Ion Pair Recognition Receptor Based on an Unsymmetrically 1,1′-Disubstituted Ferrocene–Triazole Derivative

The ferrocene–triazole derivative <b>4</b>, available from 1,1′-bis­(diazido)­ferrocene by sequential functionalization through click-type chemistry and the Staudinger reaction, is elaborated as a lab-on-a-molecule for the selective sensing of HP₂O₇^3– and Hg²⁺. Receptor <b>4</b> behaves as a ratiometric fluorescent probe for HP₂O₇^3– with a good selectivity over other anions, whereas in the presence of Hg²⁺ it modifies the fluorescent emission of the pyrene unit, acting as a selective on–off fluorescent sensor for Hg²⁺ with a low detection limit. The most salient feature of compound <b>4</b> is its behavior as an excellent electrooptical ion pair recognition receptor able to simultaneously recognize Pb²⁺ cations in the presence of HP₂O₇^3– anion through multichannel perturbations of the redox potential of the ferrocene unit, the emission spectrum, and a noticeable color change from yellow to green