Fluorescent Detection of Nitroaromatics and 2,3-Dimethyl 2,3-dinitrobutane (DMNB) by a Zinc Complex: (salophen)Zn
ABSTRACT Fluorescent sensors for the detection of chemical explosives are in great demand. It is shown herein that the fluorescence of ZnL* (H2L=N,N'-phenylene-bis-(3,5-di-tert-butylsalicylideneimine)) is quenched in solution by nitroaromatics and 2,3-dimethyl-2,3-dinitrobutane (DMNB), chemical signatures of explosives. The relationship between the structure and fluorescence of ZnL is explored, and crystal structures of three forms of ZnL(base), (base=ethanol, tetrahydrofuran, pyridine) are reported, with the base=ethanol structure exhibiting a four-centered hydrogen bonding array. Solution structures are monitored by 1H NMR and molecular weight determination, revealing a dimeric structure in poor donor solvents which converts to a monomeric structure in the presence of good donor solvents or added Lewis bases to form five-coordinate ZnL(base). Fluorescence wavelengths and quantum yields in solution are nearly insensitive to monomer-dimer interconversion, as well as to the identity of the Lewis base; in contrast, the emission wavelength in the solid state varies for different ZnL(base) due to pi-stacking. Nitroaromatics and DMNB are moderately efficient quenchers of ZnL*, with Stern-Volmer constants KSV=2-49 M-1 in acetonitrile solution.
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ABSTRACT: We demonstrate here that supramolecular interactions enhance the sensitivity towards detection of electron-deficient nitro-aromatic compounds (NACs) over discrete analogues. NACs are the most commonly used explosive ingredients and are common constituents of many unexploded landmines used during World War II. In this study, we have synthesised a series of pyrene-based polycarboxylic acids along with their corresponding discrete esters. Due to the electron richness and the fluorescent behaviour of the pyrene moiety, all the compounds act as sensors for electron-deficient NACs through a fluorescence quenching mechanism. A Stern–Volmer quenching constant determination revealed that the carboxylic acids are more sensitive than the corresponding esters towards NACs in solution. The high sensitivity of the acids was attributed to supramolecular polymer formation through hydrogen bonding in the case of the acids, and the enhancement mechanism is based on an exciton energy migration upon excitation along the hydrogen-bond backbone. The presence of intermolecular hydrogen bonding in the acids in solution was established by solvent-dependent fluorescence studies and dynamic light scattering (DLS) experiments. In addition, the importance of intermolecular hydrogen bonds in solid-state sensing was further explored by scanning tunnelling microscopy (STM) experiments at the liquid–solid interface, in which structures of self-assembled monolayer of the acids and the corresponding esters were compared. The sensitivity tests revealed that these supramolecular sensors can even detect picric acid and trinitrotoluene in solution at levels as low as parts per trillion (ppt), which is much below the recommended permissible level of these constituents in drinking water.Chemistry - A European Journal 10/2014; 20(42). DOI:10.1002/chem.201403345 · 5.70 Impact Factor
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ABSTRACT: Artificial light-harvesting systems, Ar,O-BODIPY dyads and triads conjugated with a light harvester, were synthesized in high yield by the reaction of an N2O2-type dipyrrin with boronic acids. Dyad having a pyrene unit underwent quantitative Förster resonance energy transfer (FRET) from the antenna unit, pyrene, to the fluorophore unit, Ar,O-BODIPY. Triads · and · were quantitatively prepared by mixing pyridine-appended compounds and with saloph·Zn complex , respectively. Triad · underwent efficient FRET from the saloph·Zn complex unit to the fluorophore unit at the rate of 2.0 × 10(11) s(-1). Interestingly, the fluorescence quenching process in the excited state of the triad · took place following the energy transfer event. Thus, appropriate positioning of the energy donor and acceptor is necessary to construct a highly efficient FRET system.Organic & Biomolecular Chemistry 01/2015; 13(9). DOI:10.1039/c4ob02351j · 3.49 Impact Factor
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ABSTRACT: Zinc(II) complexes are effective and selective nucleic acid-binders and strongly fluorescent molecules in the low energy range, from the visible to the near infrared. These two properties have been often exploited to quantitatively detect nucleic acids in biological samples, in both in vitro and in vivo models. In particular, the fluorescent emission of several zinc(II) complexes is drastically enhanced or quenched by the binding to nucleic acids and/or upon visible light exposure, in a different fashion in bulk solution and when bound to DNA. The twofold objective of this perspective is 1) to review recent utilisations of zinc(II) complexes as selective fluorescent probes for nucleic acids and 2) to highlight their novel potential applications as diagnostic tools based on their photophysical properties.Dalton Transactions 10/2014; 44:3527. DOI:10.1039/C4DT02881C · 4.10 Impact Factor