H2-decoupling-accelerated H1 spin diffusion in dynamic nuclear polarization with photoexcited triplet electrons

Abstract

In dynamic nuclear polarization (DNP) experiments applied to organic solids for creating nonequilibrium, high H1 spin polarization, an efficient buildup of H1 polarization is attained by partially deuterating the material of interest with an appropriate H1 concentration. In such a dilute H1 spin system, it is shown that the H1 spin diffusion rate and thereby the buildup efficiency of H1 polarization can further be enhanced by continually applying radiofrequency irradiation for deuterium decoupling during the DNP process. As experimentally confirmed in this work, the electron spin polarization of the photoexcited triplet state is mainly transferred only to those H1 spins, which are in the vicinity of the electron spins, and H1 spin diffusion transports the localized H1 polarization over the whole sample volume. The H1 spin diffusion coefficients are estimated from DNP repetition interval dependence of the initial buildup rate of H1 polarization, and the result indicates that the spin diffusion coefficient is enhanced by a factor of 2 compared to that without H2 decoupling.This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in M. Negoro, K. Nakayama, K. Tateishi, A. Kagawa, K. Takeda, and M. Kitagawa, J. Chem. Phys. 133, 154504 (2010) and may be found at https://doi.org/10.1063/1.3493453