The Measurement of Circular Polarization in the Near-IR Luminescence from Chiral Complexes of Yb(III) and Nd(III)

This work describes the measurement and analysis of circular polarization in the luminescence (CPL), in the near-IR spectral region, from chiral complexes of Yb(III) and Nd(III) in solution. The experimental technique is based upon previous measurements of CPL in the visible region. Instrumentation design, performance, and calibration are discussed. The experimental technique has been applied to several related complexes of Yb(III) and Nd(III) with chiral macrocyclic ligands based on 1,4,7,10-tetraazacyclododecane that have approximate C₄, symmetry. In addition, CPL from D₃ complexes of Yb(III) with 2,6-pyridinedicarboxylate, which were prepared as a solution of enriched enantiomers by the addition of (+)-dimethyltartrate, is also presented. It is demonstrated that CPL from the ²F_5/2 → ²F_7/2 transition of Yb(III) at 980 nm is particularly suited for CPL studies because this transition satisfies magnetic-dipole selection rules. The luminescence from the ⁴F_3/2 → ⁴I_9/2 and ⁴F_3/2 → ⁴I_11/2 transitions of Nd(III) centered at 880 and 1060 nm, respectively, showed only weak CPL signals. The usefulness of these types of polarization measurements in the near-IR is discussed.