Water-soluble polyaromatic-based imidazolium for detecting picric acid: Pyrene vs. anthracene

Highly water-soluble fluorescent polyaromatic-based imidazolium compounds capable of detecting a wide-range of nitroaromatics, e.g., nitrophenols and picric acid in aqueous solution with fully quenched fluorescence are reported. The two probes contained an anthracene and pyrene group with the increased size and angularity of the pyrene ring in pyrene-based imidazolium (PIM) raising the hydrophobicity or π-π stacking and sensitivity of the probe towards all mono-, di-, and trinitrophenols even under harsh conditions (pH 4-8). The high affinity for nitrophenols was confirmed by single crystal X-ray crystallography. Time-dependent density functional theory (TD-DFT) reveals cation-anion interactions between the imidazolium and picrate ions causing fluorescent quenching through PET and charge transfer involving a dark S₁ excited state.