Pyrene‐Based Emitters with Ultrafast Upper‐Level Triplet–Singlet Intersystem Crossing for High‐Efficiency, Low Roll‐Off Blue Organic Light‐Emitting Diode

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 (S₁) of CPPCN, which facilitate the RISC from the high‐lying triplet state (hRISC) to the S₁ state. The corresponding hRISC rate constant is determined to be as high as 2.86 × 10⁸ 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 T₉₅ lifetime of the CPPCN‐based device with a structure of commercial applications is evaluated to be ≈368 h at 1000 cd m⁻².