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Abstract:
The mesomorphic properties of 3,4,10,11,17,18,24,25-octaalkyloxy and octaalkanoyloxycyclotetraveratrylene (orthocyclophane) have been investigated by differential scanning calorimetry (DSC), polarizing optical microscopy, NMR and X-ray diffraction. Twelve homologues of the octaalkyloxy series, with equal side chains containing n = 5 to 16 carbons per side chain, were studied and found to be mesomorphic with at least one columnar mesophase. All members of the series exhibit a biaxial columnar mesophase denoted by D1. The homologues, with n = 10 to 16, also exhibit a uniaxial columnar mesophase, between the D1 and the liquid phase, which is denoted by D2. Miscibility studies show that the D1 phases of all the compounds, and the D2 mesophases of the high members of the series are isomorphic. The D1 and D2 phases are completely miscible with M1 and M2 of the hexaalkanoyloxytriphenylene series respectively. They may, therefore, be classified as discotic B and discotic A respectively. Both phases remain stable upon addition of substantial amounts of non-mesogenic aromatic compounds. The transition between D2 and D1 is weakly first order (not observed by DSC), but the interconversion is spread over a wide temperature range (∼20°C for the n = 13 homologue). The analysis of the X-ray results shows that D2 is hexagonal and that D2 is rectangular, with one and two molecules per unit cell respectively. The lattice parameters for all measured compounds in the two mesophases are reported.
Four homologues of the octaalkanoyloxy derivatives of cyclotetraveratrylene with side chains containing 12, 14, 15 and 16 carbons were also studied by X-ray diffraction. These compounds exhibit a single discotic columnar mesophase with essentially rectangular symmetry.
