A pyranopyrazole-rhodamine chemosensor for selective Pb²⁺ detection: dual colorimetric-fluorescent sensing and...

The physiological and environmental impacts of toxic heavy metal ions have driven the development of selective and sensitive chemosensors. In this study, a pyranopyrazole-appended rhodamine B derivative (PR) was synthesized and evaluated as a selective chemosensor for Pb²⁺ detection. The probe exhibited distinct colorimetric and fluorescence "turn-on" responses upon interaction with Pb²⁺ ions in both solution and solid-state systems. Spectroscopic studies indicated the formation of a stable 1:1 complex with a binding constant of 1.523 × 10⁴ M^-1 and a detection limit of 4.392 nM. The sensing mechanism involves the opening of the spirolactam ring, which is supported by fluorescence studies and density functional theory (DFT) calculations. The probe demonstrated good selectivity in the presence of competing metal ions and showed practical applicability in real sample analysis. Additionally, the system was used to construct molecular logic gate operations. This combined experimental and theoretical investigation demonstrates the potential of PR as a multifunctional sensing platform for Pb²⁺ detection.