Effect of ligand structure on synergism in Tb 3+-aromatic acid complexes: fluorescence lifetime studies

Abstract

The fluorescence of Tb 3+ sensitized by aromatic carboxylic acid ligands (benzoic, monomethylphthalic, monomethylterephthalic, trimesic, terephthalic, isophthalic, phthalic and mellitic acids) and the synergism displayed by these complexes when treated with TOPO/Triton X-100 have been studied by measuring lifetimes of Tb 3+ emission. The lifetime of Tb 3+ fluorescence was not significantly altered following complex formation with aromatic carboxylic acids, even though a significant enhancement in the Tb 3+ fluorescence intensity was observed in every single case. However, when these Tb 3+-aromatic acid complexes were treated with TOPO/Triton X-100, the lifetimes of the Tb 3+ fluorescence increased markedly, but only with certain acids. Interestingly, even amongst the acids that showed an increase in lifetime with TOPO/Triton X-100, the lifetimes as a function of the pH of the solution was strongly dependent on the structure of the ligand. These differences and the reasons for such behavior are discussed, which shed light on the role of the structure of the ligand on the synergism process.