A fluorescent colorimetric vanillin di-Schiff base chemosensor for detection of Cu(ii) and isolation of trinuclear Cu(ii)–dihydrazide

Abstract

In this work, we developed a simple fluorescent colorimetric chemosensor H₂L [6,6′-((1,1′)-hydrazine-1,2-diylidene bis(methanylylidene)) bis(2-(6-methoxy)) phenol] for rapid detection of Cu²⁺ in aqueous solution. The method for synthesis of H₂L is very simple and environment friendly. This organic Schiff base probe was characterized by ¹H-NMR, FT-IR and ESI-MS spectroscopy along with single-crystal XRD analysis. It exhibited binding-induced colour change with Cu²⁺ion from colourless to intense yellow and fluorescence enhancement. The LOD values of H₂L towards Cu²⁺ were calculated to be 7.1 × 10⁻⁸ M (colorimetrically) and 3.8 × 10⁻⁸ M (fluorometrically). The interactions between H₂L and Cu²⁺ were studied by Job's plot, ESI-MS, FT-IR spectroscopy and DFT calculations. The crystal structure of the L–Cu²⁺ adduct was also determined by single-crystal X-ray analysis, and it was found that two molecules of L coordinate with three molecules of Cu²⁺ ions. The receptor H₂L could operate in a wide pH range and can be successfully applied for detection and quantification of Cu²⁺ ions in environmental samples and logic applications.