Photo-induced anisotropic films based on liquid crystalline copolymers containing stilbene units

8 pages, 7 figures, 3 tables.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 °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 Tg 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.This work was supported by the EC Brite/Euram project BE97-4210 Photoflu, the CICYT–FEDER Spanish projects MAT 2002-04118-C02-01 and MAT 2003-07806-C02-01, the Government of Aragon and the Programas Ramón y Cajal and FPI (MCyT–MEC, Spain).Peer reviewe