Hybridized through-bond/through-space charge transfer enables efficient blue emitters with the Rec. 2020 color gamut

Abstract

Achieving efficient deep-blue emission with high color purity remains a critical challenge for BT.2020-compliant OLEDs. Herein, we present a rational molecular design strategy by tuning the hybridization between through-bond charge transfer (TBCT) and through-space charge transfer (TSCT) in a series of A1–D1–D2–A2 structured TADF emitters. Two proof-of-concept emitters, BOtC and BOCC, were synthesized with symmetric and asymmetric 1,1′-bicarbazole donors, respectively. Comprehensive theoretical and photophysical analyses reveal that BOtC exhibits balanced TBCT/TSCT hybridization, leading to a small energy difference (ΔE_ST) between the first singlet (S₁) and triplet (T₁) excited states, fast reverse intersystem crossing, and efficient triplet exciton utilization. In contrast, TSCT-dominated BOCC shows slower RISC and reduced exciton recycling. Consequently, BOtC-based OLEDs achieve deep-blue emission (CIE: 0.157, 0.047) and a high external quantum efficiency (EQE) of 14.4%, whereas BOCC-based devices display a lower EQE of 6.5%. This work establishes TBCT/TSCT hybridization control as a general strategy to simultaneously achieve high efficiency and ultrahigh color purity in blue TADF emitters, providing guidance for next-generation display applications.