Dependence of the anisotropic absorption coefficient on the thickness of molecularly oriented organic dye films

The dependence of the anisotropic absorption coefficient on the thickness of a polarizing layer, which is a molecularly oriented him of an organic dye, is studied. The polarizing layer, gray in color and 340-1200 nm thick, is formed on the surface of a polyethylene terephthalate film from water-soluble dyes. The dyes are the mixture of sulfonation products of indanthrone and dibenzimidazole derivatives of naphthalene- and perylenetetracarboxylic acids. The absorption coefficients, k(parallel to) and k(perpendicular to), of a polarized light are measured in the parallel and orthogonal directions with respect to the orientation field. It is found that with increasing film thickness k(parallel to) remains unchanged, whereas k(perpendicular to) decreases. This result is explained by the orientational disordering of dye molecules, which occurs solely in the plane perpendicular to the direction of the orientation field. (C) 1999 The Optical Society of America. [S1070- 9762(99)01506-7].