Colorimetric and ratiometric fluorescent chemosensor for fluoride ions based on phenanthroimidazole (PI): spectroscopic, NMR and density functional studies

The anion chemosensor based on the phenanthroimidazole conjugate of biscarbanohyrazone, probe PI was designed, synthesized and characterized. Probe PI detected fluoride ions selectively with unique absorption as well as fluorescence changes which were not observable for other halides & anions. H-1 NMR and density functional studies on the system have been carried out to determine the nature of the interaction between probe PI and F- responsible for the significant fluoride-induced changes in the absorption and emission properties of probe PI. The experimental results reveal that hydrogen-bonding followed by abstraction of acidic protons of imidazole -NH and urea -NH of probe PI by the fluoride ion, leading to the formation of anionic species, is responsible for the spectral changes. Finally, the use of a test strip of the probe PI to detect fluoride was also reported.