Palladium induced activation of a substituted naphthopyran for smartphone assisted sensitive and selective sensing in aqueous solution

Abstract

A substituted naphthopyran moiety was synthesized to act as a probe for metal ions. Structural characterization techniques such as IR, NMR, HRMS, and single-crystal X-ray crystallography were used to establish the structure of the light-responsive photochromic probe. The intermolecular interactions were quantitatively investigated using the crystal explorer program. The affinity of the naphthopyran derivative as a probe for metal ion was investigated using different metal ions in a buffered medium to avoid the effect of change in pH during the recognition process. A bathochromic shift in the absorption band from ~354 nm to ~365 nm (broad band extended up to 450 nm) was observed upon addition of 10 equivalents of palladium ions. The smartphone assisted sensing of palladium ion based on digital images provided an excellent value of LOD (0.69 µM), which was better than the LOD value obtained using UV–visible spectroscopy. The process of complex formation between the probe and the palladium ions was also investigated using NMR and computational methods. The computational methods were used to investigate the effect of water on the stability of the complex geometries. Furthermore, time-dependent DFT calculations were carried out to investigate the UV-Visible absorption spectra observed experimentally for the probe and the complex.