Description
We’ve all seen glow sticks in action, but have you ever wondered how they work? At the heart of their glowing magic lies a chemical reaction known as chemiluminescence. This occurs when specific chemicals mix together, producing light without the need for heat. By understanding the science behind glow sticks, we can appreciate the chemistry that brings these vibrant colors to life.
Source
- Reference: Shakhashiri, B.Z.
- Title: Chemical Demonstrations: A Handbook for Teachers of Chemistry
- Year: [Not specified]
- Volume: 2
- Page: 297
How It Works
Glow sticks emit light when the fragile glass container inside breaks, mixing the two chemicals together. This chemical reaction spreads throughout the glow stick as the chemicals mix. Initially, only a small part of the stick glows when snapped.
Dangers
Glow sticks contain hydrogen peroxide, and phenol is produced as a by-product. It is advisable to keep the mixture away from skin and prevent accidental ingestion if the glow stick case splits or breaks. Spills on skin can cause slight irritation, swelling, or, in extreme cases, vomiting and nausea. Some users apply the glowing solution directly to skin, but the chemicals are toxic, corrosive, and classified as category 3 mutagens. Avoid contact with eyes or nasal membranes. Despite rumors, it is not safe to smoke or ingest glow stick chemicals, and they do not produce drug-like effects. The fluid can also dissolve some types of plastic.
Chemistry
The glow stick contains two chemicals and a suitable fluorescent dye (sensitizer or fluorophor). The chemicals in the glass vial include diphenyl oxalate, while the plastic tube contains hydrogen peroxide. When mixed, the peroxide oxidizes the ester, resulting in phenol and an unstable peroxyacid ester (1,2-dioxetanedione). The peroxyacid decomposes to carbon dioxide, releasing energy that excites the dye, which then relaxes by emitting a photon. The emitted light’s wavelength—and thus its color—depends on the dye’s structure.
The dyes used in glow sticks typically exhibit fluorescence under ultraviolet radiation. Even spent glow sticks shine under black light. Manufacturers can adjust the concentrations of the two chemicals to produce glow sticks that glow brightly for a short time or more dimly for a longer duration.
Heating a glow stick accelerates the reaction, causing it to glow brighter but for a shorter duration. Cooling slows the reaction, extending the glow time but dimming the light.
Fluorophores Used
- Blue: 9,10-diphenylanthracene
- Green: 9,10-bis(phenylethynyl)anthracene
- Yellow: 1-chloro-9,10-bis(phenylethynyl)anthracene
- Rubrene: Emits yellow
- Orange: 5,12-bis(phenylethynyl)-naphthacene, Rhodamine 6G
- Red: Rhodamine B
Reactions
Three compounds are essential for glow sticks to produce light: bis(2,4,6-trichlorophenyl)oxalate (TCPO), hydrogen peroxide, and a dye (typically an anthracene derivative).
The hydrogen peroxide oxidizes TCPO, forming trichlorophenol and an unstable peroxyacid ester. The ester decomposes, resulting in phenol and 1,2-dioxetanedione. The dioxetanedione complexes with the dye, releasing light. The color of the emitted light is dictated by the dye’s molecular structure.
Mechanisms
The Mechanism can be found at the below reference.
Reference for mechanism:
- T. G. Chasteen, “The Chemiluminescence of Luminol and bis(2,4,6-trichlorphenyl)oxalate (TCPO)” [See: http://www.shsu.edu/%7Echm_tgc/JPPdir/JPP1999/]