One- and Two-Color Photon Echo Peak Shift Studies of Photosystem I

Department of Chemistry, University of California, Berkeley, Berkeley, California, United States
The Journal of Physical Chemistry B (Impact Factor: 3.3). 01/2007; 110(51):26303-12. DOI: 10.1021/jp061008j
Source: PubMed


Wavelength-dependent one- and two-color photon echo peak shift spectroscopy was performed on the chlorophyll Qy band of trimeric photosystem I from Thermosynechococcus elongatus. Sub-100 fs energy transfer steps were observed in addition to longer time scales previously measured by others. In the main PSI absorption peak (675-700 nm), the peak shift decays more slowly with increasing wavelength, implying that energy transfer between pigments of similar excitation energy is slower for pigments with lower site energies. In the far-red region (715 nm), the decay of the peak shift is more rapid and is complete by 1 ps, a consequence of the strong electron-phonon coupling present in this spectral region. Two-color photon echo peak shift data show strong excitonic coupling between pigments absorbing at 675 nm and those absorbing at 700 nm. The one- and two-color peak shifts were simulated using the previously developed energy transfer model (J. Phys. Chem. B 2002, 106, 10251; Biophysical Journal 2003, 85, 140). The simulations agree well with the experimental data. Two-color photon echo peak shift is shown to be far more sensitive to variations in the molecular Hamiltonian than one-color photon echo peak shift spectroscopy.

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    ABSTRACT: A time-nonlocal quantum master equation coupled with a perturbative scheme to evaluate the third-order polarization in the phase-matching direction k(s) = -k(1) + k(2) + k(3) is used to efficiently simulate three-pulse photon-echo signals. The present method is capable of describing photon-echo peak shifts including pulse overlap and bath memory effects. In addition, the method treats the non-Markovian evolution of the density matrix and the third-order polarization in a consistent manner, thus is expected to be useful in systems with rapid and complex dynamics. We apply the theoretical method to describe one- and two-color three-pulse photon-echo peak shift experiments performed on a bacterial photosynthetic reaction center and demonstrate that, by properly incorporating the pulse overlap effects, the method can be used to describe simultaneously all peak shift experiments and determine the electronic coupling between the localized Q(y) excitations on the bacteriopheophytin (BPhy) and accessory bateriochlorophyll (BChl) in the reaction center. A value of J = 250 cm(-1) is found for the coupling between BPhy and BChl.
    Preview · Article · Oct 2007 · The Journal of Physical Chemistry A
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    ABSTRACT: The echo-peak shift (EPS) technique, frequently used to study ultrafast solvation dynamics, can be remarkably insensitive to changes in systems' dynamical properties. This is illustrated by comparing the results of EPS and time-resolved photon echo experiments on ternperature-dependent optical dephasing in a glass-forming liquid. The observed failure of the EPS technique appears to be a fundamental problem for systems with strong inhomogeneous contribution to the line broadening. (c) 2007 Elsevier B.V. All rights reserved.
    Full-text · Article · Nov 2007 · Chemical Physics Letters
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    ABSTRACT: In this chapter, we discuss the theories applicable for calculating energy transfer kinetics and optical spectra of photosynthetic pigment-protein complexes. The various theoretical approaches for obtaining expressions for rate constants and optical spectra are reviewed. At the extremes we distinguish weak and strong coupling between electronic excitations of the pigments. If the coupling is strong compared to the dynamic and static disorder introduced by the protein environment, then delocalized electronic states are formed after light excitation. The excitation energy relaxes between those delocalized states. In the weak coupling limit localized states are created by excitation and the excitation energy is transferred via a hopping mechanism. In general in photosynthetic antenna and reaction centers neither limit applies in a strict sense. Thus more sophisticated theories describing the intermediate cases have to be applied, and these should also account for the coupling of the excited states to the vibrational states of the environment. We discuss the recent attempts of solving the challenging problem to apply a non-perturbative description of both the pigment-pigment as well as the pigment-protein couplings. Applications of these theories to the spectroscopy of photosynthetic systems over the last decade are also reviewed.
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