Variable Acquisition Angle Total Internal Reflection Fluorescence:A New Technique for Orientation Distribution Studies of Ultrathin Films

摘要

A new technique for the determination of the orientation distribution of a fluorophore within an ultrathin film, in terms of the mean tilt angle relative to the monolayer normal and the distribution width, is described. The technique utilizes the measurement of polarized fluorescence, excited by the evanescent field appearing upon total internal reflection. The main difference between this and existing techniques is that the fluorescence intensity is measured as a function of the acquisition angle with low aperture detection. The potential of the technique was investigated with the help of computer modeling and experimentally utilizing a Langmuir-Blodgett film of arachidic acid doped with a fluorophore DiI. Both computer modeling and the measurements show that the acquisition of the angular dependence of the fluorescence dramatically improves the technique, increasing manyfold the accuracy and resolution of the determined orientation distrbution parameters.