A seleno-pyrene selective probe for Hg²⁺ detection in either aqueous or aprotic systems

A new fluorescent molecular probe (compound 7) assembled from the amide bond between the 1-pyrenecarboxylic acid (6) and 2-(butylselenyl)ethanamine (5) was designed, synthesized and its structure accurately characterized. The photophysical properties of 7 were evaluated among a wide range of metallic cations (Na⁺, K⁺, Ca²⁺, Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Hg²⁺, Ag⁺, Al³⁺, Fe³⁺, Ga³⁺and Cr³⁺) in water and in acetonitrile, which showed selective interaction with Hg²⁺. However, the sensing mechanism was found to be different in each solvent. Dynamic light scattering (DLS) studies revealed that compound 7 organizes itself as monodisperse aggregates in aqueous solution, nonetheless, as Hg²⁺ was added to the aqueous solution, disruption of aggregates was observed, resulting in a coordination complex under strong CHEQ (Chelation-Enhanced Fluorescent Quenching). Conversely, in acetonitrile solution, 7 exhibited monomeric pyrene emissive pattern and, as the addition of Hg²⁺ proceeded, a coordination compound of excimer-type fluorescence emission was observed. UV–vis absorption, steady state, and time-resolved emission spectroscopy were employed. The stoichiometry of the 7-Hg²⁺ complexes was found to be 1:1 for both aqueous (log β = 6.19 ± 0.009) and acetonitrile (log β = 8.59 ± 0.04) solutions. The lowest value of a detectable amount of 0.15 μmol/L for Hg²⁺ was achieved for fluorescence measurements in aqueous solution. The aqueous system was applied for the detection of Hg²⁺ in real samples of spring water, where the added amounts of the analyte could be detected and quantified.