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

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 x 10(4) M-1 with a lowest detection limit (LOD) of 0.50 mu M for F- ions. The interaction mechanism was studied by H-1-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.