Polymer, Vol.47, No.16, 5707-5714, 2006
Photo-induced anisotropic films based on liquid crystalline copolymers containing stilbene units
New poly(methacrylate) copolymers containing 90 mol% of a promesogenic unit based on the 4-butoxybenzanilide, 4-cyanobiphenyl or 4-cyanoterphenyl cores and 10 mol% of a photosensitive push-pull substituted 4-(N-methylamino)-4'-nitrostilbene group have been prepared. All polymers are liquid crystalline and thermally stable with decomposition temperatures above 320 degrees C. The irradiation with linearly polarised light (either 325, 365 or 488 nm) results in the induction of a small optical anisotropy in the films due to an angular-selective photoreaction, whereas the absorbance perpendicular to the electric field vector of the incident light becomes larger compared to the absorbance parallel to it. In films of the copolymer containing 4-cyanobiphenyl and 4-(N-methylamino)-4'-nitrostilbene units, the anisotropy was significantly enhanced by annealing above T-g up to a dichroism D = 0.5. A thin film aligned by this procedure shows an anisotropic red emission with a ratio of 2.8 between emission intensities in the parallel and perpendicular directions due to the presence of oriented fluorescent stilbene units. (c) 2006 Elsevier Ltd. All rights reserved.