Chiral sensing using an achiral europium(III) complex by induced circularly polarized luminescence

Eu(bda)(2)](-) (bda = 2,2'-bipyridine-6,6'-dicarboxylic acid) produces intense circularly polarized luminescence (CPL) in aqueous solutions in the presence of (S)-2-pyrrolidone-5-carboxylic acid upon UV irradiation, although the molecular structure of the europium(III) complex is achiral. The mechanism for the induction of CPL was preliminarily attributed to distortions induced by association with an amino acid to generate chirality in the achiral complex. The optical anisotropy factor (g(lum) value) for the (5)D(0) → (7)F(1) transition was 0.03 in the presence of 1.0 mol dm(-3) of the amino acid. Analysis of the CPL intensity as a function of the amino acid concentration gave an association constant between those of Eu(bda)(2)](-) and the amino acid, K(aso) = 0.55 ± 0.09 mol(-1) dm(3). These results demonstrate the potential of Eu(bda)(2)](-) to act as a luminescent chiral-sensing reagent in microscopic spectroscopy.