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

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 × 105 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 × 105 s-1 for DCT-1 and 1.05 × 106 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.