Theoretical Investigation of High-Performance Pure Red Multiple Resonance Thermally Activated Delayed Fluorescence Organic Lasers with Suppressed Efficiency Roll-Off

Organic laser materials are widely utilized in optoelectronic displays owing to their significant wavelength tunability, large stimulated emission cross-section, and considerable molecular design flexibility. In recent years, multiple resonance thermally activated delayed fluorescence (MR-TADF) organic laser molecules have emerged as a favored option due to their narrow full-width at half-maximum and higher luminescence efficiency. However, the design strategies for MR-TADF organic laser emitters in the red region are notably constrained. Meanwhile, under high excitation intensities, MR-TADF molecules typically experience severe efficiency roll-off, which significantly restricts their application in high-performance optoelectronic devices. Herein, we propose a strategy to achieve red MR-TADF organic laser molecules by incorporating nitrogen atoms rich in lone-pair electrons and triphenylamine functional groups. A pure red MR-TADF laser molecule (PPzBN2) with a large emission cross-section of 6.2 × 10^-17\,^2 was designed. Furthermore, the efficient exciton radiation process (radiative rate from 2.83 × 10^7\,^-1 to 2.95 × 10^7\,^-1) and reduced exciton binding energy (dipole moment increasing from 1.15 Debye to 4.07 Debye) minimize triplet-state accumulation, thereby effectively mitigating efficiency roll-off (with figure of merit increasing from 1.97 × 10^4\,^-1 to 2.04 × 10^7\,^-1). This work establishes a theoretical foundation for designing red MR-TADF organic laser emitters and contributes to the advancement of novel, high-efficiency near-infrared MR-TADF organic laser molecules.