A highly selective and sensitive fluorescent chemosensor for distinguishing cadmium(II) from zinc(II) based on amide tautomerization
A naphthalimide-derived fluorescent sensor termed L2 was designed and synthesized. This sensor showed a highly selective, sensitive, and reversible turn-on response to Cd2+ over other metal ions in a wide pH range with a detection limit of 2.35 × 10−10 M. The amide/di-2-picolylamine receptor binds Cd2+ in the imidic acid tautomeric form but other metal ions in the amide tautomeric form. Moreover, the sensor can be used to distinguish Cd2+ and Zn2+ with the naked eye. The Cd2+-binding mode and the recognition mechanism of the sensor were investigated using Job's plot, 1H NMR, HRMS, IR and DFT calculations. Furthermore, the sensor was successfully applied as the active component of indicator papers for on-site detection of Cd2+ in pure water and in fluorescence imaging of Cd2+ in HeLa cells.