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Light harvesting complex II B850 excitation dynamics
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Image of FIG. 1.
FIG. 1.

Patch of the chromatophore from purple photosynthetic bacteria Rhodobacter sphaeroides showing the placement of LH2 and LH1-RC complexes as determined from atomic force microscopy and computational modeling (Ref. 5). Pools of LH2 antenna complexes are seen to surround the LH1-RC core complexes; lipids are not shown. As the primary antennae of the chromatophore most of the intercomplex excitation transfer occurs between LH2s.

Image of FIG. 2.
FIG. 2.

(a) The structure of LH2 showing the - and -subunits of each -dimer in yellow and pink, respectively, the B850 BChls in green and the B800 BChls in blue. The cytoplasmic side is on the bottom. (b) 18 BChls (green) form the so-called B850 ring and 9 BChls (blue) form the so-called B800 ring. Nine carotenoid molecules also present are not shown.

Image of FIG. 3.
FIG. 3.

(a) B850 ring showing the alternating transition dipole moment orientations giving rise to the ninefold symmetry. The arrows placed over the Mg atoms show the transition dipole moments from the atom to the atom of each Bchl (Ref. 11). (b) Exciton spectrum of B850 shown with the familiar -labels (Ref. 30). The arrows indicate the two states with the highest oscillator strength, the so-called 850 nm states.

Image of FIG. 4.
FIG. 4.

(a) Population dynamics of BChls 1, 2, and 10 starting from . The transfer of excitation across half the ring takes about 65 fs. The difference between neighboring Bchl populations is seen by the steady state difference of BChls 1 and 2 and is due to the alternating site energies in the Hamiltonian. (b) Time evolution of the coherence length in the B850 ring as measured by the inverse participation ratio starting from . The coherence length converges to . (c) Time evolution of the nine lowest energy exciton states with . (d) Time evolution of the nine highest energy exciton states starting from .

Image of FIG. 5.
FIG. 5.

Steady state populations (solid lines) and Boltzmann populations (dashed lines) of the exciton states of LH2 B850. The inset shows the exciton populations of the highest energy states. The state labels on the left of the lines denote the Boltzmann populated states and the labels on the right denote the steady state populations.

Image of FIG. 6.
FIG. 6.

Transfer of excitation from donor to acceptor ring, showing single exponential decrease (increase) for the donor (acceptor). The transfer time is 9.1 ps, the transfer time resulting from the generalized Förster calculation is 10.2 ps.

Image of FIG. 7.
FIG. 7.

Distortion of B850 exciton states due to Gaussian diagonal disorder. The dashed lines correspond to the exciton spectrum of the averaged B850 ring showing the degeneracy for all the states with the exception of the and states. The solid lines show the exciton spectrum of a single realization of Gaussian diagonal disorder with a width . With the inclusion of disorder, the degeneracies are lifted, yet the exciton states of the disordered Hamiltonian can be linked to those of the ideal Hamiltonian [cf. Fig. 3(b)].


Generic image for table
Table I.

Boltzmann populations of the exciton states of a B850 ring along with the transfer rates from these states to another B850 ring, averaged over 10 000 realizations of diagonal disorder.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Light harvesting complex II B850 excitation dynamics