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Abstract The reverse intersystem crossing (RISC) process from triplet to singlet manifold can efficiently improve the efficiencies of organic light‐emitting diodes (OLEDs). The relevant RISC rate ( k RISC ) is one of the key factors that affect the efficiency roll‐off and stability of devices. Here, a new blue “hot exciton” material, CPPCN, with pyrene as the core, is designed and synthesized. Photophysical studies indicate there are multiple high‐lying triplet states near the lowest singlet excited state ( S 1 ) of CPPCN, which facilitate the RISC from the high‐lying triplet state (hRISC) to the S 1 state. The corresponding hRISC rate constant is determined to be as high as 2.86 × 10 8 s −1 , a value some two to three orders of magnitude higher than typical thermally activated delayed fluorescence materials emitters. Benefiting from this ultrafast hRISC process, non‐doped blue OLED based on CPPCN reaches a high maximum external quantum efficiency (EQE) of 11.64% with suppressed efficiency roll‐off (begin roll‐off at a high brightness of 3732 cd m −2 and retains EQE >8.5% at 10 000 cd m −2 ). The T 95 lifetime of the CPPCN‐based device with a structure of commercial applications is evaluated to be ≈368 h at 1000 cd m −2 .
Yu et al. (Sun,) studied this question.