9-Anthracenecarboxamide fluorescent probes for selective discrimination of picric acid from mono- and di-nitrophenols in ethanol

A new class of 'switch off' anthracenecarboxamide-based sensing probes (1-3) for the detection of picric acid (PA) was designed and synthesized. Probe 1 exhibited the highest sensitivity and selectivity toward PA, enabling complete fluorescence quenching and exhibiting a high association constant (4.14 × 10⁵ M^-1) with a 1:1 stoichiometric ratio of 1 to PA in EtOH. Probe 1 was able to detect PA through multiple synergic interactions such as hydrogen bonding, π-π interactions between the electron-rich aromatic rings of anthracene and the electron-deficient aromatic ring of PA that resulted in a favorable fluorescence resonance energy transfer from the latter to the former. The ability of probe 1 to sense PA was investigated by UV-visible, fluorescence, and ¹H NMR spectroscopies, as well as DFT calculations.