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

The mechanism of energy transfer in the antenna system of purple bacteria i s investigated by combination of photon echo spectroscopy and disordered ex citon theory. In the B800 component of light harvesting complex 2 (LH2), a picture of incoherent hopping between monomers provides an excellent descri ption of the photon echo data recorded as a function of excitation waveleng th. In the B850 pigments of LH2, and to a somewhat greater extent in the B8 75 pigments of light harvesting complex 1 (LH1), the excitation is delocali zed over several pigments. The observed dynamics correspond to relaxation b etween exciton states as a result of exciton-phonon coupling. Nonetheless, a picture of "hopping" between small groups of molecules provides a crude d escription of the motion of the excitation in B850, and B875. The electroni c coupling required to simulate the experimental absorption spectrum and ph oton echo data is larger in LH1 than in LH2 (B850). (C) 2001 Published by E lsevier Science B.V.