Methylene Spacer Mediated Detection Switch Between Copper and Zinc Ions by Two Coumarin‐Pyrene Based Chemosensors

Abstract Pyrene linked‐coumarin based fluorescent chemosensors L1 and L2 are utilized for the selective detection of Cu 2+ and Zn 2+ ions, respectively. Both chemosensors differed by a methylene spacer that connects the coumarin and pyrene rings through an imine group. The inclusion of methylene spacer dramatically changed the detection profiles of two chemosensors. While L1 showed fluorescence “turn‐off” response towards the Cu 2+ ion; L2 showed “turn‐on” emission enhancement with the Zn 2+ ion. Both chemosensors illustrated nano‐molar detection limits and were selective even in the presence of other competing metal ions. The 1 : 1 stoichiometry between a chemosensor and Cu 2+ /Zn 2+ ion was supported by the binding studies, Job's plot, NMR spectral titrations, mass spectra and density functional theory (DFT) studies. The detection ability of both chemosensors was utilized by fabricating the filter paper test‐strips as well as polystyrene films for quick and visual monitoring of these ions in different water samples. Chemosensor L2 was further utilized for the “turn‐on” detection of Zn 2+ ion in HepG2 cells whereas solution generated L2 ‐Zn species functioned as a secondary chemosensor for the detection of cystine, an important amino acid.