Optical coherences in light-harvesting chlorosomes from green photosynthetic bacteria

Abstract

Chlorosomes are light-harvesting assemblies that are found in green photosynthetic bacteria [1]. The principal antenna in a chlorosome consists of ~104 bacteriochlorophyll (BChl) c, d, or e pigments, which give rise to a broad Qy electronic absorption band centered at ~ 740 nm. Excitations in the BChl c/d/e antenna are transferred to a lower- energy BChl a antenna absorbing at ~795 nm, prior to trapping at the reaction centers [2]. BChl c/d/e antennae in chlorosomes appear to be pigment oligomers whose structure is determined by pigment-pigment rather than pigment-protein interactions, because spectroscopically similar BChl aggregates self-assemble spontaneously from the pigment monomers in solution [3]. The internal energy transfer kinetics of reconstituted BChl c aggregates from the green bacteria Chloroflexus aurantiacus and Chlorobium tepidum closely resemble those found in the BChl c antennae of the intact chlorosomes [4].