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PHOTOCHROMISM

Vocabulary

Paintwork Nátěr

Fission Štěpení

Lifetime Doba života

Self-staining Samozbarvovací

Direction Směr

Eyepiece Okulár

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.

B A

B A slyspontaneou Δ,,hν

hν

2

1

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 S0 to excited state S1. From state S1 it can be transmuted to new configuration, changed to triplet state T1, then there might be non radiate drive to state S0 or radiate drive to state S0. Last eventuality is called fluorescence.

Principle of photochromism 2.

From triplet state T1 molecules can be transmuted to new configuration, with non radiate drive to state S0 or radiate drive to state S0. Last eventuality is called fosforescence. Triplet state T1 is very reactive. Molecules react with enviroment in the presence of oxygen or radicals. Their lifetimes in state S1 is 10-8s and in state T1 are 10-3s.

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 Thank you for for attention.“ attention.“