Evaluation of circularly polarized luminescence in a chiral lanthanide ensemble

This work demonstrates a methodology for the evaluation of circularly polarized luminescence of a chiral europium(III)) (Eu-III) complex species in an ensemble system. The chiral Eu-III complex species consists of chiral bis(oxazolinyl)pyridine [(R)- or (S)-iPr-Pybox] and beta-diketonate ligands with a pendant nitro group (DK-NO2). The pendant NO2 group in [iPr-Pybox](Eu-III)(DK-NO2)(3) (monometallic Eu-III species) coordinates to the Eu-III center of another Eu-III complex, giving rise to the generation of a chiral Eu-III ensemble consisting of mono-, di-, and the other oligomeric Eu-III species, {[iPr-Pybox](Eu-III)(DK-NO2)(3)}(n). The luminescence dissymmetry factors (g(lum)) of the chiral Eu-III ensemble have been successfully determined by using a commercially available fluorescence spectrophotometer attached with a rotatable lambda/4 filter and a fixed linearly polarized plate. This study suggests that the chiral Eu-III ensemble in solution displays a large circularly polarized luminescence (vertical bar g(lum vertical bar) = 0.19) as compared to that of a reference monometallic complex [iPr-Pybox](Eu-III)(DK-CN)(3) (vertical bar glum vertical bar = 0.11-13). The larger glum is primarily attributed to the contribution of the dimetallic Eu-III species exhibiting a high degree of circular polarization in luminescence (g(lum2) = 0.27) in the ensemble. Conversely, a large linearly polarized component was observed in luminescence from the chiral Eu-III ensemble in the solid state (KBr pellet).