A heterocyclic chalcone-based fluorescent chemosensor for selective Cu(II) detection: mechanistic insights and...

Chalcones are attractive scaffolds for fluorescent sensing applications in environmental and biological matrices. Herein, a heterocyclic arylchalcone-based fluorescent chemosensor (2-TIO) with pronounced intramolecular charge transfer (ICT) character was synthesized and spectroscopically characterized for selective Cu(II) detection. Its exploratory bacterial imaging application was also evaluated. The compound exhibits suitable photophysical properties, displaying fluorescence quenching and colorimetric response upon interaction with Cu(II), enabling both spectrophotometric and fluorimetric detection. The chemosensor showed high selectivity toward Cu(II) over interfering metal cations. Fluorescence measurements revealed higher sensitivity than UV-Vis detection, with limits of detection of 0.0988 μM and 1.02 μM, respectively. Competitive and kinetic studies confirmed rapid and selective interaction between 2-TIO and Cu(II). The sensing mechanism was investigated through density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations, supported by experimental IR and UV-Vis characterization. The results suggest coordination between the carbonyl oxygen atom and Cu(II) with a 2:1 stoichiometry (ligand:metal), perturbing the ICT process and promoting fluorescence quenching through excited-state deactivation pathways. The applicability of the chemosensor was evaluated in real water samples, where fluorescence-based detection showed improved analytical performance compared to UV-Vis measurements. Additionally, preliminary biological imaging experiments demonstrated that the photophysical behavior of the chalcone scaffold supports exploratory fluorescence-based bacterial labeling, with preferential staining of Helicobacter pylori and Enterococcus faecalis and negligible fluorescence in mammalian HEK-293 cells. This study highlights the value of combining experimental and computational approaches for developing multifunctional fluorescent chemosensors and positions 2-TIO as a promising fluorescent scaffold for environmental Cu(II) sensing and exploratory fluorescence-based bacterial labeling applications.