Ligand Confinement for Fast‐Decay Cu─I Chain Scintillators Enabling High‐Resolution X‐ray Imaging and 3D Tomography

Chain-like one-dimensional (1D) copper(I) iodide cluster complexes are promising scintillator candidates due to their enhanced x-ray absorption, robust frameworks, and excellent photostability. However, their emission efficiencies remain significantly lower than those of zero-dimensional analogues. Herein, we propose a ligand-confinement strategy that employs sterically hindered, electronically tuned pyrimidine-based bridging ligands to simultaneously boost x-ray excited luminescence (XEL) and accelerate decay dynamics in 1D Cu-I cluster scintillators. Rigid, compact bidentate ligands increase structural rigidity while reducing the organic fraction for enhanced x-ray absorption. Meanwhile, asymmetric substituents induce coupled spatial and electronic confinement, giving rise to quantum-wire-like electronic states that promote radiative transitions. As a result, CuI(4-Mepym) exhibits a six-fold enhancement in photoluminescence quantum yield compared to CuI(2-Mepym), together with a fast decay lifetime of 1.28 µs, surpassing most reported copper(I) iodide cluster complexes. Combined with high stability, good solution processability, and a light yield comparable to commercial LuAG:Ce (∼25 000 ph MeV^-1), CuI(4-Mepym) breaks the conventional brightness-speed trade-off and enables high-resolution static imaging (>20 lp mm^-1), artifact-free dynamic x-ray imaging, and high-fidelity 3D tomography. This work establishes ligand confinement as an effective design principle for developing high-brightness, fast-decay 1D Cu-I cluster scintillators for advanced x-ray imaging applications.