A comparison of sensitized Ln(iii) emission using pyridine- and pyrazine-2,6-dicarboxylates

Abstract

The synthesis, X-ray structure, solution stability, and photophysical properties of Eu(III) complexes with pyrazine-2,6-dicarboxylic acid (H₂PYZ) are reported, and compared to structurally analogous complexes with pyridine-2,6-dicarboxylic acid (H₂DPA). The [Eu(PYZ)₃]³⁻ complex demonstrates highly efficient metal-centered Eu(III) luminescence in the solid state (Φ_total ∼ 60.9%). In aqueous solution, moderate stability is retained at pH 7.4 (pEu ∼ 10.5), although hydrolysis of the complex anion becomes competitive below mM concentrations, and the observed luminescence intensity from the Eu(III) metal ion is reduced as a result. A complete evaluation of the thermodynamic solution stability has allowed the observed differences in the solution behaviour luminescence properties of these complexes to be rationalized. An analysis of their luminescence behaviour in the solid state has also allowed a direct comparison of the sensitisation behaviour for these isostructural compounds.