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Enhancing Thermally Activated Delayed Fluorescence by Fine-Tuning the Dendron Donor Strength.

Eimantas DudaDavid HallSergey BagnichCameron L Carpenter-WarrenRishabh SaxenaMichael Y WongDavid Bradford CordesAlexandra M Z SlawinDavid BeljonneYoann OlivierEli Zysman-ColmanAnna Köhler
Published in: The journal of physical chemistry. B (2022)
Thermally activated delayed fluorescence (TADF) relies on a small energy gap between the emissive singlet and the nonemissive triplet state, obtained by reducing the wave function overlap between donor and acceptor moieties. Efficient emission, however, requires maintaining a good oscillator strength, which is itself based on sufficient overlap of the wave functions between donor and acceptor moieties. We demonstrate an approach to subtly fine-tune the required wave function overlap by employing donor dendrons of changing functionality. We use a carbazolyl-phthalonitrile based donor-acceptor core (2CzPN) as a reference emitter and progressively localize the hole density through substitution at the 3,6-positions of the carbazole donors (Cz) with further carbazole, (4- tert -butylphenyl)amine ( t BuDPA), and phenoxazine (PXZ). Using detailed photoluminescence studies, complemented with density functional theory (DFT) calculations, we show that this approach permits a gradual decrease of the singlet-triplet gap, Δ E ST , from 300 to around 10 meV in toluene, yet we also demonstrate why a small Δ E ST alone is not enough. While sufficient oscillator strength is maintained with the Cz- and t BuDPA-based donor dendrons, this is not the case for the PXZ-based donor dendron, where the wave function overlap is reduced too strongly. Overall, we find the donor dendron extension approach allows successful fine-tuning of the emitter photoluminescence properties.
Keyphrases
  • energy transfer
  • density functional theory
  • air pollution
  • molecular dynamics
  • quantum dots
  • light emitting
  • solar cells
  • crystal structure