Chemical Department of Engineering,NIT Warangal: What Makes Light Sticks Glow?

What Makes Light Sticks Glow?

If you've ever bent a light stick and stared in amazement as it produced light from two liquids then you know what makes chemiluminescence so interesting. Chemiluminescence is defined as the production of light energy from a chemical reaction without the use of heat or a flame.

On the molecular level, chemiluminescence can be explained as a reaction that produces atoms in an excited state. An excitation reaction that produces 40-70 kcal/mole of energy can be seen by the naked eye. These are the types of reactions that are used in making these amazing light sticks that many of us enjoyed as children. As is often the case, nature helped lead scientists to the discovery of these reactions. The firefly is the model of efficiency when it comes to producing light from chemical reactions. The firefly is able to reach an efficiency of 88% while synthetic reactions are only able to achieve a 23% efficiency at best.Light sticks are activated by bending them and rupturing a capsule inside the stick. This allows the two liquids to mix and the reaction begins. The liquid that makes up the majority of the light stick is called the "oxalate." A typical oxalate solution is prepared by mixing bis(2,3,5-trichloro-6-carbonpentoxyphenyl) oxalate and dibutyl phthalate. This mixture is heated under nitrogen for an hour. Then another component called 9,10-bis(phenylethynyl) anthracene is added. A typical activator can be prepared as shown below. The light stick contains three parts oxalate and one part activator (contained in the capsule).