Highly Sensitive and Fast‐Responsive Fluorescent Chemosensor for Palladium: Reversible Sensing and Visible Recovery

The well‐known rhodamine spiro‐lactam framework offers an ideal model for the development of fluorescence‐enhanced chemosensors through simple and convenient syntheses. Herein, we report a new tridentate PNO receptor, which was introduced into a rhodamine spiro‐lactam system to develop Pd 2+ ‐chemosensor RPd4 , that displayed significantly improved sensing properties for palladium. Compound RPd4 shows a very fast response time (about 5 s), high sensitivity (5 n M ), and excellent specificity for Pd 2+ ions over other PGE ions (Pt 2+ , Rh 3+ , and Ru 3+ ). In addition, RPd4 displays quite different responses to different valence states of the Pd ions, that is, very fast response towards Pd 2+ ions but slow response towards Pd 0 , which may provide us with a convenient method for the selective discrimination of Pd species in different valence states. According to proof‐of‐concept experiments, RPd4 has potential applications in Pd 2+ ‐analysis in drug compounds, water, soil, and leaf samples. Owing to its good reversibility, RPd4 can also be used as a sensor material for the selective detection and visual recovery of trace Pd 2+ ions in environmental samples.