Through-Space InteractionsEnable Aggregation-InducedQuenching Suppression and Spin-Flipping Enhancement of Carbonyl-Nitrogen-BasedMultiple 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.