A FLUORESCENCE DEPOLARIZATION STUDY OF THE ORDER AND DYNAMICS OF 1,8-DIPHENYLOCTATETRAENE IN A NEMATIC LIQUID-CRYSTAL

The time-dependent fluorescence depolarization of all-trans 1,8-diphenyloctatetraene has been studied at a series of temperatures within the nematic and isotropic range of the transparent mesophase mixture ZLI-1167. The probe order parameter < P2 > and the perpendicular rotational diffusion coefficient have been determined, together with the fluorescence lifetime τF at a series of temperatures in the liquid crystal and isotropic phase. This information is extracted applying a previously proposed theory for rotational fluorescence depolarization in a mesophase and the global target analysis deconvolution procedure. Various models for the probe ordering have been tried. We have found that a mean field theory model for the probe which keeps into account the molecular biaxiality of the solvent explains the data in the most economic way. Comparison with 1,6-diphenylhexatriene results in the same mesophase is provided. © 1990.