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Figure 8.10
(A) Molecular structure of porphyrin trimer
, which has
chiral alkyl chains. (B) AFM image of the fibre-like structures
obtained when an
5
is evaporated on
mica. The inset shows a cross section, the bar represents
2
n
-hexane solution of
5
m, and the dashed circles indicate locations where the
fibres cross each other. Copyright American Chemical Society,
2008.
µ
In addition to the changes in surface and solvent, also changes to
the molecular structure of the trimeric disks based on BTA turned
out to have a dramatic influence on their self-assembly behaviour.
When instead of a porphyrin trimer, corrole trimer
(Fig. 8.11A)
was subjected to self-assembly and dewetting, no line patterns
were observed when a chloroform solution of the compound was
dropcasted on mica [18]. Instead, extended 2D patches of material
were observed by AFM (Fig. 8.11B), which remarkably again had
the height of a single molecule (2.9 nm, Fig. 8.11C). NMR and UV-
vis studies revealed that in the solution the molecules of
6
still
self-assembled in columnar stacks. A closely packed arrangement
of these stacks on the surface upon dewetting of the solution can
subsequently account for the observed 2D patches with a thickness
of a single molecule. It is believed that favourable lateral
6
stacking
interactions between the corrole moieties in adjacent stacks are
responsible for this 2D self-assembly. In the porphyrin trimers this
stacking is absent owing to the presence of an extra alkyl chain on
each of the chromophore moieties.
π
-
π
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