Through-Space Interactions Enable Aggregation-Induced Quenching Suppression and Spin-Flipping Enhancement of Carbonyl-Nitrogen-Based Multiple Resonance Thermally Activated Delayed Fluorescence Emitters

Multiple resonance (MR) thermally activated delayed fluorescence (TADF) materials hold significant potential for applications in high color purity and highly efficient organic light-emitting diodes (OLEDs). However, their inherently large planar structures often result in severe aggregation-induced quenching and slow spin-flip processes, presenting significant challenges that limit their practical applications. In this study, we designed and synthesized two MR-TADF molecules, tCON-Cz and tCON-2tBuCz, by incorporating a tCON backbone with carbazole or 3,6-di-<i>tert</i>-butylcarbazole at the ortho position of the phenyl ring. This strategic design introduces a highly twisted three-dimensional structure, effectively mitigating aggregation-induced quenching. Additionally, it creates a through-space charge transfer channel that facilitates reverse intersystem crossing, thereby enhancing TADF efficiency. As a result, both molecules exhibit high photoluminescence quantum yields. When incorporated into devices, these OLEDs demonstrated remarkable performance, achieving high external quantum efficiencies of 23.70% for tCON-Cz and 22.84% for tCON-2tBuCz at doping concentrations as high as 20%. Notably, both devices retained the narrow full width at half-maximum of around 36 nm, consistent with the parent tCON skeleton, ensuring superior color purity.