Orientation of pentyl-cyanobiphenyl layers and variations in their luminescence spectra under UV irradiation

Polarized fluorescence spectra of layers of a nematic liquid crystal (LC) of n -pentyl- n ′-cyanobiphenyl (5CB), oriented by two different methods, namely, by rubbing the polyimide-coated substrates holding the LC layer and by irradiating the LC layer placed between isotropic fused quartz substrates by polarized UV radiation, are comparatively analyzed. The photoluminescence spectra in the two cases show anisotropy with parameters virtually independent of the orientation method. Contrary to the case of rubbing orientation, the photoluminescence spectrum of the LC layer, oriented by irradiation, substantially differs from the initial one. Possible photochemical processes and mechanisms of photoorientation are discussed.