The dynamics of the excited states of the light-harvesting complexes LH1 and LH2 of Rhodobacter sphaeroides are governed, mainly, by the excitonic nature of these ring-systems. In a pump-dump-probe experiment, the first pulse promotes LH1 or LH2 to its excited state and the second pulse dumps a portion of the excited state. By selective dumping, we can disentangle the dynamics normally hidden in the excited-state manifold. We find that by using this multiple-excitation technique we can visualize a 400-fs reequilibration reflecting relaxation between the two lowest exciton states that cannot be directly explored by conventional pump-probe. An oscillatory feature is observed within the exciton reequilibration, which is attributed to a coherent motion of a vibrational wavepacket with a period of ∼150 fs. Our disordered exciton model allows a quantitative interpretation of the observed reequilibration processes occurring in these antennas. © 2011 by the Biophysical Society.
Cohen Stuart, T. A., Vengris, M., Novoderezhkin, V. I., Cogdell, R. J., Hunter, C. N., & van Grondelle, R. (2011). Direct Visualization of Exciton Reequilibration in the LH1 and LH2 Complexes of Rhodobacter sphaeroides by Multipulse Spectroscopy. Biophysical Journal, 100(9), 2226-2233. https://doi.org/10.1016/j.bpj.2011.02.048