The charge-transfer character of the S0 → S2 transition in the carotenoid peridinin is revealed by stark spectroscopy

Lavanya Premvardhan*, Emmanouil Papagiannakis, Roger G. Hiller, Rienk Van Grondelle

*Corresponding author for this work

    Research output: Contribution to journalReview articlepeer-review

    57 Citations (Scopus)

    Abstract

    Peridinin, the carotenoid in the peridinin chlorophyll a protein (PCP), was studied by Stark (electroabsorption) spectroscopy to determine the change in electrostatic properties produced on excitation within the absorption band, in methyl tetrahydrofuran (MeTHF) versus ethylene glycol (EG), at 77 K. Strikingly, a large change in the permanent dipole moment (|Δμ|) was found between the ground state, S0 (11Ag*-) , and the Franck-Condon region of the S2 (11B u*+) excited state, in both MeTHF (22 D) and EG (∼27 D), thus revealing the previously unknown charge transfer (CT) character of this π-π* transition in peridinin. Such a large |Δμ| produced on excitation, we suggest, facilitates the bending of the lactone moiety, toward which charge transfer occurs, and the subsequent formation of the previously identified intramolecular CT (ICT) state at lower energy. This unexpectedly large 82 dipole moment, which has not been predicted even from high-level electronic structure calculations, is supported by calculating the shift of the peridinin absorption band as a function of solvent polarity, using the experimentally derived result. Overall, the photoinduced charge transfer uncovered here is expected to affect the excited-state reactivity of peridinin and, within the protein, be important for efficient energy transfer from the carotenoid S2 and S1/ICT states to the chlorophylls in PCP.

    Original languageEnglish
    Pages (from-to)15589-15597
    Number of pages9
    JournalJournal of Physical Chemistry B
    Volume109
    Issue number32
    DOIs
    Publication statusPublished - 18 Aug 2005

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