Phase-Transition-Induced Photoluminescence Change in Two Hybrid Manganese Halide Crystals

Much effort has been devoted to rationally manipulating photoluminescence (PL) properties in hybrid metal halides for applications in advanced optical materials. Among them, phase-transition-induced PL change has emerged as a promising approach for efficient PL transformation. However, complicated intermolecular interactions remain challenging, making the underlying mechanisms hard to understand and design. In this work, we present two new organic-inorganic hybrid manganese(II) halides, (C₉H₁₃N₂)₂MnCl₄·0.5H₂O (1) and (C₉H₁₃N₂)₂MnBr₄ (2), which undergo yellow-to-green PL color change with thermally driven phase transitions and recover the initial phase with humid stimulation or recrystallization. Detailed structural analyses revealed that coordination geometry distortion and enhanced intermolecular interactions weaken the crystal field, which results in blue-shifting emission. The diverse structural transformations under multiple stimuli enable applications of 1 and 2 in multilevel information anticounterfeiting. This discovery establishes the interplay between intermolecular interactions and structural deformations in phase-transition-induced PL change, providing valuable insights for the rational design of novel dynamic luminescence materials.