Preprint Article Version 1 Preserved in Portico This version is not peer-reviewed

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

Version 1 : Received: 28 August 2020 / Approved: 31 August 2020 / Online: 31 August 2020 (04:11:54 CEST)

A peer-reviewed article of this Preprint also exists.

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. 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.

Journal reference: Molecules 2020, 25, 4230
DOI: 10.3390/molecules25184230

Abstract

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.

Subject Areas

metal organic frameworks; SURMOF; absorption; emission; time-dependent density functional theory; aggregation

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