create atmosphere in concerts and climbing ladders at night. Glow sticks are a common choice. Have you ever wondered why these plastic sticks start to glow after breaking?

the glow stick actually contains two groups of chemicals: one is a variety of fluorescent dyes plus a substance called diphenyl oxalate, and the other is hydrogen peroxide solution, or hydrogen peroxide. The two groups of ingredients will not meet before they are put into use, because one of them is encapsulated in a glass tube. The process of breaking the glow stick breaks the glass tube, when different components come into contact with each other and the reaction begins.

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the chemical reaction actually takes place between hydrogen peroxide and diphenyl oxalate. Under the oxidizing action of hydrogen peroxide, an intermediate product of 1pyr2-dioxanedione (the one with a four-membered ring in the image below) is formed. The product is so unstable that it decomposes spontaneously into carbon dioxide and releases energy in the process. This energy can be transferred to the fluorescent dye molecule, allowing it to enter the excited state. The excited state is also unstable and will eventually return to the low-energy ground state. So where's the extra energy? It becomes the light we see.

(the dye in the picture above is the dye, dye* is the dye that enters the excited state, and hv is the light emitted)

fluorescent dyes with different chemical structures can produce different colors of light. The common ones are the following:

(picture from compoundchem click to see a larger picture)

of course, the final reactant will always be consumed, so the fluorescent rod can not continue to shine at this time. However, there is also a way to extend the life of the glow stick a little bit: put it in the refrigerator. The chemical reaction rate is affected by temperature, and if it is stored in a cold place, the rate of reactant consumption will be slower. On the contrary, in a higher temperature environment, the glow will become brighter, but the duration will be shorter accordingly.

PS: the luminescence process of a glow stick is not fluorescence, but chemiluminescence, because it is not excited by light, but draws energy from chemical reactions. Similarly, the luminol reaction belongs to chemiluminescence.

however, the luminous dyes used in fluorescent rods do generally have fluorescence.

because of the irritation of substances such as hydrogen peroxide, it is not recommended to take the glow stick apart and play.

-- but we can show it to you! There will be another live broadcast of the experiment tomorrow. At that time, we will disassemble the glow stick with the students in the fruit shell lab. If you are interested, you can have a look at it. 3:00-4:00 on December 27th, you can go to bilibili or Youku to search for "fruit shell video" to find the studio, or follow the live broadcast preview _ (: fruit "∠) _