Achieving Dual-Color Luminescence via Halogen Regulation in Copper-Based Halides for Anticounterfeiting

Multicolor luminescent materials have gained widespread attention due to their promising applications in anticounterfeiting and information security. Herein, two novel zero-dimensional copper-based halides, (C5H11N3)2Cu3Cl7·H2O and (C5H11N3)2Cu2Br6, with tunable yellow and blue dual-color emission via a halogen regulation strategy have been synthesized. Both crystals exhibit a zero-dimensional structure that is composed of isolated organic [C5H11N3]2+ cations and an inorganic [Cu3Cl7]4–/[Cu2Br6]4– cluster. Notably, broad emission peaks located at 549 and 457 nm, large Stokes shifts of 216 and 156 nm, and long lifetimes of 10.15 and 13.45 μs that separately correspond to yellow and blue emission were determined for (C5H11N3)2Cu3Cl7·H2O and (C5H11N3)2Cu2Br6, respectively, which can be ascribed to self-trapped exciton (STE) emission. Furthermore, a higher PLQY of 23.79% was obtained for (C5H11N3)2Cu2Br6 compared to the value of 15.90% for (C5H11N3)2Cu3Cl7·H2O, which may be related to their different inorganic cluster configurations and distortion. To further elucidate the structure–property relationship, density functional theory (DFT) calculations were also conducted, indicating that copper halide clusters predominantly contribute to their optical performances. Taking advantage of the tunable dual-color emission, multiple anticounterfeiting modes were successfully designed to achieve information security. This research offers new insights into modulating the multicolor luminescence of copper-based halides, expanding their potential application in anticounterfeiting.