Terahertz Spectroscopy Used to Characterize Liquid Crystals

A recent study published in the journal Spectroscopy Letters explored the terahertz (THz) spectroscopic characterization of benzoic acid class liquid crystals using Fourier transform infrared (FT-IR) spectroscopy (1). The research team from Botswana International University of Science and Technology investigated 4-octyloxybenzoic acid, 4-decyloxybenzoic acid, and 4-hexylbenzoic acid liquid crystals, which are characterized by distinct absorption bands in the 6–18 THz frequency range (1).

THz spectroscopy is an emerging field of study with broad applications in the fields of material science, chemistry, and biology. It involves using radiation with a frequency range between microwaves and infrared light to study the properties of materials at the molecular level. The ability to characterize the behavior of liquid crystals using THz spectroscopy could have significant implications for the development of liquid crystal-based technologies, such as displays, sensors, and optical devices.

The research team consisted of Lucia M. Lepodise and Tshepo Pheko-Ofitlhile (1). They conducted density functional theory (DFT) calculations to obtain the theoretical frequencies of the single molecule for each compound, comparing them with the experimental frequencies obtained from the THz spectroscopic studies (1). The results showed a good correspondence between the theoretical and experimental frequencies for all three compounds (1).

The study also found that even though compounds of almost identical molecular structure might output bands at the same frequencies, the correspondence might not be immediately apparent (1). The spectra of the studied compounds had three bands that appeared at similar frequencies and with the same vibration modes (1). However, 4-octyloxybenzoic acid, 4-decyloxybenzoic acid, and 4-hexylbenzoic acid had two absorption bands that appeared at similar frequencies, but they exhibited different vibration modes (1).

Further analysis of the single molecule model frequencies and experimental frequencies for 4-decyloxybenzoic acid and 4-octyloxybenzoic acid revealed that all the observed bands are because of intramolecular interaction (1). However, the 4-hexylbenzoic acid spectrum had one apparently intermolecular band (1).

This study highlights the robustness of FT-IR and the technique’s potential at identifying materials with similar attributes while addressing the limitations of intermediate THz spectroscopic studies of liquid crystals (1). The results of this study could have implications for the development of liquid crystal-based technologies.

Overall, this study provides new insights into the THz spectroscopic characterization of benzoic acid class liquid crystals using FT-IR spectroscopy, highlighting the potential of this technique for the development of new materials and technologies.

Reference

(1) Lepodise, L. M.; Pheko-Ofitlhile, T. Terahertz (6–18 THz) Spectroscopic Characterization of Benzoic Acid Class Liquid Crystals Using Fourier Transform Infrared Technique. Spec. Lett. 2023, ASAP. DOI: 10.1080/00387010.2023.2197992