The role of NMR in the study of partially ordered materials: Perspectives and challenges

Abstract

The development of NMR techniques applied in the last 10 years to partially oriented systems, and in particular to liquid crystals (LCs), is the object of this brief perspective. The evolution of NMR methods (i.e., new NMR pulse sequences) and the improvement of both theoretical models and mathematic tools for the analysis of NMR data (specifically, for partially ordered systems) allowed scientists to extend their research to increasingly complex materials, such as dendrimers, polymers, and membranes, and to investigate unique phenomena, such as field-induced alignment and confining effects. Furthermore, the fast development of nanoscience and biomedicine is offering a rich variety of new “physical chemical” problems related to partially ordered materials. Starting from a brief perspective of recent works on thermotropic and lyotropic LCs based on different NMR methods, new challenges in this field will be drawn. Moreover, recent selected research works will be discussed in detail with particular emphasis on: (i) the effect of high magnetic fields on the supramolecular structure of chiral liquid-crystalline phases, such as the SmC*, TGBA*, and “de Vries”-type SmA* phases, by means of solid-state 2H NMR; (ii) the slow dynamics in the isotropic phase of bent-core LCs (BLCs) and of liquid single-crystal elastomers evidenced by 2H NMR relaxation studies; and (iii) the influence of the LC environment on the conformational properties of rod-like mesogens studied by high-resolution solid-state 13C NMR methods. This work aims to offer an occasion of reflection on this field of physical chemistry with a glance at future trends and challenges in view of the celebration of the International Year of Chemistry, 2011. \ud \ud *Pure Appl. Chem. 83, 1–252 (2011). A collection of invited, peer-reviewed articles by former winners of the IUPAC Prize for Young Chemists, in celebration of the International Year of Chemistry 2011

Conformational Properties and Orientational Order of a de Vries Liquid Crystal Investigated through NMR Spectroscopy

“…This NMR study [5] showed also that the smA phase of the investigated de Vries smectogen has a quite high orientational order, typical of regular smectic phases; this result was also confirmed by X-ray and Raman techniques on the same smectogen. [32] In the present work, we show that a combination of different NMR techniques [33][34][35][36][37][38][39][40] can help in understanding basic molecular and conformational properties within the whole de Vries SmA mesophase and at the SmA-SmC* transition, thus adding fundamental information to discriminate among the theoretical models reported in the literature. In particular, we focus our attention to the representative de Vries smectogen 9HL, a (S)-hexyl-lactate derivative, which consists of a rigid core of three benzoate moieties and a lactate unit, and two linear alkyl chains of 6 and 9 carbon atoms respectively (see Figure 1).…”

Nuclear magnetic resonance: a powerful tool to study liquid crystals

“…A detailed description of these terms is out of the scope of this brief review, and a comprehensive explanation can be found in many books and reviews on NMR of liquid crystals, such as those reported in references [3][4][5][6][7]. Figure 2 (a)).…”

Recent NMR Studies of Thermotropic Liquid Crystals

“…Recently, 2 H T 2 measurements have been used to investigate single molecular motions, such as overall ROT in BCMs [203][204][205], and LC dendrimers [206]. Here several of these deuterium T 2 relaxtion studies of BCMs are briefly outlined.…”