Although widely used in bioassays, the spectrofluorimetric method described here uses the antenna effect as a tool to probe the thermodynamic parameters of ligands that sensitize lanthanide luminescence. The Eu3+ coordination chemistry, solution thermodynamic stability, and photophysical properties of the spermine-based hydroxypyridonate octadentate chelator 3,4,3-LI(1,2-HOPO) are reported. The complex [Eu-III(3,4,3-LI(1,2-HOPO))](-) luminesces with a long lifetime (805 mu s) and a quantum yield of 7.0% in aqueous solution, at pH 7.4. These remarkable optical properties were exploited to determine the high (and proton-independent) stability of the complex (log beta(110) = 20.2(2)) and to define the influence of the ligand scaffold on the stability and photophysical properties.