Molecular vibration mode assignment of nematic liquid crystal 5CB on Terahertz spectra

Abstract

2015): Molecular vibration mode assignment of nematic liquid crystal 5CB on Terahertz spectra, Liquid Crystals, Using DFT/B3LYP/6-311++G** method, the molecular structure and absorption spectra in terahertz (THz) range of liquid crystal 5CB are investigated. In a frequency range 0-15 THz, an assignment of the vibrational modes corresponding to absorption frequencies is performed using potential energy distribution for the first time. It is found that the cyano group radical (-CN) do actively take part in the strongest THz absorption of 1.743, 3.942, 5.169 and 14.769 THz in different vibration modes. The results suggest that the strong polar group should be avoided in designing liquid crystal molecule and mixtures in order to reduce the absorption intensity in THz range.

Unveiling Low THz Dynamics of Liquid Crystals: Identification of Intermolecular Interaction among Intramolecular Modes

“…The steady advancements in tabletop THz sources led to intense ongoing research on possible devices and materials to modulate and control THz waves in a similar manner. Nematic LCs were already demonstrated to be low-loss and tunable birefringent materials for THz-wave plates and phase shifters. − However, their applicability is still limited because of the counteracting combination of birefringence and necessary thickness of the medium. , The long THz wavelengths (3000–30 μm) require considerably larger LC thicknesses to obtain a reasonable phase shift, such that losses become no longer negligible. To design new switching devices or guide molecular design targeting such THz performances, we need a detailed understanding of the microscopic properties of the LC in the THz range.…”

“… 5 − 8 However, their applicability is still limited because of the counteracting combination of birefringence and necessary thickness of the medium. 9 , 10 The long THz wavelengths (3000–30 μm) require considerably larger LC thicknesses to obtain a reasonable phase shift, such that losses become no longer negligible. To design new switching devices or guide molecular design targeting such THz performances, we need a detailed understanding of the microscopic properties of the LC in the THz range.…”

Spectroscopic Studies of BA Class Liquid Crystals in the 6–15 THz Range Using the Fourier Transform Infrared (FT-IR) Method

“…16,17 Terahertz spectroscopic studies of liquid crystals have focused mostly on the CB family, with 4-cyano-4pentylbiphenyl (5CB) being the commonly studied LC material. [18][19][20] This has left a gap in the THz spectroscopic characterization of LCs belonging to the BA class, and thus this paper addresses the scarcity of the THz spectroscopic studies of these materials. Liquid crystals have generally attracted a lot of research because of their possible applications across the electromagnetic spectrum with the inclusion of the THz field.…”