Flavones Fluorescence-Based Dual Response Chemosensor for Metal Ions in Aqueous Media and Fluorescence Recovery.

Responsiveness of sensing materials 3-hydroxyflavone (3HF) towards metal ions in aqueous medium has been explored following photoexcitation. 3HF exhibited both colorimetric and fluorescence (FL) turn-off response towards Cu and Fe with high sensitivity and selectivity. Meanwhile, the distinct colour change and the rapid quenching of FL intensity provide naked-eye detection. On successive addition of Cuand Fe ions, FL of 3HF was "turned off," whereas there is no change in wavelength of FL bands. Quenching efficiencies for Cuand Fe ions are 88% and 49%, respectively. The detection limit of the sensor towards Cu and Fe was 1.54 μM and 1.98 μM, respectively. The binding strategy between 3HF and metal ions (Cu, Fe) and the nature of quenching have been explored with the Benesi-Hildebrand and Stern-Volmer plots, respectively. The FL of 3HF significantly quenched in the presence of Cu ions, and then recovered upon addition of HCl, providing the possibility of constructing a sensitive Cu-HCl off-on fluorescent probe. Moreover, the proposed simple, quick response and visual test strip-based chemosensor could be used for the detection of Fe and Cu ions.