High Exciton Utilization Red Hot Exciton Electro‐Fluorescence Diodes Based on Emitters with Anti‐Kasha High‐Lying Triplet Emission

Abstract Red hot exciton emitters with high exciton utilization efficiencies (EUEs) are scarce. Herein, three red emitters, 2TPA, TPAPXZ, and TPAPXZCN, are designed and synthesized. These emitters have large rigid structures and large spin‐orbit coupling between the high‐lying triplet and adjacent singlet states. Photophysical studies show that these emitters exhibit anti‐Kasha high‐lying triplet emissions. Moreover, the MADN host is doped with 5 wt.% of these emitters, which inhibits the internal conversion (IC) rate (k_IC^Tn ∼ 10⁸ s⁻¹) of the high‐lying triplet state, making it similar to the high‐lying reverse intersystem crossing (hRISC) rate (k_hRISC ∼ 10⁸ s⁻¹). It provides a basis for doped devices to achieve high EUEs. Using 2TPA, TPAPXZ, and TPAPXZCN as emissive layers, the doped devices achieve red emission with emission peaks at 628, 626, and 647 nm, respectively. Notably, these devices achieve high EUEs of 43.9%, 81.0%, and 62.6%, respectively. To this knowledge, the EUE of these devices is among the highest values reported for hot exciton material devices. This study provides a novel approach for addressing low EUEs of hot exciton materials and improving their design strategies.