Microscopic organization of molecules in smectic A and chiral (racemic) smectic C phases: Dynamic molecular deformation effect on the S_Ato S_C∗ (S_C) transition

Abstract

Abstract We investigated the correlation between orientational order and microscopic organization of the molecules in smectic A and chiral (racemic) smectic C phases by means of solid-state C-13 NMR, powder X-ray diffraction, and electrooptical measurements. The compounds under investigation are 4-((S)-2-methyloctanoyl)phenyl 4′-nonylbiphenyl-4-carboxylate ((S)-MONBIC) and its corresponding racemic compound ((S, R)-MONBIC). Static C-13 NMR indicates that: (1) the orientational angle of the tail with respect to the magnetic field decreases slightly both in the SA and S∗C phases as decreasing temperature, and (2) the angle of the core with respect to the field decreases in the SA phase but increases in the S∗C phase as decreasing temperature. Analysis of C-13 T 1 reveals that the dynamic molecular deformation for the core part can occur near the transition. We discuss the dynamic molecular deformation in comparison with the reorientation of the director at the SA to S∗C transition. Based on the experimental results, we propose the structural model in which describes the microscopic organization of the molecules in the mesophases.