Pyrene‐Functionalized Pyridinium Ionic Liquid Schiff Base as a Sensitive Fluorescent Probe for Picric Acid Detection and Real‐Sample Analysis
Ishan Chaturvedi, Roli MishraABSTRACT
The development of highly selective fluorescent probes for nitroaromatic explosives is of considerable importance for environmental monitoring and homeland security. Herein, a novel pyrene‐functionalized pyridinium ionic liquid Schiff base, [BPyP‐SB] [Br] , was synthesized through a simple two‐step strategy and fully characterized by FT‐IR, ^1H/^13C NMR, ESI‐MS, UV–vis, TGA, and DSC analyses. The probe exhibited strong blue fluorescence in DMSO (λ_em = 427 nm) with a quantum yield of 0.50 and showed efficient turn‐off fluorescence upon interaction with picric acid (PA). Fluorescence titration revealed a low detection limit of 4.07 × 10 − 5 M and a high binding constant of 4.55 × 10 5 M − 1 , while Job's plot confirmed a 1:2 binding stoichiometry. The sensor demonstrated excellent selectivity toward PA over other nitroaromatic compounds, metal ions, anions, and common oxidizing species, with stable fluorescence over a broad pH range (1–11). Density functional theory calculations revealed a HOMO–LUMO energy gap of 2.06 eV , supporting a synergistic quenching mechanism involving photoinduced electron transfer (PET) and Förster resonance energy transfer (FRET). Furthermore, [BPyP‐SB] [Br] ‐coated paper strips enabled rapid visual detection of PA, while recovery studies in spiked environmental water samples (93%–101%) confirmed its practical applicability for portable and reliable on‐site detection.