Asymmetric Coordination in a Thermoluminescent Pb-Based MOF Enables High-Dose X-ray Detection

Metal-organic frameworks (MOFs) are emerging as promising thermoluminescent (TL) materials due to their structural tunability, mild synthesis conditions, and well-defined structure-property relationships. However, their application in high-dose X-ray detection remains largely unexplored. Herein, we report SCU-600, a Pb-based MOF featuring asymmetric coordination of the organic ligand 2,6-dimethylterephthalic acid, in which the two inequivalent carboxylate groups adopt different binding modes with Pb²⁺ ions. This coordination asymmetry induces significant steric effects, giving rise to an ant-type topology and a wide bandgap of 3.48 eV. Owing to this wide bandgap, SCU-600 exhibits a broad linear TL response over 1-280 Gy (R² = 0.994). SCU-600 also demonstrates high sensitivity with a low detection threshold of 2.89 × 10^-2 Gy, excellent thermal stability up to 657.8 K, strong radiation resistance under 10 kGy γ-ray exposure, and robust reusability over 12 cycles. Mechanistic studies reveal that the TL emission originates from radiation-induced oxygen-centered radicals generated through intramolecular charge transfer. Furthermore, electron paramagnetic resonance confirms the formation of two distinct radical species in SCU-600, attributed to the asymmetric coordination environment. This work not only demonstrates the potential of SCU-600 for high-dose radiation detection in applications such as clinical radiotherapy and agricultural irradiation but also establishes coordination symmetry as a key design parameter for tailoring TL performance in MOF-based materials.