Solid-State NMR Characterization and Determination of the Orientational Order of a Nematogen

• Published in: The journal of physical chemistry. B Vol. 109; no. 42; pp. 19696 - 19703
• Main Authors: Narasimhaswamy, T, Monette, M, Lee, D. K, Ramamoorthy, A
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 27-10-2005
• Subjects: Aniline Compounds - chemical synthesis; Benzoates - chemical synthesis; Crystallization; Indicators and Reagents; Isomerism; Magnetic Resonance Spectroscopy; Solutions; Thermodynamics
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp052343v

Thermotropic liquid crystalline compounds are of considerable importance due to their potential applications as advanced functional materials. A mesogen consisting of a terminal dimethylamino group, which can act as a charge-transfer donor, is particularly valuable for its light emission and nonlinear optical properties. In this study, we report the solid-state NMR investigation of the nematic behavior of one such novel mesogen (4-(dodecyloxy)benzoic acid 4-[((4-(dimethylamino)phenyl)imino)methyl]phenyl ester). Static and MAS experiments were performed on nematic and crystalline phases of the compound to measure 13C chemical shift, 13C−H dipolar coupling, and 1H chemical shift values. 2D chemical shift correlation of 1H and 13C nuclei confirmed the 13C chemical shift values determined from 1D CPMAS experiments. The appearance of more peaks in both CPMAS and 13C−1H HETCOR spectra of a crystalline solid suggests the heterogeneous orientations of phenyl rings of the mesogenic core. Variable-temperature experiments infer the motional averaging of these orientations before melting. The 1H−13C dipolar coupling values, measured by 2D PITANSEMA experiments, were used to determine the orientational order of the mesogenic core at various temperatures. The influence of the linking unit and terminal substituents on the order parameter values of the mesogenic core is discussed.