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

Pyrene linked-coumarin based fluorescent chemosensors L1 and L2 are utilized for the selective detection of Cu2+ and Zn2+ 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 Cu2+ ion; L2 showed turn-on emission enhancement with the Zn2+ 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 Cu2+/Zn2+ 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 Zn2+ ion in HepG2 cells whereas solution generated L2-Zn species functioned as a secondary chemosensor for the detection of cystine, an important amino acid.

Automated summary

Selective detection of Cu2+ and Zn2+ ions was achieved using pyrene linked-coumarin based fluorescent chemosensors L1 and L2, respectively, which showed different detection profiles due to the inclusion of a methylene spacer. Both chemosensors exhibited nano-molar detection limits and selectivity even in the presence of other competing metal ions.