Lead and Mercury Sensing by Calixarene‐Based Fluoroionophores Bearing Two or Four Dansyl Fluorophores

Abstract A detailed study on the photophysical and complexing properties of calixarenes bearing two and four dansyl derivatives (Calix‐DANS2 and Calix‐DANS4) in a CH 3 CN/H 2 O mixture (60:40 v / v ) is reported. Calix‐DANS2 shows a high selectivity towards Hg 2+ over interfering cations (Na + , K + , Ca 2+ , Cu 2+ , Zn 2+ , Cd 2+ and Pb 2+ ) and a sensitivity in the 10 −7 mol L −1 concentration range. The complexation of mercury ion induces a strong fluorescence quenching due to a well‐defined electron transfer process from the fluorophore to the metal center. Calix‐DANS4 exhibits an extremely high affinity for Pb 2+ with a high selectivity over various competing ions. The unprecedented detection limit (4 μg L −1 ) is fully compatible with the level defined by the World Health Organisation. The affinity of Calix‐DANS4 for Pb 2+ can be rationalized by the activation of the inert pair of electrons on Pb 2+ . The number of fluorophores involved in the complexation can be determined from a careful time‐resolved fluorescence characterization.