EXCITATION and DE‐EXCITATION PROCESSES IN LANTHANIDE CHELATES BEARING AROMATIC SIDECHAINS

Chelating agents comprised of an ethylenediaminetetraacetate group covalently attached to an aromatic sidechain (indole, benzyl, p ‐methoxybenzyl, or p ‐cyanobenzyl) have been used to investigate interactions between each sidechain and a lanthanide ion chelated by the ethylenediaminetetraacetate group. Lanthanum, samarium, europium, gadolinium, terbium, dysprosium, and ytterbium were studied. Results from measurements of fluorescence, phosphorescence, and lanthanide luminescence indicate the importance of electron transfer, as well as energy transfer, processes in these chelates. Because of the structure of the chelates studied, the sidechains and bound metals do not interact strongly enough to perturb their energy levels; however, large effects on quantum yields, including quenching or enhancement of aromatic phosphorescence, quenching or enhancement of lanthanide luminescence, and quenching of aromatic fluorescence are observed. Applications to studies of proteins are discussed.