Supramolecular Chloride Reservoirs Enable Homogeneous Halide Distribution and Near-Unity Blue Luminescence in...

Blue-emitting metal halide perovskites remain difficult to stabilize because mixed-halide compositions suffer from halide heterogeneity, defect formation, and rapid phase segregation. Here, we report a supramolecular host engineering strategy that stabilizes mixed-halide perovskites using a quaternary ammonium chloride-functionalized cationic β-cyclodextrin (C-βCD). The cyclodextrin host simultaneously functions as a chlorine reservoir, defect passivator, and supramolecular stabilizer, enabling homogeneous halide incorporation and strong host-guest interactions with the Cs₄PbBr₆-CsPbBr₃ heterostructured perovskite surface. This cooperative regulation effectively suppresses halide segregation and non-radiative recombination, yielding tunable blue emission with exceptional color purity and a near-unity photoluminescence quantum yield (PLQY) of 99.9%, among the highest values reported for blue-emitting perovskites. The resulting supramolecular perovskite luminescent membranes further exhibit remarkable stability against water exposure (93.3% of initial PL intensity retained after 626 h) and ambient environmental stress (a PLQY half-life of 27457 h), establishing a new benchmark for environmentally robust blue emitters. Integration of the supramolecular perovskites within porous membranes enables multifunctional operation, including foldable display, white light-emitting diodes, as well as pioneer application of fluorescence detection and visible-light-driven degradation of perfluorinated pollutants. These results highlight supramolecular host-guest chemistry as a powerful molecular strategy for stabilizing mixed-halide perovskites and engineering robust luminescent materials.