Excited-State Engineering toward Accelerated Reverse Intersystem Crossing in Diindolocarbazole-Embedded Multiple-Resonance Emitters for High-Performance Blue OLEDs

Simultaneously achieving a narrow emission band, high efficiency, and excellent color purity remains a formidable challenge in the development of blue organic light-emitting diodes (OLEDs). Diindolocarbazole-embedded multiple-resonance emitters show great potential owing to their extremely narrow emission band, but the practical applications are severely limited by the slow reverse intersystem crossing rate (k_RISC) with the order of magnitude value of 10². Herein, we present an effective strategy to accelerate the RISC process by acceptor decoration to regulate the excited state. Through modulating the electron-withdrawing ability from TFB to TPT, the long-range charge transfer excited state is successfully induced, which leads to the decreased ΔE_ST and increased spin-orbital coupling (SOC) matrix elements, contributing to the dramatically accelerated k_RISC up to 1.11 × 10⁴ s^-1 for pICz-TPT. Moreover, the narrowband blue emission is basically retained for the proof-of-concept pICz-TPT with an emission peak at 449 nm, a full width at half-maximum of 44 nm, and CIE coordinates of (0.15, 0.10). Impressively, the nonsensitized OLEDs based on the pICz-TPT emitter exhibit the highest maximum external quantum efficiency (EQE_max) of 14.4% among all the reported blue OLEDs on the basis of pICz derivatives (which typically remained below 5%), and a further boost of efficiency with EQE_max of 24.2% is realized in the hyperfluorescent OLEDs. This work provides a powerful design tool toward highly efficient emitters with good color purity.