Johan Strümpfer and Klaus Schulten.
Excited state dynamics in photosynthetic reaction center and light
harvesting complex 1.
Journal of Chemical Physics, 137:065101, 2012.
(8 pages).
(PMC: 3427344)
STRU2012B
Key to efficient harvesting of sunlight in photosynthesis is the first energy conversion
process in which electronic excitation establishes a trans-membrane charge gradient.
This conversion is accomplished by the photosynthetic reaction center (RC) that is, in case
of the purple photosynthetic bacterium Rhodobacter sphaeroides studied here, surrounded
by light harvesting complex 1 (LH1). The RC employs six pigment molecules to initiate the
conversion: four bacteriochlorophylls and two bacteriopheophytins. The excited states of
these pigments interact very strongly and are simultaneously influenced by the
surrounding thermal protein environment. Likewise, LH1 employs 32 bacteriochlorophylls
influenced in their excited state dynamics by strong interaction between the pigments and
by interaction with the protein environment.
Modeling the excited state dynamics in the RC as well as in LH1 requires theoretical
methods, which account for both pigment-pigment interaction and environment
interaction. In the present study we describe the excitation dynamics within a RC and
excitation transfer between light harvesting complex 1 (LH1) and RC, employing the
hierarchical equation of motion method. For this purpose a set of model parameters that
reproduce RC as well as LH1 spectra and observed oscillatory excitation dynamics in the RC
is suggested. We find that the environment has a significant effect on LH1-RC excitation
transfer and that excitation transfers incoherently between LH1 and RC.
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