Chemistry is all around us. Every time someone eats chocolate, every time a pesticide is used, every time an oil painting dries, chemistry is at play. We often don’t think about how this amazing and intricate world around us works on a molecular level: we accept that it works and move on. However, understanding how and why the world works the way it does can help us make it better. And understanding how things work can help us relate seemingly unrelated matters.
There is a fantastic website called Compound Interest, which educates people of all and any background regarding the chemistry that makes up their every day worlds. On this blog, I found a particularly interesting article about glow sticks.
We all know how glow sticks work right? You snap the little tube and all the sudden it glows so brightly and brilliantly. When I was little glow sticks were magic, a magic which I could control with the bending of that little stick. But I always wondered why breaking the stick made it glow. Turns out glow sticks glow because of a chemical reaction we set into process by snapping the tube.
Glow sticks are made up of two compartments, each with a different chemical solution. One compartment is glass and is inside of the other. The outer compartment usually contains a diphenyl oxalate compound and a dye that corresponds to the desired color. The solution inside the little glass container is hydrogen peroxide. When you bend the stick, the glass container breaks and releases the hydrogen peroxide, which then reacts with the diphenyl oxalate. When diphenyl oxalate and hydrogen peroxide react, diphenyl oxalate is oxidized and produces the unstable compound 1,2-dioxetanedione. This product is so unstable that it quickly decomposes into carbon dioxide, releasing energy in the process.
Where do the colors come from? The answer is the process of chemiluminescence. The dye itself thus far has been uninvolved in the reaction, however, at this point the electrons of the dye’s molecules absorb the released energy and become excited. When the excited electrons fall back to their ground state, they release energy in the form of light. The type of dye determines the color perceived. The stick stops glowing when one of the reactants, either diphenyl oxalate or hydrogen peroxide runs out and the reaction stops.
So glow sticks work because of dye and a chemical reaction. What else “works” because of dye? This is where another article I found comes in: the chemistry of highlighter colors.
The color of a highlighter depends on the type of dye used, much like a glow stick. But how do chemicals and colors relate? Chemicals appear colored because they absorb some wavelengths of light and not others. When a molecule has a large amount of alternating single and double bonds, it is called a highly conjugated molecule, and it can an absorb visible wavelengths of light. The color seen depends on the wavelengths of visible light absorbed. So highlighter inks are colored because of alternating types of bonds within a molecule which allow for absorption of visible light. However, many dyes have this property yet are not fluorescent like highlighters. So why are highlighters fluorescent?
Highlighters are fluorescent because they do not just absorb visible light on the electromagnetic spectrum; they absorb UV wavelengths as well as visible ones. The light excites the dyes’ electrons which eventually fall back to their ground states, releasing energy as light in the process. This released light has a longer wavelength than that of the originally absorbed, so what was absorbed as UV light is released as visible. (Visible light has a longer wavelength than UV, making it less energetic and able to be seen by the human eye. Thus when the light released has longer wavelength, we are able to perceive what used to be low wavelength UV light). So fluorescence is the product of UV light being absorbed and released as visible light.
These two topics are incredibly related. Both glow sticks and highlighters appear colored because electrons are excited, either with energy from a reaction (glow sticks) or energy from light photons (highlighters), and then said electrons fall back to a ground state and release energy as a specific wavelength of visible light. The electromagnetic spectrum catalogues the different “types” of light if you will. It expresses the range of wavelengths and properties of radiation. Imagine a wave, on which little packets of energy, called photons, ride. The shorter the wavelength, that is the distance between the crests of a wave, the higher the frequency. Frequency measures the amount of wave cycles that pass within a given amount of time. Higher frequency means greater energy. Ultraviolet light, which falls directly above violet on the visible spectrum, has a shorter wavelength and higher frequency than visible light. So the amount of energy delivered in UV light is greater than in visible light.
Energy is needed to excite an electron, which means to raise it from a lower energy orbital to a higher energy orbital. Of course the electron cannot maintain that higher energy level forever, so it eventually falls back to it’s initial state. When it falls, the difference in energy between the orbitals is released. This energy is released as photons, which have a specific wavelength based on the material being excited. The visible spectrum corresponds to the 400 to 700 nm wavelength area of the electromagnetic spectrum. Chemicals need a certain amount of energy to excite an electron, which is taken from a specific wavelength delivering the needed amount. The wavelengths which are absorbed (used to excite the electrons) are not seen by the naked eye. Everything else is reflected. For example, when everything but red is absorbed by the fabric of a sweater, red is reflected and thus the color we perceive the sweater to be.
In examining glow sticks and highlighters, another topic came to mind: skin cancer. Now what on earth do highlighters and glow sticks have to do with skin cancer? Light. UV rays are harmful to skin because the high energy rays excite electrons within cells, which can mutate regular DNA into harmful, cancerous DNA. About 99% of non-melanoma skin cancers and 95% of melanoma cancers are caused by too much UV exposure. It’s amazing to think that the light that makes highlighters so fluorescent also causes skin cancer! I find these previous two topics related to skin cancer because they all are based off of energy expressed as light. Some of this is harmful, like when skin is exposed to high energy light. Some of this light is just beautiful and used as entertainment for children or as a study tool for college kids. It is amazing to see how the same basic chemical principle is expressed in so many different ways.
In studying chemistry, even the most different of subjects can be found to be related. As a potential art major, I never invested too much in chemistry growing up. But the more I learn about chemistry, the more I learn about the world. I am studying real, pressing issues and am connecting dots I thought impossible. It’s pretty amazing the connections you can make with a basic understanding of chemistry and a good website to turn to. I encourage everyone to read just one of these articles a week and see if you don’t find something that blows your mind or changes the way you live your life. Personally, I will be piling on the sun screen.