Spectral properties of single light-harvesting complexes in bacterial photosynthesis

Photosynthetic light-harvesting complexes play important roles in the early events in photosynthesis in nature, and have been studied by various spectroscopic methodologies. Single molecule spectroscopy is one of the recent powerful methods to study fine electronic structures of photosynthetic light-harvesting complexes without averaging over an ensemble of the complexes. In this review, we focus on spectroscopic properties of single light-harvesting complexes in anoxygenic photosynthetic bacteria. In single supramolecule spectroscopy of light-harvesting complexes of purple photosynthetic bacteria, information on excitonic (de)localization on the arrangements of bacteriochlorophyll (BChl) a molecules, which is hidden in conventional measurements, has been obtained in detail. Single supramolecule spectroscopy has been applied to major antenna complexes (=chlorosomes) in green photosynthetic bacteria, revealing the spectral properties in relation to anisotropy and excitation energy transfer in single chlorosomes, their heterogeneity, and the number of BChl molecules per chlorosome.