Chemiluminescence: What’s Inside of a Light Stick Anyway?

WARNING NOTICE The experiments described in these materials are potentially hazardous. Among other things, the experiments should include the following safety measures: a high level of safety training, special facilities and equipment, the use of proper personal protective equipment, and supervision by appropriate individuals. You bear the sole responsibility, liability, and risk for the implementation of such safety procedures and measures. MIT and Dow shall have no responsibility, liability, or risk for the content or implementation of any of the material presented. Chemiluminescence What’s inside of a light stick anyway? Photo taken at MIT 150th Celebration Open House Under the Dome April 30, 2011 Courtesy of Nathan Sanders. Used with permission. Abstract Three plastic cups containing solutions are poured simultaneously into three other plastic cups containing solutions and chemical reactions occur producing different colors in each of the cups that glow in the dark. 1 Materials 5 red light sticks 5 green light sticks 5 blue light sticks 6 plastic cups scissors knife gloves goggles Safety Wear gloves and safety goggles when handling the chemicals in a light stick. H2O2 is a strong oxidizing agent that can cause burns. The fluorescent dyes should be considered toxic and not be ingested. Caution! Never ever try to open a glow stick up with your mouth. When opening a glow stick and breaking the glass vial inside make sure you wear safety goggles to prevent shards of glass or chemicals from reaching the eye. Procedure Create two solutions from each of the three colors of light sticks as follows: Solution 1: Using a knife cut the top off the plastic light sticks and carefully pour out the solutions into plastic cups. Pour all the red light stick solutions into the same cup and so on for the blue and green. Carefully remove the inner glass vials and reserve for Solution 2. Solution 2: Using a pair of scissors snip open the glass vials that you removed from the opened light sticks and pour those solutions into the other three cups. Get three volunteers to come up give each one-cup containing solution 1 and one cup containing solution 2. The solutions are then poured together resulting in a chemical reaction resulting in different colors of light that glow in the dark. Discussion This is a classic reaction where energy is released in the form of light without heat. In Chemiluminescence, two molecules react together to create a third excited intermediate molecule. This molecule finally relaxes back to the ground state with 2 the release of a photon of light at a frequency, which we can see in the visible range of the electromagnetic spectrum. A general scheme for Chemiluminescence is shown below: In our case, each light stick contains three chemicals. The chemical in the inner glass vial Solution 2 is H2O2. The chemicals inside of the plastic light stick that were poured out into Solution 1 consists of Cyalume a Phenyl Oxalate Ester plus a fluorescent dye molecule. When the H2O2 in Solution 2 is poured into Solution 1 a chemical reaction occurs that produces energy. The energy produced is transferred to the dye molecule, which gets excited and converts the energy into light. Depending on what type of dye is present you will get different colors of light given off. The general reaction scheme for the reaction inside of a light stick is shown below: 3 4 When the two solutions are mixed the hydrogen peroxide oxidizes the phenyl oxalate ester, which produces phenol plus an unstable compound called 1,2dioxetanedione. This unstable ester breaks apart releasing energy and CO2. The energy gets transferred to the dye molecule causing the electrons to jump to higher levels, when they relax and fall back down, energy is released in the form of light. Disposal The contents of the reaction and any leftover solutions should be combined into a properly labeled waste bottle and disposed of properly in labeled waste containers. References Michael M. Rauhut, Acc. Chem. Res. 1969, 2(3), pp. 80-87. Elizabeth Wilson, Chemical and Engineering News, 1999, 77(3), p 65. Edwin A Chandross, Tetrahedron Letters 1963, 4(12) pp. 761-765. 5