Turn-on detection of Al3+ and Zn2+ ions by a NSN donor probe: reversibility, logic gates and DFT calculations

Abstract

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 Al³⁺ and Zn²⁺ 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 Zn²⁺ (λ_em = 416 nm) and Al³⁺ (λ_em = 469 nm) ions due to the chelation-enhanced fluorescence (CHEF) effect. The limit of detection (LoD) values for Al³⁺ and Zn²⁺ have been determined to be 38.0 nM and 43.0 nM, respectively. The binding constants for Al³⁺ and Zn²⁺ were found to be 1.18 × 10⁶ M⁻¹ and 3.5 × 10⁵ M⁻¹, respectively. The NpSb also acted as a colorimetric sensor for Al³⁺ as the colour of the probe's solution turned to pale green from colourless upon Al³⁺ addition. The binding mechanism between NpSb and Zn²⁺/Al³⁺ 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 Al³⁺ ions in real samples such as tap water, distilled water and soil samples.