MOF-1 membrane showed a relatively high surface sensitivity (11,000 times cm-1) after 60 min of growth, and it could quickly (in less than 2 s) detect 1 ppb of EDA gas with a significant response (S/N = 3.45). During the static gas adsorption process, the EDA gas adsorption kinetics fit well with pseudo-second-order (PSO) model, and the adsorption capacity (qe) on a unit surface showed a high value of 33.91 μg cm−2 at 283 K. The high selectivity and sensitivity of the PR-MOF-1 membrane for EDA gas indicate the effectiveness of the light irradiation method for alteration of the metal– organic framework membrane structure and control of the gas sensing properties.

Heterometallic Actinide-Containing Photoresponsive Metal-Organic Frameworks: Dynamic and Static Tuning of Electronic Properties.

Acquiring fundamental knowledge of properties of actinide-based materials is a necessary step to create new possibilities for addressing the current challenges in the nuclear energy and nuclear waste sectors. In this report, we established a photophysics-electronics correlation for actinide-containing metal-organic frameworks (An-MOFs) as a function of excitation wavelength, for the first time. A stepwise approach for dynamically modulating electronic properties was applied for the first time towards actinide-based heterometallic MOFs through integration of photochromic linkers. Optical cycling, modeling of density of states near the Fermi edge, conductivity measurements, and photoisomerization kinetics were employed to shed light on the process of tailoring optoelectronic properties of An-MOFs. Furthermore, the first photochromic MOF-based field-effect transistor, in which the field-effect response could be changed through light exposure, was constructed. As a demonstration, the change in current upon light exposure was sufficient to operate a two-LED fail-safe indicator circuit.

Synthesis and environmental applications of defective metal organic frameworks

Metal organic frameworks (MOFs) are attracting increasing attention in the field of pollution control due to their inherent characteristics, such as high porosity, large specific surface areas, and tunable structure and composition. Though more than 20000 kinds of MOFs structures have been reported so far, the majority of them are regular and composed of different kinds of building units. Defect engineering in MOFs is an exciting concept for tailoring material properties, which opens up novel opportunities in practical application. Defects are usually present in MOFs, which would alter the performance of MOFs by changing surface properties, pore structure, and the number of active sites. Since defects can enhance the performance of MOFs in adsorption and catalytic degradation of pollutants, various methods for designing and generating defects have been employed. Based on selected reports spanning the last decades, this review focuses on the most recent and significant developments in the classification of defects in MOFs and methods of introducing defects into MOFs. According to the composition of MOFs, defects can be divided into missing-linkers defect and missing-clusters defect. The main methods of introducing defects into MOFs include de novo synthesis and post-synthetic treatment. De novo synthesis method includes mixed linker approach, modulation approach and fast crystal growth approach. Post-synthetic treatment method involves acid/base treatment approach, harsh activation approach, solvent-assisted linker exchange and mechanical treatment approach. The use of defective MOFs as adsorbent and catalyst in pollutant removal is also highlighted. Because single physical-chemical characterization has its limitations, researchers adopt various techniques to characterize the existence and concentration of defects, such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), etc. Reasonable defects could be controlled by adjusting the synthesis conditions in an attempt to obtain MOFs with excellent performance in adsorption and catalysis. At the hand of adsorption, the adsorption of pollutants in water and gases onto defective MOFs is mainly affected by pore distribution, specific surface area and surface charge. The introduction of missing-linkers defect or missing-clusters defect would make the regular pore structure into locally disordered structure, and create new micropores, mesopores even macropores. Thereby, the pore volume and specific surface area of MOFs are increased, and then enhancing the adsorption performance. In view of photocatalysis, introducing defects into photo-responsive MOFs can not only promote the transfer of photo-generated electrons, but also inhibit electron-hole recombination, and even optimize the energy band structure, which synergistically results in the improvement of photocatalytic performance. From the perspective of chemical catalysis, the pores formed by missing-linkers defect or missing-clusters defect in MOFs would expose the interior surface, which creates additional catalytic sites for pollutants reaching, and then enhances the catalysis performance of MOFs. In short, defective MOFs have a wide range of applications in the fields of adsorption and catalysis. After summarizing the recent progress of the field, the advantages and shortcomings of present defective MOFs in pollution control are presented. On the basis of this, it is apparent that further deepening the basic theoretical study of defective MOFs will be helpful for its wide applications. The defect engineering of MOFs is beneficial for further industrialization. Finally, some potential research topics in construction of defects in MOFs for environmental application have also been proposed in the review.

Three-in-one: achieving a robust and effective hydrogen-evolving hybrid material by integrating polyoxometalate, a photo-responsive metal–organic framework, and in situ generated Pt nanoparticles

A three-in-one hybrid material (P2W18@NU-1000-Pt) was constructed and investigated as an effective and robust photocatalyst towards hydrogen production in a water-compatible photocatalytic system.

Coupling the Individual Motions of the Machine-like Components of Zirconium(IV) Organic Frameworks

Controlling the internal molecular dynamics in reticular materials is a major challenge for the development of nanotechnological applications. In this issue of Chem, Schurko, Loeb, and co-workers show how the ring motion of the [2]rotaxane-based linker and that of the surrounding triphenylene-based struts influence each other within a series of robust zirconium(IV) organic frameworks.

Enhanced photocatalytic and photothermal properties of ecofriendly metal-organic framework heterojunction for rapid sterilization

Injured tissues are susceptible to infections that suppress wound healing. Rapid and safe sterilization is therefore urgent for bacteria-infected wounds, especially under harsh conditions without antibiotic availability. In this work, we developed a photoresponsive metal–organic framework (MOF) heterojunction that responds to 660 nm light irradiation. It is composed of two kinds of MOFs (Prussian blue [PB] and PCN-224), which exhibited an enhanced photocatalytic performance due to the accelerated charge transfer of the heterojunction and the fast separation of photogenerated electron-hole pairs between PB and PCN-224. The combination of the enhanced photocatalytic performance and the intrinsic photothermal effect of PB endowed the MOFs heterojunction with highly effective sterilizing rates of 99.84% and 99.3% against Staphylococcus aureus and its biofilm after 660 nm light irradiation for 15 min, respectively. The iron and zirconium ions released from PB-PCN-224 composites were biocompatible and their cytotoxicity was negligible. More importantly, in vivo experiments showed that PB-PCN-224 can expedite wound healing.

Copper-Linked Rotaxanes for the Building of Photoresponsive Metal Organic Frameworks with Controlled Cargo Delivery.

We have prepared a photoresponsive metal-organic framework by using an amide-based [2]rotaxane as linker and copper(II) ions as metal nodes. The interlocked linker was obtained by the hydrogen bond-directed approach employing a fumaramide thread as template of the macrocyclic component, this latter incorporating two carboxyl groups. Single crystal X-ray diffraction analysis of the metal-organic framework, prepared under solvothermal conditions, showed the formation of stacked 2D rhombohedral grids forming channels decorated with the interlocked alkenyl threads. A series of metal-organic frameworks differing in the E/Z olefin ratio were prepared either by the previous isomerization of the linker or by postirradiation of the reticulated materials. By dynamic solid state 2H NMR measurements, using deuterium-labeled materials, we proved that the geometry of the olefinic axis of the interlocked struts determined the obtention of materials with different independent local dynamics as a result of the strength of the intercomponent noncovalent interactions. Moreover, the usefulness of these novel copper-rotaxane materials as molecular dosing containers has also been assayed by the diffusion and photorelease of p-benzoquinone, evaluated in different solvents and temperatures.

Computational Design of a Photoresponsive Metal–Organic Framework for Post Combustion Carbon Capture

A Mg-IRMOF-74-III structure with azopyridine molecules attached to its unsaturated metal sites is proposed as a new photoresponsive metal–organic framework (MOF) for CO2 capture. Computational simu...