Kagawa, A.; Murokawa, Y.; Takeda, K.; Kitagawa, M. J. Magn. Reson. 2009, 197, 9.
In dynamic nuclear polarization (DNP) using photo-excited triplet electron spins, known as Microwave-Induced Optical Nuclear Polarization (MIONP), the attainable 1H polarization is determined by the ratio of the buildup rate and the spin-lattice relaxation rate, in turn depend on the 1H spin density. It is shown that the final 1H polarization can be enhanced by diluting the 1H spins with partial deuteration. The DNP experiments are demonstrated in 0.05 mol% pentacene-doped p-terphenyl for various 1H abundances. It is also shown that the 1H spin diffusion coefficient can be determined by examining the initial buildup rate of 1H polarization for various repetition rates of the DNP sequence.