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.

The development of active, acid-stable and low-cost electrocatalysts for oxygen evolution reaction is urgent and challenging. Herein we report an Iridium-free and low ruthenium-content oxide material (Cr0.6Ru0.4O2) derived from metal-organic framework with remarkable oxygen evolution reaction performance in acidic condition. It shows a record low overpotential of 178 mV at 10 mA cm−2 and maintains the excellent performance throughout the 10 h chronopotentiometry test at a constant current of 10 mA cm−2 in 0.5 M H2SO4 solution. Density functional theory calculations further revealed the intrinsic mechanism for the exceptional oxygen evolution reaction performance, highlighting the influence of chromium promoter on the enhancement in both activity and stability.

An important aspect in the research and development of white light-emitting diodes (WLEDs) is the discovery of highly efficient phosphors free of rare-earth (RE) elements. Herein we report the design and synthesis of a new type of RE-free, blue-excitable yellow phosphor, obtained by combining a strongly emissive molecular fluorophore with a bandgap modulating co-ligand, in a three-dimensional metal organic framework. [Zn6(btc)4(tppe)2(DMA)2] (btc = benzene-1,3,5-tricarboxylate, tppe = 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)ethene, DMA = dimethylacetamide) crystallizes in a new structure type and emits bright yellow light when excited by a blue light source. It possesses the highest internal quantum yield among all RE-free, blue-excitable yellow phosphors reported to date, with a value as high as 90.7% (λex = 400 nm). In addition to its high internal quantum yield, the new yellow phosphor also demonstrates high external quantum yield, luminescent and moisture stability, solution processability, and color tunability, making it a promising material for use in phosphor conversion WLEDs.

Surface-directed corner-sharing MnO 6 octahedra within numerous manganese oxide compounds containing Mn 3+ or Mn 4+ oxidation states show strikingly different catalytic activities for water oxidation, paradoxically poorest for Mn 4+ oxides, regardless of oxidation assay (photochemical and electrochemical). This is demonstrated herein by comparing crystalline oxides consisting of Mn 3+ (manganite, γ-MnOOH; bixbyite, Mn 2 O 3 ), Mn 4+ (pyrolusite, β-MnO 2 ) and multiple monophasic mixed-valence manganese oxides. Like all Mn 4+ oxides, pure β-MnO 2 has no detectable catalytic activity, while γ-MnOOH (tetragonally distorted Mn 3+ O 6 , D 4h symmetry) is significantly more active and Mn 2 O 3 (trigonal antiprismatic Mn 3+ O 6 , D 3d symmetry) is the most active. γ-MnOOH deactivates during catalytic turnover simultaneous with the disappearance of crystallographically defined corner-sharing Mn 3+ O 6 and the appearance of Mn 4+ . In a comparison of 2D-layered crystalline birnessites (δ-MnO 2 ), the monovalent Mn 4+ form is catalytically inert, while the hexagonal polymorph, containing few out-of-layer corner-sharing Mn 3+ O 6 , has ∼10-fold higher catalytic activity than the triclinic polymorph, containing in-plane edge-sharing Mn 3+ O 6 . These electronic and structural correlations point toward the more flexible (corner-shared) Mn 3+ O 6 sites, over more rigid (edge-shared) sites as substantially more active catalytic centers. Electrochemical measurements show and ligand field theory predicts that, among corner-shared Mn 3+ O 6 sites, those possessing D 3d ligand field symmetry have stronger covalent Mn−O bonding to the six equivalent oxygen ligands, which we ascribe as responsible for more efficient and faster electrolytic water oxidation. In contrast, D 4h Mn 3+ O 6 sites have weaker Mn−O bonding to the two axial oxygen ligands, have separated electrochemical oxidation waves for Mn and O, and are catalytically less efficient and exhibit slower catalytic turnover. By controlling the ligand field geometry and strength to oxygen ligands, we have identified the key variables for tuning water oxidation activity by manganese oxides. We apply these findings to propose a mechanism for water oxidation by the CaMn 4 O 5 catalytic site of natural photosynthesis.

Effective capture of radioactive organic iodides from nuclear waste remains a significant challenge due to the drawbacks of current adsorbents such as low uptake capacity, high cost, and non-recyclability. We report here a general approach to overcome this challenge by creating radioactive organic iodide molecular traps through functionalization of metal-organic framework materials with tertiary amine-binding sites. The molecular trap exhibits a high CH3I saturation uptake capacity of 71 wt% at 150 °C, which is more than 340% higher than the industrial adsorbent Ag0@MOR under identical conditions. These functionalized metal-organic frameworks also serve as good adsorbents at low temperatures. Furthermore, the resulting adsorbent can be recycled multiple times without loss of capacity, making recyclability a reality. In combination with its chemical and thermal stability, high capture efficiency and low cost, the adsorbent demonstrates promise for industrial radioactive organic iodides capture from nuclear waste. The capture mechanism was investigated by experimental and theoretical methods.

A water stable zirconium-porphyrin MOF (PCN-222) was synthesized according to the reported method and found to produce a distinct reversible colorimetric and fluorescent "turn-off-turn-on" pH response. The colorimetric response is achieved under acidic conditions starting at pH ~3 and persists under concentrated acidic conditions. To the best of our knowledge, this is the first report of a colorimetric MOF pH sensor.

Catalytically active MnOx species have been reported to form in situ from various Mn-complexes during electrocatalytic and solution-based water oxidation when employing cerium(IV) ammonium ammonium nitrate (CAN) oxidant as a sacrificial reagent. The full structural characterization of these oxides may be complicated by the presence of support material and lack of a pure bulk phase. For the first time, we show that highly active MnOx catalysts form without supports in situ under photocatalytic conditions. Our most active (4)MnOx catalyst (∼0.84 mmol O2  mol Mn(-1) s(-1)) forms from a Mn4O4 bearing a metal-organic framework. (4)MnOx is characterized by pair distribution function analysis (PDF), Raman spectroscopy, and HR-TEM as a disordered, layered Mn-oxide with high surface area (216 m(2) g(-1)) and small regions of crystallinity and layer flexibility. In contrast, the (S)MnOx formed from Mn(2+) salt gives an amorphous species of lower surface area (80 m(2) g(-1)) and lower activity (∼0.15 mmol O2  mol Mn(-1) s(-1)). We compare these catalysts to crystalline hexagonal birnessite, which activates under the same conditions. Full deconvolution of the XPS Mn2p3/2 core levels detects enriched Mn(3+) and Mn(2+) content on the surfaces, which indicates possible disproportionation/comproportionation surface equilibria.

We report the synthesis, structure, and photoluminescence properties of a new bismuth based luminescent metal−organic framework (LMOF). The framework is comprised of a 9-coordinated Bi 3+ building unit and 4′, 4‴, 4⁗′, 4⁗‴-(ethene-1,1,2,2-tetrayl)tetrakis([1,1′-biphenyl]-4carboxylic acid) (H 4 tcbpe) organic linker, which has strong yellow aggregation induced emission (AIE). The structure can be viewed as two interpenetrated 4,4-anionic nets that are stabilized by K + ions forming one-dimensional helical inorganic chains by connecting bismuth nodes through shared oxygen bonds. The as-made LMOF has a bluish emission centered at 459 nm with an internal quantum yield of 57% when excited at 360 nm. The emission properties of the LMOF were found to be highly solvochromic with respect to DMF. Upon partial solvent removal, the framework undergoes significant red-shifting to a greenish emission centered at 500 nm. Complete removal of DMF results in additional red-shifting fluorescence coupled with structural changes. The resulting material has strong blue-excitable (455 nm) yellow emission centered at 553 nm, with a quantum yield of 74%, which is maintained after heating in air for 5 days at 90 °C. This is the second highest quantum yield value for blue-excited yellow emission among all reported LMOFs.