CROSS-POLARIZATION DYNAMICS AND SPIN-DIFFUSION IN SOME AROMATIC-COMPOUNDS

The inversion-recovery cross-polarization (IRCP) magic-angle spinning experiment has been applied to study the C-13-H-1 cross-polarization d ynamics of protonated aromatic carbons in ferrocene, 5,6-dimethoxyindo le (DMI) and some indole derivatives. Using the C-13-detected proton s pin diffusion (SD) experiment recently developed by Zhang et al. [Soli d State Nucl. Magn. Reson., 1 (1992) 313], the slow decaying or incohe rent stage of the IRCP experiment is shown to be controlled by the spi n diffusion process at the directly bound proton. Moreover, a simple p henomenological model treating spin diffusion as a relaxation process provides an excellent agreement with both the IRCP and SD experimental data for all the different C-H pairs of DMI and its derivatives. The resulting time constants of the non-exponential spin diffusion decays are related to the local intra- and intermolecular network of dipolar interactions. This model is nevertheless found to be inadequate for fe rrocene because intramolecular spin diffusion then has an inhomogeneou s character.