Dynamics of electric-field-induced molecular reorientation and segmental mobility in the smectic-C^{*} phase of a ferroelectric liquid crystal: Faster reorientation of cores than the alkyl chains revealed by time-resolved infrared spectroscopy

Abstract

We report a study of the dynamics of molecular reorientation and segmental mobility of a ferroelectric liquid crystal in the smectic-C* ͑Sm-C*͒ phase having 2-hydroxy-benzilidenianiline as the mesogen core and (S)-2-chloro-3-methylbutanoyl as the chiral terminal group, at different temperatures during electric-field-induced switching between the two surface-stabilized states by use of a time-resolved Fourier-transform infrared technique. From polarized infrared spectra under static dc electric fields, details of mutual arrangement of different molecular segments in the Sm-C* phase have been obtained. Contrary to the usual expectations, the average alkyl chain axis does not coincide with the mesogen axis and is less tilted with respect to the layer normal than the mesogen. On the other hand, motion of the carbonyl groups is found to be strongly hindered and the distribution function for the CvO bonds is not cylindrically symmetric with respect to the long molecular axis. Time-resolved infrared measurements at different temperatures and voltages have revealed that, on switching the polarity of the electric field, the hydrogen-bonded CvO group moves with the mesogen which reaches equilibrium orientations at a faster rate compared to the alkyl chain at the temperatures and voltages employed in this study. ͓S1063-651X͑97͒09209-X͔

Molecular Dynamics at Electrical- and Optical-Driven Phase Transitions: Time-Resolved Infrared Studies Using Fourier-Transform Spectrometers

“…As demonstrated in Fig. 2(d) the very thin layer of polyimide does not affect the overall light transmission of the system in the relevant frequency range in agreement with previous results [15,42,19]. Both plates have been clued together with a UV glue mixed with small macroscopic plastic spheres with a diameter of d = 5 µm which serve as spacer to keep the windows on a constant distance, as sketched in Fig.…”

Polarized IR spectra of resonance assisted hydrogen bond (RAHB) in 2-hydroxyazobenzenes

“…The basis for the quantitative analysis of the order degree and the transition dipole moments presents Fig. 5, as follows from literature [37][38][39][40].…”

Origin of the liquid-liquid phase transition for trans-1,2-dichloroethylene observed by IR spectroscopy

“…[9][10][11][12][13][14][15][16][17] The technique of IR spectroscopy is widely used for the characterization of vibrational bands for examining molecular conformational behavior 11 and for dynamic measurement of the rotational motion of molecules around their molecular axies. [9][10][11][12][13][14][15][16][17] The technique of IR spectroscopy is widely used for the characterization of vibrational bands for examining molecular conformational behavior 11 and for dynamic measurement of the rotational motion of molecules around their molecular axies.…”