Diphenyl oxalate


Audio Files

Meera Senthilingam

This week, Stephen Wallace releases some energy.

© Shutterstock

Stephen Wallace

Visually striking luminescence is a phenomenon found throughout the natural world. Termed “bioluminescence” it is a frequent and dramatic characteristic of deep-sea marine organisms, microorganisms and terrestrial invertebrates. Bioluminescence is typically exemplified by the green fluorescent proteins of the crystal jellyfish, by the luciferase enzymes of the big dipper firefly and by the symbiotic bacterium Aliivibrio fischeri. What makes this final example particularly extraordinary is that the bacteria are found inside a pouch located beneath the head of the Hawaiian bobtail squid, where its bioluminescence assists the squid to hunt at night in the shallow waters of the Pacific islands.

All of these examples of natural bioluminescent processes result from the excitation and fluorescence of small organic molecules by enzymes. Not to be outdone by nature, scientists achieve similar illumination processes in the laboratory using a combination of organic chemistry and photophysics.

This process is called chemiluminescence: the process by which light is emitted as the direct result of a chemical reaction, requiring no light bulb and no battery whilst giving off no heat. This is typically achieved by exciting a fluorescent molecule from its electronic ground-state configuration to a higher excited vibronic state using energy released by a chemical reaction. The excited molecule will spontaneously relax back to its more stable ground state configuration with the emission of a photon of light. It is this emission of light that we observe with the human eye.

In chemiluminescence, in place of using an enzyme to induce the molecular excitation, we use instead small organic molecules. Such a molecule needs to be completely inert until the point at which an external stimulus is applied, causing the molecule to react and release energy in a controlled and safe manner.

‘Diphenyl oxalate-induced chemiluminescence is now frequently used in scuba diving and camping equipment, as well as being widely used in nighttime medical and military rescue operations’
Whilst not necessarily familiar with their chemistries, you have undoubtedly seen such molecules in use, as they are responsible for the glow sticks you may find at fairgrounds and in nightclubs. The molecule diphenyl oxalate is responsible for initiating the chain of chemical reactions that results in a glow stick’s chemiluminescence.

If you were to cut an unused glow stick open (and I don’t recommend it), you would find it contains a small glass tube, floating in a liquid. Inside the tube is a mixture of diphenyl oxalate and a colored fluorescent dye. The liquid outside is a solution of aqueous hydrogen peroxide. When you bend the glow stick and break the inner container, the two solutions mix and a chemical reaction initiates between the hydrogen peroxide and diphenyl oxalate ester producing two molecules of phenol and one molecule of a cyclic peroxyacid ester called 1,2-dioxetanedione. This is a high-energy molecule that spontaneously decomposes to form two molecules of carbon dioxide, releasing energy in the process. This energy is absorbed by the fluorescent dye, which excites it into a higher vibronic state. When it then relaxes to its ground state configuration, it releases a photon of light, which we observe as a coloured glow. The wavelength of the emitted photon is dependent on the chemical structure of the fluorescent dye. Therefore, different colors of glowstick result from simply changing the dye molecule in solution with the diphenyl oxalate. As there is only a limited concentration of diphenyl oxalate in the glowstick interior, the excitation reaction can only proceed until no more diphenyl oxalate remains, resulting in the glowstick fading over time.

Diphenyl oxalate-induced chemiluminescence has only been in existence for the past 30 years. However, during this period the commercialization of this non-thermal energy-releasing chemical decomposition reaction has been extensive. From the better-known applications of chemiluminescence in fancy dress outfits and in nightclubs as quirky fashion accessories, diphenyl oxalate-induced chemiluminescence is now frequently used in scuba diving and camping equipment, as well as being widely used in nighttime medical and military rescue operations around the world.

Meera Senthilingam

From glowsticks to global rescues. That was Stephen Wallace from the Medical Research Council, with the chemistry of diphenyl oxalate. Now there’s more to next week’s compound than its name might suggest.

Brian Clegg

There are some compounds that are blest with evocative names. Admittedly, you could call naphthalene ‘bicyclo[4.4.0]deca-1,3,5,7,9-pentene’ if you wanted to be pedantic (or a chemist), but naphthalene gives us a double dose of meaning that isn’t there in the systematic name.

Meera Senthilingam

Brian Clegg reveals this double meaning in next week’s Chemistry in its Element. Until then, thank you for listening, I’m Meera Senthilingam.

Subscribe to our podcasts

Subscribe in iTunes RSS feed Chemistry World Monthly podcast

Subscribe in iTunes RSS feed The Compounds weekly podcast


Related Content

Oxalic acid

25 April 2013 Podcast | Compounds

news image

Lars Öhrström finds a link between Napoleon III and rhubarb

Uranium complexes unlock feedstock potential of carbon dioxide

25 July 2014 Research

news image

Carbon dioxide and depleted uranium both put to good use

Most Read

UC Davis chemist sentenced to four years over explosion

19 November 2014 News and Analysis

news image

Postdoc sentenced over attempt to make explosive device and reckless disposal of hazardous waste

Grad student blamed for research misconduct at Utah

13 November 2014 News and Analysis

news image

Two papers have been retracted due to image falsification at the University of Utah

Most Commented

Beetle behind breath test for bank notes

17 November 2014 Research

news image

Photonic crystal inks inspired by longhorn beetle could help to fight counterfeiting

Bayer wins race to buy Merck & Co consumer care

9 May 2014 Business

news image

$14bn deal will make Aspirin inventor the number two over-the-counter healthcare company