One-Pot Three-Component Cascade Synthesis of Pyrazolopyrido[2,3-h]Quinazolines: Effective Fluorescent Turn-Off Probes for Sensing Pd2+ Ions

Palladium(II) ions (Pd²⁺) are crucial in various fields, including catalysis, medicine, electronics, hydrogen storage, sensors, and imaging. However, their uncontrolled use can lead to toxicity and environmental hazards. Therefore, developing selective and sensitive Pd²⁺ sensing probes is vital for ecological safety, biomedical monitoring, and sustainable resource management. Herein, we report the synthesis of novel pyrazolopyrido[2,3-h]quinazoline-based probes (PQMe and PQCl) for the selective and sensitive detection of Pd²⁺ ions among various metal ions. An environmentally benign multicomponent cascade strategy was employed to synthesize these hybrid heterocycles. The detection limits of the probes PQMe and PQCl for Pd²⁺ were determined to be 0.55 µM and 0.71 µM, respectively. The binding interaction between the probes and Pd²⁺ was confirmed through ¹H NMR titration experiments. Furthermore, fluorescence lifetime measurements supported the fluorescence quenching mechanism upon Pd²⁺ binding. The applicability of these probes for real-world analysis was evaluated by detecting Pd²⁺ ions in various water samples. Additionally, we demonstrated the potential of these probes to be fabricated into test strips or swabs for efficient on-site detection of Pd²⁺ ions.