Chiral Manganese Halide Co‐Crystals: A New Avenue for Efficient Circularly Polarized Luminescence

Chiral metal halides have emerged as promising candidates for circularly polarized luminescence (CPL) due to their structural versatility and exceptional optoelectronic properties. However, achieving both a high luminescence dissymmetry factor ( g lum ) and photoluminescence quantum yield (PLQY) remains a critical challenge due to the inherent trade‐off between inducing chirality and minimizing non‐radiative losses driven by polyhedral distortion. Here, we present a ligand‐engineering approach to design a pair of chiral metal halide co‐crystals, achieving near‐unity PLQY (98%) and a | g lum | of 7.4 × 10 −3 . By leveraging Coulomb interactions instead of conventional hydrogen bonding between ligands and inorganic halide units, we effectively circumvent polyhedral distortions and substantially reduce electron–phonon coupling. This structural innovation reduces the non‐radiative decay rate by nearly three orders of magnitude, from 2.20 × 10 4 to 51.9 s −1 , thereby substantially enhancing luminescence efficiency. Consequently, the resulting figure‐of‐merit (FOM = PLQY × | g lum |) reaches an impressive 7.25 × 10 −3 , surpassing conventional hydrogen‐bonded counterparts by more than an order of magnitude (6.7 × 10 −4 ). This co‐crystal strategy paves the way for developing advanced CPL emitters with superior performance.