pH modulated luminescent switching and discriminative detection of amino acid based on metal-organic framework.

The detection of glutamic (Glu) or aspartic (Asp) acids is vital for human nutrition and diagnosis of disease. Herein, the dht ligand containing hydroxy group (-OH) is used to design and synthesize a 2D luminescent [Cd2(idc)(dht)(H2O)4] (1); H2idc = 4,5-imidazoledicarboxylic acid and H2dht = 2,5-dihydroxyterephthalic acid for sensing amino acids. The compound 1 can discriminatively detect Asp and Glu among other amino acids through blue-shifted emission (yellow → green). The dual sensing mechanism may be attributed to the intermolecular excited-state proton transfer between MOF and water to produce keto form along with the subsequent switching of keto form to enol form by protonation causing the increased band gap energy. This material can serve several benefits in terms of high selectivity, fast response (30s), good reproducibility and low LOD value of 11.34 µM which is less than the harmful concentration of Glu for human health (>400 µM). In addition, 1 shows the broad range detection of Glu covering in safe and unsafe levels. For on-site detection of Glu, MOF-based paper is devised and can be applied through color-scanning application in smartphone. Besides, this sensor can serve to detect Glu in real samples with good recovery.

Dual Function Based on Switchable Colorimetric Luminescence for Water and Temperature Sensing in Two-Dimensional Metal-Organic Framework Nanosheets.

A simple, rapid, highly selective, and real-time determination of water is urgently required for preventing danger from water contamination in materials. Herein, the excited-state proton transfer (ESPT) concept-based luminescent sensor [Cd2(2,5-tpt)(4,5-idc)(H2O)4] (1) (2,5-tpt = 2,5-dihydroxyterephthalic acid and 4,5-idc = 4,5-imidazoledicarboxylic acid) has been designed for discriminative detection via enol-keto tautomerism. To improve the sensitivity, two-dimensional (2D) nanosheets of 1 have been synthesized by top-down liquid ultrasonic exfoliation technology for sensing water in dimethylformamide, which lead to fast detection (<30 s), high selectivity, broad-range detection (0-50% v/v), and a low detection limit value (0.25% v/v). This sensor can serve dual sensing mechanisms along with a luminescent color change via shifted emission (green→yellow) in low water content and a turn-off method in high water content. For ease of use, the test-strip paper-based 2D nanosheets of 1 have been prepared and applied for water detection with long-term stability, pH stability, and good reusability. On-site water detection in real time can be evaluated using a smartphone color-scanning application for quantitative scanometric assays coupled with test-strip paper-based 2D nanosheets of 1. Also, 1 can be utilized for a colorimetric luminescent thermometer in the ranges of physiological and high temperature with good linearity and recyclability.

Sonochemical synthesis of microscale Zn(ii)-MOF with dual Lewis basic sites for fluorescent turn-on detection of Al3+ and methanol with low detection limits.

The effects of synthetic methods, modulator types, the content of the modulator, and reaction time on the size and morphology of a microscale Zn-MOF containing dual Lewis basic amino and carbonyl groups, namely [Zn(NH2-bdc)(4,4'-bpy)] {NH2-H2bdc = 2-amino-1,4-benzenedicarboxylic acid and 4,4'-bpy = 4,4'-bipyridine}, were systemically investigated. Uniform octahedral microparticles of Zn-MOF with an average size of 1.7 µm were obtained within an hour at ambient temperature under ultrasound irradiation using sodium acetate as a modulating agent. Interestingly, Zn-MOF has been demonstrated for the dual-functional fluorescent detection of Al3+ and methanol based on a fluorescent turn-on strategy. Very low detection limits (LODs) for Al3+ and methanol were achieved using microcrystalline Zn-MOF and reached 30 nM and 0.7% (v/v), respectively. In comparison to the larger size of the polycrystalline Zn-MOF, the microparticles obtained from the ultrasonic route exhibited an improvement in the detection sensitivity. The dual uncoordinated Lewis basic sites play an important role in the sensitivity and selectivity of the detection. Additionally, the fluorogenic change in the sensing process can be observed by the naked eye under UV-light, allowing preliminary on-field screening.

Sonochemical Synthesis of Carbon Dots/Lanthanoid MOFs Hybrids for White Light-Emitting Diodes with High Color Rendering.

Although lanthanoid metal-organic frameworks (Ln-MOFs) have been widely developed for white light-emitting diodes (WLEDs), the color rendering index (CRI) values are still lower than 80. To overcome this limitation, a series of CDs/Ln-MOFs hybrids, namely, CDs-2@Ln-MOF, CDs-3@Ln-MOF, and CDs-4@Ln-MOF containing blue-emitting CDs and yellow-emitting bimetallic [(Eu1.22Tb0.78(1,4-phda)3(H2O)](H2O)2 were prepared via sonication at room temperature to restrict the self-quenching of CDs in composite materials. The as-synthesized composite materials were investigated by Fourier transform infrared, powder X-ray diffraction, transmission electron microscopy, scanning electron microscopy, and photoluminescence. The luminescent color of the materials can be adjusted by varying the amount of CDs and excitation wavelengths. The resulting CDs-3@Ln-MOF achieved excellent CRI up to 93 with the ideal Commission International ed'Eclairage coordinate (0.334, 0.334) and appropriate correlated color temperature (CCT) (5443 K). In addition, the tunable multicolored luminescence based on single and bimetallic EuxTb2-x(1,4-phda)3(H2O)](H2O)2, x = 0, 0.73, 1.22, 1.57, 1.94, and 2, were applied as the luminescent security inks for anti-counterfeiting application through encoding/decoding and rewritable data.

A novel one-dimensional metal-organic framework with a µ-cyanido-argentate group: catena-poly[[(5,5'-dimethyl-2,2'-bipyridyl-κ(2)N,N')silver(I)]-µ-cyanido-κ(2)N:C].

The design and synthesis of metal coordination and supramolecular frameworks containing N-donor ligands and dicyanidoargentate units is of interest due to their potential applications in the fields of molecular magnetism, catalysis, nonlinear optics and luminescence. In the design and synthesis of extended frameworks, supramolecular interactions, such as hydrogen bonding, π-π stacking and van der Waals interactions, have been exploited for molecular recognition associated with biological activity and for the engineering of molecular solids.The title compound, [Ag(CN)(C12H12N2)]n, crystallizes with the Ag(I) cation on a twofold axis, half a cyanide ligand disordered about a centre of inversion and half a twofold-symmetric 5,5'-dimethyl-2,2'-bipyridine (5,5'-dmbpy) ligand in the asymmetric unit. Each Ag(I) cation exhibits a distorted tetrahedral geometry; the coordination environment comprises one C(N) atom and one N(C) atom from substitutionally disordered cyanide bridging ligands, and two N atoms from a bidentate chelating 5,5'-dmbpy ligand. The cyanide ligand links adjacent Ag(I) cations to generate a one-dimensional zigzag chain. These chains are linked together via weak nonclassical intermolecular interactions, generating a two-dimensional supramolecular network.

Crystal structure of a two-dimensional grid-type iron(II) coordination polymer: poly[[di-aqua-tetra-µ-cyanido-diargentate(I)iron(II)] trans-1,2-bis(pyridin-2-yl)ethyl-ene disolvate].

In the title compound, {[Ag2Fe(CN)4(H2O)2]·2C12H10N2} n , the asymmetric unit contains one Fe(II) cation, two water mol-ecules, two di-cyanido-argentate(I) anions and two uncoordinating 1,2-bis-(pyridin-2-yl)ethyl-ene (2,2'-bpe) mol-ecules. Each Fe(II) atom is six-coordinated in a nearly regular octa-hedral geometry by four N atoms from di-cyanido-argentate(I) bridges and two coordinating water mol-ecules. The Fe(II) atoms are bridged by di-cyanido-argentate(I) units to give a two-dimensional layer with square-grid spaces. The inter-grid spaces with inter-layer distance of 6.550 (2) Šare occupied by 2,2'-bpe guest mol-ecules which form O-H⋯N hydrogen bonds to the host layers. This leads to an extended three-dimensional supra-molecular architecture. The structure of the title compound is compared with some related compounds containing di-cyanido-argentate(I) ligands and N-donor organic co-ligands.