Use of terbium(III) as a probe for the ion-binding properties of tactic polyacids and triacidic model compounds

The binding properties of Tb(III) ions in configurationally different envir onments were investigated using luminescence intensity and lifetime measure ments. The emission intensity of TD(III) (D-5(4)- F-7(5) transition) is dir ectly dependent upon the number of coordinated water molecules (quenchers) bound in the inner coordination sphere. The more efficiently a ligand coord inates to To(III) ion, the more water molecules are expelled from the coord ination sphere, thereby enhancing the luminescence intensity and lifetime o f the ion. Isotactic and syndiotactic poly(methacrylic acids) (PMAs) were n eutralized and complexed with Tb(III) ions in aqueous solutions. The lumine scence intensities and lifetimes were monitored with lambda(exc) = 265, the hypersensitive excitation band at 286 and 370 nm. The isotactic PMA/Tb(III ) complex exhibited a six times greater luminescence intensity than the syn diotactic PMA complex. Lifetime measurements showed 2.4 water molecules coo rdinated to Tb(III) ion in the isotactic PMA complex, while 3.4 water molec ules were found to remain in the syndiotactic complex. Similar studies were also conducted on small organic model compounds such as Kemp's triacid and its configurational isomer. These data supported the polymeric results whe re the isotactic model, Kemp's triacid, exhibited a higher luminescence int ensity and a longer lifetime than the Kemp's isomer. Lifetime results showe d the Kemp's molecule retained approximately 2.7 water molecules, compared to four water molecules for the isomer. The validity of using the Kemp's mo lecules as polymeric models is also discussed.