Dynamics and molecular order of the liquid-crystalline complexes of 5-octadecyloxyisophthalic acid and cyclic oligo-amines, investigated by 2H N.M.R. spectroscopy

Complexes of 5-octadecyloxyisophthalic acid with piperazine, 1,4,7-triazacyclononane and 1,4,7,10-hexaazacyclooctadecane were selectively deuterated in various positions, and investigated with variable-temperature solid-state 2 H n.m.r. spectroscopy. All systems form stable, enantiotropic liquid-crystalline phases at high temperature, and the dynamics in these phases can be described by a single motional model. This model involves fast rotation around the director coupled with a rapid phenyl flip. Macroscopically oriented liquid-crystalline phases with the director parallel to the magnetic field are found on cooling in a magnetic field of 7 T for the piperazine complexes, but only partial macroscopic order was achieved for the complexes with 1,4,7,10-hexaazacyclooctadecane and 1,4,7-triazacyclononane under these conditions, and also for the former in a magnetic field of 11 T. In contrast to the pure acid C 18 ISA, the stability of the phases is determined by the hydrogen/ionic bonds between the acid and the bases, and not by the alkyl-alkyl interactions.