Solid-state fluorescence sensing of amine vapours by an anthracene-based Zn(ii) complex, its phosphatase activity and theoretical calculations

Abstract

Here we have synthesized a novel mononuclear Zn(II) complex, [ZnLCl₂], of an anthracene-based ligand (N¹-(anthracen-9-ylmethyl)-N²,N²-dimethylethane-1,2-diamine). The characterization of the complex was done by UV-vis, IR, and NMR spectroscopy and ESI-MS. We have also performed X-ray crystallography of the complex to confirm its actual structure. X-ray crystal structure analysis shows that the molecular unit is mononuclear and the Zn(II) centre is tetra-coordinated with two N-donors of the ligand and two chlorine atoms, obtaining a distorted tetrahedral geometry. Phosphatase-like activity of the complex was studied spectrophotometrically using 4-nitrophenylphosphate (PNPP) as the substrate and the investigation shows that the complex efficiently catalyses phosphate ester hydrolysis. A kinetic study of PNPP hydrolysis was performed by the initial rate method at 25 °C, which yielded the k_cat value as 4.78 × 10² h⁻¹. Therefore, we can conclude that the complex is a good catalyst for phosphate ester hydrolysis. Also, the complex in the solid state can act as a potential fluorescent sensor for detecting volatile amines. When the solid complex was exposed to vapours from different amines it was found to quench the fluorescence of the complex, and the extent of quenching is dependent on the nature of the amines. From the photoluminescence study we have compared the quenching ability of different amines at a fixed temperature.