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Electron spin-lattice relaxation in triplet-state oligoacenes: a first-principles-based approach
Katsuki Miyokawa1, Yuki Kurashige1,2,3
1Department of Chemistry, Graduate School of Science, Kyoto University, Kitashirakawa Oiwake-cho, Sakyo-ku Kyoto, 606-8502, Japan. miyokawa@theoc.kuchem.kyoto-u.ac.jp.
Physical Chemistry Chemical Physics : PCCP
|December 12, 2025
Summary
Organic spin polarization, crucial for quantum technologies, is influenced by spin-lattice relaxation time. This study reveals librational motions dominate relaxation in oligoacenes, with pentacene
Area of Science:
- Quantum Chemistry and Materials Science
- Spin Physics and Quantum Technologies
Background:
- Organic chromophores in triplet states exhibit spin polarization, a phenomenon with potential in quantum sensing and computing.
- Molecular spin polarizing agents offer tunable properties, but understanding structure-property relationships, especially spin-lattice relaxation, is crucial for molecular design.
- Spin-lattice relaxation time, governing polarization lifetime, is poorly understood due to complex spin-phonon couplings and limitations of conventional theoretical models.
Purpose of the Study:
- To investigate the electron spin-lattice relaxation mechanisms in triplet-state oligoacenes using first-principles calculations.
- To elucidate the contributions of different molecular vibrational modes to spin relaxation in these important spin polarizing agents.
- To establish a foundation for understanding molecular structure and packing effects on spin relaxation dynamics.
Main Methods:
- Employed first-principles calculations within the Redfield relaxation model to study electron spin-lattice relaxation.
- Utilized quantum chemical calculations to determine parameters for the relaxation model.
- Analyzed the contribution of individual molecular vibrational modes to the overall relaxation process.
Main Results:
- Librational motions were identified as the dominant contributor to spin relaxation in oligoacenes, directly affecting zero-field splitting axes.
- In pentacene, out-of-plane molecular vibrations were found to significantly contribute to spin relaxation, potentially explaining experimental observations of anisotropic relaxation.
- The study provides detailed insights into the molecular mechanisms governing spin relaxation in triplet-state oligoacenes.
Conclusions:
- First-principles calculations offer a powerful approach to understanding spin relaxation dynamics in molecular systems.
- The findings highlight the importance of specific vibrational modes, like librational and out-of-plane motions, in determining spin polarization lifetimes.
- This work paves the way for rational molecular design of advanced spin polarizing agents for quantum applications.
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