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

Abstract

A prime factor determining the formation of the liquid crystalline phase is the overall molecular shape as molecules undergo rotational motion about the long axis. Molecular topology deals with the...

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

“…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. 32,42 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.…”

“…31 This is perhaps due to the orientation of a particular molecular fragment with reference to the overall orienting axis. In a couple of earlier studies, for example with a phenyl ring connected by a flexible ring 24 or occurring in a lateral arm, 32 it is noticed that the major and minor order parameter values are interchanged.…”

“…29−31 Additionally, crucial evidence pertaining to the molecular topology of mesogens can be extracted from the 13 C 1D and 2D NMR experiments. 32,33 The site-specific information accessible across the molecule from 13 C NMR in the liquid crystalline phase has led to NMR being the choice of method. 34,35 In this work, we demonstrate the use of 13 C NMR for the structural assignment and probe the orientation of thiophene unambiguously.…”