Understanding the spin coherence of molecular photoexcited triplet states from first principles

• URL: http://arxiv.org/abs/2609.16851v1
• Date: Tue, 15 Sep 2026 08:43:40 GMT
• Title: Understanding the spin coherence of molecular photoexcited triplet states from first principles
• Abstract summary: Photoexcited spin-triplet states in organic molecules are appealing in supporting high optical-spin contrast at room temperature.<n>We systematically explore the Hahn-echo decoherence of the benchmark molecular system for room-temperature optically detected spin coherence.<n>We describe how zero-field decoherence is driven by 6 nuclei on the guest, while high-field decoherence is driven by 600 nuclei in the host.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: Optically readable molecular spins are attractive as quantum sensors due to their nanoscale modularity, synthetic tunability, and scope for sensitive readout. In particular, photoexcited spin-triplet states in organic molecules are appealing in supporting high optical-spin contrast at room temperature. Their utility is underpinned by their coherence, which warrants a detailed understanding of it. Here, from first principles, we systematically explore the Hahn-echo decoherence of the benchmark molecular system for room-temperature optically detected spin coherence---pentacene guest molecules coupled to a para-terphenyl host. Using generalized cluster-correlation expansion methods, we investigate the mechanisms of nuclear-spin-induced decoherence from zero to high magnetic field, exploring the role of guest vs host molecules, specific nuclei, zero-field splitting interactions, and hyperfine parameters. We describe how zero-field decoherence is driven by ~6 nuclei on the guest, while high-field decoherence is driven by ~600 nuclei in the host; how the longitudinal zero-field splitting parameter, $D$, can prolong $T_2$; and the magnetic-field-dependent processes which drive decoherence. These results advance our understanding of decoherence in optically readable molecular spins, providing insight for their synthetic enhancement and deployment as quantum probes.

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