A new lawsone azo-dye for optical sensing of Fe<sup>3+</sup> and Cu<sup>2+</sup> and their DFT study

<p>A new lawsone-based azo-dye 2-hydroxy-3-((pyridin-2-ylmethyl)diazenyl)naphthalene-1,4-dione (<b>1</b>) was synthesized and applied for sensing of metal ions. Receptor <b>1</b> showed selective fluorescent and colorimetric response for the detection of Cu<sup>2+</sup> and Fe<sup>3+</sup> over other tested metal ions. The fluorescence intensity of <b>1</b> was significantly quenched allowing detection of Fe<sup>3+</sup> and Cu<sup>2+</sup> down to 0.61 and 6.06 μM, respectively. The binding has been established by fluorescence spectroscopic method. Receptor <b>1</b> provided a 1 : 1 binding scaffold for recognition of Fe<sup>3+</sup> and Cu<sup>2+</sup> ions with the association constant of 3.33 × 10<sup>6</sup> and 3.33 × 10<sup>5</sup> M<sup>−1</sup>, respectively. The B3LYP/6-31G/LANL2DZ method was employed for the optimization of <b>1</b> and <b>1</b>·Fe<sup>3+</sup> and <b>1</b>·Cu<sup>2+</sup>.</p>