Regensburg 2010 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 17: Interfaces and Thin Films I

CPP 17.9: Talk

Tuesday, March 23, 2010, 12:00–12:15, H39

Single molecule diffusion in liquid crystals — •Martin Pumpa and Frank Cichos — Molecular Nanophotonics Group, University of Leipzig

Liquid crystals show a strong orientational order along a certain director, while lacking spatial order of their centers of mass. For uniaxial molecules the orientational properties lead to an anisotropy in the optical properties of the material and the mobility as well.

Recent studies have focused on the diffusion of macroscopic particles in the matrix of the liquid crystal. In case of macroscopic probes the director structure around such colloids is strongly altered due to anchoring effects at the particle surface, leading to distortions in the orientation of the liquid crystal and therefore to an rotational contribution to the measured drag forces. Such effects are absent in the study of single molecule diffusion in liquid crystals. We thus present results on the translational and rotational diffusion of single fluorescent probe - molecules in the nematic phase of 5CB and the smectic phase of 8CB. We used single molecule tracking to determine the anisotropy of translational diffusion of PDI molecules and time resolved fluorescence microscopy to observe their rotational behavior. We are able to relate our results directly to the director structure of the liquid crystalline phases by means of polarization contrast microscopy.