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Photodetectors play an essential role in optical communications, environmental monitoring, and medical imaging, and their performance strongly depends on the properties of the optoelectronic materials. Therefore, the exploration of high-performance optoelectronic materials has long been a research focus in the field of materials science. Viologen-based organic materials, owing to their unique redox and chromic characteristics, have been extensively utilized in electrochromic devices, biosensors, and flow batteries. In this work, a viologen complex containing the transition metal element Co, {[Co(BPYBDC) (H2O)5]·(BDC)·H2O} (denoted as 1-Co) was designed and successfully synthesized. A series of in-situ high-pressure characterization techniques were employed to systematically investigate its structural and optoelectronic behaviors. The results reveal that 1-Co crystallizes in the Pc space group and remains structurally stable up to 11.6 GPa without any phase transition. UV-visible absorption spectroscopy shows a red-shift of the absorption edge upon compression, accompanied by a color change from colorless and transparent to yellow, indicating a pressure-induced narrowing of the optical bandgap. Consistent with the bandgap narrowing, impedance measurements demonstrate a significant reduction in the total resistance under compression, which remains about two orders of magnitude lower than the initial value after decompression. Furthermore, the photocurrent response is markedly suppressed under compression and barely recovers upon pressure release. This behavior can be attributed to the enhanced recombination of electrons with viologen groups under compression, leading to the formation of stable viologen radical states. These localized radicals cannot effectively participate in the separation and transport of photogenerated carriers, thereby contributing little to the photocurrent. These findings suggest that high pressure effectively modulates the optical and electrical behaviors of 1-Co by tuning intermolecular interactions and the electronic band structure, providing valuable insights into the pressure-dependent behavior of viologen-based materials.
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Keywords:
- Viologen metal-organic materials /
- high-pressure regulation /
- crystal structure /
- optoelectronic properties
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