Terminal Diazirines Enable Reverse Polarization Transfer from ¹⁵ N ₂ Singlets

Abstract Diazirine moieties are chemically stable and have been incorporated into biomolecules without impediment of biological activity. The 15 N 2 labeled diazirines are appealing motifs for hyperpolarization supporting relaxation protected states with long‐lived lifetimes. The (‐CH 15 N 2 ) diazirine groups investigated here are analogues to methyl groups, which provides the opportunity to transfer polarization stored on a relaxation protected (‐CH 15 N 2 ) moiety to 1 H, thus combining the advantages of long lifetimes of 15 N polarization with superior sensitivity of 1 H detection. Despite the proximity of 1 H to 15 N nuclei in the diazirine moiety, 15 N T 1 times of up to (4.6±0.4) min and singlet lifetimes T s of up to (17.5±3.8) min are observed. Furthermore, we found terminal diazirines to support hyperpolarized 1 H 2 singlet states in CH 2 groups of chiral molecules. The singlet lifetime of 1 H singlets is up to (9.2±1.8) min, thus exceeding 1 H T 1 relaxation time (at 8.45 T) by a factor of ≈100.