Coordination‐Driven Reversible Thermochromic Luminescence in a Hybrid Manganese Halide for Thermal Sensing

Abstract With the growing demand for smart sensing and information encryption technologies, stimuli‐responsive luminescent materials are emerging as key candidates for temperature monitoring and security applications. This study presents a Mn ²⁺ ‐based hybrid halide, (MAMP)MnBr ₃ ·Br [MAMP = 2‐[(methylamino)methyl]pyridine], exhibiting reversible thermochromic luminescence, ideal for smart thermal sensing. The material undergoes a red‐to‐green emission shift triggered by a heat‐induced coordination transformation, transitioning from octahedral [MnBr ₆ ] ⁴⁻ to tetrahedral [MnBr ₄ ] ²⁻ units. Upon heating to 455 K, the Mn‐Br bonds are broken, leading to a structural transformation from octahedral [MnBr ₆ ] ⁴⁻ to tetrahedral [MnBr ₄ ] ²⁻ . This coordination change causes a red‐to‐green luminescence shift (651–515 nm). The material delivers strong red emission at 651 nm with an internal quantum efficiency of 21.6%, exhibits high thermal stability, and demonstrates efficient X‐ray scintillation. These properties make it suitable for non‐contact temperature sensing and dynamic information encryption. The material's excellent performance opens new opportunities for applications in temperature history tracking, anti‐counterfeiting, and flexible optoelectronic devices.