Microscopic Heterogeneity in a Bowlic Columnar Mesophase as Probed with Fluorescence Depolarization Measurements

Abstract

The time-dependent fluorescence depolarization decays of the fluorescent probe 1,6-diphenyl-1,3,5-hexatriene (DPH) in the ordered and isotropic phase of a columnar liquid crystal formed by bowl-shaped metacyclophane cores symmetrically substituted by twelve alkanoyloxy chains have been recorded at various temperatures and analyzed using the global target approach. The measurements in the mesophase can be successfully analyzed only assuming a microscopic inhomogeneity of the columnar phase, with the probe partitioned between two environments, Le. polar cores and apolar aliphatic chains, showing very different ordering and dynamical characteristics. This behavior becomes evident only when all the fluorescence intensities, corresponding to different parallel and perpendicular orientations of the excitation and observation polarizers, are analyzed simultaneously. The picture emerging from the analysis supports other recent findings on this class of columnar systems.

Distribution of Hydrophobic Probe Molecules in Lipid Bilayers. 2. Time-Resolved Fluorescence Anisotropy Study of Perylene in Vesicles

“…41 Similarly, a two-population model was invoked in order to account for the fluorescence depolarization of DPH in columnar liquid crystals, where it is found to partition between the core and chain regions. 42 In the preceding paper Monte Carlo dynamics (MCD) simulations are used to demonstrate how two populations of nonanchored probe molecules such as DPH and perylene can arise within a lipid bilayer. It is shown that the tendency of these molecules to access the regions of free volume at the center of the bilayer can be counteracted by invoking a repulsive potential, the so-called burial potential.…”

“…It is important to realize that the center of the bilayer is a region with considerable free volume as the result of the imperfect packing of the lipid chains belonging to the two opposing monolayers . Similarly, a two-population model was invoked in order to account for the fluorescence depolarization of DPH in columnar liquid crystals, where it is found to partition between the core and chain regions …”

A theory of fluorescence depolarization in mesophases with tilted distribution of directors

“…This latter case may appear rather unphysical for a rod-like probe but it might gain significance in some complex systems, reflecting e.g. an average orientation of the probe perpendicular to the local phase director [19]. The effects of a moderate biaxiality of the probe have been explored by allowing D 2 02 to be either 0 or 0.04.…”