Spin-Vibronic Coupling in Indenoindenodibenzothiophene Diradicaloids

Liu L, Huang G, Chai Y, Lu X, Vidal E, Haley MM, Guldi DM (2026)

Publication Type: Journal article

Publication year: 2026

Journal

Journal of the American Chemical Society American Chemical Society

Book Volume: 148

Pages Range: 31829-31836

Journal Issue: 30

DOI: 10.1021/jacs.6c03953

Abstract

Understanding how molecular structure governs photoinduced spin evolution in organic diradicals is essential for the rational design of spin-responsive molecular materials. Here, we investigate temperature-dependent excited-state relaxation dynamics of syn- and anti-indenoindenodibenzothiophene (IIDBT) diradicaloids using variable-temperature steady-state and transient absorption spectroscopies. Vibronic progressions in the high-energy, nonfrontier-orbital π-π* transition absorptions and low-energy frontier-orbital transition absorptions prompt strong couplings between electronic excitation, on one hand, and molecular vibrations, on the other hand. With the help of ultrafast spectroscopy, we identified multistep excited-state relaxation pathways including a "hot" singlet excited state, an intermediate state of mixed electronic and spin character, and a long-lived triplet excited state, following either low- or high-energy excitations. Notably, intersystem crossing (ISC) in IIDBT diradicaloids is enabled by vibrationally activated spin-orbit coupling, in which spin-vibronic coupling enhances singlet-triplet mixing along nuclear coordinates, leading to a fast and efficient interconversion between singlet and triplet excited states. Molecular control over both the vibronic coupling strength and spin evolution is also emphasized. This work establishes a clear experimental link between molecular vibration and spin-dependent excited-state dynamics in organic diradicals, providing a general framework for understanding and controlling ISC in open-shell organic systems.

Authors with CRIS profile

Yongqiang Chai Lehrstuhl für Physikalische Chemie I Dirk Michael Guldi Lehrstuhl für Physikalische Chemie I

Additional Organisation(s)

Interdisziplinäres Zentrum für Molekulare Materialien (ICMM)

Involved external institutions

Hainan Medical University (HMU) / 海南医学院 CN China (CN) Huazhong University of Science & Technology CN China (CN) University of Oregon (UO) US United States (USA) (US)

How to cite

APA:

Liu, L., Huang, G., Chai, Y., Lu, X., Vidal, E., Haley, M.M., & Guldi, D.M. (2026). Spin-Vibronic Coupling in Indenoindenodibenzothiophene Diradicaloids. Journal of the American Chemical Society, 148(30), 31829-31836. https://doi.org/10.1021/jacs.6c03953

MLA:

Liu, Liping, et al. "Spin-Vibronic Coupling in Indenoindenodibenzothiophene Diradicaloids." Journal of the American Chemical Society 148.30 (2026): 31829-31836.

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