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Simultaneously Improving Radiative Decay and Reverse Intersystem Crossing in Space‐Confined Through‐Space Charge‐Transfer (TSCT) Emitter by Strong Intermolecular TSCT Enabled by a Planar Donor

Year: 2024
Type: article
Abstract: Simultaneously improving radiative decay and reverse intersystem crossing (RISC) of through‐space charge‐transfer (TSCT) thermally‐activated delayed fluorescence (TADF) emitters has remained a challenge. Here, space‐confined TSCT‐TADF emitters are developed with a planar indolo[3,2,1‐kl]phenoxazine donor, a spiro‐carbon‐fixed benzophenone acceptor, and a fluorene (for 1) or xanthene (for 2) bridge. Close, cofacial donor/acceptor alignments and efficient intramolecular TSCT have been observed for both emitters. Intriguingly, emitter 1 exhibits an intermolecular donor/acceptor interaction as strong as the intramolecular one, which opens efficient intermolecular TSCT, improving the radiative decay rate (kr,s) to the same level as emitter 2 featuring a much stronger intramolecular donor/acceptor interaction. The intermolecular TSCT also largely enhances the RISC rate (kRISC). In the 20 wt.% doped films, emitters 1 and 2 show green TADF with high kr,s/kRISC at 1.1 × 107 s−1/1.3 × 106 s−1 and 1.2 × 107 s−1/7.7 × 105 s−1, respectively. Organic light–emitting diodes (OLEDs) using the emitters show high external quantum efficiencies (EQEs) up to 27.5% and low‐efficiency roll‐offs. Hyperfluorescent OLEDs using the emitters as sensitizers afford narrowband blue‐green emission with high EQEs up to 30.6% and largely suppressed efficiency roll‐offs. The work reveals that strengthening intermolecular TSCT is a promising avenue to simultaneously improve kr,s, and kRISC of TSCT‐TADF emitters for high‐performance OLEDs.
DOI: 10.1002/adfm.202411957
Language: English
Open Access status: bronze
OpenAlex ID: W4405943265
FWCI: 3.123
Cites: 63
Cited by: 30
Related to: 10