Rotating the C–N Bond in a Coumarin–Pyridine-Based Sensor for Pattern Recognition of Versatile Metal Ions

A cross-reactive sensor array is powerful for high-throughput discrimination of various kinds of metal ions. However, the construction of a multicomponent sensor array is always time-consuming and cost-ineffective. Herein, a practical four-component X1-based sensor array (X1SA) was obtained by simply dissolving a single dye molecule X1 in respective solvents such as methanol, ethanol, dimethyl sulfoxide, and acetonitrile. In this design, X1 exhibits strong solvatochromic fluorescence properties via an excited-state intramolecular proton transfer and intramolecular charge transfer combined mechanism. Moreover, rotation of the C–N bond between the pyridine and coumarin units in X1 enabled it to coordinate with metal ions through different binding modes, which acted as an additional dimension of the sensor array. Inspired by this C–N bond rotation strategy, X1SA was determined to be powerful in discriminating 20 kinds of metal ions in both phosphate-buffered saline and 5% serum media in a range of 0.1–100 μM. In addition, the sensor array was also successfully applied in differentiating similar and mixed metal ions such as Fe3+/Fe2+, Cd2+/Hg2+, and Sn2+/Pb2+ in serum samples, which is meaningful for investigating the biological roles of iron and early diagnosis of related metal poisoning accidents.