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Molecular compounds, comprised of mechanically interlocked components, can now be obtained[1-3] efficiently using template-directed protocols that rely upon supramolecular assistance to covalent synthesis. Since the weak noncovalent interactions that orchestrate the synthesis of such compounds e.g., catenanes and rotaxanes containing mechanical bonds live on between the components inside the molecules thereafter, they can be activated such that their components move with respect to each other in either a linear fashion (e.g., the ring component along the rod of the dumbbell component of a [2]-rotaxane[4]) or a rotary manner (e.g., one ring in a [2]-catenane circumrotating through the other ring[5]). Thus, [2]-rotaxanes can be likened to linear motors and [2]-catenanes to rotary motors. Moreover, these molecules can be activated[6,7] by switching the recognition elements on and off between the components chemically, electrically, and optically such that they perform motions e.g., shuttling actions or muscle-like elongations and contractions reminiscent of the moving parts in macroscopic machines. Such motor-molecules and molecular machines hold considerable promise for the fabrication of sensors, actuators, amplifiers and switches at the nanoscale level.

Beyond the verification[4-7] of solution-phase mechanical processes, we have demonstrated[8-11] recently that relative mechanical movements between the components in interlocked molecules can be stimulated (i) chemically[8] in condensed phases (e.g., Langmuir monolayers and Langmuir-Blodgett films), (ii) electrochemically[9] as self-assembled monolayers on gold, and (iii) electronically within the settings of solid-state devices. Not only has reversible, electronically-driven switching been observed[10] in devices incorporating a bistable [2]-catenane but a crosspoint random access memory circuit and a simple logic circuit have been fabricated[11] recently using an amphiphilic, bistable [2]-rotaxane. The experiments provide compelling evidence that switchable catenanes and rotaxanes perform mechanically in a soft-matter environment.

The lecture will highlight how the emergence of the mechanical bond in chemistry in chemistry during the last two decades has brought with it a real prospect of integrating a bottom-up approach, based on self-assembly and self-organization of motor-molecules, with a top-down approach, based on micro- and nanofabrication, to harness molecular machinery.[12,13] It all adds up to an integrated systems-oriented approach to nanotechnology that finds its inspiration in the transfer of concepts like molecular recognition from the life sciences into materials science.

  1. A [2]Catenane Made to Order, Angew. Chem. Int. Ed. Engl. 1989, 28, 1396.
  2. Self-Assembly in Natural and Unnatural Systems, Angew. Chem. Int. Ed. Engl. 1996, 35, 1155.
  3. Interlocked Macromolecules, Chem. Rev. 1999, 99, 1643.
  4. A Molecular Shuttle, J. Am. Chem. Soc. 1991, 113, 5131.
  5. A Chemically and Electrochemically Switchable Molecular Shuttle, Nature 1994, 369, 133.
  6. Artificial Molecular Machines, Angew. Chem. Int. Ed. 2000, 39, 3349.
  7. A Photochemically Driven Molecular-Level Abacus, Chem. Eur. J. 2000, 6, 3558.
  8. Operating Linear Motor-Molecules Mechanically in Condensed Phases, Nano Letters Submitted.
  9. The Metastability of an Electrochemically Controlled Nanoscale Machine on Gold Surfaces, ChemPhysChem 2004, 5, 111.
  10. A [2]Catenane-Based Solid State Electronically Reconfigurable Switch, Science 2000, 289, 1172.
  11. Two-Dimensional Molecular Electronics Circuits, ChemPhysChem 2002, 3, 519.
  12. An Operational Supramolecular Nanovalve, J. Am. Chem. Soc. 2004, 126, 3370.
  13. A Molecular Elevator, Science 2004, 303, 1845.