THE MESOPHASES OF OCTA-ALKANOYLOXY-9,10-ANTHRAQUINONE

Nine members of the octa-n-alkanoyloxy-9,10-anthraquinone series, rang ing from octanoyloxy (n = 8) to hexadecanoyloxy (n = 16) (where n is t he number of carbon atoms per chain), were prepared and their mesomorp hic properties studied by differential scanning calorimetry and optica l microscopy. All the compounds studied are mesomorphic with the highe r homologues exhibiting two (for n greater-than-or-equal-to 12) or eve n three (for n greater-than-or-equal-to 14) columnar mesophases. For n = 8 to 11, the phase sequence is C-D(B)-1, where D(B) is an optically biaxial mesophase with a two-dimensional pgg symmetry. For n = 12, 13 , the phase sequence is C-M3-D(B)-I, where M3 is a highly ordered phas e whose structure has not been identified. Finally for n = 14 to 16, t he phase sequence is C-M3-D(B)-D(A)-I, where D(A) is an hexagonal phas e. In all cases, the phases change from high to low order with increas ing temperature and all transitions are first order. Compared with the corresponding hexa-substituted naphthoquinones the present series gen erates larger mesomorphic ranges and the higher homologues exhibit a u niaxial phase which is lacking in the hexa-substituted series. The inc rease in volume occupied by the aliphatic chains in the octasubstitute d series is evidently sufficient to reduce the interaction between the aromatic cores of the different columns to permit the stability of a uniaxial phase.