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.