Modelling of structure and interpretation of IR absorption spectra for crystals of substituted aryl propargyl ethers of phenols

Abstract

535.34:547IR absorption spectra of mesogenic crystals based on substituted aryl propargyl ethers of phenols (APEP) are calculated and analyzed using the LADY program. Force constants and interatomic potentials of atoms not covalently bonded adequately describe experimental IR spectra. The corresponding bands in the absorption spectra are interpreted. The influence of the substitution type on the force field of separate molecules in APEP crystals is clarified.Introduction. Nematic liquid crystals based on arylpropargyl ethers of phenols (APEP) [1-5] are promising materials for improving the temperature characteristics of liquid-crystal devices. However, the relationships of the macro-and microparameters of the materials and their structures must be understood before they can be used. It is important to find the effect of the type of substitution for the H atoms in the benzene rings on the physicochemical properties of the crystals.The need for a detailed study of the structure and properties of the liquid-crystalline states of APEP has focused attention on the solid crystalline state preceding the mesophase because it generates and is mainly responsible for its properties. The principal value of studying the crystal structure of liquid-crystalline compounds is that conclusions can be made about the structure and presence of molecular degrees of freedom that probably occur in the mesophase based on the molecular organization observed in the solid phase and calculated energies of the intermolecular interactions [6].Herein we use IR absorption vibrational spectroscopy (experiment, theory) to study IR spectra of APEP. Spectra were recorded on a Fourier-transform Avatar 360 ESP spectrometer in the range 4000-400 cm -1 with 4 cm