Metal–organic frameworks (MOFs) are a unique class of crystalline solids comprised of metal cations (or metal clusters) and organic ligands that have shown promise for a wide variety of applications Over the past 15 years, research and development of these materials have become one of the most intensely and extensively pursued areas A very interesting and well-investigated topic is their optical emission properties and related applications Several reviews have provided a comprehensive overview covering many aspects of the subject up to 2011 This review intends to provide an update of work published since then and focuses on the photoluminescence (PL) properties of MOFs and their possible utility in chemical and biological sensing and detection The spectrum of this review includes the origin of luminescence in MOFs, the advantages of luminescent MOF (LMOF) based sensors, general strategies in designing sensory materials, and examples of various applications in sensing and detection

Luminescent metal–organic frameworks for chemical sensing and explosive detection

Metal–organic frameworks (MOFs) or porous coordination polymers (PCPs) are open, crystalline supramolecular coordination architectures with porous facets. These chemically tailorable framework materials are the subject of intense and expansive research, and are particularly relevant in the fields of sensory materials and device engineering. As the subfield of MOF-based sensing has developed, many diverse chemical functionalities have been carefully and rationally implanted into the coordination nanospace of MOF materials. MOFs with widely varied fluorometric sensing properties have been developed using the design principles of crystal engineering and structure–property correlations, resulting in a large and rapidly growing body of literature. This work has led to advancements in a number of crucial sensing domains, including biomolecules, environmental toxins, explosives, ionic species, and many others. Furthermore, new classes of MOF sensory materials utilizing advanced signal transduction by devices based on MOF photonic crystals and thin films have been developed. This comprehensive review summarizes the topical developments in the field of luminescent MOF and MOF-based photonic crystals/thin film sensory materials.

Metal-organic frameworks: functional luminescent and photonic materials for sensing applications.

Among the large family of metal–organic frameworks (MOFs), Zr-based MOFs, which exhibit rich structure types, outstanding stability, intriguing properties and functions, are foreseen as one of the most promising MOF materials for practical applications. Although this specific type of MOF is still in its early stage of development, significant progress has been made in recent years. Herein, advances in Zr-MOFs since 2008 are summarized and reviewed from three aspects: design and synthesis, structure, and applications. Four synthesis strategies implemented in building and/or modifying Zr-MOFs as well as their scale-up preparation under green and industrially feasible conditions are illustrated first. Zr-MOFs with various structural types are then classified and discussed in terms of different Zr-based secondary building units and organic ligands. Finally, applications of Zr-MOFs in catalysis, molecule adsorption and separation, drug delivery, and fluorescence sensing, and as porous carriers are highlighted. Such a review based on a specific type of MOF is expected to provide guidance for the in-depth investigation of MOFs towards practical applications.

Zr-based metal-organic frameworks: design, synthesis, structure, and applications.

: The unpolarized absorption and circular dichroism spectra of the fundamental vibrational transitions of the chiral molecule, 4-methyl-2-oxetanone, are calculated ab initio. Harmonic force fields are obtained using Density Functional Theory (DFT), MP2, and SCF methodologies and a 5S4P2D/3S2P (TZ2P) basis set. DFT calculations use the Local Spin Density Approximation (LSDA), BLYP, and Becke3LYP (B3LYP) density functionals. Mid-IR spectra predicted using LSDA, BLYP, and B3LYP force fields are of significantly different quality, the B3LYP force field yielding spectra in clearly superior, and overall excellent, agreement with experiment. The MP2 force field yields spectra in slightly worse agreement with experiment than the B3LYP force field. The SCF force field yields spectra in poor agreement with experiment.The basis set dependence of B3LYP force fields is also explored: the 6-31G* and TZ2P basis sets give very similar results while the 3-21G basis set yields spectra in substantially worse agreements with experiment. jg

Ab initio calculation of vibrational absorption and circular dichroism spectra using density functional force fields

Recent Developments in the Preparation and Chemistry of Metallacycles and Metallacages via Coordination

Two new lanthanide metal–organic frameworks Ln(FBPT)(H2O)(DMF) (FBPT = 2′-fluoro-biphenyl-3,4′,5-tricarboxylate, Ln = Eu and Tb) were prepared under solvothermal conditions. Single crystal X-ray diffraction analyses reveal that the two compounds are isostructurally related with the same one-dimensional channel structure on the basis of FBPT as an organic linker. Herein, the Eu(FBPT)(H2O)(DMF) (EuL) is selected as a representative sample for luminescent measurements. Study of the photoluminescence properties reveals that the EuL exhibits red emission, corresponding to the 5D0 → 7FJ (J = 1–4) transitions of the Eu3+ ion under UV light excitation. Most interestingly, when this compound was immersed in the different organic solvents and metal ion DMF solutions, it shows highly selective and sensitive sensing for small organic molecules and Cu2+ ions. In connection to this, a probable sensing mechanism was also discussed in this paper.

One-dimensional channel-structured Eu-MOF for sensing small organic molecules and Cu2+ ion

MOF-76: from a luminescent probe to highly efficient U(VI) sorption material.

Fe3O4@ZIF-8: a magnetic nanocomposite for highly efficient UO22+ adsorption and selective UO22+/Ln3+ separation.

Nanoscale Tb-active coordination polymers Tb(BTC)(H2O)6 were facilely, rapidly and environmentally-friendly fabricated at room temperature. The structures of the samples were confirmed by powder X-ray diffraction and elemental analyses, and the morphologies were characterized by SEM. The studies of the photoluminescence properties reveal that these nanostructured coordination polymers exhibit green emission, corresponding to the 5D4 → 7FJ transitions of the Tb3+ ions under UV light excitation, which represents highly selective and sensitive sensing for metal ions and acetone molecules in aqueous solution, and the probable sensing mechanisms were discussed.

Facile and rapid fabrication of nanostructured lanthanide coordination polymers as selective luminescent probes in aqueous solution

Solvothermal reaction of Cd2+ ions and a hexavalent carboxylic acid (H6666666L) afforded a Cd(II) metal organic framework (Cd-MOF), namely {[Cd3(L)(H2O)2(DMF)2]·5DMF}n (1) Its structure consists of trinuclear CdII building units, which are further bridged by the carboxylic ligand, resulting in a 4,4-connected topological net (sra) By introducing a rigid N-donor ligand 1,4-bis(1-imidazolyl)benzene (dib), a new Cd-MOF (2) {[Cd3(L)(dib)]·3H2O·5DMA}n was isolated, in which the coordinated sites of solvent molecules in 1 were completely replaced by dib The resulting trinuclear Cd3 subunits are further bridged into a two-fold interpenetrating network with DMA and water molecules located in the void space The luminescent properties of the two microporous Cd-MOFs dispersed in different solvents have been investigated systematically, demonstrating unique selectivity for the detection of acetone via a fluorescence quenching mechanism Their luminescence intensities decreased to 50% at an acetone content of 03 vol% and were almost completely quenched at a concentration of 10 vol%, thus, they can be considered as excellent potential luminescent probes for the detection of acetone

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Weiting Yang

Papers

One-dimensional channel-structured Eu-MOF for sensing small organic molecules and Cu2+ ion

MOF-76: from a luminescent probe to highly efficient U(VI) sorption material.

Fe3O4@ZIF-8: a magnetic nanocomposite for highly efficient UO22+ adsorption and selective UO22+/Ln3+ separation.

Facile and rapid fabrication of nanostructured lanthanide coordination polymers as selective luminescent probes in aqueous solution

Highly selective acetone fluorescent sensors based on microporous Cd(II) metal–organic frameworks