Fused Dual‐Donor Design for Accelerating Reverse Intersystem Crossing Rates of Spatially Folded Through‐Space Charge Transfer Emitters

Abstract

Abstract The development of through‐space charge transfer (TSCT)‐thermally activated delayed fluorescence (TADF) material is defective in relatively low reverse intersystem crossing (RISC) rates (commonly <5 × 10 5 s −1 ). Herein, we fuse two 3,6‐dimethyl‐8H‐indolo[3,2,1‐ de ]acridine (IAc) donor units to obtain large planar donors ( m ‐bIAc and p ‐bIAc) for forming spatially folded A–D|D–A configured TSCT emitters (DCT‐1 and DCT‐2). The configuration of highly parallel and large‐plane intramolecular multiple π‐stacking has been achieved. The symmetrical multi‐channel charge transfer networks of emitters induce multiple energetically proximal excited states within a small energy range (<0.12 eV) at the lowest excited state, creating additional configuration interaction and spin‐orbit coupling channels to accelerate the RISC process. This molecular configuration yields enhanced RISC rates of 6.19 × 10 5  s −1 for DCT‐1 and 1.05 × 10 6 s −1 for DCT‐2. Solution‐processed organic light‐emitting diodes employing these emitters achieve maximum external quantum efficiencies of 18.9% (DCT‐1, 474 nm sky‐blue emission) and 23.9% (DCT‐2, 498 nm green emission), with attenuated efficiency roll‐offs of DCT‐2 (12% at 1000 cd m −2 ). This work provides a critical pathway for manipulating dense excited states to address the bottleneck of the RISC rates while maintaining structural rigidity, promoting further advancement of TSCT‐TADF materials.