Achieving Circularly Polarized Luminescence in Chiral N,O-Ligand-Modified Indium Chlorides

Chiral organic-inorganic hybrid metal halides (OIMHs) have emerged as promising materials for applications in circularly polarized luminescence (CPL), yet achieving high luminescence dissymmetry factor (glum) remains challenging. Herein, we report a pair of zero-dimensional chiral indium chloride enantiomers, (R/S-2-MPH₂)[InCl₄(bp2do)]₂ (R/S-1; R/S-2-MP = R/S-2-methylpiperazine, bp2do = 2,2'-bipyridyl-1,1'-dioxide), which feature chiral cations and ligand-modified anionic units. The bp2do ligand adopts a noncoplanar conformation due to the steric hindrance from its oxygen atoms. The In³⁺ center, leveraging its high coordination affinity, binds to this ligand along with halide ions. This coordination yields the structurally asymmetric anion [InCl₄(bp2do)]⁻. Crucially, the chiral cations induce distinct M or P-helical arrangements of these anions along the crystallographic b-axis, mediated by synergistic hydrogen-bonding and anion···π interactions. Effective chirality transfer is thereby accomplished. The study demonstrates that the bp2do ligand's incorporation is indispensable, endowing the otherwise nonemissive and CPL-inactive systems such as (R/S-2-MPH₂)₂[InCl₆]Cl with luminescence and substantial CPL activity (|glum| ∼ 10⁻²). This work demonstrates the effectiveness of anion engineering strategy for achieving high-performance metal halide CPL materials and opens a new avenue in chiral optoelectronics.