Tailoring Noncovalent Interactions for Optimal Ultrafast X‐Ray Scintillation in Organic Cocrystals

Abstract The trade‐off between high radioluminescence (RL) and fast decay time is a common challenge facing almost all X‐ray scintillators. Organic fluorescence scintillators, with ultrafast response, readily available, and low cost, are promising for imaging and detection. Here, organic cocrystals of halogen‐bonded acceptors and donors with heavy halogen atoms (Br and I) are designed and fabricated to achieve high RL and ultrafast decay time simultaneously. The noncovalent interactions in cocrystals play the following roles: 1) The strong halogen bonds C≡N···X (X = I, Br) promoted X‐ray RL by providing effective pathways for electron transfer, whereas the relatively weaker C–X···π do not contribute to this enhancement. 2) Halogen‐bonded donors can accelerate fluorescence decay, resulting in ultrafast decay time as the interaction strength increases. 3) The π–π interactions modified their molecular packing to affect fluorescence. Through the modulation of these noncovalent interactions, the cocrystal of 1,4‐bis‐p‐cyanostyrylbenzene (CSB) and 1,4‐diiodotetrafluorobenzene (IFB) exhibited the best scintillation performance with a lifetime of 0.58 ns and a detection limit of 144.59 nGy s⁻¹, achieving a resolution of 10 lp mm⁻¹. The molecular design combined with the cocrystallization strategy provides new insights into designing scintillator for advanced imaging and detection applications.