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Orientation of Azo-Dye molecules in polymer films, via photoisomerization: Dichroism measurements and second harmonic generation

Ngan Nguyen Thi Kim, M. Dumont , J. A. Delaire, K. Nakataki, Mol. Cryst. Liq. Cryst. 430, 249-256 (2005)

Photoinduced Anisotropy and All-Optical Poling are the result of two mechanisms, the angularly selective excitation of molecules (Angular Hole Burning) and the rotation of molecules during the excitation–relaxation cycle (Angular redistribution). In this paper we recall some previous results and we present two new experiments. The first one demonstrates the prime importance of reversible photoisomerization for angular redistribution: we compare dichroism and second harmonic generation, with photoisomerizable molecules and non photoisomerizable ones. The second experiment shows an example of the behavior of photoinduced anisotropy, in a liquid crystal azo-polymers: a 3D characterization of anisotropy is necessary.

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