Breaking the red-limit: efficient trapping of long-wavelength excitations in chlorophyll f-containing Photosystem I.
Photosystem I (PSI) converts photons into electrons with a nearly 100% quantum efficiency. Its minimal energy requirement for photochemistry corresponds to a 700 nm photon, representing the well-known ‘red limit’ of oxygenic photosynthesis. Recently, some cyanobacteria containing the red-shifted pigment chlorophyll f have been shown to harvest photons up to 800 nm. To investigate the mechanism responsible for converting such low-energy photons, we applied steady-state and time-resolved spectroscopies to the chlorophyll f-containing PSI and chlorophyll a-only PSI of various cyanobacterial strains. Chlorophyll f-containing PSI displays a less optimal energetic connectivity between its pigments. Nonetheless, it consistently traps long-wavelength excitations with a surprisingly high efficiency, which can only be achieved by lowering the energy required for photochemistry, i.e. by ‘breaking the red limit’. A mechanism involving charge separation via a low-energy charge transfer state is proposed to reconcile this finding with the available structural data that show that no chlorophyll f is involved in photochemistry.
|Work Title||Breaking the red-limit: efficient trapping of long-wavelength excitations in chlorophyll f-containing Photosystem I.|
|License||In Copyright (Rights Reserved)|
|Publication Date||November 19, 2020|
|Publisher Identifier (DOI)||
|Deposited||November 16, 2021|
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