1 research outputs found
Trapping Dynamics in Photosystem I‑Light Harvesting Complex I of Higher Plants Is Governed by the Competition Between Excited State Diffusion from Low Energy States and Photochemical Charge Separation
The
dynamics of excited state equilibration and primary photochemical
trapping have been investigated in the photosystem I-light harvesting
complex I isolated from spinach, by the complementary time-resolved
fluorescence and transient absorption approaches. The combined analysis
of the experimental data indicates that the excited state decay is
described by lifetimes in the ranges of 12–16 ps, 32–36
ps, and 64–77 ps, for both detection methods, whereas faster
components, having lifetimes of 550–780 fs and 4.2–5.2
ps, are resolved only by transient absorption. A unified model capable
of describing both the fluorescence and the absorption dynamics has
been developed. From this model it appears that the majority of excited
state equilibration between the bulk of the antenna pigments and the
reaction center occurs in less than 2 ps, that the primary charge
separated state is populated in ∼4 ps, and that the charge
stabilization by electron transfer is completed in ∼70 ps.
Energy equilibration dynamics associated with the long wavelength
absorbing/emitting forms harbored by the PSI external antenna are
also characterized by a time mean lifetime of ∼75 ps, thus
overlapping with radical pair charge stabilization reactions. Even
in the presence of a kinetic bottleneck for energy equilibration,
the excited state dynamics are shown to be principally trap-limited.
However, direct excitation of the low energy chlorophyll forms is
predicted to lengthen significantly (∼2-folds) the average
trapping time