A zwitterionic probe for ratiometric fluorescent detection of aluminium(III) ion in aqueous medium and its...

In the present study, we have synthesized an aminobenzoic acid containing Schiff base (compound 1) and its structure was confirmed through single crystal X-ray study. Importantly, the compound 1 crystallizes in the zwitterionic form, with an anionic carboxylate group (-COO^-) and a cationic iminium group (-C = NH⁺-). The compound 1 is highly soluble in water due to its zwitterionic feature in the solid state. Interestingly, compound 1 acts as a ratiometric fluorescent probe for the selective detection of Al³⁺ ion in aqueous solution without organic cosolvent. It can also detect Al³⁺ ion by visual colour change to bluish-green fluorescence under 365 nm UV light. The association constant between compound 1 with Al³⁺ ion was estimated to be 1.67 × 10⁴ M^-1. The lowest detection limit for Al³⁺ ion was calculated to be 7.05 × 10^-8 M in water. Compound 1 in combination with Al³⁺ ion demonstrated fluorescent imaging potential of the nucleus of in RAW 264.7 murine macrophage cell line. In addition, the sensing model is developed as paper based sensor ''Test Kit' 'for its practical applicability.