Dipodal fluorescent chemosensor for Fe3+ and resultant complex as a chemosensor for fluoride

A novel selective fluorescent chemosensor based on a 2,2′-bisbenzimidazole derivative (L) was synthesized and characterized. Once combined with Fe3+, it displayed high specificity for fluoride anion. It can display on-off-type fluorescence charged with high selectivity toward Fe3+ among 12 metal ions in H2O/DMSO (4:6, v/v) solutions. Furthermore, in the situ generated L–Fe3+ ensemble could recover the quenched fluorescence upon the addition of fluoride anion resulting in an off-on-type sensing with a detection limit of 1.0 × 10−9 mol/L in the same medium. Notably, the sensor was retrievable to indicate fluoride anions with Fe3+, and F−, in turn, increased. The mechanisms of “on-off-on” signaling have been supported by IR, 1H NMR, 13C NMR, ESI-MS, crystal data, and emission spectral studies.