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.