University of Connecticut

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Atomic, Molecular, and Optical Physics Seminar

Monday, February 1, 2016
4:00pm – 5:00pm

Storrs Campus
Gant Science Complex, Physics, Room PB-121

Warren F. Beck, Department of Chemistry, Michigan State University

“Femtosecond Nonlinear Optical Studies of Excitation Energy Transfer and Radiationless Decay Pathways by Carotenoids in Photosynthetic Light-Harvesting Proteins”


Carotenoids perform essential photoprotection and excitation energy transfer functions in photosynthetic light-harvesting proteins. We have made recent progress towards an understanding the earliest events that follow optical excitation of carotenoids using information from femtosecond transient grating spectroscopy with optical heterodyne detection. Combined with numerical simulations of the third-order nonlinear optical signal, the heterodyne detection scheme has allowed us to detect definitively the ultrafast (<20 fs) formation of a distorted conformation of the S2 (11Bu+) state in solutions of two carotenoids, β-carotene (1) and peridinin. This distorted S2 state, which we call Sx, plays an important role in light harvesting (2). In the peridinin–chlorophyll a protein, the Sx state serves as a principal excitation energy-transfer donor to chlorophyll a acceptors. The binding sites for peridinin in the protein impose strained ground-state conformations that obtain especially long-lived Sx intermediates upon optical excitation. The results show how a light-harvesting protein can engineer the excited-state properties of its intrinsic carotenoids to optimize the quantum yield of excitation energy transfer.

(1) Ghosh, S.; Bishop, M. M.; Roscioli, J. D.; Mueller, J. J.; Shepherd, N. C.; LaFountain, A. M.; Frank, H. A.; Beck, W. F. Femtosecond heterodyne transient-grating studies of nonradiative decay of the S2 (11Bu+) state of β-carotene: Contributions from dark intermediates and double-quantum coherences. J. Phys. Chem. B 2015, 119, 14905-14924. DOI: 10.1021/


Dawn Rawlinson, 486-4916,

Physics Department (primary)

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