A quinoline derived Schiff base as highly selective ‘turn-on’ probe for fluorogenic recognition of Al3+ ion

An efficient quinoline-derived Schiff base probe QnSb has been developed for fluorescence detection of metal ions. QnSb exhibits a highly selective OFF-ON type fluorescence response for Al3+ in aqueous-organic solvent system. The binding mechanism between QnSb and Al3+ was supported by ESI-MS, NMR and DFT studies. [Display omitted] •An efficient quinoline-derived Schiff base probe (QnSb) has been developed.•This probe displayed a fluorescent OFF-ON selective behaviour for Al3+ ions.•The limit of detection (LoD) for Al3+ was calculated to be 31.0 nM.•The binding mechanism has been established by 1H NMR, ESI-mass, and DFT analyses. A quinoline-derived Schiff base QnSb has been synthesized for fluorescent and colorimetric recognition of Al3+ ions in a semi-aqueous medium. The compound QnSb has been characterized by elemental analysis, FT-IR, 1H/13C 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 Al3+ by inducing a remarkable fluorescence enhancement at 422 nm when excited at 310 nm. The probe QnSb exhibited high selectivity for Al3+ in CH3CN/H2O (4:1, v/v) solution over several competing metal ions (e.g., Mg2+, Pb2+, Zn2+, Cd2+, Co2+, Cu2+, Ca2+, Ni2+, Fe3+/2+, Cr3+, Mn2+, Sn2+, and Hg2+). 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 Al3+ ions in drinking water. A 1:1 binding stoichiometry of complex QnSb-Al3+ 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 Al3+ could clearly be demonstrated on the filter paper test strips.