Photochemically induced dynamic nuclear polarization (photo-CIDNP) is a method to hyperpolarize nuclear spins using light. In most cases, CIDNP experiments are performed in high magnetic fields and the sample is irradiated by light inside a nuclear magnetic resonance (NMR) spectrometer. Here we demonstrate photo-CIDNP hyperpolarization generated in the Earth's magnetic field and under zero- to ultralow-field (ZULF) conditions. Irradiating a sample containing tetraphenylporphyrin and para-benzoquinone for several seconds with light-emitting diodes produces strong hyperpolarization of H and C nuclear spins, enhancing the NMR signals more than 200 times. The hyperpolarized spin states at the Earth's field and in ZULF are different. In the latter case, the state corresponds to the singlet order between scalar-coupled H-C nuclear spins. This state has a longer lifetime than the state hyperpolarized at Earth's field. The method is simple and cost-efficient and should be applicable to many molecular systems known to exhibit photo-CIDNP, including amino acids and nucleotides.

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http://dx.doi.org/10.1021/acs.jpclett.1c00503DOI Listing

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Article Synopsis
  • Dynamic nuclear polarization (DNP) and quantum technologies utilize the spin transfer in electron-nuclear quantum systems, but larger couplings like hyperfine interactions can hinder these processes.
  • The Schrieffer-Wolff transformation is applied to analyze a system of two electrons and two nuclei, focusing on polarization-transfer methods, including an energy-conserving electron-nuclear four-spin flip-flop.
  • The study connects magnetic resonance and quantum information, demonstrating a model where all nuclear spins can aid in hyperpolarization without being impeded by a spin diffusion barrier in DNP.
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