Identical Metal-Organic Frameworks with Distinct Colors: The Role of Modulator in Directing Photophysical Properties

The modulator plays a crucial role in controlling the crystal size, morphology, and defects of metal-organic frameworks (MOFs), but its impact on color and photophysical properties remains unexplored. Here, we demonstrate that tuning the concentration of modulator (CF₃COOH) during synthesis yields two structurally identical thorium-based MOFs, Th-ADC-Y and Th-ADC-R, with distinct yellow and red colors. Spectroscopic investigations reveal that the different colors of Th-ADC-Y and Th-ADC-R originate from acid-induced radicals and light-induced radicals, respectively. Optical bandgap analysis reveals the semiconducting nature of both materials, with Th-ADC-Y demonstrating lower X-ray detection limit than Th-ADC-R. These findings highlight the potential of modulator-induced radical formation in tailoring the optical and photophysical properties of MOFs for applications in optoelectronics and sensing.