Angle-Resolved Techniques in Studies of Organic Molecules in Ordered Systems Using Polarized Light

Abstract

Angle-resolved linear dichroism and fluorescence depolarization experiments on organic and biological molecules aligned in stretched polymer films, liquid crystalline materials and biological membranes are described. The theory underlying the experiments is set out in detail and the experimental procedures and sources of error are discussed and illustrated. The mathematical treatment makes use of the Wigner rotation matrix formalism so as to provide a unified description of the static orientational order and reorientational dynamics of the guest molecules in their host medium. It is shown that angle-resolved fluorescence depolarization measurements afford the simultaneous determination of the directions of the transition moments of the guest molecules as well as their orientational order in the medium. The application of the technique to the study of the reorientational motions of the molecules is also discussed. It is argued that angleresolved measurements on ordered systems under conditions of continuous illumination provide a valuable approach to the characterization of the dynamic behaviour of the molecules.