Identification and low-frequency vibrational analysis of three free anthraquinones via terahertz spectroscopy

Senlin Hou; Quancheng Liu; Hu Deng; Jun He; Wei Zhao; Zhixiang Wu; Qi Zhang; Liping Shang

doi:10.1016/j.saa.2023.122439

Identification and low-frequency vibrational analysis of three free anthraquinones via terahertz spectroscopy

Spectrochim Acta A Mol Biomol Spectrosc. 2023 May 15:293:122439. doi: 10.1016/j.saa.2023.122439. Epub 2023 Feb 4.

Authors

Senlin Hou¹, Quancheng Liu², Hu Deng³, Jun He¹, Wei Zhao¹, Zhixiang Wu¹, Qi Zhang⁴, Liping Shang⁵

Affiliations

¹ School of Information Engineering, Southwest University of Science and Technology, Mianyang 621010, China.
² School of Information Engineering, Southwest University of Science and Technology, Mianyang 621010, China. Electronic address: lqcswust@foxmail.com.
³ School of Information Engineering, Southwest University of Science and Technology, Mianyang 621010, China; Tianfu Institute of Research and Innovation, Southwest University of Science and Technology, ChengDu 610299, China.
⁴ Institute of Chemical Materials, China Academy of Engineering Physics, Mianyang, China.
⁵ School of Information Engineering, Southwest University of Science and Technology, Mianyang 621010, China; Tianfu Institute of Research and Innovation, Southwest University of Science and Technology, ChengDu 610299, China. Electronic address: shangliping@swust.edu.cn.

PMID: 36773425
DOI: 10.1016/j.saa.2023.122439

Abstract

In this study, terahertz time-domain spectroscopy (THz-TDS) was used to obtain the terahertz absorption spectra of three free anthraquinones (Chrysophanol, Emodin, Physcion) in the frequency range of 0.2-4.3 THz. The results show that terahertz spectroscopy is an effective detecting such compounds. Meanwhile, the theoretical spectrum using density functional theory calculations agrees well with the experimental spectrum. A modal decoupling method was used to identify each low-frequency vibrational mode and determine the average contribution of different atoms and groups. Modal decoupling provides a better understanding of molecules' mixed vibrational modes and enables quantifying the atoms' vibrational contributions. Results show that the substituent group facilitates the transition between the fundamental vibrational modes; subsequently, the substituent group shifts the vibrational centre of gravity of the three molecules and affects the vibrational contribution of hydrogen bonds. Furthermore, insignificant Emodin absorption is related to the nearly symmetrical structure formed by the substituents. The feasibility of terahertz analysis of differential molecular structures has also been confirmed.

Keywords: Anthraquinones; DFT; Modal decoupling; Substituent; Terahertz spectroscopy.