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

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)₂MnX₄ (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)₂MnCl₄ and the other thermodynamically stable metal halides NII₂MnBr₄ (NII = C₁₂H₁₇NH⁺) which is yellow-emitting, (4-P)₂MnBr₄ achieves dual anti-counterfeiting via thermal-optical dual-response mechanisms. Furthermore, white light-emitting diodes (WLEDs) are prepared by (4-P)₂MnCl₄ and (4-P)₂MnBr₄, 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.