Complex Vibrational Analysis of an Antiferroelectric Liquid Crystal Based on Solid-State Oriented Quantum Chemical Calculations and Experimental Molecular Spectroscopy

Abstract

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.

Studies of New Antiferroelectric Liquid Crystal Based on Quantum-Chemical Model

“…Similar results for the liquid crystalline compound e.g. crystallization in the same space group was reported in [13]. Fig.…”

Spectroscopic Signatures of Hydrogen-Bonding Motifs in Protonic Ionic Liquid Systems: Insights from Diethylammonium Nitrate in the Solid State

“…At this stage, we note that a detailed interpretation of the IR spectrum in the ν[CH] regime is beyond the capabilities of the adopted methodology, being affected by Fermi resonances along with combinations and overtones prohibiting a straightforward assignment. 91 − 93 A high density of vibrational states for hydrogen atoms associated with the alkyl fragments also clarifies the presence of the hump in the INS spectrum over ca. 1500–1300 cm –1 .…”

“…As clearly seen from the calculated VDoSs compared to the INS spectrum, a pronounced intensity of the ν­[N–H] band observed in IR stems from large charge fluctuations induced by H-bond formation, which otherwise could not be detected due to the prevalent number of CH 2 CH 3 protons (see the INS spectrum for comparison, emphasizing the ν­[CH 2 ] and ν­[CH 3 ] modes). At this stage, we note that a detailed interpretation of the IR spectrum in the ν­[CH] regime is beyond the capabilities of the adopted methodology, being affected by Fermi resonances along with combinations and overtones prohibiting a straightforward assignment. − A high density of vibrational states for hydrogen atoms associated with the alkyl fragments also clarifies the presence of the hump in the INS spectrum over ca. 1500–1300 cm –1 .…”

Temperature-Dependent Infrared Spectroscopy Studies of a Novel Antiferroelectric Liquid-Crystalline Thiobenzoate

“…25−27 As modern quantum chemistry allows us to predict the vibrational spectra with very good accuracy, the experimental data may be nowadays deeply understood and interpreted, giving even further information about the components of the related transition moments, despite the high complexity of the recorded data. 28−31 Recently, the vibrational spectrum of MHPSBO10 has been extensively analyzed in terms of solid-state oriented quantumchemical calculations and presented elsewhere, 32 delivering unambiguous knowledge of band assignment, their composition, and the related transition moment geometry. Such knowledge in relation with the spectra observed for the samples in confined geometries allows us to probe directly the structural properties of mesophases at the molecular level, building a bridge between the macroscopic and molecular sample properties, which may be quantifiably defined in terms of the order parameters.…”

“…As mentioned before, such data along with the discussion of the vibrational transition moments were presented in detail elsewhere. 32 On the basis of the previously reported computations, we take further insight into the absorbance components by studying the system in confined geometries. Here, instead of the reported QUANTUM ESPRESSO (QE) results, we present the same quality CASTEP 35 data obtained with exactly the same computational conditions to get the further absorbance components which were not delivered by the QE computations.…”