Catecholboryl-functionalized ferrocene based Lewis acid system: A selective probe for fluoride ion through multiple channels

The design and synthesis of two new receptors, C20H19O3BFe and C20H21O3BFe and their anion sensing properties through multiple channels are reported. Both the receptors, having chelating boronic ester Lewis acidic centre as the sole binding site, selectively bind fluoride ion in micromolar concentration. The binding constant of C20H19O3BFe with the fluoride ion has been found to be quite high [K = 10(6) M-1], whereas it displays a negligible affinity towards other effective competitors, for example acetate and cyanide (K = 10 M-1) and no sensitivity towards other halide ions. Upon selective recognition of F- in acetonitrile, the redox potential of C20H19O3BFe shifted by Delta E = 200 mV and the fluorescence emission was quenched drastically. The considerable changes in their absorption spectra are accompanied by the appearance of a new low energy (LE) peak at 566 nm and by a strong colour change from yellow to deep green which allows the prospective for naked eye detection of F- anion. (C) 2012 Elsevier B. V. All rights reserved.