Vibronic Structure and Coherence in the Bacterial Reaction Center*

Much of our current understanding of photosynthetic charge separation has been derived from studies of the bacterial reaction center (BRC) from purple bacteria. We report two-dimensional electronic spectroscopy (2DES) experiments on the BRC that reveal previously hidden excitonic and vibronic structure. Through analysis of the coherent dynamics of the BRC and careful comparison with monomeric bacteriochlorophyll we report vibronic coherence and identify resonances between a number of key intramolecular pigment vibrations and electronic energy gaps in the BRC. Such resonances have been proposed to play a functional role in photosynthetic energy transfer and charge separation.