Noncovalent Interaction‐Mediated Space Charge Transition Facilitated Isolated Copper(I)‐Iodide Clusters: Enabling High‐Resolution X‐Ray Imaging and Dynamic Encryption

ABSTRACT The exploration of solvent‐driven reversible structural transformation in clusters is crucial for advanced stimulus‐responsive optical applications and understanding of structure‐property relationships. Herein, we report a solvent‐driven reversible transformation between two copper(I) clusters: [Cu(totp)(CH 3 CN) 3 ][Cu 2 I 3 (totp)(DPPPy)]·CH 3 CN 1 and Cu 4 I 4 (DPPPy) 2 ·0.5CH 2 Cl 2 2 (totp = tri‐o‐tolylphosphine, DPPPy = 2‐[diphenylphosphino]pyridine). X‐ray radioluminescence and encryption applications were studied based on structure‐dependent photophysical properties difference. The noncovalent interaction‐mediated space charge transition between isolated ion units of 1 enables more efficient thermally activated delayed fluorescence by reverse intersystem crossing, accounting for structure‐dependent luminescence. Notably, compared to 2 , 1 exhibits a higher scintillation light yield of 14832 photons MeV −1 , exceeding that of the commercial scintillator Bi 4 Ge 3 O 12 (8000 photons MeV −1 ), and a low X‐ray detection limit of 22.49 nGy s −1 , far below the typical diagnostic dose (5.5 µGy s −1 ). Furthermore, scintillating film fabricated by 1 achieves X‐ray imaging with a high spatial resolution of 16 lp/mm. The reversible structural interconversion enables solvent‐responsive luminescent switches, and thus, the dynamic encryption system capable of multistage decryption was developed. This work not only offers new insight into solvent‐regulated clusters transformations but also provides a promising strategy for developing high‐performance copper(I) clusters‐based scintillators and stimulus‐responsive optical devices.