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Kirsten Griffiths
BS Clarkson University
An Intramolecular Photo-Driven Linear Molecular Motor
People Involved: Sourav Saha and Amar Flood
Since Richard Feynman’s famous 1959 address1 entitled “There’s Plenty of Room at the Bottom,” scientists have contemplated the possibilities of constructing small but functional machines. Feynman’s challenge is being met, in part, by recent advances in the construction of mechanically interlocked molecules - namely, catenanes and rotaxanes – which can be designed to switch between two states upon electrical, photochemical or chemical stimulation.2
Light is unique in its ability to apply energy selectively and quantitatively to a molecular motor and therefore, it is an attractive means with which emerging molecular machines will be driven in future systems. Our group has developed piston-type molecular motors, based on rotaxanes with redox-active stations, powered by electrochemical and chemical energy sources. Many cycles of the molecular motor can be completed and the linear motion displayed by these bistable [2]rotaxanes are reminiscent of a piston’s movement. By extending this system such that it uses photochemical energy as the power source for shuttling, its scope could be greatly expanded, allowing it to be used in more diverse applications and environments.
Thus, the aim of this project is to build a photo-driven molecular motor through the combination of the concepts of molecular motors and photoinduced electron transfer. These fields will be linked conceptually and physically through a tetrathiavulvalene (TTF) unit. The molecular motor is composed of a fullerene (C60) electron acceptor, a porphyrin (P) chromophore, a TTF electron donating station, and a 1,5-dioxynaphthalene (DNP) unit as a second electron donating station. In its ground state, the cyclobis(paraquat)-p-phenylene tetracationic cyclophane (CBPQT4+) should encircle the TTF unit. Light excitation of the porphyrin unit, enables it to transfer an electron to the C60 unit followed by electron transfer from the TTF to the porphyrin unit will establish a charge separated species (TTF+∑-P-C60-∑). The oxidized TTF+ unit should repel the CBPQT4+ allowing it to shuttle to the DNP station. Following back electron transfer, the CBPQT4+ should diffuse back to the TTF unit, resulting in one full cycle of the molecular motor. This system should demonstrate conversion of energy from light to electrical energy, and ultimately, to mechanical energy - a substantial accomplishment.References
1. R. P. Feynman, “There’s Plenty of Room at the Bottom,” Eng. Sci. 1960, 23, 22.
2. Balzani, V.; Credi, A.; Raymo, F.M.; Stoddart, J.F., “Artificial Molecular Machines,” Angew. Chem. Int. Ed. 2000, 39, 3348.
3. Ashton, P.; Ballardini, R.; Balzani, V.; Credi, A.; Dress, K.; Ishow, E.; Kleverlaan, C.; Kocian, O.; Preece, J.; Spencer, N.; Stoddart, J.F.; Venturi, M.; Wenger, S., “A Photochemically Driven Molecular-Level Abacus,” Chem. Eur. J. 2000, 6, 3558.
4. Imahori, H.; Tamaki, K.; Yamada, H.; Sakata, Y.; Nishimura, Y.; Yamazaki, I.; Fujitsuka, M.; Ito, O., “Photosynthetic Electron Transfer Using Fullerenes as Novel Acceptors,” Carbon 2000, 38, 1599.
5. Kodis, G.; Liddell, P.; Garza, L.; Moore, A.; Moore, T.; Gust, D., “Photoinduced Electron Transfer in p-Extended Tetrathiafulvalene-Porphyrin-Fullerene Triad Molecules,” J. Mater. Chem. 2002, 12, 2100.More About Kirsten
Kirsten Griffiths started at UCLA during Fall ’03 as a graduate student having completed her undergraduate degree at Clarkson University in Potsdam, NY. While at Clarkson she completed her senior/honors thesis with Devon Shipp titled “Photo-initiated Nitroxide-Mediated Polymerizations.” She has also traveled extensively, working at the Université Louis Pasteur with Jean-Pierre Sauvage on the synthesis of an iridium (III) bis-terpyridine dyad; with Dario Bassani on the template-assisted photodimerization of cinnamic ester derivatives at the Université de Bordeaux with Nick Turro on the photo-oxidation of biphenyl and the photochemistry of chlorofluorocarbons (CFC’s) at Columbia University in New York City. In her spare time, Kirsten enjoys baking delicious treats and traveling to exotic places. Someday she hopes to complete the journey across Russia, Siberia and China on the Trans-Siberian Railway, but for now she must settle for a daily ride on the Big Blue Bus.
