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Three Ni(ii)-POCOP pincer complexes [NiCl{CH-4-OH-2,6-(OPPh)}], 1; [NiCl{CH-4-OH-2,6-(OPtBu)}], 2 and [NiCl{CH-4-OH-2,6-(OPiPr)}], 3 were studied as bifunctional molecular sensors for inorganic anions and acetate. In CHCN, fluoride generates a bathochromic shift with a colorimetric change for 1-3 with a simultaneous fluorescence turn on, this optical effect is based on deprotonation of the para-hydroxy group of the POCOP ligand. On the other hand, in a neutral aqueous solution of 80 vol% CHCN, additions of cyanide produce a distinct change of color by forming very stable complexes with the nickel-based receptors 1-3 with log K in the range of 4.38-5.03 M and pronounced selectivity over other common anions such as iodide, phosphate, and acetate. Additionally, bromide shows a modest spectral change and affinity, but lower than those observed for cyanide. On the basis of H NMR experiments, UV-vis titrations, ESI-MS experiments, and the crystal structure of the neutral bromo complex of 1, it is proposed that the colorimetric change involves an exchange of chloride by CN on the Ni(ii) atom. The Ni(ii)-based sensor 1 allows the fluorescent selective detection of fluoride with a limit of 5.66 μmol L and colorimetric sensing of cyanide in aqueous medium in the micromolar concentration range.

Three new diboronic acid-substituted bisquinolinium salts were synthesized, structurally described by single-crystal X-ray diffraction, and studied in-depth as fluorescent receptors for six monosaccharides and two open-chain polyols in water at physiological pH. The dicationic pyridine-2,6-dicarboxamide-based receptors contain two N-quinolinium rings as the fluorescent units covalently linked to three different isomers of phenylboronic acid (ortho, 2; meta, 3; and para, 4) as chelating binding sites for polyols. Additions of glucose/fructose in the micromolar concentration range to receptors 2 and 3 induce significant fluorescence changes, but in the presence of arabinose, galactose, mannose, and xylose, only modest optical changes are observed. This optical change is attributed to a static photoinduced electron transfer mechanism. The meta-diboronic receptor 3 exhibited a high affinity/selectivity toward glucose (K = 3800 M −1 ) over other monosaccharides including common interfering species such as fructose and mannitol. Based on multiple spectroscopic tools, electrospray ionization high-resolution mass spectrometry, crystal structures, and density functional theory calculations, the binding mode between 3 and glucose is proposed as a 1:1 complex with the glucofuranose form involving a cooperative chelating diboronate binding. These results demonstrate the usefulness of a new set of cationic fluorescent diboronic acid receptors with a strong ability for optical recognition of glucose in the sub-millimolar concentration range.

Biological catecholamines such as L-DOPA and dopamine play vital physiological roles in brain, and are chemical indicators of human diseases. A new range of fluorescent Zn(II)-terpyridine complexes are described and...