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.

In this work, two Schiff-base-based chemosensors L1 and L2 containing electron-rich quinoline and anthracene rings were designed. L1 is AIEE active in a MeOH-H2O solvent system while formed aggregates as confirmed by the DLS measurements and fluorescence lifetime studies. The chemosensor L1 was used for the sensitive, selective, and reversible ‘turn-on’ detection of Al3+ and Ga3+ ions as well as Aspartic Acid (Asp). Chemosensor L2, an isomer of L1, was able to selectively detect Ga3+ ion even in the presence of Al3+ ions and thus was able to discriminate between the two ions. The binding mode of chemosensors with analytes was substantiated through a combination of 1H NMR spectra, mass spectra, and DFT studies. The ‘turn-on’ nature of fluorescence sensing by the two chemosensors enabled the development of colorimetric detection, filter-paper-based test strips, and polystyrene film-based detection techniques.

Two novel coumarin-based Schiff-base chemosensors are presented. Courtesy to an extended conjugation between the coumarin ring and the attached π-containing groups, both chemosensors display noteworthy photo-physical properties including emission maxima at > 550 nm. Both chemosensors function as the selective sensors for the 'turn-off' detection of copper ion with the significant nanomolar detection limits. The sensing event was investigated through proton NMR and mass spectroscopy; pH studies; life-time and quantum yield measurements and DFT studies. The solution-generated [chemosensor-Cu] species illustrated remarkably selective secondary 'turn-on' detection of the citrate ion. The sequential detection of the copper and citrate ions have been utilized for the construction of logic gates as well as several low-cost detection methods.