Electroabsorption Spectroscopy as a Tool to Probe Charge-Transfer and State Mixing in Thermally-Activated Delayed Fluorescence Emitters

De Sa Pereira, Daniel; Menelaou, Christopher; Danos, Andrew; Marian, Christel Maria; Monkman, Andrew P.

Abstract

Solid-state electroabsorption is demonstrated as a powerful tool to probe the charge-transfer (CT) character and state mixing in the low energy optical transitions of two structurally similar thermally-activated delayed fluorescent (TADF) materials with divergent photophysical and device performances. The Liptay model is used to fit differentials of the low energy absorption bands to the measured electroabsorption spectra, with both emitters showing CT characteristics and large changes of dipole moments on excitation despite the associated absorption bands appearing structured. High electric fields then reveal transfer of oscillator strength to a state close to the CT in the better performing molecule. With supporting TDDFT-TDA and DFT/MRCI calculations, this state showed ππ* characteristics of a local acceptor triplet that strongly mixes with the σπ* of the CT. The emitter with poor TADF performance showed no evidence of such mixing.

Citation

De Sa Pereira, D., Menelaou, C., Danos, A., Marian, C. M., & Monkman, A. P. (2019). Electroabsorption Spectroscopy as a Tool to Probe Charge-Transfer and State Mixing in Thermally-Activated Delayed Fluorescence Emitters. Journal of Physical Chemistry Letters, 10(12), 3205-3211. https://doi.org/10.1021/acs.jpclett.9b00999

• Journal Article Type: Article
• Acceptance Date: May 21, 2019
• Online Publication Date: May 22, 2019
• Publication Date: Jun 20, 2019
• Deposit Date: May 24, 2019
• Publicly Available Date: Jun 25, 2019
• Journal: Journal of Physical Chemistry Letters
• Electronic ISSN: 1948-7185
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 10
• Issue: 12
• Pages: 3205-3211
• DOI: https://doi.org/10.1021/acs.jpclett.9b00999
• Public URL: https://durham-repository.worktribe.com/output/1330189