fotodimerointi

Fotodimerointi, also known as photodimerization, is a photochemical reaction in which two identical molecules join together to form a dimer. This process typically occurs when the molecules absorb light energy, which excites them to a higher energy state. In this excited state, the molecules are more reactive and can then combine. A common example of fotodimerointi is the dimerization of thymine bases in DNA upon exposure to ultraviolet radiation, which can lead to DNA damage.

The reaction usually involves molecules with unsaturated bonds, such as double or triple bonds. Upon absorption of a photon, an electron in the molecule is promoted to a higher energy level, creating an excited state. This excited molecule can then interact with another molecule in its ground state or in an excited state, leading to the formation of a new covalent bond and the creation of a dimer. The reverse reaction, known as photodissociation or photoreversal, can also occur, where the dimer breaks apart back into the original monomers upon absorption of light of a different wavelength or under different conditions.

Fotodimerointi has applications in various fields, including materials science, where it is used to create cross-linked polymers and photoresists for lithography. It also plays a role in photodynamic therapy, a medical treatment that uses light to activate drugs that kill cancer cells. Understanding the mechanisms and controlling the outcomes of fotodimerointi is crucial for optimizing these applications and for comprehending fundamental photochemical processes.