Dual detection of mercury (II) and lead (II) ions using a facile coumarin-based fluorescent probe via excited state intramolecular proton transfer and photo-induced electron transfer processes

[Display omitted] •A dual-responsive Schiff base chemosensor Cou-S for Hg2+ and Pb2+ detection was designed.•Both ESIPT and PET as the sensing strategies were investigated.•Detection limit values of 8.3 and 10.5 nM for Hg2+ and Pb2+, respectively, was obtained.•Real water sample measurement suggests the accuracy of Cou-S.•Discriminative images were observed in paper sensor strips and bioimaging. A Schiff base fluorophore coumarin incorporated 4-(diethylamino)salicylaldehyde (Cou-S) is designed and synthesized to allow an excited state intramolecular proton transfer and photo-induced electron transfer processes for detecting toxic heavy metal ions of Hg2+ and Pb2+ in aqueous samples. The solid blue emission of Cou-S was gradually quenched to weak cyan in Hg2+ detection and to green channels in the presence of Pb2+. The coordination behaviours of the probe with Hg2+/Pb2+ are studied using a series of spectroscopic measurements and density functional theory (DFT) calculations. The probe exhibited good water solubility, great selectivity and excellent sensitivity with the LOD values of 8.3 and 10.5 nM for Hg2+ and Pb2+ in aqueous medium, respectively. The utility of Cou-S towards dual ions detection was explored in various sources of water samples, Whatmann paper strips, Boolean logic NOR gate operations and PC3 live cells, demonstrating the promising on-site visualization of the probe in controlling the toxicity levels in waste water sources and biosystems.