Donor-modified multiple resonance emitters with accelerated reverse intersystem crossing towards high-efficiency and narrowband deep-blue OLEDs

The development of blue thermally activated delayed fluorescence (TADF) emitters that can simultaneously achieve narrowband emission, high efficiency, and low efficiency roll-off in organic light-emitting diodes (OLEDs) remains a significant challenge. In this study, we present the successful design and synthesis of a series of TADF emitters by directly incorporating an electron donor into a boron/nitrogen/oxygen ternary doped multiple resonance (MR) skeleton. By carefully manipulating the donor strength, we were able to induce a long-range charge transfer triplet state to accelerate the reverse intersystem crossing (RISC) process. Meanwhile, the MR character of the first singlet excited state was preserved. As a result, the optimized emitter not only maintained the intrinsically excellent properties of the MR-TADF skeleton, such as deep-blue emission and high photoluminescence quantum yield of up to 89%, but also achieved a high RISC rate constant of 1.9 x 105 s(-1). The corresponding deep-blue device exhibited a maximum external quantum efficiency (EQE(max)) of 28.7%, with a full width at half maximum (FWHM) of only 36 nm and CIE coordinates approaching the NTSC blue standard. This study presents a simple yet effective approach for constructing high-performance deep-blue emitters for wide-color-gamut OLED displays.