Self-decoupling of N-15-N-14 dipole-quadrupole couplings was studied by variable temperature N-15 CPMAS line-shape analysis of singly N-15-labeled hydrazine sulfate and (diethylamino)benzaldehyde diphenylhydrazone in various solid phases. This phenomenon is caused by molecular motions leading to fast N-14 longitudinal relaxation. In the crystalline room temperature phase of hydrazine sulfate, these motions are identified as 180 degrees jumps of hydrazonium perpendicular to the NN-axis. p-(Diethylamino)benzaldehyde diphenylhydrazone (DEH) is used as a charge transport agent in organic layered photoconductors. In the crystalline state of this compound, no self-decoupling is observed; in contrast, self-decoupling is observed in solid solutions of DEH in bisphenol A polycarbonate (PC), indicating the presence of molecular motions causing fast N-14 longitudinal relaxation. We assign these motions to an internal mobility of the phenyl groups of DEH in the glassy solution, The N-15 CPMAS NMR line shapes are interpreted in terms of a broad distribution of activation energies of the motions.