INTRAMOLECULAR FEMTOSECOND CONVERSION OF ENERGY IN THE CHLOROSOMES OF PHOTOSYNTHETIC GREEN BACTERIA CHLOROFLEXUS AURANTIACUS

In the green bacteria Chlorofl exus aurantiacus, the process of photosynthesis begins with the absorption of light by unique light-harvesting complexes, chlorosomes, which consist of ~104 bacteriochlorophyll (BChl) c molecules combined into complex spatial structures. Upon absorption of blue light (~460 nm) by the B band of chlorosomes, ultrafast energy conversion occurs, resulting in the excitation of the red Qy band (~740 nm). We studied this process using difference (light-dark) absorption spectroscopy with a high time resolution (20 fs). We have found that the characteristic conversion time is 35 fs. We have shown that energy conversion precedes slower processes of exciton relaxation in the Qy band (100–300 fs) and energy transfer from the chlorosome to the baseplate and further to the reaction center (tens of ps). The physicochemical foundations of intramolecular energy conversion in chlorosomes and the signifi cance of this process for photosynthesis are discussed.