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Light-induced orientation of dyes in azobenzene containing LC polymers

 
: Rosenhauer, R.; Fischer, Th.; Stumpe, J.; Gimenez, R.; Pinol, M.; Serrano, J.L.; Broer, D.

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Khoo, I.-C.:
Liquid crystals VI : 8 - 9 July 2002, Seattle
Bellingham/Wash.: SPIE, 2002 (Proceedings of SPIE 4799)
ISBN: 0-8194-4567-3
pp.121-135
Conference "Liquid Crystals" <2003, San Diego/Calif.>
English
Conference Paper
Fraunhofer IAP ()

Abstract
Liquid crystalline polymethacrylates with benzanilide and photochromic azobenzene side groups and a related terpolymer containing an additional side group with a phenylethynyl substituted anthracene chromophore were oriented by the irradiation with linearly polarized light. The orientation of both polymers were compared irradiating with polarized visible or, alternatively, UV light. Caused by the co-operativity of the photoorientation process, the light-induced orientation of the azobenzene groups is connected to the alignment of the non-photochromic side groups below the glass transition temperature. The light-induced order generated in the glassy state was significantly amplified by the subsequent annealing of the irradiated films at temperatures in the mesophases. Factors of amplification of about 30 were found in the case of both polymers. The photo-induction process and its amplification by thermotropic self-organization were investigated in dependence on the polym er composition, the irradiation dose and the wavelength of the incident light with respect to the absorption of the dye and its limited photo-stability. The required dose or the irradiation time, respectively, were significantly reduced by the optimization of the light-induced and thermal processing. In this way, dichroic films of co- and terpolymers were created. However, the green fluorescence of the anthracene chromophore is effectively quenched by the azobenzene side group within the film.

: http://publica.fraunhofer.de/documents/N-170117.html