Comparative study on fluorescence enhancement and quenching of europium and terbium chelate anions in cationic micelles.

Fluorescence enhancement and quenching of water soluble chelates of terbium (Tb3+) with Tiron, salicylic acid (SA), 4-sulfonyl salicylic acid (SSA) and acetylacetone (AA) and sparingly soluble chelates of europium (Eu3+) with beta-diketones were comparatively examined in the presence of cetyltrimethyl ammonium bromide (CTMAB) and cetylpyridinium chloride (CPC). By the composition of the complexes, surface tension measurements and spectral analysis, the binding mode of chelate anions to the micellar surface of cationic surfactants was discussed in terms of ion-exchange model. Quenching effect of CPC on the fluorescence of association complexes seems to arise from the charge transfer from a fluorescent ligand to pyridinium cation. In the case of the chelates of Eu3+ with beta-diketones, however, pyridinium ion is only capable of overlapping the aromatic ring of beta-diketones to less extent since the poorly soluble charged chelates have a weak affinity for the highly polar surface of pyridinium cationic micelles. Efficient charge transfer between the excited aromatic beta-diketone and pyridinium cation fails to be established. CPC also shows enhanced effect on fluorescence like CTMAB.