Jul 12, 2019

Nonpentacene Polarizing Agents with Improved Air Stability for Triplet Dynamic Nuclear Polarization at Room Temperature

Kouno, Hironori, Yusuke Kawashima, Kenichiro Tateishi, Tomohiro Uesaka, Nobuo Kimizuka, and Nobuhiro Yanai. “Nonpentacene Polarizing Agents with Improved Air Stability for Triplet Dynamic Nuclear Polarization at Room Temperature.” The Journal of Physical Chemistry Letters 10, no. 9 (May 2, 2019): 2208–13.


Triplet dynamic nuclear polarization (triplet-DNP), a method to enhance the NMR and MRI sensitivity using photo-excited triplet electrons, has a great potential to hyperpolarize nuclear spins at room temperature. Since the first report of room-temperature triplet-DNP in 1990, pentacene has been the only and best option of triplet polarizing agents. However, the poor airstability of pentacene has severely limited the applicability of triplet-DNP. Here, we report the first example of polarizing agents with significant air-stability as well as high polarizing ability comparable to pentacene. The introduction of electron-withdrawing diaza-substitution to pentacene and tetracene reduces the LUMO level and endows much-improved stability under the ambient condition. Importantly, the diaza-substituted pentacene and tetracene offer similar, or even slightly better, 1H NMR signal enhancement compared with pentacene in the prototypical triplet-DNP test using p-terphenyl crystals. This work removes one of the largest obstacles towards the application of triplet-DNP for hyperpolarization of biological molecules.