PROPOSAL OF A NEW METHOD TO DETERMINE TILT ANGLES OF ABSORPTION TRANSITION MOMENTS IN HOST-GUEST LIQUID-CRYSTAL CELLS

An idea for a method of experimental determination of tilt angles and order parameters of cylindrosymmetric transition moments of liquid cry stals and of dyes in host-guest systems is described. Furthermore, fir st experimental hints are given. With freely rotating molecules, all t ransition moments result in an isotropic absorbance for UV/VIS-spectro scopy using polarized light. The resulting absorbance becomes anisotro pic if the transition moment of the molecules is polarized, the molecu les are aligned in a preferential direction, and the free rotation is suppressed. In this case, the measurement of A(iso), A(tilt)(perpendic ular to) and A(tilt)(parallel to), using polarized light is sufficient to calculate the related tilt angle Psi, the order parameter S, and t he absorbance A angle as a function of the polarization angle. The loc al electric field and its influence on the dichroic ratio of an absorp tion band has not been considered. The precision of this method is sti ll limited by the photometric accuracy of the spectrometer and the mec hanical precision of the goniometric adjustment of the experimental ap paratus.