N. Spielberg et al., THE DISCOTIC MESOPHASES OF OCTAALKYLOXYORTHOCYCLOPHANES AND OCTAALKANOYLOXYORTHOCYCLOPHANES, Liquid crystals, 15(3), 1993, pp. 311-330
The mesomorphic properties of 3,4,10,11,17,18,24,25-octaalkyloxy and o
ctaalkanoyloxycyclotetraveratrylene (orthocyclophane) have been invest
igated by differential scanning calorimetry (DSC), polarizing optical
microscopy, NMR and X-ray diffraction. Twelve homologues of the octaal
kyloxy series, with equal side chains containing n = 5 to 16 carbons p
er side chain, were studied and found to be mesomorphic with at least
one columnar mesophase. All members of the series exhibit a biaxial co
lumnar mesophase denoted by D1. The homologues, with n = 10 to 16, als
o exhibit a uniaxial columnar mesophase, between the D1 and the liquid
phase, which is denoted by D2. Miscibility studies show that the D1 p
hases of all the compounds, and the D2 mesophases of the high members
of the series are isomorphic. The D1 and D2 phases are completely misc
ible with M1 and M2 of the hexaalkanoyloxytriphenylene series respecti
vely. They may, therefore, be classified as discotic B and discotic A
respectively. Both phases remain stable upon addition of substantial a
mounts of non-mesogenic aromatic compounds. The transition between D2
and D1 is weakly first order (not observed by DSC), but the interconve
rsion is spread over a wide temperature range (approximately 20-degree
s-C for the n = 13 homologue). The analysis of the X-ray results shows
that D2 is hexagonal and that D1 is rectangular, with one and two mol
ecules per unit cell respectively. The lattice parameters for all meas
ured compounds in the two mesophases are reported. Four homologues of
the octaalkanoyloxy derivatives of cyclotetraveratrylene with side cha
ins containing 12, 14, 15 and 16 carbons were also studied by X-ray di
ffraction. These compounds exhibit a single discotic columnar mesophas
e with essentially rectangular symmetry.