Dynamic nuclear polarization by electron spins in the photoexcited triplet state: II. High polarization of the residual protons in deuterated naphthalene

Experiments of dynamic nuclear polarization by electron spins in the photoexcited triplet state were made using single crystal and polycrystalline samples of 99.21%-deuterated naphthalene doped with 0.015 mol% pentacene. In the single crystal sample, the polarization of the residual protons was built up to 0.7 at 105 K, reaching the ultimate polarization equal to the photo-induced electron spin polarization. A doublet due to the two protons which happen to be adjacent to each other in a deuterated naphthalene molecule was observed in the single crystal under deuteron double-quantum decoupling; it exhibits polarization-induced asymmetry when observed by a small-tip angle pulse. In the polycrystalline sample the resultant H-1 polarization was 0.033. The H-1 NMR lineshape under deuteron decoupling in the single crystal and the inhomogeneous H-1 distribution in a deuterated naphthalene molecule are discussed.