A simple artificial light-harvesting dyad as a model for excess energy dissipation on oxygenic photosynthesis
Under excess illumination, plant photosystem II 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 S1 state of the carotenoid, coupled to an intramolecular charge-transfer state. The mechanism for excess energy dissipation in photosystem II is discussed in view of the insights obtained on this simple model system.
| Main Authors: | , , , , , , , , , , , |
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| Format: | Article/Letter to editor biblioteca |
| Language: | English |
| Subjects: | antenna, carotenoids, chlorophyll fluorescence, complex, dynamics, excited singlet-state, green plants, photosystem-ii, s-1 state, xanthophyll cycle, |
| Online Access: | https://research.wur.nl/en/publications/a-simple-artificial-light-harvesting-dyad-as-a-model-for-excess-e |
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