Molecular Dynamics in Liquid-Crystalline Systems Studied by Fluorescence Depolarisation Techniques

Abstract

Fluorescence depolarisation experiments provide detailed information about molecular orientational dynamics on the nanosecond time scale. However, as in general, liquid-crystalline systems do not exhibit an intrinsic fluorescence emission, the technique can only be exploited through the introduction of fluorescent probes into the structure. In this way, the dynamics of the mesophase is studied indirectly by monitoring the behaviour of the probes. In this Chapter we present a summary of the principles of fluorescence spectroscopy and discuss the instrumentation necessary for time resolved and steady state experiments. In particular, we review the theory of experiments applied to oriented and macroscopically isotropic samples and consider the problems arising in the analysis of the experimental data. It is argued that angle resolved experiments on ordered systems under conditions of continuous illumination provide a valuable approach to the characterisation of the molecular dynamics in liquid-crystalline mesophases.