Reversible Thermodynamic Phase‐Transition in Zero‐Dimensional Manganese Halides Enables Dual‐Secure Optical Information Anti‐Counterfeiting and Encryption

Abstract Stimuli‐responsive manganese halides have emerged as eco‐friendly systems for optical information security, yet achieving reversible phase transition with optical switching remains a formidable challenge. Herein, two isostructural 0D Mn (II) halide hybrids, (4‐P) 2 MnX 4 (4‐P = 4‐pyrrolidylpyridine, X = Cl, Br) are demonstrated, featuring halogen‐modulated exciton confinement effects. The bromide derivative exhibits thermally triggered phase transition (at 120 °C) with reversible yellow↔green emission switching (Δλ = 10 nm). Combined with (4‐P) 2 MnCl 4 and the other thermodynamically stable metal halides NII₂MnBr₄ (NII = C 12 H 17 NH + ) which is yellow‐emitting, (4‐P) 2 MnBr 4 achieves dual anti‐counterfeiting via thermal‐optical dual‐response mechanisms. Furthermore, white light‐emitting diodes (WLEDs) are prepared by (4‐P) 2 MnCl 4 and (4‐P) 2 MnBr 4 , respectively, indicating they are also state‐of‐the‐art Mn(II)‐based phosphors. This work pioneers a thermodynamic phase‐transition strategy to design intelligent optical materials for next‐generation information.