Diketopyrrolopyrrole-based chemosensors for selective recognition of fluoride ions

A series of diketopyrrolopyrrole (DPP) derivatives DPPPHs based on phenylhydrazone group were designed and synthesized. The presence of nitro moiety at ortho-position of phenylhydrazone in o-NO₂-DPPPH and o,p-di-NO₂-DPPPH significantly altered the electronic properties through intramolecular hydrogen bonding. Among these receptors, p-NO₂-DPPPH showed excellent selectivity toward fluoride anions in both UV-vis and fluorescence channels in DMSO solution. Experimental results, ¹H NMR and ¹⁹F NMR revealed that the formation of anionic species from deprotonation of the hydrazone N-H moiety by fluoride ion was responsible for the spectral changes. Density function theory calculations were conducted to rationalize the optical response of sensors. Especially, the spectral responses of sensors could be switched back and forth alternatively by adding F^- and HSO4- anions in DMSO solution.