Triple Long-Range Charge-Transfer Channels Enable Efficient LRCT/SRCT Hybridization in Narrowband Deep-Blue TADF...

To accelerate the reverse intersystem crossing (RISC) process of multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters, constructing hybridized long-range charge-transfer (LRCT) and short-range charge-transfer (SRCT) states within MR-TADF molecules is a promising strategy. However, the conventional hybrid LRCT-SRCT strategy proves less effective in enhancing the performance of deep-blue emitters. In this study, we propose a novel triple-LRCT-channel strategy to markedly enhance spin-orbit coupling (SOC) interactions in deep-blue LRCT/SRCT type TADF emitters. Based on the pronounced differentiation among the excited states enabled by this strategy, the proof-of-concept emitter DABNA-CN-PXZ exhibits multiple RISC channels, resulting in a tenfold faster RISC rate than its MR prototype. The corresponding device achieves a high maximum external quantum efficiency of 24.4% and a narrow FWHM of 24 nm, which ranks among the lowest reported for boron-nitrogen-based LRCT/SRCT type TADF emitters, arising from the judicious selection of substituents in DABNA-CN-PXZ that enables precise control over molecular rigidity and LRCT characteristics. These results demonstrate that DABNA-CN-PXZ is among the purest deep-blue LRCT/SRCT type TADF emitters, delivering excellent device performance under BT.2020-compliant conditions and thus validating the superiority of our molecular design strategy.