These perturbations break the symmetry of the B850 ring that, in turn, affects the degree of delocalization. It is not clear yet whether the controversial measurements reported in the literature (Freiberg et al. 2003; AZD6738 Ketelaars et al. 2001; Rätsep et al. 2005; Reddy et al. 1992, 1993; Timpmann et al. 2004; Wu et al. 1997a, b, c; Zazubovich et al. 2002b) are related to the different experimental procedures used and/or to the differences in the bacteria studied. We wanted to get a better understanding of the controversies and of the interplay between the coherence Selleck MCC950 of the

excitation that originates from the strong electronic coupling and the energy disorder in the B850 ring that tends to destroy the coherence. To this end, we have performed experiments in our laboratory on four types of LH2 complexes of purple bacteria at low temperature with one technique, spectral HB, for comparison (L. van den Aarssen, V. Koning and N. Verhart, unpublished

results). In addition, we have done simulations of the total absorption band of the B850 ring, of the lowest k = 0 band and of their relative spectral positions and intensities (R Vlijm, L. van den Aarssen, V. Koning and N. Verhart, unpublished results) to test whether the assumptions made in a theoretical model developed by Silbey and collaborators (Jang et al. 2001; R. J. Silbey, personal communication) agree with the experiments. In the simulations, we have taken into account various types of static disorder, in addition selleck screening library to different coupling strengths

and fast relaxation rates from higher-lying exciton states. Here, we focus on one system only, Rb. sphaeroides (2.4.1, wt), as an example, to show how we have made visible the spectral distribution of the lowest k = 0 exciton states, hidden under the broad B850 absorption band, by measuring the hole depth as a function of excitation wavelength. Similar type of hole depth experiments on B850 have been reported by Freiberg et al. (2003, 2009, and references therein), and by Wu et al. (1997a, b, c) and Zabubovich et al. (2002b, and references therein). The burning-fluence densities used CYTH4 in the latter HB experiments, however, were more than 1,000 times larger than those used in our laboratory. Also, the detection of individual k = 0 states by single-molecule experiments on B850 of LH2 has been reported, but not their spectral distribution (Ketelaars et al. 2001). The B850 band of LH2 consists of a number of exciton states with their homogeneous and inhomogeneous bandwidths. The inhomogeneous bandwidth of B850 is determined by intra- and inter-complex disorder, i.e. by disorder arising from within the B850 ring and between the rings. The individual exciton bands are thus hidden in the total B850 band.