Electrogenerated chemiluminescence. 58. Ligand-sensitized electrogenerated chemiluminescence in europium labels


The electrochemistry and electrogenerated chemiluminescence (ECL) of a series of europium chelates, cryptates, and mixed-ligand chelate/cryptand complexes were studied. The complexes were of the following general forms: EuL4- where L = β-diketonate, a bis-chelating ligand (such as dibenzoylmethide), added as salts (A)EuL4, where A = tetrabutylammonium ion or piperidinium ion (pipH+); Eu(crypt)3+, where crypt = a cryptand ligand, e.g., 4,7,13,16,21-pentaoxa-1,10-diazabicyclo[8,8,5]-tricosane; and Eu(crypt)(L)2+ for the mixed-ligand systems. ECL was obtained for the chelates and mixed-ligand systems by reducing the complexes at a Pt electrode in the presence of peroxydisulfate in acetonitrile solutions and was attributed to the electron-transfer reaction between the reduced bound ligands and SO4.-, followed by intramolecular excitation transfer from the excited ligand orbitals to the metal-centered 4f states. No ECL was observed under the same conditions for the europium complexes incorporating only the cryptand ligands in aqueous solution. The ECL spectra matched the photo-luminescence spectra with a narrow emission band observed at 612 nm, corresponding to a metal-centered 4f-4f transition. The ECL efficiencies for the ECL-active species were low, about 10-1-10-4% of that of the Ru-(bpy)32+/S2O82- system under similar conditions.

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Analytical Chemistry