CALIX[4]ARENE-TRIACIDS AS RECEPTORS FOR LANTHANIDES - SYNTHESIS AND LUMINESCENCE OF NEUTRAL EU3+ AND TB3+ COMPLEXES

Calix[4] arene triacids (3a-d) have been prepared that are able to for m neutral complexes with lanthanides. Complexes of 3a-d with Eu3+ and Tb3+ have been studied with respect to their luminescent properties in a protic solvent (methanol). In all cases it was found that the lumin escent lifetime of the complexed lanthanide ions is significantly enha nced compared with that of the free ions in the same solvent. Solvent deuterium isotope effects confirm that shielding of the lanthanide ion from the solvent in the calixarene complexes is the main mechanism re sponsible-for the lifetime difference between free and complexed ions, however, the calixarene itself also exerts a moderate lifetime-shorte ning effect. Excitation spectra show that in the complexes efficient e nergy transfer to the lanthanide ions occurs both from the calixarene aromatic moieties as well as from aromatic (pyridine) chromophores att ached to it.