Probing Pb²⁺ cation via the iridium based phosphorescent dye

We demonstrate the concept of Pb²⁺ cation sensing using the emissive Ir(III) complex (1) based on the associated decrease of room-temperature phosphorescence upon forming the 1:1 adduct 1-Pb²⁺. Complex 1 bears two cyclometalated N-phenyl pyrazoles with pyrazoles residing at the mutual trans dispositions as well as one 3,5-di(pyridyl) pyrazolate chelate. X-ray structural analyses on the adduct 1-Pb²⁺ confirm the key function of 3,5-di(pyridyl) pyrazolate as it forms chelate interaction with the metal analytes, while quenching of phosphorescent emission is probably due to the Pb²⁺ induced perturbation, which increases the intersystem crossing to another lower-lying triplet state for the host chromophore via an enhanced spin-orbit coupling.