Fluoride recognition by a chiral urea receptor linked to a phthalimide chromophore.

The anion chemosensor 1 based on a urea-activated phthalimide with a stereogenic centre was synthesized using an efficient procedure involving a Curtius rearrangement. Its photophysical properties were estimated in several solvents. Sensor 1 detected fluoride with absorption as well as fluorescence changes and was only observable for this case and not for other halides. The appearance of a new CT complex emission at a longer wavelength and no changes in the singlet lifetime of 1 in the presence of fluoride supported a fluorescence static quenching mechanism. 1H-NMR studies, together with theoretical calculations based on DFT methods at the B3lYP/6-31G* level of theory confirmed the formation of a [1-F]- complex through H-bonding interactions rather than receptor deprotonation in the recognition process. Reversibility of this process was observed upon addition of a protic solvent.