Linearly polarized light can induce an order parallel to the polarization direction of light in polymer films containing different photochromic groups. In principle, this offers the possibility to generate prolate in-plane orders in polymer films. Two such photochemical processes are investigated in this paper. One of them is the irradiation of azobenzene-containing polymer films with linearly polarized red light after an unpolarized UV preirradiation step. The other one is the angular selective photocycloaddition of cinnamate-containing polymer films induced by linearly polarized UV light. Because in both cases the order is low after the irradiation, the liquid crystalline polymer films are annealed in their mesophase to modify the photoinduced order by thermotropic self-organization. The resulting threedimensional indicatrices, as determined by waveguide spectroscopy, are found to be prolate in-plane, biaxial, or homeotropic in dependence on the polymer structures, preparation conditions, and irradiation conditions of the films.

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Films of azobenzene-containing polymers were photooriented in the glassy state in such a way that the azobenzene side groups were oriented preferably perpendicular to the electric field vector. In the case of liquid crystalline polymers ,the photoinduced anisotropies generated in the glassy state were modified by thermotropic self-organization due to annealing above T(g). The conventional photoorientation process results in an oblate order. The changes in photoinduced anisotropies brought about by annealing in the liquid crystalline phase were investigated quantitatively for the first time by us for different polymer compositions and experimental conditions. Different biaxial and homeotropic orders result for liquid crystalline polymers, depending on the experimental conditions. Different polymer structures are compared and the influence of the interfaces is investigated. Orientational gradients can be induced by irradiation or annealing and are for the first time determined by the WKB (Wentzel-Kramers-Brillouin) method.