Spectral diffusion of the lowest exciton component in the core complex from Rhodopseudomonas palustris studied by single-molecule spectroscopy.

We have recorded fluorescence-excitation spectra from individual RC-LH1 complexes from Rhodopseudomonas palustris. The spectra feature a few broad bands accompanied by a sharp line at the low-energy side of the spectrum which is ascribed to the lowest exciton state of the BChl a assembly. Recording several fluorescence-excitation spectra from the same individual complex in rapid succession reveals that the linewidth of the lowest exciton transition is determined by spectral diffusion which increases for higher excitation energies.