D ₂ -Symmetrical Cu ₈ S ₄ Clusters Supported by Chiral Carbenes Exhibiting Circularly Polarized Luminescence

Circularly polarized luminescence (CPL) holds transformative potential for quantum communication and displays, yet the structural design rules for maximizing chiroptical performance remain elusive. While high molecular symmetry often drives superior CPL in lanthanide systems, its role in copper-based architectures is largely underexplored. Herein, we report enantiopure D2-symmetric Cu8S4 clusters supported by chiral menthol-derived cyclic (alkyl)(amino)carbene (D/L-MenthCAAC) ligands to investigate how molecular symmetry influences chiroptical performance. Single crystal X-ray diffraction confirmed the retention of the Cu8S4 core, but with systematic structural distortions relative to the achiral CyCAAC analogue including elongated outer Cu–Cu distances, widened Cu–S–Cu angles, and flattened Cu3(μ3-S) tetrahedra. Despite these distortions, the cluster’s photophysical properties remain largely unchanged, displaying broad emission at 569 nm and a quantum yield of 5.1%. Crucially, CPL was detected with a dissymmetry factor (glum) of 0.8 × 10–3 and CPL brightness (BCPL) of 0.13 M–1 cm–1. This work demonstrates that polarization can be imparted to copper cluster luminescence. Furthermore, the synthetic accessibility of chiral CAAC ligands provides a versatile entry point for future systematic studies targeting higher-symmetry architectures to potentially improve CPL metrics in copper-based emitters.