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23 January 1997 Photosensitive organized organic films in the light of bound electromagnetic waves
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This paper describes recent advances in the field of photochromic polymeric structures for optical data storage. In particular, we discuss photo-induced effects in supramolecular assemblies containing azobenzene molecules (e.g. Langmuir-Blodgett-Kuhn structures and ultrathin silane layers). Reorientation of azobenzenes in these structures is compared to that observed in spin-cast films. Photoisomerization and photo-induced orientation of azobenzene molecules is studied at the molecular level by means of azosilane molecules chemisorbed on silicon oxide substrates. The study of the thermal back isomerization reaction of the azobenzene molecules in these layers reveals steric hindrance at the molecular level. These ultra-thin photochromic self-assembled monolayers (SAMs) exhibit persistent dichroism upon linearly polarized light irradiation. This dichroism could be both written and erased by irradiation with light of an appropriate wavelength. In addition, the sign of this dichroism can be inverted by choosing the appropriate polarization of the irradiating light, thus showing a 'smart communication' between the light polarization and the ultra-thin photochromic layers. Photoisomerization also induces reversible changes in the optical thickness of these molecularly thin SAMs. Langmuir- Blodgett-Kuhn (LBK) multilayer assemblies of 'hairy-rod' polyglutamates with stiff main chains and flexible side chains containing photochromic azo units exhibit a highly optically anisotropic structure when the azo molecules are in the trans form, and a nearly optically isotropic structure when the azo molecules are in the cis form. The trans $ARLR cis photoisomerization of the azo molecules switches them between a highly oriented trans configuration and a bend cis configuration, thus turning the anisotropy 'on' and 'off.' In contrast to spin-cast polymer films containing azobenzene units, photoselection under polarized light irradiation does not occur in these LBK structures. The study of the electronic density distribution of these films show that a remarkable variation in the LBK structures' stability comes with a seemingly small change in the side-chain structure. All the structures described here, form thin films that can be very sensitively characterized, by using surface plasmons and guided optical waves as electromagnetic modes bound to an interface.
© (1997) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Zouheir Sekkat and Wolfgang Knoll "Photosensitive organized organic films in the light of bound electromagnetic waves", Proc. SPIE 2998, Photosensitive Optical Materials and Devices, (23 January 1997);

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