THE DISCOTIC MESOPHASES OF OCTAALKYLOXYORTHOCYCLOPHANES AND OCTAALKANOYLOXYORTHOCYCLOPHANES

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.