Guest Orientation in Uniplanar-Axial Polymer Host Films and in Co-Crystal Unit-Cell, Determined by Angular Distributions of Polarized Guest Fluorescence

Syndiotactic polystyrene (sPS) films with uniplanar-axial orientation of their co-crystalline phase with a fluorescent guest (naphthalene, NP) have been prepared and the orientation of their crystalline phase has been fully characterized by X-ray diffraction measurements. The prepared films have been examined in detail using Nishijima's method, where angular distribution of NP polarized fluorescence intensities was measured at each setting film angle by the rotation of films around the excitation light beam. This polarized fluorescence method turns out to be quite effective for monitoring the orientation of fluorescent guest molecules in the films. In particular, in semicrystalline films presenting uniplanar-axial orientation of their sPS/NP clathrate phase, NP molecules were found to exhibit a high three-dimensional orientational order all over the films. The experimental data have also allowed to determine the orientation of the NP guest molecule with respect the axes of the co-crystal unit-cell: in satisfactory agreement with molecular modeling results, angles formed by the short and the long axes of NP with the c axis are not far from 80 degrees while the angle between the short axis of NP and the a axis is nearly 105 degrees.