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--butylphenyl)amine (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, from 300 to around 10 meV in toluene, yet we also demonstrate why a small Δ alone is not enough. While sufficient oscillator strength is maintained with the Cz- and 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.

Download full-text PDF

Source
http://dx.doi.org/10.1021/acs.jpcb.1c05749DOI Listing

Publication Analysis

Top Keywords

wave function
12
function overlap
12
thermally activated
8
activated delayed
8
delayed fluorescence
8
donor acceptor
8
acceptor moieties
8
oscillator strength
8
donor dendrons
8
donor dendron
8

Similar Publications

Want AI Summaries of new PubMed Abstracts delivered to your In-box?

Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!