A stable radiochromic semiconductive viologen-based metal–organic framework for dual-mode direct X-ray detection

Direct X-ray detectors, which directly convert X-rays into electrical signals through semiconductors, have higher space solution than scintillator-mediated indirect X-ray ones and are high desirable for early cancer detection and other applications, but the mainstream commercial α-Se detector is still largely limited by high production costs, large leakage current and low stability. This article reports an easily prepared, stable radiochromic semiconductive metal–organic framework (MOF), (MV)[Cd3(tdc)4]∙2H2O (RCS-1, H2tdc = 2,5-thiophenedicarboxylic acid; MV2+ = methyl viologen cation) with direct X-ray detecting ability. With a large bulk resistivity of 8.40 × 109 Ω cm, this material ensures minimal dark current and low noise for X-ray detection. Additionally, it exhibits higher sensitivity to W Kα X-rays (98.58 μC Gy−1 cm−2) than α-Se (∼20 μC Gy−1 cm−2). Meanwhile, unlike most reported direct X-ray detecting semiconductors, compound RCS-1 shows remarkable color change upon X-ray irradiation owing to the presence of photochromism-active viologen cations. This feature offers an appealing visual detecting ability to direct X-ray detectors that provide only the electrical signals.