The Future of Molecular and Supramolecular Devices

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.

References

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).
6. Our work in this area is currently supported by the National Science Foundation, the Department of Energy, and the Kavli Foundation.