Abstrakt
Chlorosomes are light-harvesting antennas of green photosynthetic bacteria. Unlike other antennas, they contain almost no protein and the light harvesting is mediated mainly by aggregates of pigments, bacteriochlorophylls (BChls).
Important part of their function is a highly efficient transport of the absorbed energy for processing in reaction centres. We have observed superradiance (i.e., collective spontaneous emission) in these antennas as well as in artificial aggregates of BChls.
This means that fluorescence occurs from a state that is delocalized over several molecules in the aggregate and has a higher transition dipole strength than the radiative state in monomeric BChl (2-3- fold higher). The increased dipole strength increases probability of both energy transfer and radiative transition; however, the quantum yield of the aggregated BChls is decreased by several orders of magnitude (2-2.6 orders in comparison to monomeric BChl) which greatly reduces the probability of a radiative decay.
Both those factors (increased dipole strength and decreased quantum yield) contribute to the high energy transfer efficiency of chlorosomes, which can be mimicked in organic photovoltaics.