PHOTOEXCITATION OF SPACE-CHARGE FIELDS AND REORIENTATION OF A NEMATICLIQUID-CRYSTAL OF DISCOTIC MOLECULES

A new reorientation effect in nematic liquid crystals of discotic mole cules, which occurs under the combined influence of DC-electrical and optical fields, has been observed and investigated for the first time. It is shown that an illumination with intensity as low as 10(-3) W/cm (2) is sufficient for producing a strong photo-induced reorientation p rocess which indicates a rather large nonlinear optical coefficient. T he dependence of the photo-excitation on the applied voltage as well a s on the intensity and the wavelength of the light wave was investigat ed. Furthermore, a first model, which explains the experimental observ ations resulting from photo-induced space charge fields and related fi eld-induced reorientation of the discotic molecules, will be discussed . (C) 1998 Elsevier Science B.V. All rights reserved.