klorofüll a molekulide paar fotosüsteem II reaktsioonitsentris, mis absorbeerib maksimaalselt 680 nm valgust, Is the reaction-center chlorophyll a molecule in association with photosystem II. Its absorption spectrum peaks at 680 nm. Oxidized P680 (P680+) is the strongest biological oxidizing agent known. It has an estimated redox potential of ~1.3 V. This makes it possible to oxidize water during oxygenic photosynthesis.