Room-temperature hyperpolarization of polycrystalline samples with optically polarized triplet electrons: pentacene or nitrogen-vacancy center in diamond?

Koichiro Miyanishi; Takuya F Segawa; Kazuyuki Takeda; Izuru Ohki; Shinobu Onoda; Takeshi Ohshima; Hiroshi Abe; Hideaki Takashima; Shigeki Takeuchi; Alexander I Shames; Kohki Morita; Yu Wang; Frederick T-K So; Daiki Terada; Ryuji Igarashi; Akinori Kagawa; Masahiro Kitagawa; Norikazu Mizuochi; Masahiro Shirakawa; Makoto Negoro

doi:10.5194/mr-2-33-2021

Room-temperature hyperpolarization of polycrystalline samples with optically polarized triplet electrons: pentacene or nitrogen-vacancy center in diamond?

Magn Reson (Gott). 2021 Feb 17;2(1):33-48. doi: 10.5194/mr-2-33-2021. eCollection 2021.

Authors

Koichiro Miyanishi¹, Takuya F Segawa^{2

3}, Kazuyuki Takeda⁴, Izuru Ohki⁵, Shinobu Onoda^{6

7}, Takeshi Ohshima^{6

7}, Hiroshi Abe^{6

7}, Hideaki Takashima⁸, Shigeki Takeuchi⁸, Alexander I Shames⁹, Kohki Morita⁵, Yu Wang⁴, Frederick T-K So^{2

6}, Daiki Terada^{2

6}, Ryuji Igarashi^{6

7

10}, Akinori Kagawa^{1

10

11}, Masahiro Kitagawa^{1

11}, Norikazu Mizuochi⁵, Masahiro Shirakawa^{2

6}, Makoto Negoro^{6

10

11}

Affiliations

¹ Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan.
² Department of Molecular Engineering, Graduate School of Engineering, Kyoto University, Nishikyo-Ku, Kyoto 615-8510, Japan.
³ Laboratory for Solid State Physics, ETH Zurich, 8093 Zurich, Switzerland.
⁴ Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
⁵ Institute for Chemical Research, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan.
⁶ Institute for Quantum Life Science, National Institutes for Quantum and Radiological Science and Technology, 4-9-1, Anagawa, Inage-Ku, Chiba 263-8555, Japan.
⁷ Takasaki Advanced Radiation Research Institute, National Institutes for Quantum and Radiological Science and Technology, 1233 Watanuki, Takasaki, Gunma 370-1292, Japan.
⁸ Department of Electronic Science and Engineering, Kyoto University, Nishikyo-ku, Kyoto 615-8510, Japan.
⁹ Department of Physics, Ben-Gurion University of the Negev, 8410501 Beer-Sheva, Israel.
¹⁰ JST, PRESTO, Kawaguchi, Japan.
¹¹ Center for Quantum Information and Quantum Biology, Institute for Open and Transdisciplinary Research Initiatives, Osaka University, 1-2 Machikaneyama, Toyonaka, Osaka 560-0043, Japan.

Abstract

We demonstrate room-temperature $^{13}$ C hyperpolarization by dynamic nuclear polarization (DNP) using optically polarized triplet electron spins in two polycrystalline systems: pentacene-doped [carboxyl- $^{13}$ C] benzoic acid and microdiamonds containing nitrogen-vacancy (NV $^{-}$ ) centers. For both samples, the integrated solid effect (ISE) is used to polarize the $^{13}$ C spin system in magnetic fields of 350-400 mT. In the benzoic acid sample, the $^{13}$ C spin polarization is enhanced by up to 0.12 % through direct electron-to- $^{13}$ C polarization transfer without performing dynamic $^{1}$ H polarization followed by $^{1} H -^{13} C$ cross-polarization. In addition, the ISE has been successfully applied to polarize naturally abundant $^{13}$ C spins in a microdiamond sample to 0.01 %. To characterize the buildup of the $^{13}$ C polarization, we discuss the efficiencies of direct polarization transfer between the electron and $^{13}$ C spins as well as that of $^{13} C -^{13} C$ spin diffusion, examining various parameters which are beneficial or detrimental for successful bulk dynamic $^{13}$ C polarization.