Visualization of the Molecular Shape and the Orientational Distribution in the Langmuir−Blodgett Film of a Bent-Shaped Achiral Molecule As Studied by Surface Second-Harmonic Generation

Abstract

We have studied the anisotropic molecular orientational distributions of two-dimensional bent-shaped molecular monolayers by optical surface second-harmonic generation (SHG). The molecular monolayer of 1,3-phenylene bis[4-(((4-dodecylphenyl)imino)methyl)benzoate] (12-PIMB) was prepared by the Langmuir−Blodgett (LB) technique. Oblique incident surface SHG measurements from the monolayer showed that the bent-shaped molecules preferably aligned toward the dipping direction. The analysis of the experimental results provided the nonlinear-optical tensor components of the 12-PIMB LB monolayer. Using these components and a simple superposition model, the molecular orientational distribution function was determined. We successfully showed that the distribution map provides a view of the molecular shape.