Abstract
A green photosynthetic bacterium, Chlorobium limicola, has an antenna complex called ‘chlorosomes’. It absorbs the light energy and transfers its singlet energy to the reaction center. Since chlorosomes contain ‘rod elements’ consisting of higher aggregates of bacteriochlorophyll (BChl) c molecules, we expect that it has a unique excited-state dynamics, because of its cylindrical structure. In this study, we have focused our attention on subpicosecond time-resolved absorption spectroscopy in the near-infrared region.
Immediately after excitation to the Soret, chlorosomes gave rise to a broad transient absorption which decayed within ∼1 ps. In a higher in vitro aggregate, which exhibited Qy absorption almost same as chlorosomes, we observed similar excited-state dynamics. In contrast to such higher aggregates, monomeric BChl c in methanol solution exhibited completely-different excited-state dynamics. These results suggest that the former excited-state dynamics may originate from the unique aggregate structure of chlorosomes.
