Spectroscopic characterization of 1,10-phenanthroline-2,9- dicarboxylic acid and its complexes with europium (III): Luminescent europium chelates useful for analytical applications in aqueous solution

Abstract The absorption and fluorescence emission of the chelating agent 1,10-phenanthroline-2,9-dicarboxylic acid (PDA) and its complexes with Eu3+ have been measured in aqueous solution as a function of pH and concentration. Complexes have been observed of both 1:1 and 1:2 stoichiometry in Eu:PDA. Observations of the emission in other solvents and at 77 K are also reported. The coordination geometry and symmetry of the complexes are estimated based on analysis of the Eu3+ emission intensities and splittings, and on lifetime measurements in H2O/D2 O mixtures which permit estimation of the number of coordinated water molecules. The formation constant and the fluorescence quantum yield for the 5D0 to 7F2 transition have been determined for the 1:1 complex as (4.4±1.6)×108 M-1 and 0.016 respectively. These relatively high values for a europium chelate in aqueous solution make PDA a suitable europium chelator for aqueous analytical studies using luminescence techniques.

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