Multiple Electron Transfer in Semiconductive Ternary D-D'-A Metal-Organic Framework for Enhanced X-Ray Detection and Imaging.

Semiconductive metal-organic frameworks (MOFs) with donor-acceptor (D-A) characteristics have garnered attractive attention due to their capacity for separating and transferring photogenerated charges, making them promising candidates for high-performance X-ray detectors. However, the low charge transfer efficiency between the metal nodes and organic ligands limits the X-ray-to-electricity conversion efficiency of these materials. Herein, an additional photoactive donor (D') is introduced by incorporating a heavy atom-containing polyoxometalate (POM) [α-SiWO] into a binary {[Ni·bcbp·(HO)]·(HO)·Cl} (Ni-bcbp, bcbp: Hbcbp·2Cl = 1,1'-bis(4-carboxyphenyl)(4,4'-bipyridinium) dichloride) MOF, resulting in a semiconductive ternary D-D'-A framework {[Ni(bcbp)·(HO)·(DMA)]·(SiWO)} (SiW@Ni-bcbp, DMA: dimethylacetamide). The obtained material features an unprecedented porous 8-connected bcu-net structure that accommodates nanoscale [α-SiWO] counterions, displaying uncommon optoelectronic responses. In contrast to binary Ni-bcbp, the SiW@Ni-bcbp framework exhibits distinctive photochromism and robust X-ray responsiveness, which can be attributed to the synergistic effects of the electron reservoir and multiple photoinduced electron transfer originating from the POMs. As a result, the X-ray detector based on SiW@Ni-bcbp demonstrates a sensitivity of 5741.6 µC Gy cm with a low detection limit of 0.49 µGy s. Moreover, the devices demonstrated the capability of producing clearness X-ray images, providing a feasible and stable solution for constructing high-performance direct X-ray detectors.