APTA: A simple ligand for lanthanide energy transfer luminescence in aqueous solution

Amino-phenol triacetic acid (apta) has been evaluated as a potential sensitizing ligand for energy transfer luminescence to lanthanide ions in aqueous media at pH 7.2. Photophysical data including quantum yields (Phi) excitation wavelength ( 265 nm), emission wavelength ( 544 nm) and excited state lifetimes (tau(water) = 0.83 ms) for the 1: 1 complex are reported. The number of water molecules coordinated to the metal ion has been calculated using isotopic experiments and these data were compared with the octadentate ligand bis-amino-phenol tetraacetic acid (bapta). Apta demonstrates excellent discrimination between Tb3+ and Eu3+ ions and apta is the simplest ligand reported thus far capable of functioning as an electronic energy transfer sensitizing moiety.