Photo-induced orientation effects parallel and perpendicular to the polarization vector of the incident laser light observed in the same azobenzene-containing LC polymer film.
A very high spectroscopic dichroism of about 0.8 and a birefringence of about 0.3 are achieved when liq.-cryst. polyester contg. azobenzene side groups is irradiated with 488-nm light perpendicular to the polarization vector or by 633-nm light parallel to the polarization vector. The photoorientation by 488-nm light is characterized by the repetition of angular-dependent excitation causing angular-selective photoisomerization cycles and rotational diffusion. Using 633-nm light the polarization dependence of the second irradn. step which transferred the steady state further to the E isomer results in an efficient alignment of the mesogenic side groups of the liq.-cryst. polymer.
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