INTRABAND ENERGY TRANSFERS IN THE BCHL-C ANTENNA OF CHLOROSOMES FROM THE GREEN PHOTOSYNTHETIC BACTERIUM CHLOROFLEXUS-AURANTIACUS

Two-color absorption difference profiles for the bacteriochlorophyll ( BChl) c antenna of chlorosomes from Chloroflexus aurantiacus at 19 K s how photobleaching/stimulated emission rise features with similar to 3 00 fs kinetics when the probe wavelength is similar to 30 nm to the re d of the excitation wavelength. Similar rise features do not appear at 300 K, or in uphill two-color experiments at 19 K, or when the pump a nd probe wavelengths are separated by much less than 30 nm. This appea rs to be the first direct observation of downhill electronic energy tr ansfers within light-harvesting BChl c oligomers in intact chlorosomes .