Carotenoid-mediated light harvesting in plants Minjung Son, Gabriela Schlau-Cohen

Plants absorb across the visible region of the solar spectrum followed by rapid and efficient collection of the photoenergy in lower-lying states. Previous experiments have been limited to the dynamics of the low-energy states, leaving the higher-energy states, including how they transfer energy downhill, unexplored. We describe ultrabroadband 2D electronic spectroscopy that enables us to map out the excited states and dynamics of the major antenna complex of plants across the visible region. By analyzing the vibrational wavepackets in the spectra, we identify a debated dark state on a single carotenoid, lutein 2, that mediates relaxation. This result reveals that the protein binding pocket controls the electronic structure of carotenoids, and therefore their function in photosynthesis.