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J Phys Chem B. 2012 Jun 28;116(25):7449-54. doi: 10.1021/jp304649c. Epub 2012 Jun 14.

Origin of long-lived coherences in light-harvesting complexes.

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Faculty of Physics, University of Vienna, Strudlhofgasse 4, 1090 Vienna, Austria.


A vibronic exciton model is applied to explain the long-lived oscillatory features in the two-dimensional (2D) electronic spectra of the Fenna-Matthews-Olson (FMO) complex. Using experimentally determined parameters and uncorrelated site energy fluctuations, the model predicts oscillations with dephasing times of 1.3 ps at 77 K, which is in a good agreement with the experimental results. These long-lived oscillations originate from the coherent superposition of vibronic exciton states with dominant contributions from vibrational excitations on the same pigment. The oscillations obtain a large amplitude due to excitonic intensity borrowing, which gives transitions with strong vibronic character a significant intensity despite the small Huang-Rhys factor. Purely electronic coherences are found to decay on a 200 fs time scale.

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