text: The step  → P680 is performed by an imperfectly understood structure embedded within PSII called the water-splitting complex or oxygen-evolving complex (OEC). It catalyzes a reaction that splits water into electrons, protons and oxygen,
  using energy from P680. The actual steps of the above reaction possibly occur in the following way (Kok's diagram of S-states):
  (I) 2 (monoxide) (II) OH.  (hydroxide) (III)  (peroxide) (IV) (super oxide)(V)  (di-oxygen).              (Dolai's mechanism)
  The electrons are transferred to special chlorophyll molecules (embedded in PSII) that are promoted to a higher-energy state by the energy of photons.