Reliability of parameters obtained from time-resolved fluorescence polarization in macroscopically isotropic liquid crystals and membrane vesicles

Abstract

The practical possibility of extracting static and dynamic parameters from fluorescence anisotropy decays of rod-like probes in membrane vesicles and other macroscopically isotropic samples with a locally ordered structure, such as cubic liquid crystals or unoriented polymer liquid crystals is discussed. Particular attention is paid to the obtainment of the fourth-rank order parameter 〈P₄〉. For monodomain samples, global target analysis of samples at different temperatures has proved helpful. To test if this is true here as well, simulated single-photon-counting intensities at various temperatures have been prepared using a mean-field model and then analysed both individually and globally by means of target analysis. The results show that there is little hope of obtaining 〈P₄〉 from macroscopically unoriented systems, except for some limiting cases. On the other hand, the recovery of 〈P₂〉 and of the tumbling diffusion coefficient, D_⊥, seems to be quite insensitive to the selected model for the anisotropic potential.