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To study the photophysics and understand the mechanism of metal ion sensing, a luminescent cobalt-based metal–organic compound, [Co(bpds)(bdc)(H2O)2]·bpds (1), was synthesized at room temperature from 4,4′-bipyridyl disulphide (bpds) and 1,4-benzene dicarboxylic acid (bdc) by layer diffusion. Structure determination based on single-crystal X-ray analysis revealed a parallel interpenetrated structure of two-dimensional layers along with a layer of uncoordinated bpds ligand. An aqueous suspension of 1 showed intense blue emission at 421 nm. In the presence of few micromolar of Al3+ ions, a dramatic change in the luminescence spectrum around an isoemissive point was observed with the appearance of a new peak at 380 nm. A similar phenomenon was observed in the presence of Fe3+ ions. For other metal ions, no significant changes in the luminescence spectrum of 1 were observed. Detailed lifetime decay analysis and Fourier-transform infrared spectroscopy revealed that Al3+ ions form charge-transfer complexes (or adducts) with uncoordinated bpds ligands through pyridine nitrogen atoms, resulting in a new emission peak at 380 nm. Time-resolved study revealed that the quenching of luminescence was dynamic in nature and associated with an increase in the non-radiative rate constant. Moreover, the luminescence property of 1 was ultrasensitive to the presence of Al3+ and Fe3+ ions in water, even in a mixture of many other ions, with detection limits of 0.35 and 0.25 μM, respectively. [ABSTRACT FROM AUTHOR]

We have thoroughly studied the luminescence behaviour of a cadmium based MOF, [Cd(C12N2H8)(C7N1O4H3)] {C12N2H8 = 1,10-phenanthroline, C7N1O4H3 = 2,5-pyridine dicarboxylate}, 1. Both steady-state and time-resolved luminescence spectroscopic experiments were performed to understand the dissimilar responses of compound 1 towards different metal ions in aqueous medium. Upon excitation at 280 nm, compound 1 showed a luminescence spectrum centered at 365 nm, which exhibited a three-fold turn-on in the presence of a trace amount of Zn2+ in aqueous solution, whereas in the presence of Co2+, Hg2+, Ni2+, Fe2+ and Cu2+ the luminescence of compound 1 got largely quenched. Compound 1 did not show any response in the presence of other common metal ions such as K+, Mg2+, Na+, Mn2+, and Cr3+. By analysing all the experimental results, we successfully explained the versatile luminescence behaviour of compound 1. The turn-on of luminescence in the presence of Zn2+ ions was due to coordination bond formation and enhancement of the rigidity of compound 1 which resulted in the reduction of non-radiative decay processes to a large extent. The quenching of luminescence in the presence of transition metal ions was found to be static in nature, and was due to the possibility of ligand to metal charge transfer using the vacant d-orbital of the metal ions. In the case of Hg2+ which is a closed cell heavy metal ion, the quenching of luminescence was also static in nature and was due to a two-way charge transfer mechanism. We have also performed density functional theory calculations and obtained supportive results for the proposed mechanisms of luminescence turn-on and quenching. Moreover, compound 1 could be established as a selective and efficient sensor of Zn2+ in aqueous solution even in the presence of Cd2+ and other metal ions. [ABSTRACT FROM AUTHOR]

Rare-earth-based metal–organic frameworks (ReMOFs) have emerged as an interesting family of compounds, for which new properties are increasingly being found. Based on the potential of ReMOFs, resulting from their optical properties, large numbers of investigations have been carried out during the last decade. Among these investigations, ReMOFs as optical sensors, using their luminescence properties, are increasingly becoming an attractive and useful topic of research. In this study, we have provided the basics of the luminescence behaviour of ReMOFs, various possible sensing mechanisms, and a summary of the uses of ReMOFs for the sensing of nitro explosives, cations, anions, small molecules, pH, and temperature. [ABSTRACT FROM AUTHOR]

We have successfully synthesized a new europium metal-organic complex (MOC) [Eu2(pydcH)6] ·3H2O ( 1, H2pydc = 2,6-pyridinedicarboxylic acid) by the hydrothermal technique as well as simple solvent evaporation in water. Single-crystal X-ray crystallographic data of 1 confirms a molecular complex of tricapped trigonal prismatic Eu3+ ions with a free carboxylic acid site of each 2,6-pyridinedicarboxylic acid ligand. Complex 1 is water-soluble and remains stable in a broad pH range of 2-11. Upon excitation at 280 nm 1 shows a characteristic ligand-sensitized metal-centred visible red luminescence. The luminescence of complex 1 can be further enhanced by changing the pH of the solution in the range of 2-6. Besides, the luminescence response is completely reversible in the range of pH 2-6. The mechanism of the pH-dependent luminescence behaviour is successfully explained and supported by UV/Vis absorption and IR spectroscopic experiments. [ABSTRACT FROM AUTHOR]

Graphical abstract A lanthanide co-doped (Eu3+ and Tb3+) yttrium based metal–organic framework has been synthesized through isomorphous substitution strategy in a three-dimensional MOF using solvothermal procedure. This MOF shows luminescence based sensitive and selective detection of azinphos-methyl pesticide over the other analytes in aqueous medium with detection limit of 212 ppb. Abstract For the utilization of large stokes shift and low self quenching of luminescence, we have successfully constructed a luminescent europium and terbium co-doped yttrium based metal–organic framework [Y 1.8 Eu 0.1 Tb 0.1 (PDA) 3 (H 2 O) 1 ]·2H 2 O (where PDA = 1,4-phenylenediacetate), 1 , through isomorphous substitution strategy in a three-dimensional yttrium based MOF using solvothermal method. The structure and size of 1 was systematically characterized by PXRD, TGA, SEM and EDX analysis. On the exposure to UV light, the aqueous dispersion of 1 exhibits light green emission in the visible region. This emissive property was employed for the highly sensitive and selective detection of azinphos-methyl pesticide in aqueous medium through luminescence quenching for the first time. Using this compound ppb level detection of azinphos-methyl has been achieved. [ABSTRACT FROM AUTHOR]

A highly luminescent three–dimensional cadmium based metal–organic framework (Cd-MOF), 1 , has been employed for the luminescence-based aqueous phase detection of iodide ion. Emission at 290 nm upon excitation at 226 nm was used for the sensing of iodide ions in aqueous medium through very high luminescence quenching. It was also observed that in presence of other common anions such as NO 3 − , H 2 PO 4 − , CH 3 COO − , Br − , SO 4 2− , B 4 O 7 2− , Cl − , CO 3 2− , HPO 4 2− and F − in aqueous medium it shows negligible luminescence quenching. The selectivity of iodide sensing has also been performed in the presence of other halide ions (F − , Cl − and Br − ) and the quenching efficiency of iodide remains unaffected by the presence of halide ions. The compound 1 shows high sensitivity even in very low concentration regions towards the sensing of iodide with K SV (quenching constant based on linear Stern–Volmer plot) value of 1.8 × 10 4  M −1 and with detection limit of iodide of 0.63 μM (80 ppb), which is among the best value known for any luminescence based selective iodide sensor reported to date. [ABSTRACT FROM AUTHOR]

A water soluble luminescent 1D metal organic coordination polymer of Zn(II) [Zn(FDA)(2,2′-bpy)(H 2 O)]·2H 2 O (2,2′-bpy = 2,2′-bipyridine and FDA = 2,5-furandicarboxylate), 1 was successfully synthesized by solvothermal method. This crystalline compound 1 showed strong luminescence emission at 325 nm upon excitation at 290 nm in aqueous medium. The luminescence intensity was highly sensitive towards a bio-metabolized purine derivative, uric acid (UA). However, it did not show any considerable response towards structurally similar other purine derivatives like adenine (Adn), guanine (Gua) and theobromine (Tbr). The compound 1 was found to be highly selective and sensitive towards uric acid (UA) with a detection limit of 300 ppb. The sensitivity and selectivity of 1 towards UA was also investigated in the presence of several metal ions, anions and organic bio-molecules which are commonly found in human urine. The results indicated that 1 could be a potential probe for selective detection and estimation of UA in urine. The mechanism of the sensing was explained successfully and it was also supported by DFT calculation. [ABSTRACT FROM AUTHOR]

Solvation dynamics at the active site of an enzyme, glutaminyl-tRNA synthetase (GlnRS), was studied using a fluorescence probe, acrylodan, site-specifically attached at cysteine residue C229, near the active site. The picosecond time-dependent fluorescence Stokes shift indicates slow solvation dynamics at the active site of the enzyme, in the absence of any substrate. The solvation dynamics becomes still slower when the substrate (glutamine or tRNAGln) binds to the enzyme. A mutant Y211H-GlnRS was constructed in which the glutamine binding site is disrupted. The mutant Y211H-GlnRS labeled at C229 with acrylodan exhibited significantly different solvent relaxation, thus demonstrating that the slow dynamics is indeed associated with the active site. Implications for catalysis and specificity have been discussed. [ABSTRACT FROM AUTHOR]

A trace of water in alcohols and some other organic solvents has been detected by naked eye using intense green luminescence of a Tb doped MOF upon irradiation of UV light. Lattice and coordinated water molecules play crucial role in the sensitization process of Tb centre resulting intense luminescence. • Synthesized a new MOF {[Y 1.0 Mn 1.5 (PDA) 3 (H 2 O) 3 ·3.5H 2 O}, 1 , and a 10 % Tb doped {[Y 0.9 Tb 0.1 Mn 1.5 (PDA) 3 (H 2 O) 3 ·3.5H 2 O}, 1:Tb. • Ligand sensitized Tb centre green emission was used for naked eye detection of water in alcohols and other solvents. • The 1:Tb showed huge turn-on in presence of trace amounts of water in organic solvents. • The estimated detection limit was 1.12, 0.47, 0.04, 0.13 and 0.53 %(v/v) for EtOH, CH 3 OH, CH 3 CN and THF and n-heptane. • The presence of coordinated and lattice water in 1:Tb play a vital role in the sensitization process of the Tb3+ centre. It is very crucial to have a very simple, instant and low-cost detection and estimation of a trace of water in common organic solvents including alcohols. To obtain the sensor material we have synthesized a metal-organic framework (MOF) {[Y 1.0 Mn 1.5 (PDA) 3 (H 2 O) 3 ·3.5H 2 O}, 1 , (PDA = 2,6-pyridinedicarboxylic acid) through hydrothermal process. A doping of compound 1 by 10 % terbium {[Y 0.9 Tb 0.1 Mn 1.5 (PDA) 3 (H 2 O) 3 ·3.5H 2 O}, 1:Tb , was done through an isomorphous substitution technique. The most advantageous point about 1:Tb was the metal centre luminescence, which was largely stokes shifted from the excitation light making possible the naked eye observation. The weak metal centre luminescence intensity of dehydrated 1:Tb (excluding lattice and coordinated water molecules) in organic solvents EtOH, CH 3 OH, CH 3 CN, THF and n-heptane showed huge turn-on in presence of trace amounts of H 2 O in the said solvents. The luminescence intensity of Tb3+ centre was enhanced by several folds with a limit of detection 1.12 %(v/v), 0.47 %(v/v), 0.04 %(v/v), 0.13 %(v/v) and 0.53 %(v/v) respectively. The coordinated water molecules as well as the lattice water molecules in 1:Tb play a vital role during sensitization of the Tb3+ centre by enhancing the rigidity of the structure and facilitating the formation of LMCT state which ultimately results in a huge turn-on of metal centre luminescence. [ABSTRACT FROM AUTHOR]