Photochemistry is a branches of chemistry that studies about chemical effects of light. It is concerned with chemical reaction, isomerization and physical behavior that may happen due to the influence of visible and ultraviolet light.
Indeed, this is the Branches of Inorganic Chemistry. The concept of photochemistry is divided into Two Laws of Photochemistry:
- The first law of photochemistry or Grotthuss-Draper law, which told about photoexcitation. Photoexcitation is the first step in a photochemical process where reactant is elevated into an excited state, the state where higher energy exists. In other words, the first law told about states that light must be absorbed by chemical substances in order for photochemical reactions to take place.
- The second law of photochemistry or Stark-Einstein law said that for each photon of light absorbed by certain chemical system, no more than one molecule is activated for a photochemical reaction to be occurred, as defined by the quantum yield.
Applications of photochemistry are well-known for two major reactions happened in life. The two major reactions we talked about is no other than the photosynthesis occurred in plants and the formation of ozone in atmosphere. The photosynthesis reaction is a reaction that converts light energy into chemical energy. Plants get energy for food, whereas human get benefit from oxygen released from the reaction.
Meanwhile, ozone is formed by the action of ultraviolet light. Ozone in atmosphere is really useful in life since it can absorb sun’s UV which can be harmful for human. In nature, photochemistry become more important as it also become the basis of vision and the formation of vitamin D with the sunlight.
Seeing how useful it is in nature, make us wonder how photochemistry is applicated in modern life. It turns out that there are so many applications of photochemistry in the modern life. It is used widely, ranging from photography, cosmetics and mostly for industrial uses. Besides, it can be found in modern printing technology. Here is a list of the applications of photochemistry in modern life:
1. Development of Film The first application of photochemistry in modern life is in photography
The photochemistry occurred in photography is the process by which electromagnetic energy causes chemical substances change to matter. This reaction is involved in the development of film. In the development of film, the photochemistry reaction allows the images developed from a film to obtain its colors.
The chemical used in photography is silver halide crystals and spectral sensitizers. Both of them are known as the heart of photographic film. Silver halide crystals are only sensitive to the blue of the visible spectrum which is not efficient in camera film. It only produces more portions of the image. Therefore, spectral sensitizers are added to the surface of silver halide crystals. Spectral sensitizers can give them ability to be more sensitive to other colors of the visible spectrum (green and red).
An invisible latent image in the emulsion is formed shortly after capturing image. This invisible latent image can be chemically developed into a visible photograph. The photochemical process then turns the invisible latent image into a visible latent image on the film. The reaction is completed by applying spectral sensitizers to the surface of silver halide crystals. After reaction, the spectral sensitization has been increased so when film is developed in a dark room, the color appears.
2. Reversible Photochemical Reaction in CosmeticsChemical substances in cosmetics are mostly unstable to the light.
We have already known about this since so many cosmetic products used the opaque container. Photosensitization can occur in cosmetics which is caused by a reaction with the light. This condition is not good as photosensitization can harm skin. To eliminate this reaction, we need to remove the unwanted photochemical energy by simply creating the reversible of photochemical reaction.
3. Photochemical Isomerization in Industry in the field of isomerization, synthetic photochemistry has contributed for developing a large number of organic compounds.
Some of them are still not commercially used. Up to now, there are only two major kinds of photochemical isomerization reactions. They are electrocyclic ring opening in the vitamin D synthesis and thermoreversible hydrogen shift in the ultraviolet stabilization of plastics.
The synthesis of vitamin D3 which is very important in human medicine and also for animal nutrition is one of the example of organic compounds made by photochemical isomerization. Meanwhile, in plastic industry, thermoreversible hydrogen shift is the main absorber used to protect plastics from ultraviolet degradation.
4. Optical BleachesAnother industrial application is the development of optical brightener or bleaches made by one of the primary photochemical processes called luminescence.
Since many people thought that white color is associated with the terms cleanliness and purity, many commercial products made it a symbol for quality. The optimum impression of whiteness is obtained when body reflects all visible light. It can be achieved by the optical bleaches made by luminescence. Paper, cotton, detergents, wool, polyester and household linen industry are the examples of industry using this technology. ( Helium Uses)
5. Fluorescent Dyes Fluorescent dyes are somehow analogous to the optical bleaches, yet the applications are so much wider
The basic principal of fluorescent dyes is that a short-wave light is converted into long wave fluorescent light in the visible spectrum. These dyes are responsible to create luminous colors in advertising, shock colors in fashion up to warning colors in traffic. This fluorescent dye can emit twice as much light at the longer wavelengths.
Moreover, fluorescent also used in developing color of television. The green, blue and red fluorescent pigments are used for it. For automatic sorting of letters and postcards, fluorescent is also involved. Another application is in marking dials and light switches.
Now, fluorescent is not only industrially used, but also commercially used. You can find that it is placed freely in market. The products we talked are emergency lighting in mines, factories and camping sites. (Also read: What Are Some Examples of Inorganic Compounds?)
Indeed, that’s all applications of photochemistry in modern life that we use everyday to fill our daily activity, Meanwhile, keep in touch with chemistry, it makes life better as there are many Common Chemicals Used at Home