Spirooxazine-Based Dual-Sensing Probe for Colorimetric Detection of Cu and Fe and Its Application in Drinking Water and Rice Quality Monitoring.

A spirooxazine derivative, (3,3-dimethyl-1-phenethylspiro[indoline-2,3'-naphtho[2,1-][1,4]oxazine]), as a dual-sensing probe for Cu and Fe was synthesized, and its structure was confirmed by H NMR, C NMR, HRMS, and single-crystal X-ray diffraction. The results reveal that the probe is selective to both Cu and Fe through distinct colorimetric responses in acetonitrile. The sensing performance of toward Cu was investigated, and upon addition of Cu, an instant change in color from colorless to bright yellow with a strong absorption band at 467 nm was observed. Due to a dual-sensing behavior, also exhibits a unique response toward Fe that can be discovered from a color change from colorless to red at an absorption wavelength of 514 nm. Based on spectroscopic analyses and density functional theory calculations, the 1:1 stoichiometric complexation of with the targeted metal ions was proposed and the binding constants of 1.95 × 10 M for Cu and 1.29 × 10 M for Fe were obtained. In addition, the detection limits of for Cu and Fe were 0.94 and 2.01 μM, respectively. To verify its applicability in real samples, was further explored for quantitative determination of both Cu and Fe in spiked drinking water. The results showed that the recoveries of Cu and Fe examined using the probe were found comparable to those obtained from atomic absorption spectroscopy. Moreover, the strip test was developed, and its utilization for qualitative detection of Fe in real rice samples was demonstrated.