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Science 20 December 2002:
Vol. 298. no. 5602, pp. 2395 - 2398
DOI: 10.1126/science.1074685
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Reports

Photosynthetic Light Harvesting by Carotenoids: Detection of an Intermediate Excited State

G. Cerullo,1* D. Polli,1 G. Lanzani,1 S. De Silvestri,1 H. Hashimoto,2dagger R. J. Cogdell2

We present the first direct evidence of the presence of an intermediate singlet excited state (Sx) mediating the internal conversion from S2 to S1 in carotenoids. The S2 to Sx transition is extremely fast and is completed within approximately 50 femtoseconds. These results require a reassessment of the energy transfer pathways from carotenoids to chlorophylls in the primary step of photosynthesis.

1 National Laboratory for Ultrafast and Ultraintense Optical Science (INFM), Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci 32, 20133 Milano, Italy.
2 Division of Biochemistry and Molecular Biology, University of Glasgow, Glasgow, UK.
*   To whom correspondence should be addressed. E-mail: giulio.cerullo{at}fisi.polimi.it

dagger    Present address: "Light and Control," PRESTO/JST, Department of Physics, Graduate School of Science, Osaka City University, Osaka, Japan.

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Xanthorhodopsin: A Proton Pump with a Light-Harvesting Carotenoid Antenna.
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