A model photochemical compass for bird navigation

Porphyrin's excited state induces a carotenoid electron to leave its partner electron and move to fullerene's outer orbital. Since the transfer of the single electron causes the outer orbital of fullerene to gain an electron and be negatively charged and the outer orbital of carotenoid to be short one electron and positively charged, the newly formed molecule, C•+PF•-, exists in a charge-separated state.

Given that the single, or radical, electrons located in the outer orbitals of the carotenoid and fullerene units are no longer paired with their partner electrons, and are located on opposite ends of the C•+PF•- molecule, they can respond to the direction and magnitude of weak external magnetic forces of approximately 50 millionths of a tesla. After a brief moment, the lone radical electron on the fullerene returns to the carotenoid and the absorbed light energy is converted to heat.

"These results provide a clear proof-of-principle that the magnetic compass sense of migratory birds is based on a magnetically sensitive chemical reaction whose lifetime depends on the orientation of its molecules to Earth's magnetic field," said Peter Hore, professor of chemistry at Oxford University and head of the U.K. team.

Gust and Arizona State University collaborators Thomas Moore and Ana Moore originally synthesized photochemical molecules related to the CPF molecule for use in artificial photosynthetic reaction centers. These centers mimic the mechanisms by which photosynthetic organisms convert sunlight into useful forms of energy. They are now looking at developing their molecules for solar production of electricity or fuels such as hydrogen.

"The research completed by Gust and his collaborators is an excellent example of how basic research can lead to new knowledge and applications in many different fields of science and technology," said Tyrone Mitchell, director of NSF's Organic and Macromolecular Chemistry Program.

Co-authors of the Nature paper are Kiminori Maeda, Kevin Henbest, Filippo Cintolesi, Ilya Kuprov, Christopher Rodgers and Christiane Timmel of Oxford University and Paul A. Liddell of Arizona State University.

The research was supported by NSF Division of Chemistry award number 0352599.

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