13C CSA Tensors and Orientational Order of Model and Dimer Mesogens Comprising of Phenyl Benzoate

• Published in: Chemphyschem 2024-12, Vol.25 (24), p.e202300749-n/a
• Main Authors: Pratap, Gallelli, Reddy, Yanati Santhosh K., Lobo, Nitin P., Ramanathan, Krishna V., Narasimhaswamy, Tanneru
• Format: Article
• Language: English
• Subjects: 13C NMR; 13C-1H dipolar couplings; Anisotropy; Benzoates; Chemical equilibrium; Couplings; CSA; Diffraction patterns; Dimer; Dimers; Elastomers; Liquid crystal polymers; Liquid crystals; Mesogen; NMR spectroscopy; Order parameters; Structural analysis; Tensors
• ISSN: 1439-4235; 1439-7641; 1439-7641
• DOI: 10.1002/cphc.202300749

A Model mesogen and its symmetrical Dimer made up of phenyl benzoate core unit are investigated by 13C NMR spectroscopy. The existence of layer order in smectic A and smectic C phases of Dimer mesogen is established by powder X‐ray diffraction. The chemical shift anisotropy (CSA) tensors of Model mesogen are determined by 2D separation of undistorted powder patterns by effortless recoupling (SUPER) experiment and are utilized for calculating the order parameters employing the alignment‐induced chemical shifts (AIS). Additionally, 2D separated local field (SLF) NMR is availed for extracting 13C‐1H dipolar couplings for both mesogens and used for computing the order parameters. A good agreement in the order parameters calculated from 13C‐1H dipolar couplings and AIS is observed. Accordingly, the main order parameter (Szz) for the phenyl rings of the Model mesogen is found to be in the range 0.54–0.82, and for the Dimer mesogen, the values span 0.64–0.82 across mesophases. Since the phenyl benzoate core unit is frequently employed structural moiety for constructing the main chain as well as side chain liquid crystalline polymers and liquid crystalline elastomers, the CSA tensors reported here will be of immense utility for the structural characterization of these materials. A model mesogen and its dimer with phenyl benzoate core unit are investigated by 13C NMR spectroscopy in nematic, SmA, and SmC phases to determine the orientational order parameters. Excellent agreement between the order parameters determined from 13C‐1H dipolar couplings as well as CSA tensors and 13C chemical shifts is witnessed owing to the structural similarity of the core in both systems.