Ratiometric fluorescent chemosensor for fluoride ion based on inhibition of excited state intramolecular proton transfer.

ESIPT based benzimidazole derivative has been synthesized and investigated their photophysical behavior towards various anions. The probe 2 has been used for selective estimation of F(-) ions as compared to other anions and signaled the binding event through formation of new absorption band at 360nm and emission band at 420nm. The probe 2 showed fluorescence behavior towards fluoride ions through hydrogen bonding interactions and restricted the ESIPT emission at 540nm from OH to nitrogen of benzimidazole moiety to release its enol emission at 420nm.