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 photosy nthetic bacteria revealed a deformation of the circular complex into C-2 sy mmetry. The present work relates the geometry of the deformed aggregate to its spectroscopic properties. Different models of elliptical deformation ar e discussed and compared with the experimental findings. It is shown that t he model with smaller interpigment distances, where the curvature of the el lipse is small, provides the best agreement with fluorescence excitation sp ectra of individual complexes.