Photochemistry - Koukagaku

A branch of chemistry that studies the chemical aspects of the interactions between light and matter. Its current main subjects are chemical changes (photochemical reactions) and luminescence processes (fluorescence and phosphorescence) caused by light absorption, as well as luminescence phenomena caused by chemical reactions (chemiluminescence). When the wavelength of light is shorter than that of X-rays, ionization is the main initial process, so it is called radiation chemistry, which is different from photochemistry, which only focuses on the excitation process. If the absorbed light is in the visible range, it appears colored, so the colors of dyes and pigments are also a subject of photochemistry. Light absorption occurs in units of one photon, but with the development of lasers, multiphoton absorption processes in which multiple photons are absorbed simultaneously have also been observed and are being studied in detail. As a result of light absorption, excited molecules and free radicals are generated, and reactions that do not occur in normal thermal reactions occur. This has been used in organic synthesis, and the field of organic photochemistry has developed rapidly. Since the sun is an important light source, the origin of life and photosynthesis are also important issues in photochemistry, and future developments are expected.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

光と物質の相互作用のうち，化学的な側面を研究対象とする化学の一分野．光の吸収によって起こる化学変化(光化学反応)や発光過程(蛍光やりん光)，また化学反応によって起こる発光現象(化学ルミネセンス)などが現在のおもな対象である．光の波長がX線より短いときはイオン化がおもな初期過程になるので，励起過程だけを対象とする光化学とは区別して放射線化学という．吸収される光が可視領域にあれば着色して見えるから，染料や顔料の色も光化学の対象である．光の吸収は光子1個を単位として起こるが，レーザーの発達により複数の光子を同時に吸収する多光子吸収過程も観測され，詳しく研究されている．光吸収の結果，励起分子や遊離基が発生し，通常の熱反応では起こらない反応も起こる．これが有機合成に利用され，有機光化学の分野が急速に発展した．太陽は重要な光源なので，生命の起源や光合成なども光化学の重要な課題であり，今後の発展が期待される．

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