Nanotechnology is an emerging field dealing with the fabrication and
engineering of materials, architectures, and systems at the nano-scale.
Together with the development of advanced imaging techniques, the
development of nanomaterials for various applications has become
prevalent in recent years. Their distinguishing physical properties
arise from structural features that are less than one hundred
nanometers. These distinct properties can be useful for the development
of nanoelectronics, smart surfaces, medical implants, sensors,
high-powered magnets, improved insulating materials, and batteries. Part
of our research is devoted to the development of functional
nanomaterials which can acts as molecular muscles,1 light
driven molecular machines,2 molecular electronic devices,3
supramolecular polymers, nanovalves,4 molecular elevators,5
carbon nanotube based sensors, and organic field effect transistors.13
Carbon nanotubes, especially single wall carbon nanotubes (SWNTs), are
among the most attractive of all nanomaterials due to their unique
mechanical and electrical properties. One of the most challenging task
about working with SWNTs is that they are insoluble in any common
organic solvents and aqueous media. The insolubility of SWNTs results
from noncovalent forces between individual tubes which results in
spontaneous self-organization. This characteristic of SWNTs limits their
application for use in devices. As a result there is a tremendous effort
to solubilize them. Although the solubilization of the SWNTs can be
achieved by covalent modification of the surface in various solvents,
this modification drastically alters their physical properties.
For this reason great attention should be paid to non-covalent
solubilization of SWNTs. Noncovalent modification not only improves the
solubility of the SWNTs in organic and aqueous media, but it also
preserves their unique mechanical and electrical features of SWNTs.
Among the approaches for noncovalent modification that have met with
some measure of success in solubilizing the SWNTs are the use of
surfactants\] synthetic polymers (both helical and rigid),7
and biopolymers.8 We, along with others, have reported the
solubilization of carbon nanotubes in water and organic media through
the use of conjugated polymer (poly(meta-phenylenevinylene), PmPV)
derivatives (Figure 1) 7c and polysaccharides (starch (Figure
2),9 gum arabic,10 and the _-1,3-glucans, curdlan
and schizophyllan 11).
The helical structures of conjugated polymers and polysaccharides form a
hydrophobic cavity that becomes a suitable host for the nanotube
bundles. However, this approach still does not achieve the isolation of
an individual nanotube. It is important to note that the supramolecular
chemistry which operates between SWNTs and the starch (amylose-iodine
complex) can be conducted under physical, chemical, or biological
control. It constitutes an im-portant scientific development with
implications for both carbon nanotube and starch research.9a
At the simplest practical level, it is now easy to purify SWNTs cheaply,
under ambient conditions, using readily available starch complexes.
Recently our group has developed a new method for solubilizing carbon
nanotubes by using dynamic coordination and supramolecular chemistry
(Figure 3). In this study we utilized a porphyrin molecule because of
its strong interaction with the nanotube surface. A zinc-porphyrin
derivative carrying two pyridine ligands enters into a self-assembly
process with a Pd(II) complex and forms acyclic and cyclic complexes in
aqueous media.12 This dynamic complex interacts with the
nanotubes and facilitates their solubilization. This research introduces
the idea of using dynamic coordination chemistry together with
supramolecular chemistry to carry out the non-covalent functionalization.
also are able to show that nanotubes which are functionalized
noncovalently with this zinc porphyrin derivative can be used for the
detection of light in SWNT field effect transistors. This process may
form the basis for applications in artifical photosynthesis and
alternative energy sources such as solar cells.13
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