One- and two-exciton bands in the LH2 antenna of Rhodopseudomonas acidophila

The properties of one- and two-exciton states of the circular aggregate responsible for the B850 band in the peripheral light harvesting antenna (LH2), extracted from the purple bacterium Rhodopseudomonas acidophila/strain 10050, have been studied at room temperature by non-linear absorption, differential optical density spectroscopy as well as time-resolved fluorescence spectroscopy. As a main result, giant dipole moments for the transition between ground state and the one-exciton band as well as for the transition between the one-exciton band and the two-exciton band have been estimated, corresponding to a delocalization of the excitation energy over most if not all of the 18 BChl a molecules of the aggregate.