Excited-state engineering toward accelerated reverse intersystem crossing in diindolocarbazole-embedded multiple-resonance emitters for high-performance blue OLEDs

Abstract

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 (kRISC) 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 ΔEST and increased spin-orbital coupling (SOC) matrix elements, contributing to the dramatically accelerated kRISC 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 (EQEmax) 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 EQEmax of 24.2% is realized in the hyperfluorescent OLEDs. This work provides a powerful design tool toward highly efficient emitters with good color purity.