Exploring red circularly polarized multiple resonance thermally activated delayed fluorescence mechanism: From...

Due to the narrow-band emission and chiral luminescence properties, circularly polarized multiple resonance thermally activated delayed fluorescence (CP-MR-TADF) materials have garnered significant attention in organic optoelectronics in recent years. However, developing luminescent materials that simultaneously exhibit a large asymmetry factor (g), narrow-band red light emission, and high quantum efficiency remains a major challenge in this field, and related inner mechanisms are unclear. Herein, we employ density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods to systematically study the excited-state properties and luminescence mechanisms of two reported CP-MR-TADF molecules (NBNPO and NBOPO), related structure-property relationship is revealed. Furthermore, we propose a molecular peripheral modification strategy, designing a series of novel red CP-MR-TADF molecules by regulating the number and type of donor units. Theoretical calculations demonstrate that introducing donor units not only effectively reduces the singlet-triplet energy gap (∆E_st), enabling efficient red TADF emission, but also allows some molecules to retain narrow-band emission characteristics. More importantly, the designed molecules exhibit significantly superior circularly polarized luminescence properties compared to the parent molecules. Notably, molecules with phenoxazine (PXZ) as the donor achieve high asymmetric factors (∼10^-2), demonstrating outstanding chiral optical response. This study reveals the intrinsic relationship between molecular structure and luminescent properties from multiple perspectives, including molecular orbital distribution and recombination energy. Our findings could provide novel design strategies for the rational development of high-performance red CP-MR-TADF materials.