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Taking Lanthanides out of Isolation: Tuning the Optical Properties of Metal-Organic Frameworks

preprint
submitted on 02.02.2020 and posted on 04.02.2020 by Samantha L. Anderson, Davide Tiana, Christopher Ireland, Gloria Capano, Maria Fumanal, Andrzej Gładysiak, Stavroula Kampouri, Aiman Rahmanudin, Néstor Guijarro, Kevin Sivula, Kyriakos Stylianou, Berend Smit
Metal organic frameworks (MOFs) are increasingly used in applications that rely on the optical and electronic properties of these materials. These applications require a fundamental understanding on how the structure of these materials, and in particular the electronic interactions of the metal node and organic linker, determines these properties.

Herein, we report a combined experimental and computational study on two families of lanthanide-based MOFs: Ln-SION-1 and Ln-SION-2. Both comprise the same metal and ligand but with differing structural topologies. In the Ln-SION-2 series the optical absorption is dominated by the ligand and using different lanthanides has no impact on the absorption spectrum. The Ln-SION-1 series shows a completely different behavior in which the ligand and the metal node do interact electronically. By changing the lanthanide in Ln-SION-1, we were able to tune the optical absorption from the UV region to absorption that includes a large part of the visible region. For the early lanthanides we observe intraligand (electronic) transitions in the UV region, while for the late lanthanides a new band appears in the visible. DFT calculations showed that the new band in the visible originates in the spatial orbital overlap between the ligand and metal node. Our quantum calculations indicated that Ln-SION-1 with late lanthanides might be (photo)conductive. Experimentally, we confirm that these materials are weakly conductive and that with an appropriate co-catalysts they can generate hydrogen from a water solution using visible light. Our experimental and theoretical analysis provides fundamental insights for the rational design of Ln-MOFs with the desired optical and electronic properties.

Funding

Swiss National Science Foundation (SNF) Ambizione Energy Grant n.PZENP2_166888

National Center of Competence in Research (NCCR), Materials’ Revolution: Computational Design and Discovery of Novel Materials (MARVEL), of the Swiss National Science Foundation (SNSF)

Marie Curie Fellowship (705861 – ASPAir, H2020-MSCA-IF-2015)

Swiss National Science Foundation (SNF) Grant n.IZKSZ2_162130

Swiss National Supercomputing Centre (CSCS) under project no.s611

History

Email Address of Submitting Author

berend.smit@epfl.ch

Institution

Ecole Polytechnique Fédérale de Lausanne (EPFL)

Country

Switzerland

ORCID For Submitting Author

0000-0003-4653-8562

Declaration of Conflict of Interest

no conflict of interest

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