H. Lujan-upton et Y. Okamoto, Use of terbium(III) as a probe for the ion-binding properties of tactic polyacids and triacidic model compounds, J FLUORESC, 8(4), 1998, pp. 355-362
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.