Vojtěch Zeman prezents PHOTOCHROMISM

Vocabulary PaintworkNátěr FissionŠtěpení LifetimeDoba života Self-stainingSamozbarvovací DirectionSměr EyepieceOkulár

Definition of photochromism Photochromism is a phenomenon, when molecules of matter change reversibly their structure and absorption spectrum, then at least one direction must be induced only by photochemical radiation.

Some photochromic reactions 1.

Some photochromic reactions 2.

Principle of photochromism 1. Photochromism is induced by electron crossing after light up. The molecule is excited from elementar state S 0 to excited state S 1. From state S 1 it can be transmuted to new configuration, changed to triplet state T 1, then there might be non radiate drive to state S 0 or radiate drive to state S 0. Last eventuality is called fluorescence.

Principle of photochromism 2. From triplet state T 1 molecules can be transmuted to new configuration, with non radiate drive to state S 0 or radiate drive to state S 0. Last eventuality is called fosforescence. Triplet state T 1 is very reactive. Molecules react with enviroment in the presence of oxygen or radicals. Their lifetimes in state S 1 is s and in state T 1 are s.

Mechanisms of photochromism Photochromic reactions have several mechanisms. They are cis - trans isomerization, triplet - triplet photochromism, tautomerism photochromism, homolytic fission, heterolytic fission and fotodimerization.

Utilitization of photochromism Photochrimism has been known more then hundred years, but attention is given to it during last thirtyfife years. Photochromic materials are used in self-staining glass as shutters and eyepieces, dosimetric devices and decorative paintwork. It may also be used for recording information in the future.

Ouestion for a medium student How may reverse reaction can be directed in the photochromism? Where would you use photochromic matter? How long is photochromism known? (For example: h, , spontaneously.) (Self-staining glass, dosimetric matter and decorative paintwork.)

Ouestion for top of the class It´s, one of the most important photochromic molecules, spiropyrane. Project organic synthesis of this molecule!

„Thank you for attention.“