Nonlinear optical properties and the orientation of a terthiophene-vinylbenzoic acid methyl ester in Langmuir-Blodgett films

Abstract

The aim of this work was to study the nonlinear optical properties of terthiophene-vinylbenzioc acid methyl ester (TSe) Langmuir-Blodgett (LB) films and to determine the orientation of the molecules in the films. Mixed films were prepared of 50 mol-% TSe in staeryleamine (ODA) matrix. Second order nonlinear optics and UV-vis polarized absorption were used to investigate the properties of the LB films and the orientation of the molecules in the films. The results of these to methods are compared. According to the polarized absorption measurements, the molecules are oriented nearly perpendicular to the plane of the film, while the second -order nonlinear polarization measurements showed that the molecules are more tilted with respect to the substrate normal. The orientation of the molecules was improved as the number of layers in LB films was increased. Both of these measurements gave an average value of the orientation of the molecules. The real value of the tilt angle between the long axis of the molecule and the plane of the substrate is probably between the values by these two methods (from near 60° to 90°). /Kir10