Phase transition studies of a fluorinated antiferroelectric liquid crystal probed by temperature dependent Raman spectroscopy

Abstract

Fluorinated liquid crystals (LCs) have emerged as a valuable option for display technologies, rapid switching applications, and photonic devices. Addition of fluorine atoms in the LCs change the electronic distribution within the molecule, introducing required LC properties for various display techniques. In this study, the structural properties of an antiferroelectric LC, (S)-octan-2-yl 2,3-difluoro-4′'-((6-((2,2,3,3,4,4,5,5,6,6,7,7,7-tridecafluoroheptanoyl)oxy) hexyl) oxy)-[1,1′,4′,1′'-terphenyl]-4-carboxylate is investigated using Raman spectroscopy. This LC exhibits a unique orthoconic antiferroelectric arrangement along with chiral smectic C (SmC*) and smectic A (SmA*) phases. Raman spectra were recorded over a temperature range of 20 °C to 130 °C, covering the spectral region of 500–3500 cm⁻¹. Additionally, theoretical Raman spectra at room temperature is simulated using density functional theory (DFT) with the B3LYP functional and 6-31G (d, p) basis set, showing good agreement with experimental results. Through meticulous fitting of the spectral features using Lorentzian profiles, precise values for peak positions, linewidths, and integrated intensities of selected Raman bands are obtained. Changes in Raman spectral parameters at the crystalline-SmC_A*, SmC_A*-SmC*, SmC*-SmA*, and SmA*-isotropic phase transitions are analyzed in terms of molecular alignment and intra/intermolecular interactions. The Raman spectral results provide a detailed understanding of the molecular and structural behaviour of the liquid crystal as it undergoes various phase transitions with increasing temperature.