Sensing of copper ions in water using spiropyran synthesized via photochromic oxazine accompanied by alteration in oxidation state

A spiropyran derivative synthesized via photochromic oxazine was characterized using FTIR, NMR, HRMS, and single-crystal X-ray crystallographic analysis. The intermolecular interactions were quantitatively explored using Hirshfeld surface analysis and 2D fingerprint plots. Evaluation of sensing properties of the spiropyran derivative toward metal ions revealed selective interaction with copper ions. A change in color from light yellow to orange was witnessed through the naked eye detection technique, which was further exploited to develop a smartphone-assisted technique for the determination of copper ions in an aqueous solution. UV–vis analysis revealed a band in the visible region, while electrochemical analysis revealed that the copper ions promote a C-C coupling between indoline units of two spiropyran derivatives. The exposure of the complex to visible light of 450 nm led to the release of copper ions. XPS analysis indicated a change in the oxidation state of the copper ion in the complex, while NMR analysis revealed an interaction between copper ions and spiropyran derivatives at the molecular level.