Chiral Lattice Distortion Enables Bright Near-Infrared Circularly Polarized Luminescence in Lead-Free Metal Halides

Near-infrared circularly polarized luminescence (NIR CPL) materials are of growing interest for emerging photonic technologies, yet the simultaneous realization of high emission efficiency and strong chiroptical activity remains challenging. Here, we report a lattice-distortion strategy to integrate excitonic and chiroptical functionalities in lead-free zero-dimensional hybrid metal halides. Single-crystal analysis combined with theoretical calculations reveals pronounced chiral lattice distortion, characterized by large continuous chirality measure (CCM) values, substantial off-centering, and bond-length distortion of the isolated metal halide octahedra. Such distorted lattices strengthen electron-phonon coupling and promote substantial excited-state structural reorganization, facilitating efficient self-trapped exciton formation and leading to bright NIR emission centered at 728 nm with a photoluminescence quantum yield of up to 84.9%. Meanwhile, the chiral lattice environment gives rise to pronounced chiroptical activity, affording a large luminescence dissymmetry factor (|glum|) of 2.21 × 10-2. The dynamic lattice further enables an NIR to orange phase transformation accompanied by emission-color switching and CPL inversion, while the chirality of the orange phase can be generated through spontaneous symmetry breaking or biased by external chiral induction depending on the crystallization pathway. Circularly polarized NIR light-emitting devices are further demonstrated with preserved chiroptical output. More broadly, this work highlights chiral lattice distortion as a promising structural strategy for developing efficient CPL-active lead-free metal halides across the NIR spectral region.