Branched Alkyl Chains Tunable Organic‐Inorganic Hybrid Manganese Halides for Anti‐counterfeiting, White Light‐emitting Diode and X‐ray Imaging Applications

Manganese‐based organic‐inorganic metal halides (Mn‐based OIMHs) scintillators have aroused a research upsurge due to their outstanding photoluminescence performance, low toxicity, and tunable structures. Herein, we demonstrate a molecular engineering strategy that synergistically enhances luminescence efficiency and radiation sensitivity by systematic elongation of branched alkyl chains in phosphonium‐based cations. The (4‐DEATBP)MnBr4 (4‐DEATBP = (4‐(diethylamino)butyl)triphenylphosphonium) crystal exhibits remarkable thermochromic luminescence properties and anti‐thermal quenching effect, highlighting the application potential in high‐temperature anti‐counterfeiting and information encryption. Through effective chain elongation, the (4‐DBATBP)MnBr4 (4‐DBATBP = (4‐(dibutylamino)butyl)triphenylphosphonium) single crystal achieves an impressive photoluminescence quantum yield (PLQY) of 100% and exhibits superior performance under X‐ray irradiation, with a high light yield of 67953 photons MeV−1 and a low limit of detection (LOD) of 10.45 nGy s−1. Additionally, the glassy (4‐DBATBP)MnBr4 demonstrates an impressive spatial resolution of 25 lp mm−1. (4‐DBATBP)MnBr4 shows great application potential in the fields of white light‐emitting diode (WLED) and express security check due to its outstanding luminescence performance. This work not only offers two kinds of new Mn‐based OIMH materials but also authenticates the role of extending the branched alkyl chain for improving the photoluminescence performance.