by Professor Paul Weiss
Designing, synthesizing, assembling, operating, and measuring molecular
devices give us the ability to study the ultimate limits of function.1-4 We seek to understand the rules and limits associated
with such devices given that we are able to know the precise positions and
connections of all the atoms in the entire system. Experiments, theory, and
simulations are used in concert to this end.
While no one has come up with the means to "wire" these molecules and
assemblies into functional architectures for technological use, we can explore
how far precise structures might be pushed, test the extent to which cross-talk
and interference of densely packed devices affect performance, and elucidate the
role of environment on function and stability.
New nanoscale tools have enabled our exploration and ultimately the
manipulation of the atomic-scale world. In addition to structural measurements,
acquiring local spectra across the rotational, vibrational, and electronic
energy ranges has become possible. Local "action spectra" can be used to
determine the energy thresholds for motion and other dynamics. Functional
measurements at these scales in combination with the above are now enabling
comprehensive views of the relationships between molecular structure, assembly
and interactions, and operation.4
As nanoscale tools become more sophisticated, so does our ability to design
and to assemble increasingly complex, precise supramolecular structures and
devices. "Isolated" species on surfaces and in controlled matrices can be made
to function in predictable ways and with high efficiencies.2,3 The situation changes when a number of
functional or interacting components are placed together. Such interactions can
be designed to stabilize an assembly or a state of the system, or even to
interrogate the system by constraining spatial relationships. All of these
possibilities mimic biological components and systems. We are currently limited
by our ability to probe these systems.
Key to the future will be understanding and exploiting such interactions in
order to enable higher order function and greater complexity.5 This may need to include controlling precise spacings in
order to limit cross-talk, excitation transfer, and mechanical interference
(steric hindrance). Likewise, molecular and supramolecular systems may
ultimately be designed to function hierarchically with efficiencies rivaling
those found in biological systems.
1. Z. J. Donhauser, B. A. Mantooth, K.
F. Kelly, L. A. Bumm, J. D. Monnell, J. J. Stapleton, D. W. Price Jr., D. L.
Allara, J. M. Tour, and P. S. Weiss, Conductance Switching in Single Molecules
through Conformational Changes, Science 292, 2303 (2001).
2. P. S. Weiss, Functional Molecules and Assemblies in
Controlled Environments: Formation and Measurements, Accounts of Chemical
Research 41, 1772 (2008).
3. A. S.
Kumar, T. Ye, T. Takami, B.-C. Yu, A. K. Flatt, J. M. Tour, and P. S. Weiss,
Reversible Photo-Switching of Single Azobenzene Molecules in Controlled
Nanoscale Environments, Nano Letters 8, 1644 (2008).
4. A. M. Moore and P. S. Weiss, Functional and Spectroscopic
Measurements with Scanning Tunneling Microscopy, Annual Reviews of Analytical
Chemistry 1, 857 (2008).
5. D. B. Li, R. Baughman, T. J. Huang,
J. F. Stoddart, and P. S. Weiss, Molecular, Supramolecular, and Macromolecular
Motors and Artificial Muscles, MRS Bulletin 34, 671 (2009).
Our work in this area is currently supported by the National Science Foundation,
the Department of Energy, and the Kavli Foundation.
Copyright AZoNano.com, Professor Paul S. Weiss (University of
California, Los Angeles)