Nature of the singlet and triplet excitations mediating thermally activated delayed fluorescence

Y. Olivier, B. Yurash, L. Muccioli, G. D’Avino, O. Mikhnenko, J. C. Sancho-García, C. Adachi, T.-Q. Nguyen, and D. Beljonne

Phys. Rev. Materials 1, 075602 – Published 27 December 2017

Abstract

Despite significant efforts, a complete mechanistic understanding of thermally activated delayed fluorescence (TADF) materials has not yet been fully uncovered. Part of the complexity arises from the apparent dichotomy between the need for close energy resonance and for a significant spin-orbit coupling between alike charge-transfer singlet and triplet excitations. Here we show, in the case of reference carbazole derivatives, that this dichotomy can be resolved in a fully atomistic model accounting for thermal fluctuations of the molecular conformations and microscopic electronic polarization effects in amorphous films. These effects yield electronic excitations with a dynamically mixed charge-transfer and localized character, resulting in thermally averaged singlet-triplet energy differences and interconversion rates in excellent agreement with careful spectroscopic studies.

Received 25 April 2017

DOI:https://doi.org/10.1103/PhysRevMaterials.1.075602

Physics Subject Headings (PhySH)

Electronic structure Excitons

Molecular solids Organic LEDs

First-principles calculations Fluorescence recovery after photobleaching Photoluminescence

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Y. Olivier¹, B. Yurash², L. Muccioli³, G. D’Avino⁴, O. Mikhnenko², J. C. Sancho-García⁵, C. Adachi⁶, T.-Q. Nguyen², and D. Beljonne¹

¹Laboratory for Chemistry of Novel Materials, University of Mons, Place du Parc 20, B-7000 Mons, Belgium
²Department of Chemistry and Biochemistry, Center for Polymers and Organic Solids, University of California, Santa Barbara, California, USA
³Dipartimento di Chimica Industriale “Toso Montanari”, Università di Bologna, Bologna, Italy and Institut des Sciences Moléculaires, UMR 5255, University of Bordeaux, Talence, France
⁴Grenoble Alpes University, CNRS, Institut Néel, F-38042 Grenoble, France
⁵Departamento de Química Física, Universidad de Alicante, E-03080 Alicante, Spain
⁶Center for Organic Photonics and Electronics Research (OPERA) Kyushu University 744 Motooka, Nishi, Fukuoka 819-0395, Japan