Determining 3D molecular orientation from polarization-IR spectra: tutorial

Published

January 3, 2025

Author(s)

Young Jong Lee

Abstract

Despite the ubiquity of molecular alignment in natural and synthesized materials, accurate mapping of three-dimensional (3D) molecular orientations with sufficient spatial resolving power has remained challenging. Conventional analysis approaches of polarization-based optical imaging cannot measure the out-of-plane angle of molecular orientations without tilting a sample. Recently, we proposed a new theoretical algorithm to determine the 3D orientation angle of aligned molecules using polarization-controlled infrared (IR) spectral data without tilting a sample. The algorithm was based on a concurrent analysis of the absorptances of two non-parallel IR transition dipole moments using a single orientational descriptor. The outcome of the non-iterative calculation is the 3D angle of the mean orientation and the order parameter of the local orientational distribution function. The algorithm was successfully applied to the analysis of polarization-controlled hyperspectral IR imaging of semi-crystalline polymer films. This tutorial derives and summarizes various theoretical descriptions presented in our recent papers and discusses the assumptions and limitations associated with the analysis method.

Citation

Chemical Physics Reviews

Volume

42

Issue

2

Pub Type

Journals

Download Paper

https://doi.org/10.1364/JOSAA.542283

Local Download

Keywords

polarization, infrared, molecular orientation, 3D orientation angle

Citation

Lee, Y. (2025), Determining 3D molecular orientation from polarization-IR spectra: tutorial, Chemical Physics Reviews, [online], https://doi.org/10.1364/JOSAA.542283, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=956372 (Accessed January 8, 2025)