Interlayer Self-Diffusion and Structure of Chiral Smectic Phases Studied by 2H NMR Exchange Experiment.

A deuterium two-dimensional exchange NMR technique is used to study the chiral smectic C (SmC*) and chiral subphases (Sm%@mt;sys@%%@ital@%C%@rsf@%%@sx@%Fi1%@be@%*%@sxx@%%@mx@%, Sm%@mt;sys@%%@ital@%C%@rsf@%%@sx@%Fi2%@be@%*%@sxx@%%@mx@%) of a smectogen (s)-1-methylheptyl 4‘-(4-n-decyloxy-benzoyloxy)biphenyl-4-carboxylate (10B1M7). The aim is to demonstrate how this technique can be combined with sample rotation in the magnetic field to obtain the fast translational self-diffusion constant along the helical pitch in the SmC* phase and to shed light on the structure of helicoidal superlattice in the three-layer Sm%@mt;sys@%%@ital@%C%@rsf@%%@sx@%Fi1%@be@%*%@sxx@%%@mx@% and four-layer Sm%@mt;sys@%%@ital@%C%@rsf@%%@sx@%Fi2%@be@%*%@sxx@%%@mx@% phases. The cross-peak intensities in the 2D exchange spectrum are sensitive to the disposition of molecules in the three- and four-layer base unit. The results support the “asymmetric Clock model” as an appropriate description of the ferrielectric phases in this compound. [ABSTRACT FROM AUTHOR]