text: To exhibit its luminescence, the luminol must be activated with an oxidant.  Usually, a solution containing hydrogen peroxide (HO) and hydroxide ions in water is the activator.  In the presence of a catalyst such as an iron or periodate compound, the hydrogen peroxide decomposes to form oxygen and water:
  :2 HO →  + 2 HO
  :HO + KIO → KIO + O + HO
  Laboratory settings often use potassium ferricyanide or potassium periodate for the catalyst.  In the forensic detection of blood, the catalyst is the iron present in hemoglobin.  Enzymes in a variety of biological systems may also catalyse the decomposition of hydrogen peroxide.
  The exact mechanism of luminol chemiluminescence is a complex multi-step reaction, especially in aqueous conditions. A recent theoretical investigation has been able to elucidate the reaction cascade as shown below. Luminol is first deprotonated in basic conditions, then oxidized to the anionic radical. Which in turn has two paths available to give the key intermediate α-hydroxy- peroxide. After cyclization to the endoperoxide, the mono-anion will undergo decomposition  luminescence, if the pH is too low (< 8.2) for a second deprotonation. The endoperoxide dianion, however can give the retro-Diels-Alder product: 1,2-dioxane-3,6-dione dianion. And after chemiexcitation by two single-electron-transfers (SET) gives 3-aminophthalate dianion in its first singlet excited-state (S1). This highly instable molecule relaxes to the ground state, thereby emitting light of around 425 nm wavelength (purple-blue), the so-called chemiluminescence.