Unravelling the mechanism of water sensing by the Mg2+ dihydroxy-terephthalate MOF (AEMOF-1 ‘)

In this contribution we build upon our previous work on the MOF [Mg(H(2)dhtp)(H2O)(2)]center dot DMAc (AEMOF-1 center dot DMAc) and its activated dry version AEMOF-1 ‘ which has been shown to exhibit excellent luminescence sensing properties towards water in organic solvents. We demonstrate through combined structural and photophysical studies that the observed changes in the fluorescence properties of AEMOF-1 ‘ upon hydration arise from a structural transformation to the mononuclear complex [Mg(H(2)dhtp)(H2O)(5)]center dot H2O (H(4)dhtp = 2,5-dihydroxyterepthalic acid) (1). In the latter complex, excited state intramolecular proton transfer (ESIPT) is strongly favoured thereby leading to enhanced and red shifted emission in comparison to AEMOF-1 center dot DMAc. Powder X-ray diffraction measurements confirmed that complex 1 is identical to the hydrated form of AEMOF-1 center dot DMAc. As in the case of AEMOF-1 ‘, the dry form of complex 1 (1 ‘) is also an effective sensor for the determination of traces of water in tetrahydrofuran (THF). This work demonstrates that the same chromophore may exhibit very different emission properties when it exists in different chemical environments and that these transformations may be controlled and utilized in water sensing applications

Unravelling the mechanism of water sensing by the Mg 2+ dihydroxy-terephthalate MOF ( AEMOF- 1′)

International audienceThe amorphous compound [Mg(H 2 dhtp)(H 2 O) 2 ] 1′ was shown to be a highly efficient and reusable luminescent sensor for the detection of water in THF, due to its transformation to the strongly emissive complex [Mg(H 2 dhtp)(H 2 O) 5 ]·H 2 O 1

Alkaline Earth Metal Ion/Dihydroxy–Terephthalate MOFs: Structural Diversity and Unusual Luminescent Properties

Alkaline earth (group 2) metal ion organic frameworks (AEMOFs) represent an important subcategory of MOFs with interesting structures and physical properties. Five MOFs, namely, [Mg-2(H(2)dhtp)(2)(mu-H2O)(NMP)(4)] (AEMOF-2), [Mg-2(H(2)dhtp)(1.5)(DMAc)(4)]Cl center dot DMAc (AEMOF-3), [Ca(H(2)dhtp)(DMAc)(2)] (AEMOF-4), [Sr-3(H(2)dhtp)(3)(DMAc)(6)]center dot H2O (AEMOF-5), and [Ba(H2dhtp)(DMAc)] (AEMOF-6) (H4dhtp = 2,5-dihydroxy-terepthalic acid; DMAc = N,Ndimethylacetamide; NMP = N-methylpyrrolidone), are presented herein. The reported MOFs display structural variety with diverse topologies and new structural features. Interestingly, AEMOF-6 is the first example of a Ba2+-H(2)dhtp(2-) MOF, and AEMOF-5 is only the second known Sr2+-H(2)dhtp(2-) MOF. Detailed photoluminescence studies revealed alkaline earth metal ion-dependent fluorescence properties of the materials, with the heavier alkaline earth metal ions exhibiting red-shifted emission with respect to the lighter ions at room temperature. A bathochromic shift of the emission was observed for the MOFs (mostly for AEMOF-3 and AEMOF-4) at 77 K as a result of excited state proton transfer (ESIPT), which involves an intramolecular proton transfer from a hydroxyl to an adjacent carboxylic group of the H(2)dhtp(2-) ligand. Remarkably, AEMOF-6 displays rare yellow fluorescence at room temperature, which is attractive for solid state lighting applications. To probe whether the alkaline earth metal ions are responsible for the unusual luminescence properties of the reported MOFs, the potential energy surfaces (PESs) of the ground, S-0, and lowest energy excited singlet, SD states of model complexes along the intrarnolecular proton transfer coordinate were calculated by DFT and TD-DFT methods

Turn-On Luminescence Sensing and Real-Time Detection of Traces of Water in Organic Solvents by a Flexible Metal-Organic Framework

The development of efficient sensors for the determination of the water content in organic solvents is highly desirable for a number of chemical industries. Presented herein is a Mg2+ metal-organic framework (MOF), which exhibits the remarkable capability to rapidly detect traces of water (0.05-5% v/v) in various organic solvents through an unusual turn-on luminescence sensing mechanism. The extraordinary sensitivity and fast response of this MOF for water, and its reusability make it one of the most powerful water sensors known

A microporous Mg2+ MOF with cation exchange properties in a single-crystal-to-single-crystal fashion

We report herein a new alkaline earth metal ion organic framework [Mg-2(NH2BDC)(2)(HNO3)]center dot 9H(2)O (AEMOF-7), which shows a 3-D microporous structure with several unusual features, such as the rare trigonal prismatic coordination geometry of one of the crystallographically unique Mg-2(+) centers and the existence of a bridging HNO3 ligand. The H+ ions of the HNO3 ligand are dissociable as demonstrated via proton conductivity measurements. AEMOF-7 displays relatively high selectivity for CO2 vs. CH4 and negligible N-2 uptake. Interestingly, this compound was found to be capable of single-crystal-to-single-crystal (SCSC) exchange of Mg2+ by Cu2+ ions, which was observed for the first time in a MOF material. AEMOF-7 is also luminescent and its photophysical properties were investigated via solid state UV-Vis, steady-state and time-resolved luminescence studies

Alkaline Earth Metal Ion/Dihydroxy–Terephthalate MOFs: Structural Diversity and Unusual Luminescent Properties

Alkaline earth (group 2) metal ion organic frameworks (<b>AEMOFs</b>) represent an important subcategory of MOFs with interesting structures and physical properties. Five MOFs, namely, [Mg₂(H₂dhtp)₂(μ-H₂O)­(NMP)₄] (<b>AEMOF-2</b>), [Mg₂(H₂dhtp)_1.5(DMAc)₄]­Cl·DMAc (<b>AEMOF-3</b>), [Ca­(H₂dhtp)­(DMAc)₂] (<b>AEMOF-4</b>), [Sr₃(H₂dhtp)₃(DMAc)₆]·H₂O (<b>AEMOF-5</b>), and [Ba­(H₂dhtp)­(DMAc)] (<b>AEMOF-6</b>) (H₄dhtp = 2,5-dihydroxy-terepthalic acid; DMAc = <i>N,N</i>-dimethylacetamide; NMP = <i>N</i>-methylpyrrolidone), are presented herein. The reported MOFs display structural variety with diverse topologies and new structural features. Interestingly, <b>AEMOF-6</b> is the first example of a Ba²⁺–H₂dhtp^2– MOF, and <b>AEMOF-5</b> is only the second known Sr²⁺–H₂dhtp^2– MOF. Detailed photoluminescence studies revealed alkaline earth metal ion-dependent fluorescence properties of the materials, with the heavier alkaline earth metal ions exhibiting red-shifted emission with respect to the lighter ions at room temperature. A bathochromic shift of the emission was observed for the MOFs (mostly for <b>AEMOF-3</b> and <b>AEMOF-4</b>) at 77 K as a result of excited state proton transfer (ESIPT), which involves an intramolecular proton transfer from a hydroxyl to an adjacent carboxylic group of the H₂dhtp^2– ligand. Remarkably, <b>AEMOF-6</b> displays rare yellow fluorescence at room temperature, which is attractive for solid state lighting applications. To probe whether the alkaline earth metal ions are responsible for the unusual luminescence properties of the reported MOFs, the potential energy surfaces (PESs) of the ground, S₀, and lowest energy excited singlet, S₁, states of model complexes along the intramolecular proton transfer coordinate were calculated by DFT and TD-DFT methods