Tunable Emission in Heteroepitaxial Ln‐SURMOFs

By using a layer‐by‐layer (LbL) approach, lanthanide‐based, monolithic metal–organic framework (MOF) thin films are fabricated for optical applications. In particular, the LbL approach allows manufacturing of heteroepitaxial Tb(III)‐Eu(III)(BTC) coatings with precise thickness control. Adjusting the Tb(III)‐to‐Eu(III) ratio allows tuning of the emission color. The hetero‐multilayer architecture makes it possible to suppress the direct Tb(III)‐to‐Eu(III) energy transfer, an unwanted phenomenon present in the corresponding mixed‐metal bulk MOF structures. The resulting Ln‐MOF thin films, or Ln‐surface‐anchored MOFs (SURMOFs), are characterized by X‐ray diffraction, infra‐red reflection absorption spectroscopy, UV–vis, and photoluminescence measurements. The results demonstrate that the heteroepitaxial SURMOF architectures carry huge potential for fabricating optical coatings for a wide range of applications.     

High‐Throughput Fabrication of Uniform and Homogenous MOF Coatings

We describe a novel method to produce monolithic, oriented, crystalline and highly porous coatings on solid substrates. By adopting the recently described liquid‐phase epitaxy (LPE) process developed to grow metal‐organic framework coatings (MOFs) on modified Au‐substrates to the spray method, we have prepared thick (μm) layers of several MOF types on modified Au‐substrates, including HKUST‐I and layer‐pillar MOFs. The spray method not only allows such SURMOFs to be grown much faster than with the LPE‐process but the dependence of layer thickness on the number of immersion cycles also provides valuable insights into the mechanism governing the layer‐by‐layer MOF formation process.     

Self‐Healing Materials via Reversible Crosslinking of Poly(ethylene oxide)‐Block‐Poly(furfuryl glycidyl ether) (PEO‐b‐PFGE) Block Copolymer Films

The application of well‐defined poly(furfuryl glycidyl ether) (PFGE) homopolymers and poly(ethylene oxide)‐b‐poly(furfuryl glycidyl ether) (PEO‐b‐PFGE) block copolymers synthesized by living anionic polymerization as self‐healing materials is demonstrated. This is achieved by thermo‐reversible network formation via (retro) Diels‐Alder chemistry between the furan groups in the side‐chain of the PFGE segments and a bifunctional maleimide crosslinker within drop‐cast polymer films. The process is studied in detail by differential scanning calorimetry (DSC), depth‐sensing indentation, and profilometry. It is shown that such materials are capable of healing complex scratch patterns, also multiple times. Furthermore, microphase separation within PEO‐b‐PFGE block copolymer films is indicated by small angle X‐ray scattering (lamellar morphology with a domain spacing of approximately 19 nm), differential scanning calorimetry, and contact angle measurements.     

Liquid Phase Heteroepitaxial Growth of Moisture‐Tolerant MOF‐5 Isotype Thin Films and Assessment of the Sorption Properties by Quartz Crystal Microbalance

The moisture‐tolerant metal‐organic frameworks (MOFs) of formula [Zn₄O(L)₃]_n (L = di‐substituted carboxypyrazolate derivatives) are fabricated as thin films on self‐assembled monolayer (SAM) functionalized gold substrates by employing the step‐by‐step liquid phase epitaxial (LPE) deposition method in a continuous operation mode. The in situ monitoring of the deposition by quartz crystal microbalance (QCM) and grazing incidence X‐ray diffraction reveal different growth regimes and crystallinities of the obtained thin films in dependence of the chosen alkyl side chain functionality at the carboxypyrazolate linkers, L. To overcome the relatively poor crystallinity and low porosity of a particular homostructured metal‐organic framework type B film, the step‐by‐step heteroepitaxial growth of this MOF B on top of the crystallite surfaces of a well‐grown and lattice‐matched MOF type A is applied. This approach enables the fabrication of oriented, core‐shell‐like MOF B @ A surface mounted heterocrystals as an intergrown homogeneous coating for the selective adsorption of volatile organic compounds. The accessible pore volumes of the individual components and the heterostructured films are characterized by performing adsorption measurements of different organic probe molecules using an environmentally controlled QCM instrument. The results show good adsorption capacity, excellent size exclusion selectivity for alcohols, and a high degree of moisture‐tolerance of the heteroepitaxial MOF films.     

Magnetic Cores with Porous Coatings: Growth of Metal‐Organic Frameworks on Particles Using Liquid Phase Epitaxy

A novel method for the homogeneous coating of magnetic nanoparticles with metal organic frameworks (MOFs) is reported. Using a liquid phase epitaxy process, a well‐defined number of [Cu₃(btc)₂]nH₂O, HKUST‐1, layers are grown on COOH terminated silica magnetic beads. The structure and porosity of the deposited MOF coatings are studied using X‐ray diffraction and BET analysis. In addition, size and shape of the fabricated composites are analyzed by transmission electron microscopy. Potential applications of particle based MOF films include catalytic coatings and chromatographic media.     

Fluidic Processing of High‐Performance ZIF‐8 Membranes on Polymeric Hollow Fibers: Mechanistic Insights and Microstructure Control

Recently, a methodology for fabricating polycrystalline metal‐organic framework (MOF) membranes has been introduced – referred to as interfacial microfluidic membrane processing – which allows parallelizable fabrication of MOF membranes inside polymeric hollow fibers of microscopic diameter. Such hollow fiber membranes, when bundled together into modules, are an attractive way to scale molecular sieving membranes. The understanding and engineering of fluidic processing techniques for MOF membrane fabrication are in their infancy. Here, a detailed mechanistic understanding of MOF (ZIF‐8) membrane growth under microfluidic conditions in polyamide‐imide hollow fibers is reported, without any intermediate steps (such as seeding or surface modification) or post‐synthesis treatments. A key finding is that interfacial membrane formation in the hollow fiber occurs via an initial formation of two distinct layers and the subsequent rearrangement into a single layer. This understanding is used to show how nonisothermal processing allows fabrication of thinner (5 μm) ZIF‐8 films for higher throughput, and furthermore how engineering the polymeric hollow fiber support microstructure allows control of defects in the ZIF‐8 membranes. The performance of these engineered ZIF‐8 membranes is then characterized, which have H₂/C₃H₈ and C₃H₆/C₃H₈ mixture separation factors as high as 2018 and 65, respectively, and C₃H₆ permeances as high as 66 GPU.     

A Polymetallic Metal‐Organic Framework‐Derived Strategy toward Synergistically Multidoped Metal Oxide Electrodes with Ultralong Cycle Life and High Volumetric Capacity

Metal‐organic frameworks (MOFs) are very convenient self‐templated precursors toward functional materials with tunable functionalities. Although a huge family of MOFs has been discovered, conventional MOF‐derived strategies are largely limited to the sole MOF source based on a handful of the metal elements. The limitation in structure and functionalities greatly restrains the maximum performance of MOF‐based materials for fulfilling the practical potential. This study reports a polymetallic MOF‐derived strategy for easy synthesis of metal‐oxide‐based nanohybrids with precisely tailored multicomponent active dopants. A variety of MoO₂‐based nanohybrids with synergistical co‐doping of W, Cu, and P are yielded by controlled pyrolysis of tailor‐made polymetallic MOFs. The W doping induces the formation of Mo_x W_1?x O₂ solid solution with better activity. The homogeneous dispersion of Cu nanocrystallites in robust P‐doped carbon skeleton creates a conductive network for fast charge transfer. Boosting by synergistically multidoping effect, the Mo_0.8W_0.2O₂‐Cu@P‐doped carbon nanohybrids with optimized composition exhibit exceptionally long cycle life of 2000 cycles with high capacities but very slow capacity loss (0.043% per cycle), as well as high power output for lithium storage. Remarkably, the co‐doping of heavy W and Cu elements in MoO₂ with high density makes them particularly suitable for high volumetric lithium storage.     

Thermally Stable Two‐Dimensional Hexagonal Mesoporous Nanocrystalline Anatase,Meso‐nc‐TiO2: Bulk and Crack‐Free Thin Film Morphologies

Herein a novel synthetic route is described for the production of thermally stable, structurally well‐defined two‐dimensional (2D) hexagonal mesoporous nanocrystalline anatase (meso‐nc‐TiO₂), with a large pore diameter, narrow pore‐size distribution, high surface area, and robust inorganic walls comprised of nanocrystalline anatase. The synthetic approach involves the evaporation‐induced co‐assembly of a non‐ionic amphiphilic triblock‐copolymer template and titanium tetraethoxide, but with a pivotal change in the main solvent of the system, where the commonly used ethanol is replaced with 1‐butanol. This seemingly minor modification in solvent type from ethanol to 1‐butanol turns out to be the key synthetic strategy for achieving a robust, structurally well‐ordered meso‐nc‐TiO₂ material in the form of either thick or thin films. The beneficial “solvent” effect originates from the higher hydrophobicity of 1‐butanol than ethanol, enhancing microphase separation and templating, lower critical micelle concentration of the template in 1‐butanol, and the ability to increase the relative concentration of the inorganic precursor to template in the co‐assembly synthesis. Moreover, thin films with dimensions of several centimeters that are devoid of cracks down to the length scale of the mesostructure itself, having high porosity, well‐defined mesostructural features, and semi‐crystalline pore walls were straightforwardly and reproducibly obtained as a result of the physicochemical property advantages of 1‐butanol over ethanol within our synthesis scheme.     

Metal‐Organic Framework Nanoparticles in Photodynamic Therapy: Current Status and Perspectives

This feature article covers the recent applications of metal‐organic framework nanoparticles (MOF NPs) in photodynamic therapy (PDT) of cancer. It aims at giving the reader an overview about these two current research fields, i.e., MOF and PDT, and at highlighting the potential synergistic effect that could result from their association. After describing the general photophysics and photochemistry that underlie PDT, the relationship between photosensitizer (PS) properties and PDT requirements is discussed throughout the PSs historical development. This development reveals the advantages of using nanotechnology platforms for the creation of the ideal PS and leads us to define the fourth generation of PSs, which includes NPs built from the PS itself as porphysomes or PS‐based MOF NPs. Especially, the precise spatial control over the PS assembly into well‐defined MOF NPs, which keeps the PS in its monomeric form and prevents PS self‐quenching, appears as a notable feature to solve PS solubility and aggregation issues and therefore improves the PDT efficiency. Finally, we discuss the future perspectives of MOF NPs in PDT and shed light on how promising these nanomaterials are.     

Well‐Defined Pillararene‐Based Azobenzene Liquid Crystalline Photoresponsive Materials and Their Thin Films with Photomodulated Surfaces

Photoresponsive materials (PRMs) have long been a hot topic and photo‐modulated smart surface is very appealing. Particularly, liquid crystalline PRMs are able to amplify and stabilize photoinduced orientation thanks to their self‐assembling and ordering characteristics. Herein, the first pillararene‐based azobenzene liquid crystalline PRM with well‐defined structure is presented, which can avoid the usually ill‐defined composition drawback of polymer PRMs and prevent the severe H‐aggregation from suppressing or even completely blocking photoresponse in simple azobenzene derivatives. The pillar[5]arene‐based macrocyclic azobenzenes with variant length spacers show wide temperature range smectic liquid crystalline mesophases and excellent film‐formation property. The tubular pillar[5]arene macrocyclic framework provides sufficient free volume for azobenzene moieties to achieve reversible photoisomerization and photoalignment; thus, their thin films demonstrate excellent light‐triggered modulation of surface free energy, wettability, and even photoalignment‐mediated orientation of an upper layer discotic liquid crystal columnar mesophase. Such pillararene‐based azobenzene liquid crystals represent novel and promising PRMs with extensive fascinating applications.     

Metal–Organic Frameworks Derived from Zero‐Valent Metal Substrates: Mechanisms of Formation and Modulation of Properties

The replicative construction of metal–organic frameworks (MOFs) templated with solvent‐insoluble solid substrates is of marked importance, as it allows for the assembly of 2D and 3D macro‐ and mesoscopic architectures with properties that are challenging to attain by the conventional solution‐based synthesis approach. This work reports an in situ and direct construction of MOFs from zero‐valent metal substrates via a green hydrothermal oxidation–MOF construction chemistry without the use of any additional metal source, chemical reagents, or acidification of solvent, and elucidates the zero‐valent metal derived formation mechanisms of MOFs and their structure modulation to 1D nanofibers (NFs), 2D film, and 3D core–shell microstructures. Through modulation of the competing surface oxidation‐dissolution and MOF crystallization kinetics, Al@MIL‐53 core–shell microstructures and MIL‐53 (Al) NFs are obtained that exhibit unique morphologies and marked properties superior to the conventional MIL‐53 (Al) powders. The generality of zero‐valent metal‐templated synthesis of MOFs is demonstrated with formation of MIL‐53 (Al), HKUST‐1, and ZIF‐7 polycrystalline films on Al, Cu, and Zn metal meshes, elucidating the significance of the approach utilizing solid metal substrate that can be easily processed into various shapes, architectures, and compositions.     

Copper Sulfide (CuxS) Nanowire‐in‐Carbon Composites Formed from Direct Sulfurization of the Metal‐Organic Framework HKUST‐1 and Their Use as Li‐Ion Battery Cathodes

Li‐ion batteries containing cost‐effective, environmentally benign cathode materials with high specific capacities are in critical demand to deliver the energy density requirements of electric vehicles and next‐generation electronic devices. Here, the phase‐controlled synthesis of copper sulfide (Cu_xS) composites by the temperature‐controlled sulfurization of a prototypal Cu metal‐organic framework (MOF), HKUST‐1 is reported. The tunable formation of different Cu_xS phases within a carbon network represents a simple method for the production of effective composite cathode materials for Li‐ion batteries. A direct link between the sulfurization temperature of the MOF and the resultant Cu_xS phase formed with more Cu‐rich phases favored at higher temperatures is further shown. The Cu_xS/C samples are characterized through X‐ray diffraction (XRD), thermogravimetric analysis (TGA), transmission electron microscopy, and energy dispersive X‐ray spectroscopy (EDX) in addition to testing as Li‐ion cathodes. It is shown that the performance is dependent on both the Cu_xS phase and the crystal morphology with the Cu_1.8S/C‐500 material as a nanowire composite exhibiting the best performance, showing a specific capacity of 220 mAh g^?1 after 200 charge/discharge cycles.     

Structural and Electronic Properties of the First Monolayers of Spin‐Cast Poly(fluorene)‐Based Conjugated‐ Polymer Films

This study is an extended investigation on the formation of the first few monolayers of conjugated poly(fluorene)‐based polymer films prepared from solution on defined polar and nonpolar surfaces. In particular, a symmetrical A–B–A triblock copolymer consisting of poly(2‐alkylaniline) as A blocks and poly(9,9‐dialkylfluorene) as B blocks and a poly(9,9‐dialkylfluorene) homopolymer is used for this study. The dependence on drying conditions by means of solvent selection, the influence of a subsequent heat treatment, and the influence of the substrate polarity are investigated for ultrathin films as well as the transition from the first monolayers to the bulk polymer. The study is performed with optical absorption and photoluminescence spectroscopy, and atomic force microscopy to obtain complementary information of optical properties and morphological details. We find that ultrathin films (ca. 1–2 nm) prepared on mica from various solvents form highly defined, flat monolayers at the interface without lateral regularities indicating a dipole–dipole interaction between conjugated‐polymer segments and mica surface dipoles. This is further confirmed by bathochromic photoluminescence shifts observed for the ultrathin layers compared to the bulk polymer. Complementary experiments on nonpolar surfaces, highly oriented pyrolytic graphite (HOPG), show a total absence of defined flat films supporting the assumption of a dipole–dipole assisted formation on mica. For increased film thickness on mica (5 nm and more) the homopolymer does not form any regular structures or ordered layers on top of the monolayer. In contrast, the triblock copolymer, shorter in length, revealed a tendency to form a less‐defined layer‐type growth (3–3.5 nm thick) above the monolayer that was of higher order for higher‐boiling‐point solvents, indicating that the polymers are found in a different conformation. Moreover, one finds that some solvents that show partial immiscibility with the polymer strongly alter the formation of the film. The observations made for the two different types of polymers allow for an assignment of film‐formation driving forces to individual polymer segments and allow for the formulation of a growth model that explains the observed results and indicates the importance of appropriate substrate selection for organic electronic/optoelectronic devices.     

Room‐Temperature Phosphorescence From Films of Isolated Water‐Soluble Conjugated Polymers in Hydrogen‐Bonded Matrices

It is well known that luminescent conjugated polymers suffer serious loss of photoluminescence quantum yield (PLQY) in the solid state compared to dilute solution. This is due to efficient exciton migration in the solid, which enables the excitons to readily find low energy quenching sites. Here a new method to fabricate solid films with densely packed non‐interacting luminescent polymer chains, which yield very high PLQY and more astonishingly room temperature phosphorescence, is reported. Using water‐soluble conjugated polymers (WSCP) and polymeric surfactants such as poly(vinyl alcohol) (PVA) and poly(vinyl‐pyrrolidone) (PVP), films at 1:1 wt% or higher WSCP are produced and show room temperature phosphorescence; such behavior has never been observed before and clearly shows the very high degree of chain isolation that can be achieved in these hosts. The PVA or PVP not only breaks up WSCP aggregates in solution as an effective surfactant, PVA‐PVA or PVP‐PVP hydrogen bond formation upon drying locks in the isolation of the WSCP, avoiding segregation and yielding long time stability to these polymer/polymer nanomixtures. The method is found to work with a wide variety of WSCPs.     

Multi Variant Surface Mounted Metal–Organic Frameworks

Hybrid surface mounted metal–organic frameworks (h‐SURMOFs) of multi variant core‐shell (cs) and core–shell–shell (css) structures (SURMOF A ‐ B and A ‐ B ‐ C , A : [Cu₂(bdc)₂(dabco)]; B : [Cu₂(NH₂‐bdc)₂(dabco)]; C : [Cu₂(ndc)₂(dabco)], bdc = 1,4‐benzenedicarboxylate; NH₂‐bdc = 2‐amino‐1,4‐benzenedicarboxylate; ndc = 1,4‐naphtalenedicarboxylate; dabco = 1,4‐diazabicyclo[2.2.2]octane) with specific crystallographic [001] orientation and incorporated amino groups at a controllable depth within the bulk are deposited via liquid phase epitaxial (LPE) approach on pyridyl‐terminated self‐assembled monolayers (SAM). The location of the (amino) functionality can be precisely controlled through tuning the thickness (number of deposition cycles) of each sub‐multilayer block according to the LPE deposition protocol. The chemo‐selective and location‐specific post deposition (chemical) modification of the amino groups in the cs and css‐type h‐SURMOF samples is achieved. The h‐SURMOFs allow one to probe functional groups at certain location in the volume of hybrid MOF crystallites attached to surfaces as thin film coatings. Multiplex adsorption kinetics of FPI (FPI = 4‐fluorophenyl isothiocyanate) is observed in h‐SURMOFs due to their multi‐variant pore structures in samples of A‐B and A‐B‐C . Conceptually, the stepwise LPE growth method enables fabrication of hybrid SURMOFs and incorporation of multi‐variant functionalities into one homogeneous thin film material, providing precisely tunable pore environment for selective adsorption, separation, etc.     

Metal–Organic Framework Assisted and Tumor Microenvironment Modulated Synergistic Image‐Guided Photo‐Chemo Therapy

The complex tumor microenvironment (TME) and nonspecific drug targeting limit the clinical efficacy of photodynamic therapy in combination with chemotherapy. Herein, a metal–organic framework (MOF) assisted strategy is reported that modulates TME by reducing tumor hypoxia and intracellular glutathione (GSH) and offers targeted delivery and controlled release of the trapped chemodrug. Platinum(IV)‐diazido complex (Pt(IV)) is loaded inside a Cu(II) carboxylate‐based MOF, MOF‐199, and an aggregation‐induced‐emission photosensitizer, TBD, is conjugated to polyethylene glycol for encapsulating Pt(IV)‐loaded MOF‐199. Once the fabricated TBD‐Pt(IV)@MOF‐199 nanoparticles are internalized by cancer cells, MOF‐199 consumes intracellular GSH and decomposes to fragments to release Pt(IV). Upon light irradiation, the released Pt(IV) generates O₂ that relieves hypoxia and produces Pt(II)‐based chemodrug inside cancer cells. Concomitantly, efficient reactive oxygen species generation and bright emission are afforded by TBD, resulting in synergistic image‐guided photo‐chemo therapy with enhanced efficacies and mitigated side effects.     

MOF Nano‐Vesicles and Toroids: Self‐Assembled Porous Soft‐Hybrids for Light Harvesting

Metal‐organic vesicular and toroid nanostructures of Zn(OPE)·2H₂O are achieved by coordination‐directed self‐assembly of oligo‐phenyleneethynylenedicarboxylic acid (OPEA) as a linker with Zn(OAc)₂ by controlling the reaction parameters. Self‐assembled nanostructures are characterized by powder X‐ray diffraction, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and adsorption study. The amphiphilic nature of the coordination‐polymer with long alkyl chains renders different soft vesicular and toroidal nanostructures. The permanent porosity of the framework is established by gas adsorption study. Highly luminescent 3D porous framework is exploited for Froster's resonance energy transfer (FRET) by encapsulation of a suitable cationic dye ( DSMP ) which shows efficient funneling of excitation energy. These results demonstrate the dynamic and soft nature of the MOF, resulting in unprecedented vesicular and toroidal nanostructures with efficient light harvesting applications.     

Low‐Power‐Photon Up‐Conversion in Dual‐Dye‐Loaded Polymer Nanoparticles

Sensitized triplet–triplet annihilation in multicomponent organic systems is already demonstrated to be suitable for obtaining efficient up‐conversion in solution with excitation power densities comparable to solar irradiance, but loses efficiency in the solid state. Here, it is demonstrated that it is possible to reduce this limitation by incorporating a standard bicomponent system in polymer nanoparticles. The confinement of all of the involved photophysical processes in a nanometer‐scale volume makes each nanoparticle a single and isolated high‐efficiency up‐converting unit. As a consequence, these dual‐dye‐loaded nanoparticles can be used to produce drop‐cast films, as well as dopants for polymeric matrices, preserving the performances of the starting moieties in solution.     

Multifunctional Three‐Dimensional T‐Junction Graphene Micro‐Wells: Energy‐Efficient,Plasma‐Enabled Growth and Instant Water‐Based Transfer for Flexible Device Applications

The “third‐generation” 3D graphene structures, T‐junction graphene micro‐wells (T‐GMWs) are produced on cheap polycrystalline Cu foils in a single‐step, low‐temperature (270 °C), energy‐efficient, and environment‐friendly dry plasma‐enabled process. T‐GMWs comprise vertical graphene (VG) petal‐like sheets that seemlessly integrate with each other and the underlying horizontal graphene sheets by forming T‐junctions. The microwells have the pico‐to‐femto‐liter storage capacity and precipitate compartmentalized PBS crystals. The T‐GMW films are transferred from the Cu substrates, without damage to the both, in de‐ionized or tap water, at room temperature, and without commonly used sacrificial materials or hazardous chemicals. The Cu substrates are then re‐used to produce similar‐quality T‐GMWs after a simple plasma conditioning. The isolated T‐GMW films are transferred to diverse substrates and devices and show remarkable recovery of their electrical, optical, and hazardous NO₂ gas sensing properties upon repeated bending (down to 1 mm radius) and release of flexible trasparent display plastic substrates. The plasma‐enabled mechanism of T‐GMW isolation in water is proposed and supported by the Cu plasma surface modification analysis. Our GMWs are suitable for various optoelectronic, sesning, energy, and biomedical applications while the growth approach is potentially scalable for future pilot‐scale industrial production.     

Self‐Directed Localization of ZIF‐8 Thin Film Formation by Conversion of ZnO Nanolayers

Control of localized metal–organic framework (MOF) thin film formation is a challenge. Zeolitic imidazolate frameworks (ZIFs) are an important sub‐class of MOFs based on transition metals and imidazolate linkers. Continuous coatings of intergrown ZIF crystals require high rates of heterogeneous nucleation. In this work, substrates coated with zinc oxide layers are used, obtained by atomic layer deposition (ALD) or by magnetron sputtering, to provide the Zn²⁺ ions required for nucleation and localized growth of ZIF‐8 films ([Zn(mim)₂]; Hmim = 2‐methylimidazolate). The obtained ZIF‐8 films reveal the expected microporosity, as deduced from methanol adsorption studies using an environmentally controlled quartz crystal microbalance (QCM) and comparison with bulk ZIF‐8 reference data. The concept is transferable to other MOFs, and is applied to the formation of [Al(OH)(1,4‐ndc)]_n (ndc = naphtalenedicarboxylate) thin films derived from Al₂O₃ nanolayers.