Determination of some Dye Parameters by Polarized Fluorescence Spectroscopy

Many experimental methods, giving information about the molecular interactions in liquid crystalline mesophases, have been developed [1]. One of the most important ones is the polarized fluorescence experiment, which enables one to obtain the order parameters and (P4} of a dye probe dissolved in a liquid crystalline matrix ("guest-host" system) [2-9], It was shown that under particular conditions, connected with the geometry of the dye and liquid crystal molecules, the order parameters for the "guest" are the same as for the "host" [10]. Such "guest-host" systems are also applied in constructing coloured liquid crystalline displays [11-13]. The and order parameters depend on the anisotropics of absorption and emission, the dynamic behaviour of the molecules, and the angles created by the dipole transition moments with the molecular symmetry axis. In [12, 13] the equations describing the emission anisotropics were derived for the case of dye molecules with the absorption and emission transition moments parallel to the molecular symmetry axis. In this paper it is assumed that the transition dipole moments of absorption and fluorescence lie in one plane but not parallel to the molecular axis. The obtained equations are applied in investigations of bicarboxylic acid derivatives in the nematic mixture E18. A short fluorescence decay time in comparison with the correlation times of rotation is assumed (tf imn). It is shown that when knowing the value of absorption anisotropy, 5, and the angle between the