In this review, methods to obtain the orientational order of topologically variant molecular mesogens using by 1D and 2D solid-state 13 C NMR spectroscopy are described. Besides 13 C chemical shifts, the 13 C-1 H dipolar couplings measured from 2D-separated local field (SLF) technique are used for computing the order parameters of a variety of mesogens. The investigated molecules are composed of a variable number of rings in the core, i.e. core ranging from simply one ring to five rings. Among the mesogens investigated, a special focus has been placed on mesogens with thiophene rings, which are gaining popularity as liquid crystalline organic semiconductors. The replacement of a phenyl ring by thiophene in the core has a dramatic influence on molecular topology, as observed from the measured order parameters. The review highlights the advantages of the 2D SLF method for understanding the local dynamics and for mapping the topology of mesogens through the measured order parameters. SLF NMR studies of as many as 24 molecular mesogens that vary in terms of the molecular structure as well as topology are covered in the review. Order parameters of the rings have been estimated from the 13 C-1 H dipolar couplings in the nematic, smectic A, smectic C, and tilted hexatic phases as well as in B1 and B2 mesophases of various mesogens. It is anticipated that in the years to come, the 2D SLF method would provide advanced molecular information on structurally complex mesogens that are emerging in liquid crystal science through the incessant efforts of synthetic chemists.

中文翻译：

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棒状、弯曲核和噻吩介晶的 13 C 核磁共振研究

在这篇综述中，描述了使用 1D 和 2D 固态 13 C NMR 光谱获得拓扑变异分子介晶的取向顺序的方法。除了 13 C 化学位移，从 2D 分离局部场 (SLF) 技术测量的 13 C-1 H 偶极耦合用于计算各种介晶的有序参数。研究的分子由核心中可变数量的环组成，即核心范围从简单的一个环到五个环。在所研究的介晶中，特别关注具有噻吩环的介晶，其作为液晶有机半导体越来越受欢迎。从测量的有序参数观察到，核心中苯环被噻吩取代对分子拓扑结构有显着影响。该评论强调了 2D SLF 方法在理解局部动力学和通过测量的有序参数映射介晶拓扑方面的优势。该评论涵盖了多达 24 种分子介晶的 SLF NMR 研究，这些介晶在分子结构和拓扑结构方面各不相同。环的有序参数已从向列相、近晶 A、近晶 C 和倾斜六晶相以及各种介晶的 B1 和 B2 中间相中的 13 个 C-1 H 偶极耦合估计。预计在未来几年，通过合成化学家的不断努力，二维 SLF 方法将提供有关液晶科学中出现的结构复杂介晶的先进分子信息。