Design and performance optimization of circularly polarized luminescent materials based on lanthanide helicates

Chiral lanthanide complexes, due to their high luminescence dissymmetry factor (g_lum) and luminescent quantum yield, have become highly promising materials for circularly polarized luminescence (CPL). Herein, we report two novel pairs of lanthanide chiral complexes, which exhibit both a high g_lum and high luminescence quantum efficiency. Photophysical and chiroptical investigations revealed that both (NEt₄)₂[Eu₂(L₁^S)₄] and (NEt₄)₂[Eu₂(L₂^S)₄] displayed intense CPL. Their g_lum values for ⁵D₀ → ⁷F₁ transition reach + 1.34 and + 1.14, respectively, exhibiting high luminescence quantum yields of 37.43% and 30.30% for ⁵D₀ → ⁷F_J transitions (J = 0 - 4). Through the analysis of the photophysical properties and X-ray single-crystal structures of (NEt₄)₂[Eu₂(L₁^S)₄] and (NEt₄)₂[Eu₂(L₂^S)₄], it was found that the modification of the ligand significantly affected the twist angle α of the coordination polyhedron, revealing the direct cause for achieving a high g_lum. This study provides a new design concept for the development of other lanthanide-based CPL materials with high g_lum values and high luminescence quantum yields.