Intermolecular energy transfer between lanthanide complexes in aqueous solution

Intermolecular energy transfer from Tb3+ to Eu3+, and emission intensity and lifetime measurements were used to study the bonding between Tb3+ ions and malic acid. This description was aided by references to published potentiometric titration data, and to circular dichroism and circularly polarized emission spectra. Below a pH of 7 the complexes are largely monomeric and ligand chirality is only weakly transmitted to the metal. The ligands bind much more effectively to the metal when the pH is raised from 7 to 10, and polymeric association of the complexes becomes important. At high pH the complexes become extensively associated and the energy transfer is characterized by stereoselective effects. Energy is transferred more effectively among complexes containing resolved ligands than among complexes prepared from racemic ligands in this high pH region. (author)