Pyridinium‐Based Schiff‐Base Fluorescent Chemosensor for Sequential Detection of Al³⁺ Ions and TNP: Applications in Cell Imaging and Latent Fingerprint Visualization.

A fluorescent pyridinium‐based chemosensor (E)‐1‐(2‐(3‐hydroxy‐4‐((pyridin‐2‐ylimino) methyl) phenoxy) ethyl) pyridin‐1‐ium bromide (BzPySB) was synthesized and characterized using various spectroscopic techniques. The chemosensing potential of BzPySB was explored using UV‐vis and fluorescence spectroscopy in the aqueous medium. The turn‐on fluorescence behavior was observed for BzPySB in the presence of Al3+, while other metal ions were non‐responsive. The B–H and Job's plot confirmed the 1:1 stoichiometric ratio of the BzPySB and Al3+. The in situ generated complex BzPySB‐Al3+ offered selectivity toward TNP via fluorescence turn‐off phenomena with high Ksv and LOD values. The “off‐on‐off” sensing mechanism was elucidated through 1H NMR, mass spectrometry, and DFT calculations. The probe also detected Al3+ in plant and MCF‐7 cells, highlighting its potential in biological systems. Moreover, BzPySB exhibited solid‐state luminescent properties credited to weak π‐π interaction, leading to its successful application in the visualization of latent fingerprints.