Chen, H. / Vankova, N. / Jha, G. / Yu, X. / Wang, Y. / Lin, L. / Kirschhöfer, K. / Greifenstein, R. / Redel, E. / Heine, T. / Wöll, C. (2024)

Angew. Chem. Int. Ed. 2024, e202318559

Abstract:

Electron-phonon interactions, crucial in condensed matter, are rarely seen in Metal–Organic Frame-
works (MOFs). Detecting these interactions typically involves analyzing luminescence in lanthanide- or acti-
nide-based compounds. Prior studies on Ln- and Ac-based MOFs at high temperatures revealed additional
peaks, but these were too faint for thorough analysis. In our research, we fabricated a high-quality, crystalline
uranium-based MOF (KIT-U-1) thin film using a layer-by-layer method. Under UV light, this film showed two
distinct “hot bands,” indicating a strong electron-phonon interaction. At 77 K, these bands were absent, but at
300 K, a new emission band appeared with half the intensity of the main luminescence. Surprisingly, a
second hot band emerged above 320 K, deviating from previous findings in rare-earth compounds. We con-
ducted a detailed ab-initio analysis employing time-dependent density functional theory to understand this
unusual behaviour and to identify the lattice vibration responsible for the strong electron-phonon coupling.
The KIT-U-1 film’s hot-band emission was then utilized to create a highly sensitive, single-compound optical
thermometer. This underscores the potential of high-quality MOF thin films in exploiting the unique
luminescence of lanthanides and actinides for advanced applications.

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