Time resolved fluorescence depolarization in a nematic liquid crystal

Abstract

A time dependent fluorescence depolarization experiment is reported and fully analysed for the first time for a probe dissolved in an aligned nematic liquid crystal. We have investigated the popular dye all trans 1,6 diphenyl hexatriene in the transparent mesophase mixture ZLI-1167 at a series of temperatures within the nematic and isotropic range. The probe order parameter <P ₂> and perpendicular rotational diffusion coefficient have been determined, together with the fluorescence lifetime τ_F in the liquid crystal and isotropic phase. This information is extracted applying a previously proposed theory for rotational fluorescence depolarization in a mesophase (Zannoni, C., 1979, Molec. Phys., 38, 1813) and introducing a global variant of the target analysis deconvolution procedure presented earlier (Arcioni, A., and Zannoni, C., 1984, Chem. Phys., 88, 113). Our results demonstrate the possibility of employing fluorescence depolarization as a useful technique for investigating aligned mesophases.