Session: Physical Chemistry Poster:

Plants harness energy by absorbing light across the visible region of the solar spectrum and then rapidly and efficiently funneling the energy towards the reaction center. Previous experiments to understand the mechanisms by which energy relaxes across this large energy gap have been limited to the dynamics of the two lowest-energy states, leaving the higher-lying states, including how they transfer energy downhill, unexplored. We describe the development of an ultrabroadband two-dimensional (2D) electronic spectrometer that enables us to map out energy flow in the major antenna complex of plants, light-harvesting complex II (LHCII), across the visible region with high sensitivity. The 2D spectra show that one of the carotenoids, lutein 2, plays a central role in light harvesting by accepting energy from higher-lying states and funneling it downhill via two parallel pathways, including a non-adiabatic transition into a previously debated dark state.
In parallel with the light-harvesting pathways, plants have evolved pathways to protect against photodamage, where harmful energy is rapidly dissipated as heat. While the photophysical mechanism of dissipation has been widely debated, previous experiments lacked the spectral and temporal requirements to characterize the ultrafast timescales and large energy gaps involved. Using ultrabroadband 2D electronic spectroscopy, we directly resolve a dissipative chlorophyll-to-carotenoid energy transfer pathway, which had been hypothesized yet previously unobserved. These results demonstrate the capability of ultrabroadband 2D electronic spectroscopy as a promising tool to gain unprecedented insights into energy relaxation dynamics in condensed-phase systems.

Gabriela Schlau-Cohen

Massachusetts Institute of Technology

Appearances