Spectroscopy on the B850 band of individual light-harvesting 2 complexes of Rhodopseudomonas acidophila. II. Exciton states of an elliptically deformed ring aggregate.

Spectroscopy of individual light-harvesting 2 complexes from purple photosynthetic bacteria revealed a deformation of the circular complex into C(2) symmetry. The present work relates the geometry of the deformed aggregate to its spectroscopic properties. Different models of elliptical deformation are discussed and compared with the experimental findings. It is shown that the model with smaller interpigment distances, where the curvature of the ellipse is small, provides the best agreement with fluorescence excitation spectra of individual complexes.