13C–1H dipolar couplings for probing rod-like hydrogen bonded mesogens

Reddy, M. Kesava; Reddy, K. S.; Narasimhaswamy, T.; Das, Bidisa; Lobo, Nitin P.; Ramanathan, K. V.

doi:10.1039/c3nj00271c

Cited by 22 publications

(22 citation statements)

References 56 publications

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“…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.…”

Section: Methodsmentioning

confidence: 99%

“…Two-dimensional SAMPI-4 spectra of (a) M-5 at 125°C in nematic phase and (b) M-6 at 130°C in nematic phase (Adapted from Kesava Reddy et al [54] with permission from the Centre National de la Recherche Scientifique (CNRS) and The Royal Society of Chemistry) permission from Kalaivani et al [45] Copyright 2011 American Chemical Society)…”

Section: Rod-like Mesogensmentioning

confidence: 99%

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

Lobo

Ramanathan

Narasimhaswamy

2019

Magnetic Reson in Chemistry

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In this review, methods to obtain the orientational order of topologically variant molecular mesogens using by one-and two-dimensional (2D) solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy are described. Besides 13 C chemical shifts, the 13 C─ 1 H dipolar couplings measured from 2Dseparated 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, that is, 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 B 1 and B 2 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. The mini review covers the orientational order of topologically variant molecular mesogens determined by 1D and 2D solid-state 13 C NMR spectroscopy. Accordingly, rod-like, bent-core, and thiophene mesogens were subjected to 2D SLF measurements to get the order parameters from which the topology was established. The replacement of phenyl ring by thiophene and its influence on order parameters as well as on molecular topology is also discussed.

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Section: Methodsmentioning

confidence: 99%

Section: Rod-like Mesogensmentioning

confidence: 99%

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

Lobo

Ramanathan

Narasimhaswamy

2019

Magnetic Reson in Chemistry

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“…This carbon,w ith its CH vector essentially parallel to the long axis of the liquid crystal molecule, is expected to show al arge dipolar coupling. [41] For the same reason, it also has al arge chemical shift, similart ot he other quaternary carbons of the three phenyl rings in the core. For all of them, the direction of the least-shielded chemical shift direction, namely the para axes of the phenylr ings, are nearly parallel to the liquid crystal orienting axis.…”

Section: Methodsmentioning

confidence: 91%

Measurement of Large Dipolar Couplings of a Liquid Crystal with Terminal Phenyl Rings and Estimation of the Order Parameters

Kumar

Ramanathan

2015

ChemPhysChem

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NMR spectroscopy is a powerful means of studying liquid-crystalline systems at atomic resolutions. Of the many parameters that can provide information on the dynamics and order of the systems, (1) H-(13) C dipolar couplings are an important means of obtaining such information. Depending on the details of the molecular structure and the magnitude of the order parameters, the dipolar couplings can vary over a wide range of values. Thus the method employed to estimate the dipolar couplings should be capable of estimating both large and small dipolar couplings at the same time. For this purpose, we consider here a two-dimensional NMR experiment that works similar to the insensitive nuclei enhanced by polarization transfer (INEPT) experiment in solution. With the incorporation of a modification proposed earlier for experiments with low radio frequency power, the scheme is observed to enable a wide range of dipolar couplings to be estimated at the same time. We utilized this approach to obtain dipolar couplings in a liquid crystal with phenyl rings attached to either end of the molecule, and estimated its local order parameters.

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“…The same research group has reported a study of a 3-ring system PMAPH whose core is similar to mesogen I except the terminus ring III is a pyridine ring, and a hydrogen-bonded complex (PMAPHMB) using PMAPH as an acceptor and a nonmesogenic donor 4-methoxy benzoic acid [243]. The former mesogen presents a N-I transition at 152°C.…”

Section: Calamitics and Hydrogen-bonded Mesogensmentioning

confidence: 96%

“…The obvious advantage of the former is the results, though still depending on the assignment of relevant carbon peaks, do not rely on the determination of CSAs either by DFT or via measuring by NMR pulse sequences such as SUPER [237], or PASS [238]. Ramanathan and coworkers have reported new C-H dipolar couplings for a variety of LCs, including calamitics [239,240], BCMs [241,242], and hydrogen-bonded rodlike LCs [243]. These works will be mentioned below under different classes of LCs.…”

Section: Studies Of Order and Structurementioning

confidence: 99%

Recent NMR Studies of Thermotropic Liquid Crystals

Dong¹

2016

Annual Reports on NMR Spectroscopy

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13C–1H dipolar couplings for probing rod-like hydrogen bonded mesogens

Cited by 22 publications

References 56 publications

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

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

Measurement of Large Dipolar Couplings of a Liquid Crystal with Terminal Phenyl Rings and Estimation of the Order Parameters

Recent NMR Studies of Thermotropic Liquid Crystals

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13C–1H dipolar couplings for probing rod-like hydrogen bonded mesogens

Cited by 22 publications

References 56 publications

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

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

Measurement of Large Dipolar Couplings of a Liquid Crystal with Terminal Phenyl Rings and Estimation of the Order Parameters

Recent NMR Studies of Thermotropic Liquid Crystals

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

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