Fluorescence lifetime of terbium(III) as a probe for the ion-binding properties of tactic poly(methacrylic acids)

The binding properties of trivalent metal ions to polyelectrolytes were investigated through the use of terbium [Tb(III)] in fluorescence studies. The fluorescence intensity and lifetimes of the lanthanide ions are directly dependent upon the number of water molecules bound to their inner coordination sphere. The more efficiently a ligand coordinates to a lanthanide ion, the more water molecules are expelled and consequently, the greater the fluorescence intensity and lifetime. This effect was used to probe for differences in the complexation behavior of tactic polymers. Aqueous solutions of isotactic and syndiotactic poly(methacrylic acid) (PMA) were neutralized and complexed with Tb(III) ions. The fluorescence intensity of the 286 nm hypersensitive excitation band was monitored and the lifetimes were measured using several excitation wavelengths. It was found that the isotactic PMA/Tb(III) complex exhibited a six times greater fluorescence intensity than the syndiotactic PMA complex. Lifetime measurements gave the number of water molecules coordinated by Tb(III) in the isotactic complex to be 2.4 while 3.4 waters remained bound to the Tb(III) ion in the syndiotactic PMA complex. These results indicate that isotactic PMA has the greater binding affinity towards Tb(III) ions. (C) 1997 John Wiley & Sons, Inc.