| Autor: |
Duda E; Soft Matter Optoelectronics, BIMF & BPI, University of Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany., Hall D; Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, St Andrews, U.K., KY16 9ST.; Laboratory for Chemistry of Novel Materials, University of Mons, 7000, Mons, Belgium., Bagnich S; Soft Matter Optoelectronics, BIMF & BPI, University of Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany., Carpenter-Warren CL; Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, St Andrews, U.K., KY16 9ST., Saxena R; Soft Matter Optoelectronics, BIMF & BPI, University of Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany., Wong MY; Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, St Andrews, U.K., KY16 9ST., Cordes DB; Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, St Andrews, U.K., KY16 9ST., Slawin AMZ; Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, St Andrews, U.K., KY16 9ST., Beljonne D; Laboratory for Chemistry of Novel Materials, University of Mons, 7000, Mons, Belgium., Olivier Y; Unité de Chimie Physique Théorique et Structurale & Laboratoire de Physique du Solide, Namur Institute of Structured Matter, Université de Namur, Rue de Bruxelles, 61, 5000 Namur, Belgium., Zysman-Colman E; Organic Semiconductor Centre, EaStCHEM School of Chemistry, University of St Andrews, St Andrews, U.K., KY16 9ST., Köhler A; Soft Matter Optoelectronics, BIMF & BPI, University of Bayreuth, Universitätsstraße 30, 95447 Bayreuth, Germany. |
| Abstrakt: |
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. |
