Time-Resolved FT-IR Study on Reorientation of Ferroelectric Liquid Crystal, (S)-4-Methylhexyl 4-[4-(Decyloxy) Phenylethynyl]-2-Fluorobenzate

Abstract

The electric-field-induced reorientation of (S)-4-methylhexyl 4-[4-(decyloxy) phenylethynyl]-2-fluorobenzate in the Sc* phase was investigated by using an asynchronous time-resolved FT-IR technique. The band assignments were made on the basis of the polarized FT-IR spectra and FT-Raman spectrum. The time-resolved study indicates that the reorientation occurs immediately after the electric field is applied. The molecule reorients as a unit; however the rigid core of the molecule seems to be more mobile than the hydrocarbon chains and needs a shorter period of time for the reorientation. The change of orientation is not completely finished in a 500-μs time period. Of particular note is the behavior of the carbonyl band; this band, usually strong in infrared spectra, is very weak in the time-resolved spectra.

Reorientation of Nematic Liquid-Crystals and Liquid-Crystalline Polymers in an Electric Field Studied by FT-IR Time-Resolved Spectroscopy and 2D-Correlation Analysis

“…Finally, from an inspection of Figures 4-6 one can easily notice a considerable reduction of the intensity due to the ν(CdO) band in the power spectra, as was already reported for FLC samples. 13,15,21 However, the band was too intense in the time-resolved spectra (A > 2), and thus, we will not interpret this effect.…”

“…[8][9][10][11] Other authors reported that the core of 5CB and other LCs responds more sensitively to the electric field than the flexible part. [12][13][14] On the other hand, no differences were found for 5CB and other LCs; [15][16][17] the possible explanation for this disagreement was given elsewhere. 18 In the case of ferroelectric liquid-crystalline polymer, it was proposed that not only the mesogen but also the spacer and at least part of the backbone participate in the reorientation process; 19 however, 2D-correlation analysis for the same sample did not support this conclusion.…”

“…The last reports from various research groups have revealed that the mechanism of the reorientation of LC molecules may be different from that commonly accepted. It has been observed that the motion of the pentyl chain of 5CB (4-( n -pentyl)-4‘-cyanobiphenyl) precedes that of the core in the course of reorientation. − Other authors reported that the core of 5CB and other LCs responds more sensitively to the electric field than the flexible part. − On the other hand, no differences were found for 5CB and other LCs; − the possible explanation for this disagreement was given elsewhere . In the case of ferroelectric liquid-crystalline polymer, it was proposed that not only the mesogen but also the spacer and at least part of the backbone participate in the reorientation process; however, 2D-correlation analysis for the same sample did not support this conclusion .…”

Dynamical Behavior of Surface-Stabilized States of Ferroelectric Liquid Crystals in Electric Field Studied by Time-Resolved FT-IR Spectroscopy

“…In recent years significant progress in the studies of dynamics of electric field-induced switching of liquid crystals has been made owing to the application of time-resolved infrared spectroscopy. [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] The method seems to be particularly relevant to studies of the time course of reorientation because it provides information at the molecular level. Hence, one can monitor independently the movement of particular functional groups of the molecule.…”

Time resolved infrared spectroscopy of electro‐optic switching of 5CB

“…Some have reported no considerable differences in reorientation rates of the mesogenic core and tails [3][4][5][6]. In other reports, the motion of the flexible tail part precedes that of the core [7,8], and still in others, the motion of the core precedes that of the flexible part [9][10][11][12][13][14].…”