Pyrazolo[3,4- b ]quinolinone fluorophore for selective detection of picric acid via fluorescence quenching

In the present study, pyrazolo[3,4-b]quinolinone-based fluorophore, DAPQ, bearing a chalcone with an electron-donating N,N-dimethylamino (NMe2) group has been synthesized and employed as a selective fluorescent chemosensor for nitroaromatic explosives. The molecular structure of DAPQ has been confirmed using NMR, FT-IR, and ESI-HRMS . DAPQ exhibited intense yellow fluorescence, attributed to intramolecular charge transfer facilitated by the strong donor NMe2 group. Among the various nitroaromatic analytes, the probe demonstrated remarkable selectivity toward picric acid, through fluorescence quenching. The limit of detection for picric acid was found to be 2 µM, demonstrating high sensitivity. Further mechanistic insights have been obtained through NMR titration, and density functional theory calculations, which revealed that hydrogen-bonding interactions, along with charge-transfer processes, play a key role in the fluorescence quenching mechanism.