Lighting the Invisible: Tailoring Hot Exciton AIE Scintillators via Heavy‐Atom Engineering for X‐ray Detection †

Comprehensive Summary Hot exciton organic scintillators, a class of materials that utilize triplet excitons through high‐energy reverse intersystem crossing (hRISC), have attracted significant attention due to their high exciton utilization efficiency and ultrafast fluorescence lifetime. However, the limited X‐ray absorption capacity of organic molecules has restricted the diversity of organic scintillators exhibiting high radioluminescence intensity. In this study, we demonstrate strong scintillation emission by constructing a simple D‐A architecture with heavy‐ atom modification on the donor periphery, while emphasizing the critical balance between photoluminescence quantum yield (PLQY) and X‐ray absorption capability. Notably, the crystalline powder of 4‐(benzo[ c ][1,2,5]thiadiazol‐4‐yl)‐ N , N ‐bis(4‐bromophenyl)aniline (BT‐TPA‐2Br) achieves a maximum radioluminescence intensity 8.76 times that of anthracene and 1.75 times that of BGO (relative light yield of ∼33460 MeV −1 .), along with a rapid decay lifetime of 5.37 ns. This work provides a straightforward molecular design strategy for developing hot exciton organic scintillators that simultaneously possess good solubility, crystallinity, and high radioluminescence intensity.