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The fabrication of oriented, crystalline films of metal-organic frameworks (MOFs) is a critical step toward their application to advanced technologies such as optics, microelectronics, microfluidics and sensing. However, the direct synthesis of MOF films with controlled crystalline orientation remains a significant challenge. Here we report a one-step approach, carried out under mild conditions, that exploits heteroepitaxial growth for the rapid fabrication of oriented polycrystalline MOF films on the centimetre scale. Our methodology employs crystalline copper hydroxide as a substrate and yields MOF films with oriented pore channels on scales that primarily depend on the dimensions of the substrate. To demonstrate that an anisotropic crystalline morphology can translate to a functional property, we assembled a centimetre-scale MOF film in the presence of a dye and showed that the optical response could be switched 'ON' or 'OFF' by simply rotating the film.

The degree of pore filling is an important parameter for defining guest@MOF properties in applications including electronics, optics, and gas separation. However, the interplay of key aspects of host–guest interactions, such as a quantitative description of the guest alignment or the structural integrity of the host as function of pore filling are yet to be determined. Polarisation‐dependent infrared spectroscopy in attenuated total reflection configuration combined with gas sorption allowed to simultaneously study the orientation of the guest molecule and structural changes of the MOF framework during the pore filling process. Thereby we found, that initially randomly oriented guest molecules align with increasing pore filling during adsorption from the gas phase. At the same time, the framework itself undergoes a reversible, guest molecule‐dependent rotation of the aromatic linker and a linker detachment process, which induce defects. [ABSTRACT FROM AUTHOR]

Processing oriented metal–organic frameworks (MOFs) as thin films is a key challenge for their application to device fabrication. However, typical fabrication methods cannot generate precisely oriented crystals on commercially relevant scales (i.e., cm2). This limits access to applications that require anisotropic functional properties (e.g., separation, optics, and electronics). Currently, highly oriented copper‐based MOFs are synthesized via the addition of the organic MOF component to an ethanolic solution of manually aligned Cu(OH)2 nanobelt films. In this work, the optimization of a semi‐automatic method for the fabrication of precisely oriented MOF films that affords a 100% yield of high quality ceramic films at the centimeter scale is reported. This improved fabrication protocol will facilitate the progress of heteroepitaxially grown MOFs for molecular separators and micro‐opto‐electronic devices. [ABSTRACT FROM AUTHOR]

The precise alignment of multiple layers of metal–organic framework (MOF) thin films, or MOF‐on‐MOF films, over macroscopic length scales is presented. The MOF‐on‐MOF films are fabricated by epitaxially matching the interface. The first MOF layer (Cu2(BPDC)2, BPDC=biphenyl‐4,4′‐dicarboxylate) is grown on an oriented Cu(OH)2 film by a "one‐pot" approach. Aligned second (Cu2(BDC)2, BDC=benzene 1,4‐dicarboxylate, or Cu2(BPYDC)2, BPYDC=2,2′‐bipyridine‐5,5′‐dicarboxylate) MOF layers can be deposited using liquid‐phase epitaxy. The co‐orientation of the MOF films is confirmed by X‐ray diffraction. Importantly, our strategy allows for the synthesis of aligned MOF films, for example, Cu2(BPYDC)2, that cannot be grown on a Cu(OH)2 surface. We show that aligned MOF films furnished with Ag nanoparticles show a unique anisotropic plasmon resonance. Our MOF‐on‐MOF approach expands the chemistry of heteroepitaxially oriented MOF films and provides a new toolbox for multifunctional porous coatings. [ABSTRACT FROM AUTHOR]

Metal–organic framework (MOF) coatings were prepared on gold electrodes through the conversion from Cu(OH)2 nanobelts to Cu3(BTC)2 MOFs (BTC = 1,3,5-benzenetricarboxylic acid). In the conversion from Cu(OH)2 to Cu3(BTC)2, the porosity and homogeneity of the coatings are tunable by controlling the EtOH : H2O volume ratio of the MOF precursor solution. The kinetics and mechanism of the conversion from metal hydroxide nanobelts to MOFs were investigated by using the quartz crystal microbalance (QCM) technique. The Cu3(BTC)2 coatings were finally tested for the size-selective electrochemical sensing and non-enzymatic electrocatalysis of glucose. [ABSTRACT FROM AUTHOR]

A new approach for the fabrication of homogeneous HKUST-1 [Cu3(BTC)2] coatings on copper metal plates, 3D objects, and as patterns, is here proposed. The conversion can be performed at room temperature in approximately 30 minutes using an aqueous ethanolic mixture. The two step conversion mechanism occurs via the formation of Cu(OH)2 nanotubes. Microscopic time-course monitoring reveals the conversion steps. The adhesion of the metal organic-framework (MOF) crystals, as well as the functional properties of the resulting supported catalyst, are successfully tested. The versatility of the conversion mechanism on different metal copper substrates is investigated as well; in particular, a photolithography protocol is proposed for the preparation of MOF patterns. This protocol offers several features (short processing time, applicability to any copper metal object, low cost of the equipment, room temperature conditions) that would make it favorable for basic research and industrial exploitation of MOF capabilities. [ABSTRACT FROM AUTHOR]