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 (CF 3 COOH) 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.