A theory of time dependent fluorescence depolarization in liquid crystals

Abstract

The study of time dependent fluorescence polarization can give information on static and dynamic properties in liquid crystals. Here general expressions are derived for the various independent fluoresence intensities in a uniaxial mesophase in terms of reorientational correlation functions. The case of a fluorescent probe with effective cylindrical symmetry is treated in detail and the effect of varying the orientation of the absorption and emission dipole moment in the molecular frame is discussed. Explicit expressions for the time dependent intensities are obtained assuming a diffusional and a strong collision model for reorientation in a liquid crystal. Results are shown for the special case of a molecule with absorption and emission moments parallel to the long axis. Finally results for continuous illumination type experiments are obtained.