Fluorescence-emission spectroscopy of individual LH2 and LH3 complexes

The lowest exciton states of individual LH2 and LH3 complexes have been studied by fluorescence-emission spectroscopy at low temperature (1.2 K). The spectra from the two complexes are broader than expected, which we attribute to spectral diffusion. In LH3 the absence of a hydrogen bond to the C3-acetyl group of the β-B820 pigments leads to conformational freedom of the chromophore which translates into enhanced fluctuations in spectral position. A dependence of the degree of disorder on the solvent matrix was discovered by comparing the summation of the single-complex with bulk fluorescence spectra in combination with simulations of the data.