Dynamic Nuclear Polarization Using Electron Spin Cluster

Raj K Chaklashiya; Asif Equbal; Andrey Shernyukov; Yuanxin Li; Karen Tsay; Quentin Stern; Victor Tormyshev; Elena Bagryanskaya; Songi Han

doi:10.1021/acs.jpclett.4c00182

Dynamic Nuclear Polarization Using Electron Spin Cluster

J Phys Chem Lett. 2024 May 23;15(20):5366-5375. doi: 10.1021/acs.jpclett.4c00182. Epub 2024 May 12.

Authors

Raj K Chaklashiya¹, Asif Equbal^{2

3}, Andrey Shernyukov⁴, Yuanxin Li⁵, Karen Tsay⁵, Quentin Stern⁶, Victor Tormyshev⁴, Elena Bagryanskaya⁴, Songi Han^{6

7}

Affiliations

¹ Materials Department, University of California, Santa Barbara, Santa Barbara, California 93106, United States.
² Division of Chemistry, New York University Abu Dhabi, Abu Dhabi, United Arab Emirates.
³ Center for Quantum and Topological Systems, NYUAD Research Institute, New York University Abu Dhabi, PO Box 129188, Abu Dhabi, United Arab Emirates.
⁴ N.N. Vorozhtsov Novosibirsk Institute of Organic Chemistry SB RAS, Novosibirsk 630090, Russia.
⁵ Department of Chemistry & Biochemistry, University of California, Santa Barbara, Santa Barbara, California 93106, United States.
⁶ Department of Chemistry, Northwestern University, Wilmette, Illinois 60208, United States.
⁷ Department of Chemical Engineering, University of California, Santa Barbara, Santa Barbara, California 93106, United States.

PMID: 38735065
DOI: 10.1021/acs.jpclett.4c00182

Abstract

Dynamic nuclear polarization (DNP) utilizing narrow-line electron spin clusters (ESCs) to achieve nuclear spin resonance matching (ESC-DNP) by microwave irradiation is a promising way to achieve NMR signal enhancements with a wide design scope requiring low microwave power at high magnetic field. Here we present the design for a trityl-based tetra-radical (TetraTrityl) to achieve DNP for ¹H NMR at 7 T, supported by experimental data and quantum mechanical simulations. A slow-relaxing (T_1e ≈ 1 ms) 4-ESC is found to require at least two electron spin pairs at <8 Å e-e spin distance to yield ¹H ESC-DNP enhancement, while squeezing the rest of the e-e spin distances to <12 Å results in optimal ¹H ESC-DNP enhancements. Fast-relaxing ESCs (T_1e ≈ 10 μs) are found to require a weakly coupled narrow-line radical (sensitizer) to extract polarization from the ESC. These results provide design principles for achieving a power-efficient DNP at high field via ESC-DNP.