Biology Reference
In-Depth Information
certain bacteria. Scientists are often inspired by the complexity and
functionality of these elegant systems and take nature as a blueprint to
create artificial devices by employing molecular self-assembly. They
thereby make use of tailor-made components that are structurally
programmed to form a desired superstructure by self-assembly
under thermodynamic control. While such an approach can be very
successful to construct well-defined and functional assemblies up
to the micrometre scale, it is not yet very straightforward to gain
control over self-assembly at larger and multiple length scales. It is
envisaged that the production of large-scale arrays of self-assembled
components, spanning from single molecules to the macroscopic
scale, will be of essential importance for their technological
application, e.g., in (opto)electronic devices, liquid crystal displays
(LCDs), catalysts, transistors, or light-emitting diodes [2]. For that
reason, currently new methods are under investigation to gain
control over self-assembly across all length scales [3]. In this account
we will highlight the combination of molecular self-assembly and
dewetting of a surface to obtain, in a controlled fashion, well-defined
porphyrin assemblies, with sizes up to millimetres.
8.2
Ring- and Line-Shaped Porphyrin
Architectures
8.2.1
The First Rings: Porphyrin Dimers
About 15 years ago our group first discovered that ring-shaped
objects were formed when a droplet of a chloroform solution of the
porphyrin dimer
was evaporated on a carbon-coated copper grid
(Fig. 8.1) [4]. Electron microscopy images revealed the presence of
rings with diameters varying from 1 to 5
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m. These rings could also
be imaged by confocal fluorescence microscopy, near-field scanning
optical microscopy (NSOM), and atomic force microscopy (AFM)
[5,6]. With the latter two techniques, the widths and heights of the
rings could be estimated. In each of the individual rings these values
were always very similar, and, depending on the ring size, they varied
between 10 and 100 nm, corresponding to the diameter of 1-10
molecules of
. UV-vis spectroscopy on the rings showed a red-shift
of the porphyrin Soret band, suggesting the presence of head-to-tail
type aggregates of porphyrins.
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