Spectroscopy of Single Light-Harvesting Complexes from Purple Photosynthetic Bacteria at 1.2 K

In this Letter we present the first observation of the fluorescence-excitation spectra of individual light-harvesting complexes (LH2) from purple photosynthetic bacteria at 1.2 K. The spectra reveal the electronic transitions to the individual excitonic states of the assembly of absorbing bacteriochlorophyll a (BChl a) molecules. From the experiment we can extract information about site energies of the individual pigments, degree of disorder, dipolar coupling, excited-state dynamics, and spectral diffusion.