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Figure 8.11
Self-assembly of corrole trimers. (A) Molecular structure of
corrole trimer
. (B) AFM image of the 2D patches formed
after dropcasting a chloroform solution of
6
onto a mica
surface; inset: magnification; a-b-c indicate three cross
sections. (C) Cross sections corresponding to the traces a-b-c
in (B). Reproduced with permission of The Royal Society of
Chemistry.
6
8.2.4
Application of the Linear Assemblies
It was investigated whether the line patterns formed by
on glass
could be applied as alignment layers for the liquid crystalline
compound 4-pentyl-4
4
-cyanobiphenyl (5CB) [15]. In the process of
constructing conventional LCDs, such alignment layers are typically
created following a top-down approach, by mechanical rubbing of
a polymer-coated surface in a clean room. We reasoned that such
layers might also be created by a bottom-up approach, in this case by
molecular self-assembly and dewetting. A simple liquid crystal cell,
consisting of one glass plate covered with the linear aggregates of
′
4
(which are micrometres apart) and a nonrubbed counter plate spin-
coated with a commercially available polyimide, was prepared and
filled with 5CB. Polarizing optical microscopy showed that the cells
contained aligned liquid crystal domains with a size of several square
millimetres in the regions where the linear aggregates were present
on the surface, and no alignment in other areas. The alignment was
interrupted by concentric circles, which are the contact pinning
lines, consisting of amorphous porphyrin material, which were still
present after the evaporation of the chloroform droplet. Second
harmonic generation measurements revealed that the orientation
of the long axis of the 5CB molecules was parallel to the linear
aggregates on the surface (Fig. 8.12). The highly uniform alignment
of the liquid crystalline molecules cannot be governed by mechanical
factors, i.e., by means of direct interactions with the porphyrin lines,
since these lines are too far apart to order a whole domain in this
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