The crucial role of non-conjugated functional groups in the triplet manipulation of heterocycle aromaticity hot exciton materials

Hot exciton materials have gained widespread attention in the field of organic light-emitting diodes (OLEDs) on the strength of the effective triplet exciton utilization via rapid high-lying excited state reverse intersystem crossing (hRISC) processes. However, the development of hot exciton materials is subject to the lack of a practicable molecular design strategy as well as guidelines, and current material design and screening often have to rely on an experimental trial-and-error process. Taking the proposed heterocycle aromaticity design strategy as a foundation, we systematically investigated the role of non-conjugated functional groups on the fluorescence behavior and exciton dynamics based on a series of pyrazoline hot exciton materials using both theoretical and experimental evidence. Results show that beyond the steric resistance effect, as envisioned, these non-conjugated functional groups also play a crucial role in triplet manipulation via enriching the hRISC channels. A series of new blue-emitting hot exciton materials were successfully fabricated with a high luminous efficiency in the solid state (up to 87%). These findings not only provide an important supplement to the proposed heterocycle aromaticity strategy but also offer some insights into rational excited state manipulation, which could be used to design and develop new luminescent materials for OLED applications.