Substantial research effort has been undertaken in how to combine
molecules, materials, or components in to a wide variety of functional
nanosystems. Supramolecular chemistry is concerned with the study of
the basic features of interactions between molecular components and
with their implementation in specially designed nonnatural systems. As
multiple components are combined into a nanoassembly, the range of
possible functions for that material increases. Assemblies consisting of
two or more components can transfer energy and/or electric charges
between the components, allowing the assemblies to convert energy from
an external source such as light or an electric circuit into useful work. The
broad category of all such nanoassemblies has been dubbed molecular
machines (if components are covalently attached) or supramolecular
machines (if components are held together by noncovalent interactions).
These machines are comprised of organized systems of cooperating
molecules, components of a macromolecule, or a combination of solid
materials and molecules. (Supra)molecular machines are deliberately and
specifically engineered with the ability to function as sensors, processors,
and custom catalysts. Other examples of nanosystems that involve energy
or charge transfer between materials, dyes, and polymers to accomplish a
desired function include solar cells, light-emitting diodes, and transistors.
One, more fanciful but illustrative example of nanoscale machines is
“nanocars,” or molecules that have mobile, functional components that
are able to convert an external source of energy in to linear motion. An
initial design reported in Nano Letters (Shirai et al., 2005) relied on
thermally driven rotation of fullerenes to move a large (2 nm × 3 nm)
planar organic molecule across a surface, as observed by STM. A later
variant (Kudernac et al., 2011) used isomerization of double bonds driven
by the tunnel current of a STM combined with vibrational motion of an
alkyl side chain to produce linear motion in an intended direction. Figure
9.2 shows the structure and motion of such a nanocar. The same
molecular engineering techniques and physical processes used to make
nanocars have also recently been applied to make light-driven molecular
machines capable of killing cancer cells by breaching their lipid membranes, illustrating some of the potential that this technology holds
(García-López et al., 2017).
In the following sections, we will discuss key processes for functional
nanomaterials, such as charge and excitation transfer. We will also survey
organic and inorganic materials of different dimensionalities that can
be used to construct functional nanomaterials. Functional biological
NANOSCALE MACHINES 337
molecules, materials, or components in to a wide variety of functional
nanosystems. Supramolecular chemistry is concerned with the study of
the basic features of interactions between molecular components and
with their implementation in specially designed nonnatural systems. As
multiple components are combined into a nanoassembly, the range of
possible functions for that material increases. Assemblies consisting of
two or more components can transfer energy and/or electric charges
between the components, allowing the assemblies to convert energy from
an external source such as light or an electric circuit into useful work. The
broad category of all such nanoassemblies has been dubbed molecular
machines (if components are covalently attached) or supramolecular
machines (if components are held together by noncovalent interactions).
These machines are comprised of organized systems of cooperating
molecules, components of a macromolecule, or a combination of solid
materials and molecules. (Supra)molecular machines are deliberately and
specifically engineered with the ability to function as sensors, processors,
and custom catalysts. Other examples of nanosystems that involve energy
or charge transfer between materials, dyes, and polymers to accomplish a
desired function include solar cells, light-emitting diodes, and transistors.
One, more fanciful but illustrative example of nanoscale machines is
“nanocars,” or molecules that have mobile, functional components that
are able to convert an external source of energy in to linear motion. An
initial design reported in Nano Letters (Shirai et al., 2005) relied on
thermally driven rotation of fullerenes to move a large (2 nm × 3 nm)
planar organic molecule across a surface, as observed by STM. A later
variant (Kudernac et al., 2011) used isomerization of double bonds driven
by the tunnel current of a STM combined with vibrational motion of an
alkyl side chain to produce linear motion in an intended direction. Figure
9.2 shows the structure and motion of such a nanocar. The same
molecular engineering techniques and physical processes used to make
nanocars have also recently been applied to make light-driven molecular
machines capable of killing cancer cells by breaching their lipid membranes, illustrating some of the potential that this technology holds
(García-López et al., 2017).
In the following sections, we will discuss key processes for functional
nanomaterials, such as charge and excitation transfer. We will also survey
organic and inorganic materials of different dimensionalities that can
be used to construct functional nanomaterials. Functional biological
NANOSCALE MACHINES 337