Exciton dynamics in the chlorosomal antennae of the green bacteria Chloroflexus aurantiacus and Chlorobium tepidum

The energy transfer processes in isolated chlorosomes from green bacteria C hlorobium tepidum and Chloroflexus aurantiacus have been studied at low tem peratures (1.27 K) by two-pulse photon echo and one-color transient absorpt ion techniques with similar to 100 fs resolution. The decay of the coherenc e in both types of chlorosomes is characterized by four different dephasing times stretching from similar to 100 fs up to 300 ps. The fastest componen t reflects dephasing that is due to interaction of bacteriochlorophylls wit h the phonon bath, whereas the other components correspond to dephasing due to different energy transfer processes such as distribution of excitation along the rod-like aggregates, energy exchange between different rods in th e chlorosome, and energy transfer to the base plate. As a basis for the int erpretation of the excitation dephasing and energy transfer pathways, a sup erlattice-like structural model is proposed based on recent experimental da ta and computer modeling of the Bchl c aggregates (1994. Photosynth. Res. 4 1:225-233.) This model predicts a fine structure of the Q(y) absorption ban d that is fully supported by the present photon echo data.