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Science 309 (5736): 917-920

Copyright © 2005 by the American Association for the Advancement of Science

Probing the Ultrafast Charge Translocation of Photoexcited Retinal in Bacteriorhodopsin

S. Schenkl,1 F. van Mourik,1 G. van der Zwan,2 S. Haacke,1* M. Chergui1{dagger}

Abstract: The ultrafast evolution of the electric field within bacteriorhodopsin was measured by monitoring the absorption changes of a tryptophan residue after excitation of retinal. The Trp absorption decreases within the first 200 femtoseconds and then recovers on time scales typical for retinal isomerization and vibrational relaxation. A model of excitonic coupling between retinal and tryptophans shows that the signal reflects a gradual rise of the retinal difference dipole moment, which precedes and probably drives isomerization. The results suggest an intimate connection between the progressive dipole moment change and the retinal skeletal changes reported over the same time scale.

1 Ecole Polytechnique Fédérale de Lausanne, Laboratory of Ultrafast Spectroscopy, Institut de Sciences et Ingéniérie Chimiques, FSB-BSP, CH-1015 Lausanne-Dorigny, Switzerland.
2 Vrije Universiteit Amsterdam, Analytical Chemistry and Applied Spectroscopy, Faculty of Sciences, de Boelelaan 1083, 1081 HV Amsterdam, Netherlands.

* Present address: Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), Groupe d'Optique Non-linéaire et d'Optoelectronique, 23 Rue du Loess, F-67034 Strasbourg Cédex, France.

{dagger} To whom correspondence should be addressed. E-mail: majed.chergui{at}

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