A stable mixed-valent uranium(v,vi) organic framework as a fluorescence thermometer

The presence of stable U(v)-containing compounds is important for the study of radionuclides. However, pentavalent uranium is prone to disproportionation, thus U(v)-containing compounds are generally sensitive to air and water. Herein, a stable mixed-valent uranium (U(v)/U(vi))-based metal-organic framework was synthesized via an in situ hydrothermal method, which features a three-dimensional structure with 3-fold interpenetration. Moreover, it can be used as a dual-responsive fluorescence temperature sensor based on the fluorescence intensity and fluorescence lifetime in the cryogenic range of 77-197 K. The fluorescence enhancement at low temperature (77 K) is about 25 times higher that at room temperature, which is unparalleled in common fluorescent materials. The mechanism can be interpreted as the decrease of nonradiative decay with decreasing temperature. Overall, this finding is beneficial to further our understanding of actinides in this oxidation state and disclose their potential applications.

Automated summary

A stable mixed-valent uranium-based metal-organic framework with a unique three-dimensional structure was successfully synthesized, serving as a dual-responsive fluorescence temperature sensor. The fluorescence enhancement at low temperature (77 K) is significantly higher than at room temperature due to the decrease of nonradiative decay, which presents potential applications in the understanding and utilization of actinides in this oxidation state.