An Imidazole-Naphthalimide-Based pH-Sensitive Molecular Probe for Selective Detection of Picric Acid and Cell Imaging

A new naphthalimide core containing molecular probe has been designed and synthesized. The photophysical properties of the probe in solvents of different polarities showed solvatochromic behavior. Probe displayed a weak aggregation-induced emission in THF–water (fw; 80%–90%) with a blue shift. Studies under a wide pH range (HEPES buffer) displayed significant fluorescence quenching under acidic medium. Probe showed “Off–On” behavior under acid and alkaline conditions. Probe upon interaction with different classes of ions and nitroaromatic compounds (NACs) displayed remarkable fluorescence quenching (switched-Off) with picric acid (PA) selectively in aqueous-THF (9:1, v/v) solution. Similarly, upon interaction with different biomolecules and anions, a probable complex of probe with picric acid (5.PA) showed enhanced emission with uric acid (UA) selectively. Interestingly, the quenched emission of 5.PA was rejuvenated upon interaction with UA and the OH– ion. Job’s plot analysis revealed a 1:2 binding stoichiometry between probe and PA with a binding constant of 2.26 × 108 M–2 and a limit of detection (LOD) of 1.19 × 10–7 M (119 nM). Also, the 5.PA could able to detect UA with an LOD of 3.05 × 10–7 (305 nM). The optical behavior of the probe was utilized to detect the PA and UA on test paper strips through color changes that are visible with the naked eye. Additionally, the cell imaging studies showed affinity of the probe for lysosomes as well as the ability to detect PA sensitively. The “On–Off” switching behavior of the probe upon providing sequential chemical inputs of PA and OH– ion mimics the “write–read–erase–read” functions and IMPLICATION logic gate.