MICROSCOPIC ORGANIZATION OF MOLECULES IN SMECTIC-A AND CHIRAL (RACEMIC) SMECTIC-C PHASES - DYNAMIC MOLECULAR DEFORMATION EFFECT ON THE S-A TO S-C(ASTERISK) (S-C) TRANSITION

We investigated the correlation between orientational order and micros copic organization of the molecules in smectic A and chiral (racemic) smectic C phases by means of solid-state C-13 NMR, powder X-ray diffra ction, and electrooptical measurements. The compounds under investigat ion are 4-((S)-2-methyloctanoyl)phenyl 4'-nonylbiphenyl-4-carboxylate ((S)-MONBIC) and its corresponding racemic compound ((S,R)-MONBIC). St atic C-13 NMR indicates that: (1) the orientational angle of the tail With respect to the magnetic field decreases slightly both in the S-A and S-C phases as decreasing temperature, and (2) the angle of the co re with respect to the field decreases in the S-A phase but increases in the S-C phase as decreasing temperature. Analysis of C-13 T-1 reve als 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 S-A to S-C t ransition. Based on the experimental results, we propose the structura l model in which describes the microscopic organization of the molecul es in the mesophases.