Two-photon excitation study of peridinin in benzene and in the peridinin chlorophyll a-protein (PCP)

Jörg Zimmermann, Patricia A. Linden, Harsha M. Vaswani, Roger G. Hiller, Graham R. Fleming*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

46 Citations (Scopus)

Abstract

Peridinin chlorophyll a-protein (PCP) is a unique light harvesting protein found in dinoflagellates, that contains a large amount of the carotenoid peridinin. Carotenoids have unusual spectroscopic properties due to their approximate C2h symmetry, which makes transitions from their ground states to their S1 (S2) states one-photon forbidden (allowed). To gain information about one-photon forbidden electronic states in peridinin, fluorescence excitation spectra were measured after two-photon excitation for peridinin in benzene and in the PCP. The samples were excited using 920-1320 nm light. Fluorescence of the isolated peridinin S1 state was then measured at 750 nm. In PCP, the excited peridinin transfers energy to chlorophyll whose fluorescence was monitored at 670 nm. Surprisingly, two-photon absorption was observed in both the peridinin S1 and S2 regions, with the spectrum slightly red-shifted in the protein sample. The peridinin S1 energy was found to be higher than that of typical light harvesting carotenoids, making its S1 state very close in energy to its S2 state. We suggest that peridinin's polar groups, symmetry breaking, and possible mixing of electronic states lead to two-photon character of the normally one-photon allowed S0-S2 transition.

Original languageEnglish
Pages (from-to)9418-9423
Number of pages6
JournalJournal of Physical Chemistry B
Volume106
Issue number36
DOIs
Publication statusPublished - 12 Sep 2002

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