Molecular Order of Topologically Variant Flexible Mesogens by ¹³C Nuclear Magnetic Resonance

Abstract

13C nuclear magnetic resonance investigations in the nematic phase of mesogens comprising a rod-like core with three phenyl rings connected to a fourth phenyl ring via a flexible spacer are reported. The molecules are abbreviated as monomer, dimer, and trimer as they comprised one, two, and three pairs of core and spacer combinations linked to ring IV, respectively. Hot-stage optical polarizing microscopy and differential scanning calorimetry studies confirmed that all of them exhibit an enantiotropic nematic phase with additional monotropic or enantiotropic smectic mesophases. Large values of 13C–1H dipolar couplings of the order of 11 kHz are observed for all the cases for the terminal carbon C1 of the core unit. These high values indicated that the corresponding CH vector is collinear with the long axis of the molecule, which itself is aligned parallel to the magnetic field. In contrast, the terminal carbon of the ring IV (C19/C17) exhibits a relatively smaller value in the range of 2.0–2.5 kHz, reflecting the divergent local dynamics at different sections of the mesogens. The orientational order parameters of the phenyl rings computed from the 13C–1H dipolar couplings have been used to obtain the conformation of the mesogens in the nematic phase. It is concluded that the dimer and trimer exhibit C2 and C3 symmetry with the ring IV connected by spacers tilted away from the symmetry axis by 35.9 and 90° for the two cases, respectively. This leads to the interesting tripod-like molecular shape for the trimer in the nematic phase rather than the planar representation of the λ shape.

Observation and Nursing of Adverse Reactions in Severe Patients with Enhanced MRI

“…Before the examination, communicate with the patient in easy to understand language, carefully explain the necessity and safety of the examination, equip the drugs, equipment and rescue supplies required for the examination, carefully answer the patient's questions, meet their reasonable requirements, and alleviate tension and fear. The waiting hall shall be kept clean and tidy, equipped with books and pictures, film and television broadcasting system, sufficient seats and drinking water equipment to facilitate patients to save valuables, equipped with a locked extraction cabinet, the room temperature shall be controlled at 18 ∼ 25°C, the humidity shall be 50% ∼ 60%, keep the room clean and quiet, and prepare blankets, sheets and examination clothes for patients to prevent catching cold [ 13 , 14 ]. Patients should be given family support during the examination to ensure that they use a comfortable position during the examination.…”

Direct method to grasp molecular topology of mesogens through13C–1H dipolar couplings

“…S4 (ESI‡). 11 For the central phenyl ring (ring-III) of B1 mesogen, the axis passing through carbons 15 and 18 is considered as the x -axis (Fig. 8), while the axis normal to it and in the plane of the ring is the ordering axis ( z -axis).…”

“…8,9 These experiments offer a 2D plot of 13 C chemical shifts and 13 C-1 H dipolar couplings sensitive to orientational order and molecular topology. [10][11][12] The molecular structures under scrutiny include conventional rod-like molecule, mesogens with lateral phenyl ring, and unsymmetrical bent-core (banana) shape molecules. The prime emphasis of the study is to showcase the utility of ring to map the molecular topology by directly inspecting the 2D spectrum.…”

13C Nuclear Magnetic Resonance Investigations of Molecular Mesogens with a Terminal Phenyl Ring Linked via a Spacer: Odd–Even Effect

“…1D 13 C NMR of all of the five mesogens in solution and variable temperature 13 C NMR studies in the liquid crystalline phase are carried out. Additionally, the 2D SLF NMR spectra of the mesogens are obtained at selected temperatures in the mesophase region using the SAMPI-4 pulse sequence, which offered the 1 H– 13 C dipolar couplings from which the order parameters of individual phenyl rings are obtained. − ,− …”

“…The mesophase properties of the synthesized mesogens are determined, and the detailed one-dimensional (1D) and two-dimensional (2D) 13 C NMR investigations in the liquid crystalline phase have been carried out. Indeed, the 13 C NMR studies empower the determination of site-specific orientation of moieties that are part of the mesogenic core. − Further, the investigation offers direct experimental evidence of the orientation of the terminal phenyl ring connected to the mesogenic core through a spacer unit that holds odd/even number of atoms. Since the stability of the N TB phase is known to depend on the average bend angle between the two mesogenic units, the present study where the average angle between the rodlike core and the terminal phenyl ring is examined bears greater implication.…”