Circularly polarized luminescence of terbium (III) complexes in solution

Abstract

Circular dichroism (CD), total luminescence, and circularly polarized luminescence (CPL) spectra of Tb(III) : malic acid and Tb(III) : aspartic acid complexes are measured in aqueous solution at room temperature. The CD is measured in the spectral region corresponding to the Tb(III) 7F 6 → 5D 4 free-ion absorption, and the CPL spectra span the Tb(III) 5D 4 → 7F 6, 7F 5, 7F 4, and 7F 3 free-ion emissions. All solutions included in the study were at pH ≈ 8.5 and had ligand : Tb(III) concentration ratios of 5:1. Experiments were conducted using the d, ℓ, and racemic (d, ℓ) optical isomers of the ligands. Whereas the total luminescence spectra associated with the individual 5D 4 → 7F J transitions are unstructured or show, at most, two components, the CPL spectra are highly structured and demonstrate considerable splitting of the J levels by the low-symmetry ligand environment. Furthermore, CPL exhibits an extraordinary sensitivity to the chemical or stereochemical nature of the ligand environment as evidenced by the different sign patterns and splittings revealed in the CPL spectra of the malic acid and aspartic acid complexes.