Abstract: Photosystems are protein complexes located in the thylakoid membranes of plants and other organisms and are the sites of the fundamental first steps of photosynthesis. In particular, Photosystem II (PSII) absorbs solar energy to catalyze the oxidation of water, generating oxygen as a byproduct. The photocatalytic reaction in PSII also initiates an electron transport chain and proton gradient, that results in the production of NADPH and ATP molecules. These “energy” molecules are used to power the Calvin cycle to fix carbon and eventually produce carbohydrates, thus completing the whole photosynthesis process in plants. The supercomplex of plant PSII contains a core complex (CC) surrounded by several peripheral antenna complexes, mostly light-harvesting complex II (LHCII) that harvest sunlight and transfer the excitation energy to the reaction center. Understanding the intra-complex and inter-complex ultrafast excitation energy transfer (EET) dynamics within the photosystems comprising tens to hundreds of pigment chlorophyll a/b molecules, is important to get further insights about the overall photosynthetic mechanism. We report on using ultrafast coherent two-dimensional electronic spectroscopy (2DES) complemented by structure-based calculations, to reveal the femtosecond to picosecond EET network in these highly complex photosynthetic systems with densely packed pigments.
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