Benzimidazole-based fluorescent sensors for Cr3+ and their resultant complexes for sensing HSO4− and F−

A benzimidazole-based receptor that selectively recognized Cr3+ without interference from other metal ions was synthesized in this study. The resultant Cr-complex recognized HSO4− and F− via two approaches. HSO4− ions bound to the metal center, causing changes in the fluorescent spectra at different wavelengths, whereas F− ions displaced Cr3+, thereby switching ON the fluorescent spectra at the same wavelength.