‘Naked-eye’ colorimetric/fluorimetric detection of F− ions by biologically active 3-((1H-indol-3-yl)methyl)-4-hydroxy-2H-chromen-2-one derivatives

Abstract

An improved synthetic protocol has been developed for the construction of highly functionalized heterologous alkyl and benzyl indolyl-coumarin derivatives through a rapid, catalyst-free and solvent-free one-pot three-component reaction of indole, aldehyde and 4-hydroxycoumarin. The synthesized compounds display a high selectivity and sensitivity towards F⁻ ions. The detection of F⁻ ions was accompanied by fluorescence quenching with noticeable colour change, which is evident from the Stern–Volmer plot. The Stern–Volmer plot shows an association constant of 6.2625 × 10⁴ M⁻¹ with a lowest detection limit (LOD) of 0.50 μM for F⁻ ions. The interaction mechanism was studied by ¹H-NMR titration and also supported by advanced TD-DFT calculations. The designed chemosensor has been utilized as a mini colorimetric kit for F⁻ ions on test paper strips and is also capable of detecting F⁻ ions in commercially available toothpaste and mouth rinser. The chemosensors also exhibited good antifungal and antibacterial activity.