Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 103, Issue 14, Pages 5343-5348Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0508530103
Keywords
artificial photosynthesis; carotenoid; nonphotochemical quenching; photoprotection; xanthophyll cycle
Categories
Ask authors/readers for more resources
Under excess illumination, plant photosystem 11 dissipates excess energy through the quenching of chlorophyll fluorescence, a process known as nonphotochemical quenching. Activation of nonphotochemical quenching has been linked to the conversion of a carotenoid with a conjugation length of nine double bonds (violaxanthin) into an 11-double-bond carotenoid (zeaxanthin). It has been suggested that the increase in the conjugation length turns the carotenoid from a nonquencher into a quencher of chlorophyll singlet excited states, but unequivocal evidence is lacking. Here, we present a transient absorption spectroscopic study on a model system made up of a zinc phthalocyanine (PC) molecule covalently linked to carotenoids with 9, 10, or 11 conjugated carbon-carbon double bonds. We show that a carotenoid can act as an acceptor of PC excitation energy, thereby shortening its singlet excited-state lifetime. The conjugation length of the carotenoid is critical to the quenching process. Remarkably, the addition of only one double bond can turn the carotenoid from a nonquencher into a very strong quencher. By studying the solvent polarity dependence of the quenching using target analysis of the time-resolved data, we show that the quenching proceeds through energy transfer from the excited PC to the optically forbidden S, state of the carotenoid, coupled to an intramolecular charge-transfer state. The mechanism for excess energy dissipation in photosystem 11 is discussed in view of the insights obtained on this simple model system.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available