The mechanism of energy transfer in the antenna of photosynthetic purple bacteria

The mechanism of energy transfer in the antenna system of purple bacteria is investigated by combination of photon echo spectroscopy and disordered exciton theory. In the B800 component of light harvesting complex 2 (LH2), a picture of incoherent hopping between monomers provides an excellent description of the photon echo data recorded as a function of excitation wavelength. In the B850 pigments of LH2, and to a somewhat greater extent in the B875 pigments of light harvesting complex 1 (LH1), the excitation is delocalized over several pigments. The observed dynamics correspond to relaxation between exciton states as a result of exciton–phonon coupling. Nonetheless, a picture of “hopping” between small groups of molecules provides a crude description of the motion of the excitation in B850, and B875. The electronic coupling required to simulate the experimental absorption spectrum and photon echo data is larger in LH1 than in LH2 (B850). © 2001 Published by Elsevier Science B.V.