Photoisomerisaatiolla

Photoisomerization is a photochemical process where a molecule undergoes an isomerization reaction upon absorption of light. Isomerization itself is a reaction in which a molecule is transformed into another isomer, which has the same number of atoms and the same types of atoms but arranged differently. Photoisomerization specifically refers to the isomerizations that are triggered by the absorption of photons. This light energy is typically absorbed by a chromophore within the molecule, leading to an excited state. From this excited state, the molecule can then rearrange its structure, often by changing the geometry around a double bond or by ring opening or closing.

A common example of photoisomerization occurs in the cis-trans isomerization of alkenes. When light is absorbed, the pi bond in the double bond can temporarily break, allowing rotation around the sigma bond. Upon returning to the ground state, the pi bond reforms, but the relative positions of the substituents can be altered, leading to a different isomer. Another significant example is the photoisomerization of retinal in the eye, which is a key step in the process of vision. The absorption of light by retinal triggers a cis-trans isomerization, initiating a cascade of events that ultimately leads to a nerve impulse. Photoisomerization is also utilized in materials science, for instance, in the development of photochromic materials that change color upon exposure to light.