Molecular Structures of Related Compounds of Mesogens Studied by 1H NMR Using a Liquid Crystal Solvent:  Tolan and trans-Azobenzene

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 105; no. 27; pp. 6711 - 6716
• Main Authors: Inoue, Kaori, Takeuchi, Hiroshi, Konaka, Shigehiro
• Format: Journal Article
• Language: English
• Published: American Chemical Society 12.07.2001
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/jp0045944

Molecular structures of tolan and trans-azobenzene dissolved in nematic liquid-crystal ZLI 1132 have been determined by proton NMR with the aid of theoretical calculations. They are models of the cores of liquid-crystal molecules of the RC6H4XC6H4R‘ type, where R and R‘ denote flexible groups and X is the linking unit. Spectral analysis is quite difficult for such a molecule with 10 protons as C6H5XC6H5. In the present study, therefore, the initial spectral parameters that allow spectral assignment have been obtained by analyzing integral curves by means of a genetic algorithm. Structural analyses show that both compounds take planar molecular structures in ZLI 1132. The determined rotational barriers at the dihedral angle of phenyl rings, 90°, in the liquid crystal are larger than those in the gas phase for tolan and trans-azobenzene as in the cases of phenyl benzoate and biphenyl. It is reasonable to consider that the liquid-crystal solvent stabilizes the planar or nearly planar structures of solutes.