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

Huanling Liu; Yan Wang; Songsong Liu; Lili Lin; Yuzhi Song; Chuan-Kui Wang; Zhen Xie; Jianzhong Fan

doi:10.1016/j.saa.2025.126625

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

Spectrochim Acta A Mol Biomol Spectrosc. 2025 Jun 30:343:126625. doi: 10.1016/j.saa.2025.126625. Online ahead of print.

Authors

Huanling Liu¹, Yan Wang¹, Songsong Liu¹, Lili Lin¹, Yuzhi Song¹, Chuan-Kui Wang¹, Zhen Xie², Jianzhong Fan³

Affiliations

¹ Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, Institute of Materials and Clean Energy, School of Physics and Electronics, Shandong Normal University, Jinan 250014, China.
² Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, Institute of Materials and Clean Energy, School of Physics and Electronics, Shandong Normal University, Jinan 250014, China. Electronic address: xiezhen@sdnu.edu.cn.
³ Shandong Province Key Laboratory of Medical Physics and Image Processing Technology, Institute of Materials and Clean Energy, School of Physics and Electronics, Shandong Normal University, Jinan 250014, China; State Key Laboratory of Luminescent Materials and Devices, South China University of Technology, China. Electronic address: fanjianzhongvip@163.com.

PMID: 40609373
DOI: 10.1016/j.saa.2025.126625

Abstract

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.

Keywords: Intersystem crossing; N-π* transitions; Oxidation effects; Room temperature phosphorescence.