Synergistic Enhancement of Luminescence Dissymmetry Factor and Quantum Yield via Hybrid Copper(I) Iodide Cluster and Cellulose Nanocrystal Bilayer Films

ABSTRACT Circularly polarized luminescence (CPL) has emerged as a cornerstone technology for next‐generation chiral photonic applications. However, a fundamental trade‐off between the luminescence dissymmetry factor ( g lum ) and photoluminescence quantum yield (PLQY) has remained the primary bottleneck preventing the widespread practical deployment of CPL materials. Herein, we report a breakthrough solution to this long‐standing problem through a rational synergistic design that combines highly emissive copper(I) iodide clusters with chiral cellulose nanocrystal (CNC) photonic templates. The synthesized Cu 4 I 4 (2,5‐DMePi) 2 clusters exhibit an ultrahigh PLQY of 97.20% and excellent stability, allowing their facile integration into flexible polymer films. By constructing a bilayer architecture consisting of the emissive Cu–I cluster film and a left‐handed chiral nematic CNC template, we achieve the CPL performance that simultaneously delivers a near‐unity PLQY and a large g lum value of −0.9421. Most strikingly, the CPL sign can be reversibly switched between −0.9421 and 0.1021 simply by changing the observation direction. These direction‐tunable bilayer films with multimodal optical features are ideal for advanced optical anti‐counterfeiting. Collectively, this work not only breaks the fundamental g lum factor‐PLQY trade‐off but also provides a generalizable strategy for the design of next‐generation high‐performance CPL materials.