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Luminol (C8H7N3O2) exhibits strong blue Chemilumineszenz when mixed with an oxidizing agent in a basic solution. A Katalysator, often an iron compound like the heme in hemoglobin, is required. The reaction oxidizes luminol, forming an unstable peroxide which decomposes into 3-aminophthalate in an electronically excited state. This excited state then decays, emitting a blue photon.
The luminol reaction is a classic example of liquid-phase Chemilumineszenz. The process begins with the deprotonation of luminol in a basic solution (e.g., sodium hydroxide). The resulting dianion then reacts with an oxidant, typically hydrogen peroxide. This reaction is slow but is dramatically accelerated by a Katalysator. In forensic applications, the iron(II) ion in the heme group of hemoglobin acts as the catalyst. The reaction proceeds through a cyclic peroxide intermediate, which is highly unstable. This intermediate collapses, releasing nitrogen gas and forming 3-aminophthalate in an excited singlet state. The subsequent relaxation of this excited state to the ground state results in the emission of a photon, producing a characteristic blue glow around 425 nm. The sensitivity of this reaction is remarkable, allowing for the detection of blood dilutions as low as one part in a million. However, it is not specific to blood, as other substances like copper salts, horseradish peroxidase, and even some bleaches can catalyze the reaction, potentially leading to false positives in a forensic context.
Luminol
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