Computer Simulation of an Antiferroelectric Liquid Crystalline Molecule: The Origin of Bent Structure Formation and the Molecular Packing Property of MHPOBC in Crystalline Phase (original) (raw)
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The Journal of Physical Chemistry A, 2012
The experimental and theoretical vibrational spectroscopic study of one of a novel antiferroelectric liquid crystals (AFLC), known under the MHPSBO10 acronym, have been undertaken. The interpretation of both FT-IR and FT-Raman spectra was focused mainly on the solid-state data. To analyze the experimental results along with the molecular properties, density functional theory (DFT) computations were performed using several modern theoretical approaches. The presented calculations were performed within the isolated molecule model, probing the performance of modern exchange−correlations functionals, as well as going beyond, i.e., within hybrid (ONIOM) and periodic boundary conditions (PBC) methodologies. A detailed band assignment was supported by the normal-mode analysis with SQM ab initio force field scaling. The results are supplemented by the noncovalent interactions analysis (NCI). The relatively noticeable spectral differences observed upon Crystal to AFLC phase transition have also been reported. For the most prominent vibrational modes, the geometries of the transition dipole moments along with the main components of vibrational polarizability were analyzed in terms of the molecular frame. One of the goals of the paper was to optimize the procedure of solid-state calculations to obtain the results comparable with the all electron calculations, performed routinely for isolated molecules, and to test their performance. The presented study delivers a complex insight into the vibrational spectrum with a noticeable improvement of the theoretical results obtained for significantly attracting mesogens using modern molecular modeling approaches. The presented modeling conditions are very promising for further description of similar large molecular crystals.
Molecular Crystals and Liquid Crystals
Taylor & Francis Group, 2022
A DFT (B3LYP) method with a 6-311 þ G(d,p) basis set has been used for the geometric parameters NMR and UV-Vis analysis and for vibrational analysis of the 4-Methoxyphenylboronic acid (4MPBA). In the region of 4000-400cm À1 and 3500-100cm À1 , respectively, experimental FT-IR and FT-Raman were obtained. The thermodynamic and energy of HOMO and LUMO were also presented. The chemical shifts of NMR 1 H & 13 C were compared with experimental data and calculated using the Gauge Independent Atomic Orbital (GIAO) method. Furthermore, the natural bond orbital (NBO) analysis was carried out in order to have an Intramolecular Charge Transfer (ICT) with the molecule.
A bent-shape liquid crystal compound with antiferroelectric triclinic-monoclinic phase transition
Liquid Crystals, 2003
Electro-optical and polarization current measurements on 1,3-phenylene-bis[4-(3-fluoro-4-decyloxyphenyliminomethyl)benzoate] (3F-10-O-PIMB) revealed a second order phase transition between two antiferroelectric 'smectic banana' phases. The observations show that the switching between the ferroelectric states in the higher temperature (HT) phase requires higher thresholds than in the lower temperature (LT) phase. It is hypothesized that the HT phase has a lower (triclinic, C 1 ) symmetry, than that of the LT phase (monoclinic, C 2 ). It is also shown that electric fields can induce transitions between different 'smectic banana' phases.
The Journal of Chemical Physics, 2007
The authors have investigated the conformational structure of the ferroelectric liquid crystal compound 4-3-methyl-2-chloropentanoyloxy-4Љ-hexyloxy-biphenyl also known under the abbreviations 3M2CPHOB and C6 using vibrational ͑IR and Raman͒ spectroscopy. The measured spectra exhibit two bands corresponding to the C v O stretching vibration that are separated by 20 cm −1. In contrast, the molecular structure comprises only one such group. They assigned the two bands to different conformers that coexist in a temperature range between 25 and 65°C covering the entire mesophase of this material. This assignment is strongly confirmed by calculated vibrational spectra based on the density functional theory.
Journal of Molecular Liquids, 2021
Polymer stabilization offers unique opportunities for improving features of liquid crystals. In particular, it influences the static and dynamic performance of antiferroelectric liquid crystals (AFLCs) due to the stabilization of surface-stabilized geometry of such self-assembling materials forming anticlinic structures. The main advantages of polymer-stabilized AFLCs consist of a significant decrease of the electro-optical switching time, and a lower sensitivity to mechanical shock and temperature changes in working devices. This work experimentally analyzes the effect of functionality of selected mesogenic monomers on the properties of new developed high-tilted AFLC mixtures with different phase sequences, before and after polymer stabilization. It was found that tetrafunctional monomers (especially those with non-chiral terminal chains) reduce the thermal stability of antiferroelectric phase and increase helical pitch at low temperatures before polymerization. However, they reduce values of the tilt angle and spontaneous polarization and simultaneously flatten the temperature dependence after polymerization to a greater extent than bifunctional monomers. Tetrafunctional monomers improve electro-optical characteristics of tested AFLC mixtures after polymer stabilization. On the other hand, polymer-stabilized materials based on bifunctional monomers and LC mixtures with direct SmC A *-Iso phase transition show acceptable electro-optical performance in device cells. Most importantly, the obtained results confirm definite advantages of using mixtures with direct SmC A *-Iso phase transition when designing new polymer-stabilized AFLC materials with appropriate features in effects based on surface-stabilized geometry.
Ferroelectrics, 2008
(1metylheptyloxy-carbonyl)terphenyl compounds exhibiting low temperature, wide range, near orthoconic antiferroelectric phase has been synthesized . Compounds of the homologous series differ from each other by a position of a single fluorine atom substituted at the phenyl ring of the molecular rigid core. This affects the mesogenic behavior. Moreover, the molecular dipole moment of the compound as well as the physical parameters of the antiferroelectric phase are changed. The importance of the molecular dipole moment orientation and magnitude for the mesogenic behavior and physical parameters of the orthoconic antiferroelectric phase is discussed.
Molecular structure of bent-shaped liquid crystal dimers
Journal of Industrial and Engineering Chemistry, 2012
These types of compounds are not only important as a new class of liquid crystalline compositions but also as models for the corresponding main chain liquid crystalline polymers containing flexible spacers [1]. Especially, the recent discovery of bentshaped liquid crystal materials i.e., mesogenic compounds bent symmetrically along the middle of the molecules have boosted up the studies in this field [2-7]. Recently we reported the synthesis and thermotropic properties of compounds having ortho-, meta-, and para-bent shaped hydrogen bonded mesogenic cores (Series I) [2]. In the present investigation, in order to obtain further understanding of the molecular structure-property relationship of dimesogenic liquid crystal compounds, we have prepared two different series of compounds, Series I and II, shown below. Their thermal transitions and thermotropic properties were studied by differential scanning calorimetry (DSC) and on the hot-stage of a polarizing microscope. The structure and designation of the compounds are as follows:
General phase diagram for antiferroelectric liquid crystals in dependence on enantiomeric excess
2002
The phase diagram of the prototype antiferroelectric liquid crystal MHPOBC in dependence of enantiomeric excess was measured. It was shown that the SmCbeta phase in very pure samples is the SmCFI2 phase with a four layer structure, and only after small racemization it transforms into the ferroelectric SmC phase. The phase diagram was theoretically explained by taking into account longer