A quinoline derived Schiff base as highly selective 'turn-on' probe for fluorogenic recognition of Al ion.

A quinoline-derived Schiff base QnSb has been synthesized for fluorescent and colorimetric recognition of Al ions in a semi-aqueous medium. The compound QnSb has been characterized by elemental analysis, FT-IR, H/C NMR, UV-Vis and fluorescence spectral techniques. The crystal structure of the QnSb was confirmed by single crystal X-ray diffraction (SC-XRD) analysis. Notably, almost non-fluorescent QnSb served as a 'turn on' responsive probe for Al by inducing a remarkable fluorescence enhancement at 422 nm when excited at 310 nm. The probe QnSb exhibited high selectivity for Al in CHCN/HO (4:1, v/v) solution over several competing metal ions (e.g., Mg, Pb, Zn, Cd, Co, Cu, Ca, Ni, Fe, Cr, Mn, Sn, and Hg). The limit of detection (LoD) was computed as low as 15.8 nM which is significantly lower than the permissible limit set by WHO for Al ions in drinking water. A 1:1 binding stoichiometry of complex QnSb-Al was established with the help of Job's plot, ESI-MS, NMR and DFT analyses. Based on its remarkable sensing ability, the probe QnSb was utilized to establish molecular logic gates, and the fluorescence detection of Al could clearly be demonstrated on the filter paper test strips.