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Open AccessArticle

Exciton Coupling and Conformational Changes Impacting the Excited State Properties of Metal Organic Frameworks

1
Institute of Physical and Theoretical Chemistry, Graz University of Technology, NAWI Graz, Stremayrgasse 9, 8010 Graz, Austria
2
Institute of Solid State Physics, Graz University of Technology, NAWI Graz, Petersgasse 16, 8010 Graz, Austria
3
Institute of Physics, University of Graz, Universitätsplatz 5, 8010 Graz, Austria
4
Institute of Functional Interfaces (IFG), Karlsruhe Institute of Technology (KIT), Hermann-von-Helmholtz Platz-1, 76344 Eggenstein-Leopoldshafen, Germany
*
Authors to whom correspondence should be addressed.
Molecules 2020, 25(18), 4230; https://doi.org/10.3390/molecules25184230
Received: 28 August 2020 / Revised: 10 September 2020 / Accepted: 11 September 2020 / Published: 15 September 2020
(This article belongs to the Special Issue Hybrid Materials for Advanced Applications)
In recent years, the photophysical properties of crystalline metal-organic frameworks (MOFs) have become increasingly relevant for their potential application in light-emitting devices, photovoltaics, nonlinear optics and sensing. The availability of high-quality experimental data for such systems makes them ideally suited for a validation of quantum mechanical simulations, aiming at an in-depth atomistic understanding of photophysical phenomena. Here we present a computational DFT study of the absorption and emission characteristics of a Zn-based surface-anchored metal-organic framework (Zn-SURMOF-2) containing anthracenedibenzoic acid (ADB) as linker. Combining band-structure and cluster-based simulations on ADB chromophores in various conformations and aggregation states, we are able to provide a detailed explanation of the experimentally observed photophysical properties of Zn-ADB SURMOF-2: The unexpected (weak) red-shift of the absorption maxima upon incorporating ADB chromophores into SURMOF-2 can be explained by a combination of excitonic coupling effects with conformational changes of the chromophores already in their ground state. As far as the unusually large red-shift of the emission of Zn-ADB SURMOF-2 is concerned, based on our simulations, we attribute it to a modification of the exciton coupling compared to conventional H-aggregates, which results from a relative slip of the centers of neighboring chromophores upon incorporation in Zn-ADB SURMOF-2. View Full-Text
Keywords: metal organic frameworks; SURMOF; absorption; emission; time-dependent density functional theory; aggregation metal organic frameworks; SURMOF; absorption; emission; time-dependent density functional theory; aggregation
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Windischbacher, A.; Steiner, L.; Haldar, R.; Wöll, C.; Zojer, E.; Kelterer, A.-M. Exciton Coupling and Conformational Changes Impacting the Excited State Properties of Metal Organic Frameworks. Molecules 2020, 25, 4230.

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