Exciton delocalization in the antenna of purple bacteria: exciton spectrum calculations using Z-ray data and experimental site inhomogeneity.

Electron absorption and circular dichroism spectra of the peripheral light-harvesting complex (LH2) of photosynthetic purple bacteria were calculated taking into account the real-life spatial arrangement and experimental inhomogeneous broadening of bacteriochlorophyll molecules. It was shown that strong excitonic interactions between 18 bacteriochlorophyll molecules (BCh1850) within the circular aggregate of the LH2 complex result in an exciton delocalization over all these pigment molecules. The site inhomogeneity (spectral disorder) practically has no influence on exciton delocalization. The splitting between two lowest exciton levels corresponds to experimentally revealed splitting by hole-burning studies of the LH2 complex.