A novel fluoride selective optical chemosensor based on internal charge transfer signaling

A new internal charge transfer probe, NAPH-1, synthesized by incorporating photoemitive naphthalimide core with an acidic imidazolium ring, offers highly selective colorimetric and ratiometric ‘off–on’ signaling for targeting F−, while Cl−, Br−, I−, HSO 4 - , SCN−, AcO−, and NO 3 - do not appreciably perturb the photophysical properties of the probe even at relatively higher concentrations than the F−. Deprotonation of the imidazolium ring, supported by the 1H NMR and theoritical studies, seems to cause the spectral modulations.