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

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 ( k r,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 ( k RISC ). In the 20 wt.% doped films, emitters 1 and 2 show green TADF with high k r,s / k RISC at 1.1 × 10 7 s −1 /1.3 × 10 6 s −1 and 1.2 × 10 7 s −1 /7.7 × 10 5 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 k r,s, and k RISC of TSCT‐TADF emitters for high‐performance OLEDs.