H2NMR angle-dependent spectral study of core dynamics in a discotic columnar phase

Abstract

A detailed (2)H NMR study of a discotic monomer is reported in its columnar phase at 61.4 MHz. A simulation of angular-dependent spectral patterns and/or signal intensities of the aromatic deuterons is shown to provide information on the small step (or jump) diffusion rates in the low temperature region of the D(ho) phase, where the motion is in the intermediate motion regime. In the high end of this phase, the motion falls into the fast motion regime and spectral patterns become insensitive to the diffusion rate. In such a case, angular-dependent NMR signal intensities were used to give the required dynamic information. The diffusive motion about the columnar axis is found to be thermally activated with an activation energy of 69 kJ/mol. Deuteron spin-lattice relaxation rates were measured at 61.4 MHz and interpreted by a conventional rotational diffusion model in order to complement and compare with the above study when possible.