text: The excitation P680 → P680 of the reaction center pigment P680 occurs here. These special chlorophyll molecules embedded in PSII absorb the energy of photons, with maximal absorption at 680 nm. Electrons within these molecules are promoted to a higher-energy state. This is one of two core processes in photosynthesis, and it occurs with astonishing efficiency (greater than 90%) because, in addition to direct excitation by light at 680 nm, the energy of light first harvested by antenna proteins at other wavelengths in the light-harvesting system is also transferred to these special chlorophyll molecules.
  This is followed by the electron transfer P680 → pheophytin, and then on to plastoquinol, which occurs within the reaction center of PSII. The electrons are transferred to plastoquinone and two protons, generating plastoquinol, which released into the membrane as a mobile electron carrier. This is the second core process in photosynthesis. The initial stages occur within picoseconds, with an efficiency of 100%. The seemingly impossible efficiency is due to the precise positioning of molecules within the reaction center.  This is a solid-state process, not a typical chemical reaction. It occurs within an essentially crystalline environment created by the macromolecular structure of PSII. The usual rules of chemistry (which involve random collisions and random energy distributions) do not apply in solid-state environments.