Background:

• Postdoctoral Scholar, University of California, Los Angeles, 2001-2004

Molecular Nanoscience and Nanotechnology

Four projects outline my plans to develop research programs in molecular nanoscience and nanotechnology. The long-term challenge is to design and demonstrate autonomous motion. This grand challenge will be achieved in four incremental pieces. The first project begins with molecular logic gates that sense for pH to control the flow of electricity to molecular machines. A new class of machines will be produced in a second medium-term project. In particular, a generic redox-switchable ligand that switches between its quinol and quinone tautomers will be investigated as a means to develop more sophisticated molecular machines. In a third project, the operation of the logic gates and molecular machines will be imaged, from solution to surfaces—ultimately at the single molecule level—utilizing a Raman-AFM microscope. Finally, the ideal molecular logic gates and machines from each program will be brought together and integrated with a pH-based feedback mechanism to demonstrate a molecular robotics system.

Molecular Logic and Molecular Electronics. This short-term research program will be developed as a means to couple the elegant types of molecular logic gates already in existence (de Silva and Raymo) to a Si platform (Heath and Bocian). Molecular logic, on the single and ensemble molecular level, offers both nanometer feature sizes for the continued progress of Moore's Law as well as the option to integrate logical operations into a single molecule. Initially, AND logic gates will be developed around molecular recognition linked to a redox-active coordination complex. A range of polypyridyl ligands will be investigated to optimize the signal transduction from the binding event into a large shift in the redox properties of the parent complex. Subsequently, the complex will be self-assembled onto a range of electrodes in order to evaluate the magnitude of the differences in the electronic current flow between the assigned high (1) and low (0) states. This program will be extended to other logic gates, miniaturized to evaluate the limits of sensitivity, and serve as the CPU for molecular robotics systems to be developed in later projects.

Molecular Nanomechanics. Molecular machines based on ligand switching (see Figure) will be developed and studied to investigate the physical chemistry of electromechanical coupling in molecular machinery (nanomechanics) and to apply the optimized and customized molecular machinery to perform useful work in mechanical systems (NEMS). The proposed switch explores tautomerism as potential switching mechanism. Molecular machines, such as catenates and rotaxanes will be prepared from the optimized switches using templated-directed synthesis.

Single Molecule Raman Spectroscopy. Raman spectroscopy of molecular (1) machines, (2) sensors and (3) logic gates will be recorded. At the single molecule level, the corresponding (1) movements, (2) dynamic binding and release, and (3) redox chemistry are all subject to stochastic forces. Consequently, their spectra will allow for these processes to be understood as a means to control the performance of single and ensembles of molecules at the nanoscale level. Such control lays the foundation for molecular nanotechnologies. The ultimate goal is single-molecule imaging and this objective will be approached incrementally Subsequently, a new system will be developed that allows surfaces to be imaged with an AFM and a Raman microscope simultaneously. Beyond molecular machines, such an analytical system is generally applicable to single molecule sensing, imaging molecular surfaces, DNA base pairs, carbon nanotubes as well as micro-scale features of microchips, MEMS and NEMS devices as well as polymer composites.

Molecular Robotics System. Biology provides powerful images of how the organization of matter and the utilization of free energy, across many levels of integration, leads to complex and emergent behavior, of which the most thought-provoking is continuous motion within a dynamic environment consisting of matter and energy. The goal of this long-term research program is to integrate the other research programs together—sensing, logic and actuation—in order to demonstrate, by design, autonomous action from a molecular robotics system by taking natural concepts and applying them to artificial systems. In particular, to demonstrate (1) self-regulation of mechanical switching at electrode surfaces, (2) self-regulation of a photoactive power supply in solution, and (3) asynchronous unidirectional motion utilizing Brownian fluctuations within the internal coordinates of linear motor molecules.

The flood group intends to develop the building blocks behind switching systems that have applications ranging from molecular electronics to mechanical engineered systems.

Selected Publications:

"Whence Molecular Electronics" with Flood, A. H.; Stoddart, J. F.; Steuerman, D. W.; Heath, J. R., Science 2004, 306, 2055-2056.

"The Role of Physical Environment on Molecular Electromechanical Switching" with Flood, A. H.; Peters, A. J.; Vignon, S. A.; Steuerman, D. W.; Tseng, H.-R.; Kang, S.; Heath, J. R.; Stoddart, J. F., Chem. Eur. J. 2004, 24, 6558-6561.

"From Artificial Molecular Motors to Functional Nanomechanical Devices" with Huang, T. J.; Brough, B.; Ho, C.-M.; Liu, Y.; Flood A, H.; Bonvallet, P.; Tseng, H.-R.; Stoddart, J. F.; Baller, M.; Magonov, S., Appl. Phys. Lett. 2004, 85, 5391-5393. Cover Art, 29 November 2004

"Meccano on the Nanoscale - A Blueprint for making Some of the World's Tiniest Machines" with Flood, A. H.; Ramirez, R. J. A.; Deng, W.-Q.; Muller, R. P.; Goddard, W. A.; Stoddart, J. F., Aust. J. Chem. 2004, 57, 301-322.

"Revealing the Chromophoric Composition of Multichromophoric Polypyridyl Complexes of Re(I) and Os(II): A Resonance Raman Study" with Flood, A.; Girling, R.; Hester, R.; Moore, J.; Gordon, K. C.; Polson, M. I. J., J. Raman Spectrosc. 2002, 33, 434-442.