Excitonic interactions in the light-harvesting antenna of photosynthetic purple bacteria and their influence on picosecond absorbance difference spectra.

A new model of the light-harvesting antenna (core complex) of purple photosynthetic bacteria is proposed based on excitonic interactions in circular aggregates of bacteriochlorophyll molecules. The calculated absorbance difference spectra of circular aggregates demonstrate all special features observed in the experimental spectra of purple bacteria. In particular, the absorption changes with high amplitude of bleaching at the long-wavelength side of the absorption band at different excitation energy are predicted.