Issue 42, 2022

Calculation of exchange couplings in the electronically excited state of molecular three-spin systems

Abstract

Photogenerated molecular three-spin systems, composed of a chromophore and a covalently bound stable radical, are promising candidates for applications in the field of molecular spintronics. Through excitation with light, an excited doublet state and a quartet state are generated, whereby their energy difference depends on the exchange interaction JTR between the chromophore triplet state (T) and the stable radical (R). In order to establish design rules for new materials to be used in molecular spintronics devices, it is of great importance to gain knowledge on the magnitude of JTR as well as the factors influencing JTR on a molecular level. Here, we present a robust and reliable computational method to determine excited state exchange couplings in three-electron-three-centre systems based on a CASSCF/QD-NEVPT2 approach. The methodology is benchmarked and then applied to a series of molecules composed of a perylene chromophore covalently linked to various stable radicals. We calculate the phenomenological exchange interaction JTR between chromophore and radical, which can be compared directly to the experiment, but also illustrate how the individual exchange interactions Jij can be extracted using an effective Hamiltonian that corresponds to the Heisenberg–Dirac–Van-Vleck Hamiltonian. The latter procedure enables a more detailed analysis of the contributions to the exchange interaction JTR and yields additional insight that will be invaluable for future design optimisation.

Graphical abstract: Calculation of exchange couplings in the electronically excited state of molecular three-spin systems

Supplementary files

Article information

Article type
Edge Article
Submitted
23 aug 2022
Accepted
17 sep 2022
First published
19 sep 2022
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2022,13, 12358-12366

Calculation of exchange couplings in the electronically excited state of molecular three-spin systems

M. Franz, F. Neese and S. Richert, Chem. Sci., 2022, 13, 12358 DOI: 10.1039/D2SC04701B

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