approximately 2.5 Å larger than that of triphenylene. The
increase in core size may be somewhat offset in the columnar
phase by a greater degree of interdigitation of the side chains for
1b, leading to the relatively modest change in the inter-
columnar spacing.
Despite the similarity in their XRD patterns, the benzo-
triphenylene mesogen is liquid crystalline over a much broader
temperature range than HAT10, which forms a columnar
hexagonal phase from only 58–69 °C.12 This large difference
likely reflects the greater propensity of the larger cores to self-
assemble into columnar structures. Like many triphenylene
derivatives,13 compound 1b becomes homeotropically aligned
when slowly annealed from the isotropic phase.
The demonstration that compound 1b exhibits a stable, easily
aligned columnar liquid crystal phase at relatively low tem-
peratures suggests that benzo[b]triphenylene derivatives may
be promising candidates for practical applications where
formation of a broad columnar phase at room temperature is
highly desirable. We are currently investigating other members
of this series in order to gain further insight into their phase
behaviour and electronic properties.
isotropic liquid at 144 °C. For this reason, we decided to prepare
an analogue in which the methoxy groups were replaced by
longer chains that would be more conducive to liquid crystal-
linity. To this end, 1a was dealkylated using BBr3 and the
resulting hexahydroxy intermediate was converted to the
hexakis(dececyloxy)benzotriphenylene product, 1b.
The thermal properties of compound 1b were examined using
polarized optical microscopy and differential scanning calo-
rimetry (DSC). This benzotriphenylene was found to exhibit a
liquid crystal phase between 35 °C and 88 °C; the enthalpies of
these transitions were 51.4 J g21 and 1.0 J g21, respectively.
This mesophase exhibits the characteristic dendritic texture of a
columnar hexagonal phase when examined under a microscope
(Fig. 1). This assignment was confirmed by the X-ray
diffraction pattern, which has two peaks in the small angle
region that index to the (100) and (110) reflections of a two
dimensional hexagonal lattice. We also observed a broad halo
centred at 4.5 Å and a peak at 3.6 Å, which were assigned to the
spacings between alkyl chains and the central p-systems,
respectively.
Acknowledgements: The authors gratefully acknowledge the
financial assistance of Simon Fraser University and the Natural
Sciences and Engineering Research Council (NSERC).
Notes and references
It is interesting to compare the phase behaviour of this
compound with that of the analogous HAT derivative,
2,3,6,7,10,11-hexadecyloxytriphenylene (HAT10). The XRD
patterns of 1b and HAT10 are surprisingly similar; the latter
possesses a lattice constant of 25.7 Å, whereas the inter-
columnar distance observed for 1b was 26.7 Å. This difference
is smaller than anticipated based on the size of the two
molecules, since the long axis of benzo[b]triphenylene is
1 N. Boden and B. Movaghar, in Applicable Properties of Columnar
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2 N. Boden, R. J. Bushby, G. Headdock, O. R. Lozman and A. Wood, Liq.
Cryst., 2001, 28, 139.
3 A. N. Cammidge and R. J. Bushby, in Synthesis and Structural
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Vill, Wiley-VCH, New York, 1998.
4 A. N. Cammidge and H. Gopee, Chem. Commun., 2002, 966.
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6 K. Msayib, S. Mahkseed and N. B. McKeown, J. Mater. Chem., 2001,
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Fig. 1 Polarized optical micrograph of 1b obtained from cooling at 85 °C
(1003).
13 T. Christ, B. Glüsen, A. Greiner, A. Kettner, R. Sander, V. Stümpflen,
V. Tsukruk and J. H. Wendorff, Adv. Mater., 1997, 9, 48.
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