Tailoring Hybrid Copper Iodide Cluster Glasses via Ligand Design for Stable Multifunctional X‐Ray Imaging

ABSTRACT The development of glassy organic–inorganic hybrid material has attracted great interest, yet remains significantly challenging due to issues such as unstable melting, poor crystallization resistance, and limited environmental stability. In this study, we report a rational ligand engineering strategy for designing novel copper iodide cluster glasses. By using phosphine ligands with varying aromatic phenyl (Ph‐) and aliphatic cyclohexyl (Cy‐) groups, a series of zero‐dimensional Cu 4 I 4 (L) 4 (L = Ph 3 P, CyPh 2 P, and Cy 2 PhP) cubic clusters was synthesized. Variable‐temperature X‐ray absorption fine structure analysis, Raman spectroscopy, and molecular dynamics simulations reveal that melting proceeds through disruption of intermolecular electrostatic interactions rather than ligand dissociation. Density functional theory and rheological analyses further rationalize how ligand engineering regulates the thermodynamic behavior of the clusters. Systematic substitution of phenyl with cyclohexyl groups modulates intermolecular forces, effectively suppressing crystallization and enabling successful vitrification for the CyPh 2 P and Cy 2 PhP analogues. The resulting low‐melting Cu 4 I 4 (Cy 2 PhP) 4 glass exhibits a high glass transition temperature (352.3 K), excellent optical transparency (> 80%, 450–800 nm), and remarkable stability. These properties allow its application in high‐resolution, underwater, and high‐temperature X‐ray imaging. This work establishes a feasible design principle for organic–inorganic hybrid glasses and underscores their potential for advanced photonic applications.