Photoinduced 3D orientational order in side chain liquid crystalline azopolymers

摘要

We apply experimental technique based on the combination of methods dealingwith principal refractive indices and absorption coefficients to study thephotoinduced 3D orientational order in the films of liquid crystalline (LC)azopolymers. The technique is used to identify 3D orientational configurationsof trans azobenzene chromophores and to characterize the degree of ordering interms of order parameters. We study two types of LC azopolymers which formstructures with preferred in-plane and out-of-plane alignment ofazochromophores, correspondingly. Using irradiation with the polarized light oftwo different wavelengths we find that the kinetics of photoinduced anisotropycan be dominated by either photo-reorientation or photoselection mechanismsdepending on the wavelength. We formulate the phenomenological model describingthe kinetics of photoinduced anisotropy in terms of the isomer concentrationsand the order parameter tensor. We present the numerical results for absorptioncoefficients that are found to be in good agreement with the experimental data.The model is also used to interpret the effect of changing the mechanism withthe wavelength of the pumping light.