Fluorescence anisotropy studies of orientational order of Langmuir-Blodgett multilayers

Langmuir-Blodgett multilayer films of cadmium stearate labeled with 3-(7-nitrobenz-2-oxa-1,3-diazol) fluorescence probes have been fabricated and studied by fluorescence microscopy and steady state anisotropy measurements. The results indicate that there is a decrease in fluorescence anisotropy with number of layers which saturates at about 10 layers. This decrease may be modeled as a decrease in orientational order of the fluorescence probes in the multilayers. A simplified model is used to obtain values for the 〈P₂〉 and 〈P₄〉 order parameters as a function of thickness. 〈P₂〉 is 0.4 and does not change with thickness. 〈P₄〉, however, decreases from 0.1 for a monolayer to 0.04 for a 9-layer film.