Structural assignment and molecular order of three-ring mesogen by¹³C NMR spectroscopy in mesophase

13C NMR investigations of molecular order of rod‐like, bent‐core, and thiophene mesogens

“…SPINAL-64 scheme is applied during t 2 period when 13 C signals are acquired. Here, thin and thick rectangular dark boxes represent 90°and 180°pulses, respectively [52] M-2 SmA Guruprasad Reddy et al [53] M-3 Nematic, SmC, SmF Guruprasad Reddy et al [53] M-4 Nematic, SmC Kalaivani et al [45] M-5 Nematic Kesava Reddy et al [54] M-6 Nematic, SmA Kesava Reddy et al [54] (Continues) respective isotropic phases and later slowly cooling to the desired phase temperature for the measurement. One-dimentional 13 C NMR spectra in the mesophases were obtained using ramped CP scheme typically with a contact time of 3 ms and a recycle delay of 8 s. For the SAMPI-4 measurements (Figure 1a), CP was followed by polarization inversion [43] in order to get higher intensities in the 2D plots.…”

“…For the 2-and 3-substituted thiophene geometries, different coordinate axes are chosen with the z-axis taken along the bond by which thiophene is connected to the rest of the mesogen. [50,51] The remaining axes are defined in same way as the phenyl ring coordinate FIGURE 4 Two-dimensional SAMPI-4 spectra of (a) M-2 in smectic A phase at 72°C and (b) M-3 in smectic C phase at 175°C (Adapted from Guruprasad Reddy et al [53] with permission of the publisher Taylor & Francis Ltd, http://www.tandfonline.com) FIGURE 3 Two-dimensional SAMPI-4 spectrum of M-1 in nematic phase at 120°C (adopted with permission from Lobo et al [52] Copyright 2012 American Chemical Society)…”

“…[52] The two-ring mesogen, M-2 with a terminal aldehyde group was synthesized from 4-decyloxy benzoic acid, and the 13 C NMR study was extended to the mesogen. [53] As it exhibits enantiotropic smectic A (SmA) phase, the 13 C NMR and 2D SLF measurements were carried out in SmA phase (Figure 4a). For the assignment of 13 C chemical shift values for ring I in mesophase, the M-1 data were employed.…”

“…Further, to realize a three-ring mesogen (M-3), the two ring aldehyde was coupled with tetradecyloxy aniline. [53] The resultant three-ring mesogen, M-3, showed nematic, smectic C (SmC), and smectic F (SmF) phases for which the 13 C NMR measurements were carried out. The orientational order parameters for M-2 as well as M-3 were determined FIGURE 7 Two-dimensional SAMPI-4 spectrum of M-10 in nematic phase at 130°C (Adapted from Lobo et al [51] with permission from The Royal Society of Chemistry)…”

Effortless Extraction of Structural and Orientational Information from 13C–1H Dipolar Couplings for Thiophene Mesogens

“…Table lists the chemical shift assigned to core unit carbons of the Phenyl mesogen. The spectral assignment for the core unit carbons is accomplished by comparing the structurally similar mesogens for which the 13 C NMR data is accessible from the literature. , The variation of the chemical shift of the carbons of the Phenyl mesogen with temperature is shown in Figure S8A of the Supporting Information. The tendency of decreasing chemical shift with the increase of temperature is indicative of the molecule, rather than the layer normal, being aligned with the magnetic field.…”