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Title:Femtosecond Nonlinear Optical Studies Of Radiationless Decay In Carotenoids And In The Peridinin–chlorophyll A Protein
Author(s):Roscioli, Jerome D.
Contributor(s):Frank, Harry A.; Beck, Warren F.; Bishop, Michael M; Ghosh, Soumen
Subject(s):Mini-symposium: Spectroscopy in Kinetics and Dynamics
Abstract:Femtosecond transient-grating spectroscopy with optical heterodyne detection was employed to observe separately the time evolution of the absorption and dispersion components of the third-order nonlinear optical signal following resonant excitation of the S$_2$ ($^1$B$_u$$^+$) states of $\beta$-carotene in benzonitrile and peridinin in methanol using 40-fs pulses centered at 520 nm. The absorption and dispersion components exhibit distinctively different time profiles owing to the population of intermediate states. An initial intermediate state is populated on an ultrashort ($<30$ fs) time scale in both carotenoids. Owing to the fast red-shifting of the stimulated emission part of the S$_2$-state transient grating signal, we suggest that the intermediate state arises from vibrational displacements on the S$_2$-state potential surface that eventually yield twisted or bent conformations. Motions of the molecule of this type in the S$_2$-state would contribute to a mixing of the diabatic S$_2$ and S$_1$ electronic states and would promote the formation of intramolecular charge-transfer character. Both of these effects would enhance the efficiency of energy transfer from the S$_1$ state to the (B)Chl Q$_y$ state in photosynthetic light-harvesting proteins. The time-resolved transient-grating spectra obtained for peridinin in the peridinin–chlorophyll \emph{a} protein from \emph{Amphidinium carterae} suggest a more rapid formation of the intermediate than for peridinin in methanol. This finding suggests that the conformation of the peridinin chromophore is controlled in the binding site to optimize the formation of the twisted intermediate upon excitation of the S$_2$ state. (Supported by grant DE-SC0010847 from the Department of Energy, Office of Basic Energy Sciences, Photosynthetic Systems program.)
Issue Date:2014-06-17
Publisher:International Symposium on Molecular Spectroscopy
Citation Info:Roscioli, J.D.; Frank, H.A.; Beck, W.F.; Bishop, M.M.; Ghosh, S. FEMTOSECOND NONLINEAR OPTICAL STUDIES OF RADIATIONLESS DECAY IN CAROTENOIDS AND IN THE PERIDININ–CHLOROPHYLL A PROTEIN. Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.TH11
Rights Information:Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License.
Date Available in IDEALS:2014-09-17

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