FLUORESCENCE DEPOLARIZATION AND ENERGY TRANSFER IN LIQUID CRYSTALS

Claudio Zannoni

Dip. di Chimica Fisica ed Inorganica,  Università di Bologna Viale Risorgimento 4, 40136 Bologna, Italy (email: vz3bod7a@sirio.cineca.it ; fax: +39-51-6443690)

Fluorescence depolarization studies [1] offer a powerful way of obtaining information on the static and dynamic properties of  molecules dissolved in liquid crystals and other anisotropic fluids. In this talk  two types of  such studies will be discussed.
The first is the case of  rotational depolarization for probe molecules dissolved in low viscosity liquid crystals and we shall see how uniaxial and biaxial order parameters as well as information of the full rotational diffusion tensor can be obtained for  different solutes, even as complex as chlorophyll a in a nematic [2].
We shall then consider the case of depolarization through Förster type energy transfer in ordered systems, which allows obtaining structural information even in systems so viscous that rotational depolarization does not effectively occur. We shall discuss in particular an approach that we have recently proposed that couples computer simulations to obtain equilibrium configurations for the system and a stochastic approach for the energy transfer and  that we have used to investigate how the molecular organization of the phase and its changes from isotropic to nematic and smectic or respectively from isotropic to columnar affect the features of the energy transfer and its directionality.
 

  1.  A. Jablonski, Z. für Naturforschung, 16a, 1 (1961)
  2. A. Arcioni, M. A.M.J. van Zandvoort , P. Bartolini, R. Torre, R. Tarroni, R. Righini, C. Zannoni, J. Phys. Chem.B, 102, 1624   (1998) and refs. therein
  3. C. Bacchiocchi and C. Zannoni, Chem. Phys. Lett. 268, 541  (1997) and  Phys Rev E, in press (1998)