The Science of Lightsticks~ Chemiluminescence~

Darryl Ho 4L04

Contents

• What is a Lightstick?• Chemical Reactions• Various Chemicals for Various Colors

What is a Lightstick?

• A lightstick is a plastic tube with a glass vial inside it.– The tube and the vial each contain chemicals that

react with each other to produce light.

• To activate it, the tube is bent, which breaks the glass vial.

• This allows the chemicals to mix and react, producing light.

What is a Lightstick?

• Lightsticks are commonly used for decoration or lighting in conditions where electric lamps may not be suitable.– Used by divers, campers, etc.

Chemical Reactions

• Some chemical reactions release energy during the reaction, due to the formation of new bonds between ions.

• Unlike other reactions where the energy released is in the form of thermal energy, the reaction in a lightstick gives off light energy.– This is known as chemiluminescence.

Chemical Reactions

• There are three chemicals in a lightstick.– Two chemicals that react to release energy.– A fluorescent dye that accepts this energy and

converts it into light.

Chemical Reactions

• A common commercial lightstick uses a solution of hydrogen peroxide that is kept separate from a solution of phenyl oxalate ester together with a fluorescent dye.

Chemical Reactions

• The reaction between the two chemicals releases enough energy to excite the electrons in the fluorescent dye.

• This causes the electrons to jump to a higher energy level and then fall back down and release light.

Chemical Reactions

• The hydrogen peroxide oxidizes the phenyl oxalate ester, to form phenol and an unstable peroxyacid ester.

• The unstable peroxyacid ester decomposes, resulting in phenol and a cyclic peroxy compound.

• The cyclic peroxy compound decomposes to form carbon dioxide.

• These decomposition processes release the energy that excites the fluorescent dye.

Chemical Reactions

• As with all chemical reactions, the rate of reaction of a glowstick can be altered by changing its temperature.

The lightstick on the left has been left at room temperature after being activated.

The lightstick on the right has been immersed in hot water for one minute. The rate of reaction is increased, causing the stick to glow more brightly due to the increased amount of energy produced. However, it will wear out more quickly as well.

Various Chemicals for Various Colors

• There are several chemiluminescent chemical reactions, but the luminol and oxalate reactions are most commonly used for light sticks and glow sticks.

Various Chemicals for Various Colors

• American Cyanamid's Cyalume light sticks are based on the reaction of bis(2,4,5-trichlorophenyl-6-carbopentoxyphenyl)oxalate (CPPO) with hydrogen peroxide. The fluorophors (FLR) in this reaction are the chemicals that provide the color of the light stick.

Various Chemicals for Various Colors

• A similar reaction occurs with bis(2,4,6-trichlorophenyl)oxlate (TCPO) with hydrogen peroxide:

Various Chemicals for Various Colors

• Fluorescent dyes are added to light sticks to release colored light:

Blue 9,10-diphenylanthracene

Green 9,10-bis(phenylethynyl)anthracene

Yellow 1-chloro-9,10-bis(phenylethynyl)anthraceneRubrene

Orange 5,12-bis(phenylethynyl)-naphthaceneRhodamine 6G

Red Rhodamine B

Various Chemicals for Various Colors

• Although red fluorophors such as Rhodamine B are available, red-emitting light sticks tend not to use them in the oxalate reaction.

• The red fluorophors are not very stable when stored with the other chemicals in the light sticks.– Instead, a fluorescent red pigment is molded into the plastic tube that

encases the light stick chemicals. • The red-emitting pigment absorbs the light from the high

yield (bright) yellow reaction and re-emits it as red.• This results in a red light stick that is approximately twice as

bright as it would have been had the light stick used the red fluorophor in the solution.

Examples of Lighsticks in Action

The End