Modulating exciton transfer pathways via oxidation and n-π* transitions for efficient room-temperature...

Organic room-temperature phosphorescence (RTP) materials hold promising applications in the field of display technologies and information encryption. Achieving efficient RTP emission relies on precisely regulating excited-state properties and luminescence pathways. In this study, three experimentally reported donor-acceptor molecules are selected, and the effects of oxidation on their photophysical properties are systematically investigated by first-principles calculations. The results show that oxidation of the donor units effectively modulates intramolecular charge transfer characteristics and the excited state energy levels, thereby influencing the reverse intersystem crossing (RISC) and exciton transfer processes, related thermally activated delayed fluorescence (TADF) and RTP emission mechanisms are revealed. Among the studied molecules, the fully oxidized molecule DOPTZ-CO exhibits the most favorable RTP performance. Using DOPTZ as the oxidized donor, three molecules featuring pronounced n-π* transition characteristics are further designed, and a novel strategy is proposed to regulate emission pathways by incorporating non-bonding (n) orbitals. The introduction of n-π* transition is found to play a dual role: it enhances spin-orbit coupling (SOC) effect, facilitating radiative T₁-S₀ transitions and it also increases the S₁-T₁ energy gap (ΔE_ST), thereby suppressing RISC process and favoring RTP-dominated emission. Thus, molecules with moderate ΔE_ST values (approximately 0.4 eV) and strong n-π* character demonstrate efficient and controllable RTP behavior. Overall, this study underscores the critical role of excited-state modulation and orbital engineering in tuning emission pathways and provides a theoretical foundation for the rational design of high-performance organic RTP materials.