A. Petri et al., PHOTOINDUCED REORIENTATION OF CHOLESTERIC LIQUID-CRYSTALLINE POLYSILOXANES AND APPLICATIONS IN OPTICAL INFORMATION-STORAGE AND 2ND-HARMONICGENERATION, Berichte der Bunsengesellschaft fur Physikalische Chemie, 97(10), 1993, pp. 1281-1286
Citations number
23
Categorie Soggetti
Chemistry Physical
Journal title
Berichte der Bunsengesellschaft fur Physikalische Chemie
When liquid crystalline polymers, which contain an azo dye as a side c
hain, are irradiated with light which is absorbed by the azo dye, both
the index of refraction and the absorbance are changed. It was proven
that the modulation of the optical properties mainly rests upon a reo
rientation of the long molecular axis of the chromophores and of the m
esogenic units. This change of the alignment of the side chains occurs
after numerous trans-cis-isomerization cycles of the azo dye. Spectro
scopic investigations show that by irradiating the samples completely
new and well ordered textures appear. The characteristic features of t
he new textures depend on the structure of the liquid-crystalline poly
mer before irradiation and on the polarization state of the actinic li
ght. We investigated cholesteric polysiloxanes which were either irrad
iated with linearly or with circularly polarized light (unpolarized li
ght respectively). The characterization of the new textures was done w
ith different spectroscopic methods. The photochemically induced chang
es of the texture are usable in applications like optical information
storage, eg. for the generation of holograms or for the production of
displays. We further investigated samples with dipolar azo dyes which
were reoriented with light under the influence of an electrical field.
The cooperative effect of light and field results in a polar alignmen
t of the azo dye which was proven by second harmonic generation (SHG).
We compare material properties like longterm stability and efficiency
of the SHG in samples which were prepared by this new procedure, by c
ontact poling and by corona poling.