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Published August 2006 | public
Journal Article

Ultrafast Photoisomerization of Photoactive Yellow Protein Chromophore Analogues in Solution: Influence of the Protonation State


We investigate solvent viscosity and polarity effects on the photoisomerization of the protonated and deprotonated forms of two analogues of the photoactive yellow protein (PYP) chromophore. These are trans-p-hydroxybenzylidene acetone and trans-p-hydroxyphenyl cinnamate, studied in solutions of different polarity and viscosity at room temperature, by means of femtosecond fluorescence up-conversion. The fluorescence lifetimes of the protonated forms are found to be barely sensitive to solvent viscosity, and to increase with increasing solvent polarity. In contrast, the fluorescence decays of the deprotonated forms are significantly slowed down in viscous media and accelerated in polar solvents. These results elucidate the dramatic influence of the protonation state of the PYP chromophore analogues on their photoinduced dynamics. The viscosity and polarity effects are, respectively, interpreted in terms of different isomerization coordinates and charge redistribution in S_1. A trans-to-cis isomerization mechanism involving mainly the ethylenic double-bond torsion and/or solvation is proposed for the anionic forms, whereas "concerted" intramolecular motions are proposed for the neutral forms.

Additional Information

© 2006 Wiley-VCH Verlag GmbH & Co. Received: March 9, 2006. Revised: May 9, 2006. Published online on July 17, 2006. The authors thank Jean-Bernard Baudin for the synthesis of pCE and James T. Hynes for helpful discussions. A.E., P.C. , and M.M.M. are grateful to Pascal Plaza for his valuable comments on this manuscript. This collaborative work was done within the framework of a Blaise Pascal Chair AHZ was awarded at the Department of Chemistry of the Ecole Normale Supérieure (ENS) in Paris. Financial support from the ENS Foundation is acknowledged. A.E. is grateful to Caltech for a Graduate Fellowship during her stay in Pasadena.

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October 20, 2023