Abstract: Over the past decade, azobenzene-based molecular photo-switches have emerged as promising control devices in chemistry, biology, and pharmacology, due to their ability to dynamically control processes with high spatiotemporal precision using light as an external stimulus, effectively altering protein activity, controlling mitosis with single-cell spatial precision, studying the biological role of specific receptors, and storing solar energy. This study introduces an innovative approach termed Photo-SABRE[1], combining Signal Amplification by Reversible Exchange (SABRE) and parahydrogen with light irradiation at ultralow magnetic fields (400 nT) to achieve substantial nuclear spin polarization in azobenzene isomers. We report enhancements of 23,000-fold and 9,200-fold for the cis and trans isomers of azobenzene, respectively, compared to their thermal 15N NMR signals at 9.4 T. Our results demonstrate that only cis-azobenzene directly acquires significant hyperpolarization from parahydrogen via coherent polarization transfer in SABRE. Reversible photoinduced cis-trans isomerization at ultralow magnetic fields preserves the SABRE-derived nuclear hyperpolarization of cis-azobenzene, subsequently hyperpolarizing trans-azobenzene despite its sterically hindered direct coordination with the SABRE Ir-complex (Figure 1). This method also facilitates the hyperpolarization of the long-lived spin order of trans-azobenzene 15N spins, with a lifetime of about 25 minutes, greatly exceeding their relaxation times at high (10 seconds) and low (200 seconds) magnetic fields. This long-lived spin order can be detected by 15N or 1H NMR, presenting significant advantages for various applications. The efficiency of polarization transfer in the SABRE method is significantly influenced by temperature. We have developed an improved device for sample thermal stabilization in an ultralow magnetic field under light irradiation. The temperature dependence of 15N SABRE for both trans and cis azobenzene at various magnetic fields has been investigated. Our results demonstrate that the maximum polarization levels of 15N nuclei are achieved at 37 degrees Celsius. Funding: This work was supported by the Russian Science Foundation (grant number #23-73-10103)

Cite: Kiryutin A. , Kozinenko V. , Fishman N. , Yurkovskaya A.
Nuclear Spin Hyperpolarization of cis-trans Photoswitchable Molecules by Parahydrogen
In compilation Book of abstracts of Spin Chemistry Meeting. 2024.

Dates:

Submitted:	Jun 30, 2024
Published online:	Oct 1, 2024

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