Ferrocenylbenzobisimidazoles for Recognition of Anions and Cations

The preparation of 2,7-disubstituted benzobisimidazoles decorated with substituents displaying different electrooptical properties is described. The presence of reclox, chromogenic, and fluorescent groups at the heteroaromatic core, which acts as ditopic binding site, made these receptors potential candidates as multichannel probes for ions. The triad 4 behaves as a selective redox and fluorescent chemosensor for HSO4- and Hg2+ ions, whereas receptor 5 acts as a redox and chromogenic chemosensor molecule for AcO- and SO42- anions. The change in the absorption spectra is accompanied by a color change from yellow to orange, while sensing of Zn2+, Hg2+ and Pb2+ cations is carried out only by electrochemical techniques. Receptor 6 exhibits a remarkable cathodic shift of the oxidation wave only in the presence of AcO-, H2PO4-, and HP2O73- anions, whereas addition of Pb2+ induces an anodic shift. A new low energy band in the absorption spectra, which is responsible for the color change from colorless to pale yellow, and an important increase of the monomer emission band is observed only in the presence of H2PO4-, and HP2O73- anions. The most salient feature of the receptor 6 is its ability to act as a multichannel (redox, chromogenic, and fluorescent) Chemodosimeter for Cu2+, and Hg2+ metal cations.