One pot synthesis of coumarin fused fluorescein derivative for mercury ion detection: An experimental and theoretical approach

In this study, a highly fluorescent fluorescein-based derivative (2FLC) was synthesized using a one-pot synthesis method. The structure of the molecule was confirmed through physicochemical analysis, including ¹H NMR, FT-IR, and mass spectroscopy. The chemosensor property of 2FLC with different metal ions (Cu ²⁺, Al³⁺, Ag ⁺, Hg²⁺, Mg²⁺, Fe²⁺, Co²⁺, K⁺, Zn²⁺, Ni²⁺, Pb²⁺, Cd²⁺ and Mn²⁺) is investigated through absorption and fluorescence studies in a water medium. Interestingly, it is observed that the 2FLC exhibited a remarkable turn-off fluorescence response upon adding Hg²⁺ ion as compared to different metal ions. Further, competitive metal ion studies indicate that the receptor 2FLC exhibits exceptional selectivity in detecting Hg²⁺ ion without being affected by other metal ions. The detection limit of 2FLC for targeted Hg²⁺ ion was 8.87 μM. The binding stoichiometry between the receptor 2FLC and the Hg²⁺ metal ion was verified using both Job's plot and the Benasi-Hildbrand methods and found to be 1:1. Theoretical studies and FT-IR spectra confirmed the strong binding and formation of 2FLC-Hg²⁺ complex. Overall, the results suggest that the newly synthesized water-soluble 2FLC molecule may be used as a chemosensor to detect Hg²⁺ ion.