S. Zamir et al., MOLECULAR ORDERING AND DYNAMICS IN THE COLUMNAR MESOPHASE OF A NEW DIMERIC DISCOTIC LIQUID-CRYSTAL AS STUDIED BY X-RAY-DIFFRACTION AND DEUTERIUM NMR, Journal of the American Chemical Society, 116(5), 1994, pp. 1973-1980
The preparation and mesomorphic properties of a new discotic dimer, bi
s [pentakis(pentyloxy)triphenylenyloxy]- decane (DTHE5) is described.
This molecule is a perfect twin of the monomeric hexakis(pentyloxy) tr
iphenylene (THE5) in that both the spacer and the free alkyl chains ar
e linked via ether bonds and the spacer is exactly twice the length of
the free side chains. DTHE5 exhibits a columnar discotic phase which
is completely miscible with that of THE5 and is thus classified as D-A
, i.e. ordered hexagonal (D-ho. X-ray diffraction measurements confirm
the assignment and provide geometrical lattice parameters (a = 20.2 A
ngstrom; stacking distance of d = 3.48 Angstrom at room temperature) a
s well as correlation lengths for both (345 and 125 Angstrom, respecti
vely). Deuterium NMR measurements of specifically deuterated DTHE5 in
the mesophase region exhibit dynamic line shapes consistent with restr
icted, high-amplitude, planar librations of the monomeric subunits wit
hin the columns. A theory which considers the effect of this motion on
the NMR line shape in terms of a diffusion equation in a restricting
potential is developed and used to simulate the experimental spectra.
The results of the analysis provide kinetic and model related paramete
rs.