Vojtech Zeman prezents

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Vojtech Zemanprezents
PHOTOCHROMISM
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Vocabulary
Paintwork Náter Fission tepení Lifetime Doba
ivota Self-staining Samozbarvovací Direction Sme
r Eyepiece Okulár
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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.
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Some photochromic reactions 1.
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Some photochromic reactions 2.
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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.
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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.
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Mechanisms of photochromism
Photochromic reactions have several mechanisms.
They are cis - trans isomerization, triplet -
triplet photochromism, tautomerism photochromism,
homolytic fission, heterolytic fission and
fotodimerization.
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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.
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Ouestion for a medium student
(For example h?, ?, spontaneously.)
(Self-staining glass, dosimetric matter
and decorative paintwork.)
How may reverse reaction can be directed in the
photochromism? Where would you use
photochromic matter?
How long
is photochromism known?
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Ouestion for top of the class
Its, one of the most important photochromic
molecules, spiropyrane. Project organic synthesis
of this molecule!
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Thank you for
attention.