Liquid Crystalline Assembly of Rod–Coil Molecules - Liquid Crystalline Functional Assemblies and Their Supramolecular Structures - page 88

aggregates with a laterally stacked bilayer encapsulated by cyclic aliphatic
chains in which the rod building blocks are arranged with their long axes par-
allel to each other. Subsequently, the ribbon nanostructures self-organize into
a 3D body-centered orthorhombic superlattice (Fig. 17a). Both steric forces
and crystallization of the rod segments are believed to play an important part
in the formation of discrete ribbons [27]. The tendency of the rod building
blocks to pack into a parallel arrangement accompanies a strong coil defor-
mation on heating. To reduce the energetic penalty associated with coil de-
formation, while maintaining crystalline order of the rod segments, infinitely
long ribbons would break up into discrete ribbons that allow coils to splay at
the periphery of the supramolecular unit. In the birefringent mesophase of
27 , small-angle X-ray scattering showed several reflections, corresponding to
a 3D body-centered tetragonal superlattice with lattice parameters of 6.1 and
5.9 nm Wide-angle scattering showed only a broad halo, indicative of liquid
crystalline order of the rod segments within domains. On cooling from the
optically isotropic mesophase, straight lines growing in four directions with
an angle of 90 ◦ could be observed in the polarized optical microscope with
a final development of mosaic texture, indicative of the presence of a 3D non-
cubic lattice [76]. On further heating to the optically isotropic mesophase,
the small-angle X-ray scattering pattern showed three sharp peaks that could
be indexed as a 3D body-centered cubic phase with a lattice parameter of
5.7 nm. According to the number of molecules per aggregate, by using the lat-
tice constants and densities, aggregates of 27 were estimated to contain about
40 molecules each. Considering microphase separation between the rod and
coil segments, the aggregation of 40 rod-coil macrocyclic molecules in an ag-
Fig. 17 Supramolecular architectures from self-assembly of rod-coil macrocycles. a Body-
centered orthorhombic structures from ribbon-like aggregates; b body-centered tetrago-
nal structures from barrel-like aggregates