Rational Design of Organic Manganese Halides for High Quantum Efficiency and Stability

Abstract Organic manganese halides have gained attention as luminescent materials due to their characteristics, such as low toxicity, ease of synthesis, and high photoluminescence quantum yield (PLQY). This study challenges the common belief that increasing the Mn–Mn distance invariably boosts PLQY. It introduces a 3D diagram illustrating the importance of ground‐state and excited‐state band alignments in influencing PLQY. The research identifies how different organic cations result in two distinct band alignments, thus impacting PLQY. Additionally, the research delves into the effects of temperature and pressure on the stability of three organic manganese bromides. Findings indicate that the structural attributes of organic cations significantly influence the materials' responses to thermal stress and pressure. For instance, (PPh4)2MnBr4, characterized by a strong conjugation effect and stable structure, displays superior thermal stability and pressure resistance. Conversely, (N‐BHMTA) 2 MnBr 4 , with a more intricate structure and lower stability, exhibits susceptibility to irreversible structural alterations under elevated temperature and pressure. These insights are pivotal for developing stable, efficient luminescent materials across diverse applications.