2H-decoupling-accelerated 1H spin diffusion in dynamic nuclear polarization with photoexcited triplet electrons.

In dynamic nuclear polarization (DNP) experiments applied to organic solids for creating nonequilibrium, high ¹H spin polarization, an efficient buildup of ¹H polarization is attained by partially deuterating the material of interest with an appropriate ¹H concentration. In such a dilute ¹H spin system, it is shown that the ¹H spin diffusion rate and thereby the buildup efficiency of ¹H 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 ¹H spins, which are in the vicinity of the electron spins, and ¹H spin diffusion transports the localized ¹H polarization over the whole sample volume. The ¹H spin diffusion coefficients are estimated from DNP repetition interval dependence of the initial buildup rate of ¹H polarization, and the result indicates that the spin diffusion coefficient is enhanced by a factor of 2 compared to that without ²H decoupling. [ABSTRACT FROM AUTHOR]