Well-Defined Porphyrin Architectures From Self-Assembly and Dewetting - Molecular Self-Assembly: Advances and Applications - page 251

on a delicate interplay between a variety of interactions and forces.
Obviously, the nature of the surface and the solvent is of essential
importance. A super-hydrophobic, flat surface, like highly oriented
pyrolytic graphite, has strong interactions with the alkyl chains of

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and as a result a dense monolayer of closely packed columnar stacks is
obtained. The use of a hydrophilic, but not atomically flat surface, like
glass, still leads to the formation of lines but these are much shorter
and less well defined than on mica and unequally spaced. Apparently,
the best-defined patterns are obtained on a hydrophilic surface that
does not have very strong interactions with the porphyrin trimers,
and which is flat enough to allow regular dewetting of the solution to
afford the equal spacing within the line patterns.

Figure 8.8 Mechanism of formation of the linear patterns. (A) AFM

image (14

×

14

µ

m 2 ) of two domains containing line patterns

of ; the thick line is a contact pinning line. (B) Schematic of

the formation of the line patterns; 1-2-3 are contact pinning
lines, evaporation of the droplet occurs in the direction
A to B. (C) Cartoon showing the 'coffee-stain mechanism',
for explanation refer the text. (D) Cartoon showing the
undulations in the thin solvent layer, which direct the growth
of the stacks of

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resulting in the formation of equally spaced
lines. Copyright American Chemical Society, 1996.

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