Manipulating Multiple Resonance-Charge Transfer Hybrid Proportion for Developing Red Narrowband Thermally Activated Delayed Fluorescence Materials

Multiple resonance thermally activated delayed fluorescence (MR-TADF) materials have attracted increasing attention because of their 100% exciton utilization capability and narrowband emissions. However, it remains a formidable challenge to develop such red materials. Herein, we perform a theoretical investigation on the design of red narrowband TADF materials via manipulating the MR-charge transfer (CT) hybrid proportion by regulating the types of MR cores and peripheral electron-donating units. The results indicate that the MR-CT proportion in the excited states is closely relevant to the frontier molecular orbital (FMO)/hole–electron overlap, which is mainly determined by the dihedral angle between the MR cores and the peripheral units for the MR donor–acceptor molecules. The electron-donating ability of the peripheral substituents has little influence on the FMO/hole–electron overlap. Finally, c1-a and c2-a with red narrowband emissions were revealed. These findings with rich physical insights into the structure–property relationship should provide important clues for designing red narrowband optoelectronic materials.