Deciphering Core Geometry for the Rational Design of Copper(I) Iodide Cluster Scintillators Toward Computed Tomography Imaging

Scintillators are crucial for radiation detection and medical imaging, yet the simultaneous optimization of their luminescence efficiency, stability, and device compatibility via molecular design remains challenging. Here, we propose and demonstrate “coordination‐saturation isomerism” as a molecular‐design paradigm for systematically tuning the luminescence and scintillation properties of copper‐iodide clusters. By modulating the protonation state of a single A‐site cation (N‐methylpiperazine), we achieve three distinct structural modes: Ionic 1D chain (Ionic‐type Cu 2 I 5 ‐L 3 ) with excitation‐dependent dual emission; organic‐ligand saturation gives a rigid, highly symmetric 0D cluster (Coordination‐type‐ Cu 4 I 4 L 4 ) that exhibits efficient cyan emission (PLQY 86%) and outstanding scintillation performance (light yield 53,000 ph•MeV −1 ); and inorganic‐iodide‐assisted saturation results in a heterogeneous 0D cluster (“All‐in‐One” hybrid‐type Cu 4 I 6 L 2 ) with red‐shifted emission and lower efficiency. This strategy surpasses conventional dimensionality engineering, clearly revealing how structural evolution from ionic to covalent bonding and from organic to inorganic‐assisted saturation dictates excited‐state properties and device performance. A flexible scintillation film based on Cu 4 I 4 L 4 enables high‐resolution CT imaging, highlighting the potential of this material system for flexible x‐ray detection and imaging. This work provides a novel molecular blueprint for the precise design and performance regulation of metal‐halide optoelectronic materials.