A Novel Naphthylidene-diimine Chemosensor for Selective Colorimetric and Fluorometric Detection of Al³⁺ and CN^- Ions

A naphthylidene-diimine L² was newly designed, and its structure was identified by elemental analysis and spectroscopic methods. The effect of temperature, acid-base and light on enol-keto tautomerism in this Schiff base was evaluated by colorimetry, UV-Vis and fluorescence spectroscopy. Under irradiation 365 nm, L² emitted yellow, orange and strong green emission in pure, basic and aqueous DMSO media (v/v, 1/1), respectively. Its ionochromic behavior against various cations (Fe³⁺, Al³⁺, Cr³⁺, Cu²⁺, Co²⁺, Ni²⁺, Zn²⁺, Cd²⁺, Pb²⁺, Ba²⁺ and Ag⁺) and anions (F^-, Cl^-, CH₃COO^-, SO₃^2-, S₂O₃^2-, HSO₄^-, H₂PO₄^-, NO₃^-, CN^-, and OH^-) was investigated in aqueous DMSO media (v/v, 1/1) by UV-Vis and fluorescence experiments. Dark yellow color of L² changed to colorless for Fe³⁺, Cr³⁺ and HSO₄^- ions, and turned to light yellow for Al³⁺ and Cu²⁺ ions, and to orange for CN^- and OH^- ions. According to UV-Vis data, the chemosensor displayed selective recognition towards Fe³⁺, Al³⁺, Cu²⁺, HSO₄^-, CN^- and OH^- with a 1:1 stoichiometric ratio. At the excitation wavelength of 365 nm, L² gave strong yellowish white emission (λ_em = 445 and 539 nm) in the presence of Al³⁺, and the intensity increased about 12.5 times. On the other hand, the chemosensor displayed one emission band at 452 nm and 450 nm in the presence of CN^- and OH^- with 1.9 fold and 2.3 fold fluorescence enhancement, respectively.