P680

P680, or Photosystem II, (where P stands for pigment) is the reaction-center associated with photosystem II and consists of 2 chlorophyll a molecules that are not bound to proteins unlike the other chlorophyll molecules in photosystem II. Its absorption spectrum peaks at 680 nm, which is in the red part of the spectrum. When photosystem II absorbs light, an electron is excited to a higher energy level. This electron drops down to its ground state level and releases energy, which is then transmitted through a light-harvesting complex (LHCII) until it reaches a P680 chlorophyll and excites an electron on the P680 molecule. The resulting P680 with excited electron is designated P680*. The electron is subsequently captured by the primary electron acceptor. To replace the electron water will be oxidized in the Oxygen evolving complex.

P680 is the strongest biological oxidizing agent known.