Condis Crystals of Small Molecule VI. The Differences Between Smectic and Condis Phases, Evaluated by a Solid State 13C NMR Study of N,N′-bis(4-n-octyloxybenzal)-1,4-phenylenediamine (OOBPD)

Abstract

Abstract Carbon-13 NMR spectra have been obtained for N,N′-bis(4-n-octyloxybenzal)-1,4-phenylenediamine (OOBPD) in the condis and smectic phases. Sharp, well-resolved spectra were obtained without magic angle sample spinning in the smectic phases under the conditions of cross-polarization or single carbon pulse followed by high-power proton decoupling. The smectic I-to-smectic C transition involves a discontinuous change in 13C chemical shifts due to a large degree to orientational disordering. Similar behavior was found between the spectra of smectic C and the isotopic state. Order parameters for various smectic phases are calculated based on the observed differences in 13C chemical shift between the isotropic state and the smectic phase. The spectra were measured at different sample orientation with respect to the external magnetic field, and show that reorienting the smectic molecules in a magnetic field is facile. Larger difference can be found between the spectra obtained by cross polarization and th...