A new anion selective chemosensor L was derived through a direct condensation reaction between pyridoxal and thiosemicarbazide. Sensor L showed selective recognition and sensing ability towards F− and AcO− anions through a naked-eye detectable color change from colorless to light yellow, appearance of a new charge transfer absorption band at 404 nm and significant “turn-on” fluorescence at 506 nm. The detection limit of L as a fluorescent ‘turn-on’ sensor for the analysis of F− and AcO− was estimated to be 0.10 μM. The anion sensing mechanisms of L was supported by 1H NMR and DFT results. Finally, the cytotoxicity effect of L and its ability to image intracellular F− ions in the living HeLa cells was investigated.
