Partha Mahata

Visible detection of explosive nitroaromatics facilitated by a large stokes shift of luminescence using europium and terbium doped yttrium based MOFs

To use the large stokes shift and low self quenching of luminescence, we have successfully constructed two luminescent yttrium based MOFs doped with europium and terbium, [Y0.9Eu0.1(OBA)(Ox)0.5(H2O)2], Y-MOF:Eu and [Y0.9Tb0.1(OBA)(Ox)0.5(H2O)2], Y-MOF:Tb through an isomorphous substitution technique using a two dimensional metal–organic framework (MOF) [Y1.0(OBA)(Ox)0.5(H2O)2], [OBA = 4,4′-oxybis(benzoic acid), Ox = oxalate], Y-MOF, as a structural basis. The structure and size of Y-MOF, Y-MOF:Eu and Y-MOF:Tb were systematically characterized by PXRD, TGA, SEM and EDX analysis. Y-MOF:Eu and Y-MOF:Tb shows high intensity visible red and green emission, respectively, on the exposure of UV light. These emissions of Y-MOF:Eu and Y-MOF:Tb were used for the visible detection of nitro explosives such as 2,4,6-trinitrophenol (TNP), 1,3-dinitro benzene (DNB), 2,4-dinitro toluene (DNT), nitro benzene (NB), 4-nitro toluene (NT) in acetonitrile through luminescence quenching. Y-MOF:Eu and Y-MOF:Tb shows superior sensitivity towards TNP and NT compared to other nitroaromatic explosives. The large stokes shift of Y-MOF:Eu and Y-MOF:Tb allows naked eye detection of these nitroaromatics. The observed KSV (quenching constant obtained from Stern–Volmer plots) values are in the range 3.2 × 104 to 0.4 × 104 M−1 for Y-MOF:Eu and 3.19 × 104 to 0.47 × 104 M−1 for Y-MOF:Tb. Using these materials ppm level detection of nitro explosives has been achieved.

A Co(II) complex of a vitamer of vitamin B6 acts as a sensor for Hg2+ and pH in aqueous media

A Co(II) complex of molecular formula C48H96.8N12O22.4Co2Cl2, 1, was synthesized from the Schiff base [H2pydmdp]Cl by a template reaction of pyridoxal (pyd), a vitamer of vitamin B6, N-methyl-1,3-diaminopropane (mdp) and cobalt(II) acetate. It was characterized by elemental analysis, 1H NMR, IR and UV-Vis spectroscopy, thermal analysis, electrochemistry and single crystal X-ray diffraction. The experimental results suggested that in complex 1, the central Co(II) is bonded to two phenolato-oxygens, two imine nitrogens and two amine nitrogens in an octahedral geometry. In aqueous media complex 1 exhibits an intense fluorescence emission peak at 506 nm when it was excited at 425 nm. The fluorescence behavior of complex 1 in aqueous media was employed to determine whether it acts as a chemosensor for some selective toxic metal ions. The studies showed that the present complex behaves as a promising sensor for Hg2+ even at the sub-micromolar level. In addition in aqueous solution, complex 1 acts as a sensor for the pH of the medium. A detailed study on the mechanism of sensing behavior established that Hg2+ interacts with complex 1 via weak non-covalent interaction with the N-atom of the pyridine moiety of the molecule. The pyridine nitrogen also plays a vital role in sensing the pH of the medium.