On the role of spin momentum in light-emitting and photochemical applications: A computational perspective

DIPC Seminars

Speaker: Yoann Olivier
University of Namur
When: 2025/05/27
16:30
Place: DIPC Josebe Olarra Seminar Room
Host: Claire Tonnelé
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On the role of spin momentum in light-emitting and photochemical applications: A computational perspective

In this contribution, we are going to discuss the role of spin momentum in the fields of organic electronics and photochemistry. In organic light-emitting diodes (OLEDs) efficiencies are tightly bound with the spin statistics of charge recombination which for conventional fluorescent materials results in a balance of one emissive singlet to three lost to heat triplets. Therefore, the internal quantum efficiency (IQE) is limited to 25 percents in this class of materials. Over the last years, different strategies to design fully organic light-emitting materials have been proposed. One of the most popular ones relies on thermally activated delayed fluorescence (TADF) which allows to convert the dark triplets into emissive singlets thanks to reverse intersystem crossing (RISC). Here, we will focus on a class of TADF materials called multi-resonant TADF (MR-TADF) known for their small singlet-triplet gap EST (which enhances RISC) as well as their narrow emission which allows them to meet the standards of color purity aimed by the OLED industry. Especially, we will demonstrate that high level quantum chemical calculations including electron correlation effects are key to correctly predict the excited states ordering and thus propose design rules for these materials.[1]. Photoredox catalysis is the branch of photochemistry where light is used to drive chemical reactions through single-electron transfer and has been particularly relevant in the field of phototherapy and applications aiming at the production of clean fuels such as dihydrogen. Typically, chemical reactions are initiated by the absorption of a photon by a photocatalyst that will transfer one electron (hole) to a quencher. Both chemical species form a geminate radical pair complex that needs to dissociate through the cage escape mechanism to further lead to chemical transformations. The cage escape mechanism is known back in the 60s but the microscopic origin of this phenomenon is yet to be uncovered. Here, we explore through a combination of quantum chemical calculations and molecular dynamics simulations the role of the spin momentum on the cage escape yield and in particular on the charge recombination process that enters directly in competition with the cage escape.

References:
[1] A. Pershin, D. Hall, V. Lemaur, J.C. Sancho-Garcia, L. Muccioli, E. Zysman-Colman, D. Beljonne, and Y. Olivier,
“Highly emissive excitons with reduced exchange energy in thermally activated delayed fluorescent molecules” Nat. Commun. 10, 597 (2019).
[2] A. Ripak, A.K. Vega Salgado, D. Valverde, S. Cristofaro, A. de Gary, Y. Olivier, B. Elias, L. Troian-Gautier. JACS 146, 22818 (2024).

Zoom: https://dipc-org.zoom.us/j/91595385682