Insights into the Structure–Chiroptical Property in Families of Chiral Binuclear Lanthanide Clusters with Circularly Polarized Luminescence

Abstract

The luminescence quantum yield (Φ_lum) and dissymmetry factor (g_lum) are two critical parameters for evaluating the performance of circularly polarized luminescence (CPL) materials. In this work, three pairs of chiral lanthanide clusters R-/S-Eu₂-pH, R-/S-Eu₂-BH, and R-/S-Eu₂-B exhibiting CPL properties were synthesized using R-/S-HL (R-HL = R-(−)-2-phenylpropionic acid, S-HL = S-(+)-2-phenylpropionic acid) as the chiral ligand. Intermolecular interactions within these compounds were fine-tuned by varying the types and coordination numbers of auxiliary ligands (phen = 1,10-phenanthroline, Hfac = hexafluoroacetylacetone, and Bphen = bathophenanthroline). As a result, the three pairs of compounds exhibited slightly different Φ_lum values ((93.7 ± 0.8)% for R-/S-Eu₂-pH, (83.8 ± 0.8)% for R-/S-Eu₂-BH, and (87.5 ± 0.7)% for R-/S-Eu₂-B). These variations are attributed to the difference in intermolecular interactions with both π–π and H−π stacking observed in R-/S-Eu₂-pH, weak π–π stacking in R-/S-Eu₂-BH, and moderate H−π stacking in R-/S-Eu₂-B. Additionally, g_lum can be effectively controlled by modulating the chiral environment and the symmetry of the geometric coordination configuration of the Ln³⁺ ions. Among the three pairs of compounds, R-/S-Eu₂-B displayed the largest g_lum values (−0.025/0.022), owing to the presence of more chiral ligands coordinated and a lower symmetry in the Eu³⁺ coordination environment, compared to R-/S-Eu₂-pH (−0.0042/0.0043) and R-/S-Eu₂-BH (−0.0058/0.0042). Consequently, R-/S-Eu₂-B achieves improvement of g_lum while maintaining a high Φ_lum value. Additionally, R-/S-Eu₂-B showed excellent detection capability of DCN in pesticide optical recognition, with a detection limit as low as 0.37 μM. This study not only elucidates the regulatory effects of intermolecular interactions and chiral environments on the CPL performance of chiral lanthanide clusters but also provides new insights into their potential application in environmental detection.