Recent progress in the molecular design of fluorophore-based sensors for metal ion detection: Focus on lead (Pb2+) chelation and sensing mechanisms

The molecular design of functional organic dyes as fluorescent chemosensors represents a dynamic frontier in materials chemistry, bridging synthetic dye chemistry with practical analytical applications. This review summarizes recent progress in the molecular design and photophysical properties of fluorescent sensors for metal ion detection, with particular emphasis on lead (Pb 2+ ) ions. The first part focuses specifically on Pb 2+ -responsive sensors, considering the high toxicity of lead and the need for selective chelation strategies. The second part systematically surveys diverse fluorophore backbones, including quinoline, pyrazoloquinoline, fluorescein, rhodamine, coumarin, pyrene, and Schiff base derivatives. Special attention is given to how specific structural modifications and the strategic incorporation of chelating units influence fluorescence responses and coordination selectivity. Key analytical parameters of sensor–ion systems, such as detection limits, binding constants, and complex stoichiometry, are compared across representative fluorophore-based sensorsFinally, the underlying metal-ligand interactions and fluorescence sensing mechanisms, including photoinduced electron transfer (PET), intramolecular charge transfer (ICT), chelation-enhanced fluorescence (CHEF), chelation-enhanced quenching (CHEQ) and excited state intramolecular proton transfer (ESIPT), are discussed. The review concludes with an outlook on current challenges and future perspectives in the development of selective, sensitive, and practically applicable fluorescent sensors for Pb 2+ detection.