Halide Substitution and π-Conjugated Cation Engineering Enable Large-Hysteresis Phase-Transition-Induced Thermochromic Luminescence in Zero-Dimensional Hybrid Manganese(II) Halides

Abstract Zero-dimensional (0D) organic-inorganic hybrid manganese(II) halides have attracted considerable attention for their tunable luminescence and stimulus-responsive properties, yet simultaneously achieving high-efficiency emission and large-hysteresis thermochromic behavior remains challenging. Herein, three 0D hybrid manganese(II) halides were constructed through the synergistic regulation of halide substitution and π-conjugated cation engineering. Notably, [H(4-PipPy)]2MnBr4 exhibits a high photoluminescence quantum yield of 60.95% and a reversible structural phase transition with a large thermal hysteresis of 94 K, among the largest values reported for 0D hybrid manganese halides. This transition is accompanied by reversible thermochromic luminescence with an emission shift from 530 to 549 nm. Variable-temperature photoluminescence, differential scanning calorimetry, and variable-temperature powder X-ray diffraction reveal the direct relationship between structural transformation and luminescence switching. Moreover, the complementary emissions of [H2(4-PP)]MnBr4 and [H(4-PipPy)]2MnBr4 enable information encryption and anti-counterfeiting applications. This work provides new insights into the synergistic regulation of luminescence and phase transitions in zero-dimensional hybrid manganese halides, offering a new design concept for multifunctional thermochromic luminescent materials.