Turn-on detection of Al 3+ and Zn 2+ ions by a NSN donor probe: reversibility, logic gates and DFT calculations.

An efficient dual functional naphthalene-derived Schiff base NpSb probe has been synthesised and evaluated for its fluorescence and chromogenic response towards metal ions. The NpSb probe was capable of selectively recognising Al 3+ and Zn 2+ ions when they were excited at the same wavelength in an aqueous organic solvent system. Almost non-fluorescent NpSb displayed a 'turn-on' fluorescence response when treated with Zn 2+ ( λ em = 416 nm) and Al 3+ ( λ em = 469 nm) ions due to the chelation-enhanced fluorescence (CHEF) effect. The limit of detection (LoD) values for Al 3+ and Zn 2+ have been determined to be 38.0 nM and 43.0 nM, respectively. The binding constants for Al 3+ and Zn 2+ were found to be 1.18 × 10 6 M -1 and 3.5 × 10 5 M -1 , respectively. The NpSb also acted as a colorimetric sensor for Al 3+ as the colour of the probe's solution turned to pale green from colourless upon Al 3+ addition. The binding mechanism between NpSb and Zn 2+ /Al 3+ was supported by the ESI-MS, Job's plot, NMR, and DFT studies. The reversibility experiments were carried out with an F - ion and EDTA with the development of corresponding logic gates. Moreover, NpSb could be applied to detect Al 3+ ions in real samples such as tap water, distilled water and soil samples.