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Photophysical Properties of PS-2 Reaction Centers and a Discrepancy in Exciton Relaxation Times

Renger, Thomas and Marcus, R. A. (2002) Photophysical Properties of PS-2 Reaction Centers and a Discrepancy in Exciton Relaxation Times. Journal of Physical Chemistry B, 106 (7). pp. 1809-1819. ISSN 1520-6106. doi:10.1021/jp013342f.

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Exciton relaxation in the PS-2 reaction center of green plants is studied to explain a discrepancy of 2 orders of magnitude in certain relaxation times. Structural information from an earlier computer model and a recent low resolution structural study are combined with circular dichroism (CD) at 77 K, fluorescence line narrowing spectra at 1.6 K, and pump−probe spectra at 77 K to make predictions on the linear absorption spectrum at 77 K, fluorescence spectrum at 5 K, and absorption difference spectrum for modified pheophytin of the D_2 branch at 5 K. A width of the inhomogeneous distribution function of pigment energies of Δ_(inh) = 300 cm^(-1) and a mean vertical pigment transition energy corresponding to 669 nm are assumed for all pigments, based on the CD data, and a correlation radius of 5 Å for the protein vibrations is deduced from the pump−probe data. The two peripheral chlorophylls resolved in a recent structure are calculated to give rise to optical dephasing times larger than 10 ps at wavelengths shorter than 670 nm, in agreement with dephasing times obtained in hole burning experiments. It is proposed, thereby, that the 2 orders of magnitude discrepancy between the fastest transfer times observed in hole burning and these in pump−probe experiments is due to the peripheral chlorophylls. Non-Markovian effects in the exciton-vibrational coupling are found to contribute significantly to optical line shape functions in the form of vibrational sidebands but to have minor influence on the relaxation dynamics of the excitons.

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Marcus, R. A.0000-0001-6547-1469
Additional Information:© 2002 American Chemical Society. Received: August 29, 2001; In Final Form: November 29, 2001. Published on Web January 30, 2002. We would like to acknowledge support of a Lynen Research Fellowship from the Alexander von Humboldt Foundation to one of us (T.R.). The support of the National Science Foundation and the Office of Naval Research is also appreciated. We thank Prof. A. Holzwarth and Dr. V. Prokhorenko for bringing the exciton vibrational dynamics in the PS-2 reaction center to our attention, and thank Dr. M. Hodoscek for preparing Figure 2. We also thank Prof. G. Small and Dr. R. Jankowiak for helpful comments.
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Alexander von Humboldt FoundationUNSPECIFIED
Office of Naval Research (ONR)UNSPECIFIED
Issue or Number:7
Record Number:CaltechAUTHORS:20150316-142918406
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Official Citation:Photophysical Properties of PS-2 Reaction Centers and a Discrepancy in Exciton Relaxation Times Thomas Renger and and R. A. Marcus The Journal of Physical Chemistry B 2002 106 (7), 1809-1819 DOI: 10.1021/jp013342f
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:55809
Deposited By: Tony Diaz
Deposited On:16 Mar 2015 21:35
Last Modified:10 Nov 2021 20:50

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