1
|
Phani Kumar BVN, Lobo NP, Mattea C, Stapf S. Exploring Crystal-Phase Molecular Dynamics of the Low-Viscous Mesogen 6CHBT: A Combined FFC and High-Field NMR Relaxometry Investigation. J Phys Chem B 2024; 128:3997-4007. [PMID: 38616575 DOI: 10.1021/acs.jpcb.3c08259] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/16/2024]
Abstract
The molecular dynamics study of thermotropic mesogens exhibiting the crystal phases is valuable in unraveling the complex global (collective) and local (noncollective) motions executed by liquid crystal molecules, which would further advance the existing knowledge on orientationally disordered crystalline (ODIC) phases. Toward the fulfillment of such a task, a combined nuclear magnetic resonance (NMR) relaxometry approach employing the fast field cycling (FFC) NMR (10 kHz-30 MHz) and high-field pulsed NMR (400 MHz) techniques is utilized to sample the broad frequency range offered by molecular motions in the crystal phase of 4-(trans-4'-n-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). The validity of the observed relaxation data is tested and interpreted by the Bloembergen-Purcell-Pound (BPP) model involving the superposition of four mutually independent Lorentzian spectral densities, reflecting molecular dynamical processes on different time scales. The salient feature of the detailed analysis reveals that the lengthening of temporal dynamics in the crystal phase due to molecular rotations by jumps, which are of intermolecular origin, is evident and further supports the presence of collective-like local dynamics. The analysis does permit decoupling of the molecular reorientations about their short axes (∼100 ns) as well as long axes (∼50 ns) and methyl group rotations (∼0.5 ns) on distinct time scales. The activation energies for reorientations about the short axes and methyl group rotations are found to be 27.3 ± 2.7 and 15.8 ± 1.1 kJ/mol, respectively. The fast methyl rotations in the crystal phase of 6CHBT obtained from FFC NMR are further well complemented by high-field NMR, where 1H NMR line shapes are relatively narrow when compared to those of the nematic phase.
Collapse
Affiliation(s)
- Bandaru V N Phani Kumar
- Department of Technical Physics II/Polymer Physics, Institute of Physics, Ilmenau University of Technology, PO Box 100565, D-98684 Ilmenau, Germany
- NMR, Centre for Analysis, Testing, Evaluation & Reporting Services (CATERS), CSIR-Central Leather Research Institute, Chennai 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
| | - Nitin P Lobo
- NMR, Centre for Analysis, Testing, Evaluation & Reporting Services (CATERS), CSIR-Central Leather Research Institute, Chennai 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
| | - Carlos Mattea
- Department of Technical Physics II/Polymer Physics, Institute of Physics, Ilmenau University of Technology, PO Box 100565, D-98684 Ilmenau, Germany
| | - Siegfried Stapf
- Department of Technical Physics II/Polymer Physics, Institute of Physics, Ilmenau University of Technology, PO Box 100565, D-98684 Ilmenau, Germany
| |
Collapse
|
2
|
Veeraprakash B, Kesava Reddy M, Das BB, Lobo NP, Ramanathan KV, Narasimhaswamy T. Effortless Extraction of Structural and Orientational Information from 13C- 1H Dipolar Couplings for Thiophene Mesogens. J Phys Chem B 2023; 127:10912-10922. [PMID: 38063349 DOI: 10.1021/acs.jpcb.3c06176] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2023]
Abstract
Five molecular mesogens containing phenyl rings and thiophene are subjected to a detailed 13C NMR investigation. The first mesogen contains only phenyl rings, while the other four have thiophene with substitution at position 2 or 3. Two of these also have a spacer inserted between the thiophene and the rest of the core unit. The mesophase properties evaluated by complementary techniques reveal an enantiotropic nematic phase for all the cases and smectic C as well as Crystal J for a few mesogens. In addition to solution 13C NMR, the samples were studied using 1D and 2D solid-state 13C NMR experiments in the liquid crystalline phase. The chemical shifts and 13C-1H dipolar couplings obtained in the mesophase provided cutting-edge information about the molecular structure and orientation of the thiophene mesogens. Accordingly, dramatic differences in these parameters are noted for the mesogens, and consequently, the identification of 2- and 3-substituted thiophene mesogens is accomplished by a simple visual examination of the 2D spectra. Furthermore, for mesogens with a spacer between thiophene and the rest of the core, 13C chemical shifts and 13C-1H dipolar couplings showed remarkable variation, which was directly reflected in the order parameters. For instance, the order parameter (Szz) of thiophene in 2- and 3-substituted mesogens in which the spacer is absent is ∼0.63 whereas for those with spacer, it is reduced to ∼0.14-0.18. In comparison, the mesogen in which the core unit is made up of phenyl rings alone that is used to benchmark the characteristics of thiophene ordering showed an order parameter of ∼0.85. The study unambiguously demonstrates the supremacy of 13C NMR in extracting the structural and orientational information on mesogens in which thiophene is a constituent of the core unit.
Collapse
Affiliation(s)
- Bathini Veeraprakash
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | | | - Bibhuti B Das
- Department of Physics, Indian Institute of Science, Bangalore 560012, India
| | - Nitin P Lobo
- Centre for Analysis, Testing, Evaluation & Reporting Services (CATERS), CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
| | | | - Tanneru Narasimhaswamy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad 201002, India
| |
Collapse
|
3
|
Veeraprakash B, Shanavas AKJ, Reddy GSM, Lobo NP, Ramanathan KV, Narasimhaswamy T. Molecular Conformations of Shape Anisometrically Variant Mesogens in Liquid Crystalline Phase Studied by 13 C NMR Spectroscopy. Chemphyschem 2023:e202300353. [PMID: 37725408 DOI: 10.1002/cphc.202300353] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2023] [Revised: 09/19/2023] [Accepted: 09/19/2023] [Indexed: 09/21/2023]
Abstract
Mesogens that vary in shape anisometry have been investigated by 13 C solid-state NMR in the liquid crystalline phase to inspect the conformations. The molecules examined comprise of (i) rod-like mesogen with three-phenyl ring core and terminal hexyloxy chains, (ii) three-ring core linked to the fourth phenyl ring via a spacer, and (iii) trimesic acid connected to three side arms core units through a spacer. The order parameter (Szz ) values for the phenyl rings of the rod-like mesogen are 0.65-0.68, while the mesogen with a three-ring core linked to a phenyl ring via spacer showed dissimilarity. Consequently, for the core unit phenyl rings, Szz is ~0.70, and the terminal phenyl ring showed a low value of 0.12. For the trimesic acid based mesogen, the Szz value for the side arm phenyl rings is ~0.53, and for the central phenyl ring, a very low value of 0.11 is witnessed. By considering the ordering of the rod-like mesogen as a yardstick and employing the ratios of Szz values of the phenyl rings, the average conformations of other mesogens are arrived. Accordingly, for the trimesic acid based mesogen, a tripod-like conformation instead of λ shape is proposed in the liquid crystalline phase.
Collapse
Affiliation(s)
- Bathini Veeraprakash
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai, 600020, India
| | - Abdul K J Shanavas
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai, 600020, India
| | - Goddeti S M Reddy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai, 600020, India
| | - Nitin P Lobo
- Centre for Analysis, Testing, Evaluation & Reporting Services (CATERS), CSIR-Central Leather Research Institute, Adyar, Chennai, 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
| | | | - Tanneru Narasimhaswamy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai, 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, 201002, India
| |
Collapse
|
4
|
Reddy MK, Shalini PJ, Lobo NP, Roy A, Narasimhaswamy T. Direct method to grasp molecular topology of mesogens through 13C- 1H dipolar couplings. Phys Chem Chem Phys 2023; 25:14158-14169. [PMID: 37162405 DOI: 10.1039/d3cp00291h] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
A prime factor in determining liquid crystalline phase formation is the overall molecular shape since molecules undergo rotational motion about the long axis. Molecular topology deals with the connectivity of atomic centers in a given molecular architecture, ultimately giving rise to the gross molecular shape. 13C NMR has emerged as the most important technique in establishing the molecular topology of mesogens in the liquid crystalline phase. In this work, we demonstrate the utility of 13C-1H dipolar couplings determined from 2D separated local field NMR for finding the topology of three different mesogens in the liquid crystalline phase. The core unit of the investigated mesogens fundamentally differs, which may be categorized as rod-like, laterally substituted, and bent-core shapes. 1D and 2D 13C NMR measurements in the liquid crystalline phase revealed fascinating information. The 13C-1H dipolar couplings extracted from 2D NMR are found to be sensitive to topologically variant core units. This permitted us to establish the molecular topology just by looking at the 13C-1H dipolar couplings of the protonated carbons of the constituent phenyl rings. By considering the dipolar couplings of rod-like mesogens as a reference, the large variation in the magnitude of 13C-1H dipolar couplings of the laterally substituted and bent-core mesogens is attributed to changes in the topology of their core units. The order parameters estimated from 13C-1H dipolar couplings enabled visualization of the ordering array of phenyl rings of the mesogens. Interestingly large 13C-1H dipolar couplings are observed for mesogens in which (a) laterally located phenyl ring and (b) central phenyl ring of bent-core mesogens exhibited different trends as revealed by the orientational order parameters.
Collapse
Affiliation(s)
- M Kesava Reddy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - P Jaya Shalini
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - Nitin P Lobo
- Centre for Analysis, Testing, Evaluation & Reporting Services (CATERS), CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh 201002, India.
| | - Arun Roy
- Soft Condensed Matter, Raman Research Institute, Bangalore, 560080, India
| | - T Narasimhaswamy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh 201002, India.
| |
Collapse
|
5
|
Gayathri V, Lobo NP, Vikash VL, Kamini NR, Samanta D. Functionalization of Bacterial Cellulose and Related Surfaces Using a Facile Coupling Reaction by Thermoresponsive Catalyst. ACS Biomater Sci Eng 2023; 9:625-641. [PMID: 36632811 DOI: 10.1021/acsbiomaterials.2c01338] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Recently, bacterial cellulose and related materials attracted significant attention for applications such as leather-like materials, wound healing materials, etc., due to their abundance in pure form and excellent biocompatibility. Chemical modification of bacterial cellulose further helps to improve specific properties for practical utility and economic viability. However, in most cases, chemical modification of cellulose materials involves harsh experimental conditions such as higher temperatures or organic solvents, which may destroy the 3-dimensional network of bacterial cellulose, thereby altering its characteristic properties. Hence, in this work, we have adopted the Suzuki coupling methodology, which is relatively unexplored for chemically modifying cellulose materials. As the Suzuki coupling reaction is tolerable against air and water, modification can be done under mild conditions so that the covalently modified cellulose materials remain intact without destroying their 3-dimensional form. We performed Suzuki coupling reactions on cellulose surfaces using a recently developed thermoresponsive catalyst consisting of poly(N-isopropylacrylamide) (PNIPAM)-tagged N-heterocyclic carbene (NHC)-based palladium(II) complex. The thermoresponsive nature of the catalyst particularly helped to perform reactions in a water medium under mild conditions considering the biological nature of the substrates, where separation of the catalyst can be easily achieved by tuning temperature. The boronic acid derivatives have been chosen to alter the wettability behavior of bacterial cellulose. Bacterial cellulose (BC) obtained from fermentation on a lab scale using a cellulose-producing bacterium called Gluconacetobacter kombuchae (MTCC 6913) under Hestrin-Schramm (HS) medium, or kombucha-derived bacterial cellulose (KBC) obtained from kombucha available in the market or cotton-cellulose (CC) was chosen for the surface functionalization to find the methodology's diversity. Movie files in the Supporting Information and figures in the manuscript demonstrated the utility of the methodology for fluorescent labeling of bacterial cellulose and related materials. Finally, contact angle analysis of the surfaces showed the hydrophobic natures of some functionalized BC-based materials, which are important for the practical use of biomaterials in wet climatic conditions.
Collapse
Affiliation(s)
- Varnakumar Gayathri
- Polymer Science & Technology division, Council of Scientific and Industrial Research (CSIR)-Central Leather Research Institute (CLRI), Adyar, Chennai600020, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad201002, India
| | - Nitin P Lobo
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad201002, India.,Centre For Analysis, Testing, Evaluation & Reporting Services (CATERS), Council of Scientific and Industrial Research (CSIR)-Central Leather Research Institute (CLRI), Adyar, Chennai600 020, India
| | - Vijan Lal Vikash
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad201002, India.,Biochemistry & Biotechnology Department, Council of Scientific and Industrial Research (CSIR)-Central Leather Research Institute (CLRI), Adyar, Chennai600020, India
| | - Numbi Ramudu Kamini
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad201002, India.,Biochemistry & Biotechnology Department, Council of Scientific and Industrial Research (CSIR)-Central Leather Research Institute (CLRI), Adyar, Chennai600020, India
| | - Debasis Samanta
- Polymer Science & Technology division, Council of Scientific and Industrial Research (CSIR)-Central Leather Research Institute (CLRI), Adyar, Chennai600020, India.,Academy of Scientific and Innovative Research (AcSIR), Ghaziabad201002, India
| |
Collapse
|
6
|
Reddy MG, Lobo NP, Roy A, Ramanathan KV, Narasimhaswamy T. Strikingly different molecular organization and molecular order of tetracatenar mesogens in columnar mesophases revealed by XRD and 13C NMR. Phys Chem Chem Phys 2020; 22:23986-23997. [PMID: 33073796 DOI: 10.1039/d0cp03933k] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
For a successful design of functional mesogens, it is paramount to understand factors that contribute to molecular organisation such as molecular shape, the non-covalent interactions of the constituent moieties as well as nanosegregation of incompatible molecular parts. In this study on four tetracatenar mesogens, we show that by a slight change in the length of the terminal chain, the molecular organization changes from lamellar to columnar phase and that the orientational order experiences profound change between the lamellar, the center rectangular columnar and the hexagonal columnar mesophases. We consider here, mesogens that exhibit lamellar and columnar mesophases with five phenyl rings in the central rod-like core which are subjected to XRD and high resolution solid state 13C NMR investigations in their mesophases. The XRD studies indicate that the lower homologs exhibit a lamellar mesophase while the higher homologs show either a centre rectangular columnar phase or a 2D hexagonal columnar mesophase. 13C NMR investigations reveal interesting and strikingly different molecular orientations in each of these phases. For example, values of order parameters of one of the phenyl rings in the core region of the mesogens vary from 0.75 and 0.77 for the lamellar mesogens to 0.45 and 0.17 for the centre rectangular columnar and the hexagonal columnar mesogens respectively. While these values indicate that the mesogenic molecules are oriented along the magnetic field as expected in the lamellar phases, the very low order parameter in the hexagonal columnar phase arises due to molecules distributed azimuthally in layers and undergoing motion about the columnar axis which itself is oriented orthogonal to the magnetic field. Such cutting edge information extracted from the combined use of XRD and 13C NMR studies on tetracatenar mesogens is expected to be of significant use for the study of π-conjugated polycatenar systems where functional properties depend on the molecular orientation and order.
Collapse
Affiliation(s)
- M Guruprasad Reddy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India.
| | - Nitin P Lobo
- Centre for Analysis, Testing, Evaluation & Reporting Services (CATERS), CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - Arun Roy
- Soft Condensed Matter, Raman Research Institute, Bangalore, 560080, India.
| | - K V Ramanathan
- NMR Research Centre, Indian Institute of Science, Bangalore, 560012, India.
| | - T Narasimhaswamy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India.
| |
Collapse
|
7
|
Lobo NP, Ramanathan KV, Narasimhaswamy T. 13 C NMR investigations of molecular order of rod-like, bent-core, and thiophene mesogens. Magn Reson Chem 2020; 58:988-1009. [PMID: 31770458 DOI: 10.1002/mrc.4972] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/21/2019] [Revised: 11/09/2019] [Accepted: 11/13/2019] [Indexed: 06/10/2023]
Abstract
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 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, 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 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. 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.
Collapse
Affiliation(s)
- Nitin P Lobo
- Inorganic and Physical Chemistry, CSIR-Central Leather Research Institute, Chennai, India
| | - K V Ramanathan
- NMR Research Centre, Indian Institute of Science, Bangalore, India
| | - T Narasimhaswamy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Chennai, India
| |
Collapse
|
8
|
Reddy MG, Lobo NP, Ramanathan KV, Narasimhaswamy T. Molecular Order of Topologically Variant Flexible Mesogens by 13C Nuclear Magnetic Resonance. Langmuir 2020; 36:12620-12631. [PMID: 32993293 DOI: 10.1021/acs.langmuir.0c02182] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
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.
Collapse
Affiliation(s)
- Mandadhi Guruprasad Reddy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - Nitin P Lobo
- Centre for Analysis, Testing, Evaluation & Reporting Services (CATERS) CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | | | - Tanneru Narasimhaswamy
- Polymer Science and Technology, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| |
Collapse
|
9
|
Affiliation(s)
- A. A. Boopathi
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh 201002, India
| | | | - Nitin P. Lobo
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh 201002, India
| | - T. Narasimhaswamy
- Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, Uttar Pradesh 201002, India
| |
Collapse
|
10
|
Santhosh Kumar Reddy Y, Lobo NP, Narasimhaswamy T. Effect of alkyl chain and linking units on mesophase transitions and molecular order of rod-like thiophene mesogens:13C NMR investigation. NEW J CHEM 2018. [DOI: 10.1039/c7nj03525j] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
This study provides insight into the influence of alkyl chains and linking units on the mesophase properties of thiophene-based mesogens and on the orientational constraints of the core and terminal alkyl chain.
Collapse
Affiliation(s)
| | - Nitin P. Lobo
- Inorganic & Physical Chemistry
- CSIR-Central Leather Research Institute
- Chennai 600020
- India
| | - T. Narasimhaswamy
- Polymer Science & Technology
- CSIR-Central Leather Research Institute
- Chennai 600020
- India
| |
Collapse
|
11
|
Abstract
Thiophene-based rodlike molecules constructed from a three phenyl ring core and terminal dialkoxy chains recognized as forked mesogens are synthesized, and their mesophase properties as well as the molecular order are investigated. The synthesized forked mesogens would serve as model compounds for tetracatenar or biforked mesogens. On the basis of the position of the thiophene link with the rest of the core, 2-substituted and 3-substituted mesogens are realized in which the length of the terminal alkoxy chains is varied. The mesophase properties are evaluated using a hot-stage polarizing microscope and differential scanning calorimetry. For both homologues, the appearance of either nematic phase alone or in conjunction with smectic C phase is noticed depending on the length of the terminal alkoxy chains. The existence of layer ordering characteristic of the smectic C phase is confirmed for a representative mesogen using variable-temperature powder X-ray diffraction. High-resolution solid-state (13)C NMR measurements of C12 homologues of the two series reveal orientational order parameters of all rings of the core as well as terminal chains in the liquid crystalline phase. For both homologues, because of the asymmetry of ring I, the order parameter value is higher in contrast to ring II, ring III, and the thiophene ring. The chemical shifts and (13)C-(1)H dipolar couplings of OCH2 carbons of the terminal dodecyloxy chains provide contrasting conformations, reflecting the orientational constraints. Furthermore, the investigations also reveal that the mesophase range and the tendency for layer ordering are higher for 3-substituted mesogens compared to 2-substituted homologues.
Collapse
Affiliation(s)
- K Rajasekhar Reddy
- Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute , Adyar, Chennai 600020, India
| | - Nitin P Lobo
- Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute , Adyar, Chennai 600020, India
| | - T Narasimhaswamy
- Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute , Adyar, Chennai 600020, India
| |
Collapse
|
12
|
Abstract
Three-ring mesogens with a core comprising thiophene linked to one phenyl ring directly and to the other via flexible ester are synthesized with terminal alkoxy chains to probe the mesophase properties and find the molecular order. The phenyl thiophene link in the core offers a comparison of the mesophase features with the molecular shape of the mesogen. The synthesized mesogens display enantiotropic polymesomorphism and accordingly nematic, smectic A, smectic C and smectic B mesophases are perceived depending upon the terminal chain length. For some of the homologues, monotropic higher order smectic phases such as smectic F and crystal E are also witnessed. The existence of polymesomorphism are originally observed by HOPM and DSC and further confirmed by powder X-ray diffraction studies. For the C8 homologue, high resolution solid state (13)C NMR spectroscopy is employed to find the molecular structure in the liquid crystalline phase and using the 2D SLF technique, the (13)C-(1)H dipolar couplings are extracted to calculate the order parameter. By comparing the ratio of local order of thiophene as well as phenyl rings, we establish the bent-core shape of the mesogen. Importantly, for assigning the carbon chemical shifts of the core unit of aligned C8 mesogen, the (13)C NMR measured in mesophase of the synthetic intermediate is employed. Thus, the proposed approach addresses the key step in the spectral assignment of target mesogens with the use of (13)C NMR data of mesomorphic intermediate.
Collapse
Affiliation(s)
- B Veeraprakash
- Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute , Adyar, Chennai 600020, India
| | - Nitin P Lobo
- Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute , Adyar, Chennai 600020, India
| | - T Narasimhaswamy
- Polymer Laboratory and ‡Chemical Physics Laboratory, CSIR-Central Leather Research Institute , Adyar, Chennai 600020, India
| |
Collapse
|
13
|
Kesava Reddy M, Varathan E, Lobo NP, Roy A, Narasimhaswamy T, Ramanathan KV. Monolayer to interdigitated partial bilayer smectic C transition in thiophene-based spacer mesogens: X-ray diffraction and (13)C nuclear magnetic resonance studies. Langmuir 2015; 31:10831-10842. [PMID: 26366989 DOI: 10.1021/acs.langmuir.5b02327] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
Abstract
Mesophase organization of molecules built with thiophene at the center and linked via flexible spacers to rigid side arm core units and terminal alkoxy chains has been investigated. Thirty homologues realized by varying the span of the spacers as well as the length of the terminal chains have been studied. In addition to the enantiotropic nematic phase observed for all the mesogens, the increase of the spacer as well as the terminal chain lengths resulted in the smectic C phase. The molecular organization in the smectic phase as investigated by temperature dependent X-ray diffraction measurements revealed an interesting behavior that depended on the length of the spacer vis-a-vis the length of the terminal chain. Thus, a tilted interdigitated partial bilayer organization was observed for molecules with a shorter spacer length, while a tilted monolayer arrangement was observed for those with a longer spacer length. High-resolution solid state (13)C NMR studies carried out for representative mesogens indicated a U-shape for all the molecules, indicating that intermolecular interactions and molecular dynamics rather than molecular shape are responsible for the observed behavior. Models for the mesophase organization have been considered and the results understood in terms of segregation of incompatible parts of the mesogens combined with steric frustration leading to the observed lamellar order.
Collapse
Affiliation(s)
- M Kesava Reddy
- Department of Chemistry, S. V. University , Tirupati, 517502, India
| | | | - Nitin P Lobo
- Department of Physics, Indian Institute of Science , Bangalore, 560012, India
| | - Arun Roy
- Soft Condensed Matter, Raman Research Institute , Bangalore, 560080, India
| | | | - K V Ramanathan
- NMR Research Centre, Indian Institute of Science , Bangalore, 560012, India
| |
Collapse
|
14
|
Veeraprakash B, Lobo NP, Narasimhaswamy T, Mandal AB. 2-Octyl thiophene based three ring mesogens: solid state (13)C NMR and XRD investigations. Phys Chem Chem Phys 2015; 17:19936-47. [PMID: 26166360 DOI: 10.1039/c5cp01535a] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
2-Octyl thiophene based three-ring mesogens namely 4-n-alkoxyphenyl 4-(5-n-octyl-2-thienyl)benzoates are synthesized by employing palladium acetate based direct arylation. The alkoxy terminal is varied with even carbons from C2 to C14 and enantiotropic polymesomorphism is noticed for all the homologs. Accordingly, phase sequence consisting of nematic, smectic A, smectic C and smectic B is seen for mesogens with terminal chains C6, C8, C10 and C12 on cooling the isotropic phase. For mesogens with C2, C4, C8 and C10 terminal alkoxy chains, the mesophase assignment from hot-stage optical microscopy and differential scanning calorimetry is further confirmed by variable temperature powder X-ray diffraction measurements. The appearance of smectic B phase is established by noticing sharp and intense peaks in both small-angle and wide-angle regions. For a representative mesogen, i.e. T10, high-resolution solid-state (13)C NMR investigations are carried out in all the phases, viz. nematic, smectic A, smectic C and smectic B phases. The orientational order parameters calculated from (13)C-(1)H dipolar couplings from 2D SAMPI-4 experiments are found to be 0.44, 0.67, 0.73 and 0.79 in nematic, smectic A, smectic C and smectic B mesophases for the center phenyl ring respectively. Remarkably, the thiophene order parameter in all mesophases is found to be higher than that of phenyl rings and is explained by considering the molecular shape, which has a terminal bend. Further, the mesogens are found to be photoemissive in chloroform solution with an emission band at ∼410 nm.
Collapse
Affiliation(s)
- B Veeraprakash
- Polymer Lab, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India.
| | | | | | | |
Collapse
|
15
|
Reddy MG, Lobo NP, Varathan E, Easwaramoorthi S, Narasimhaswamy T. Intramolecular charge transfer interactions and molecular order of rod like mesogens. RSC Adv 2015. [DOI: 10.1039/c5ra22261c] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Photophysical studies, VT-XRD and13C solid state NMR investigation of three ring based dimethylamino mesogens reveal intramolecular charge transfer, smectic Admesophase and molecular order.
Collapse
Affiliation(s)
- M. Guruprasad Reddy
- Polymer Laboratory
- CSIR-Central Leather Research Institute
- Chennai
- India-600020
| | - Nitin P. Lobo
- Chemical Physics Laboratory
- CSIR-Central Leather Research Institute
- Chennai
- India-600020
| | - E. Varathan
- Chemical Laboratory
- CSIR-Central Leather Research Institute
- Chennai
- India-600020
| | - S. Easwaramoorthi
- Chemical Laboratory
- CSIR-Central Leather Research Institute
- Chennai
- India-600020
| | - T. Narasimhaswamy
- Polymer Laboratory
- CSIR-Central Leather Research Institute
- Chennai
- India-600020
| |
Collapse
|
16
|
Kesava Reddy M, Varathan E, Jacintha B, Lobo NP, Roy A, Narasimhaswamy T, Ramanathan KV. Structural investigation of resorcinol based symmetrical banana mesogens by XRD, NMR and polarization measurements. Phys Chem Chem Phys 2015; 17:5236-47. [DOI: 10.1039/c4cp05844e] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The structural characterization of two bent-core mesogens DBPPD and DBPPDO which differ in terminal chains reveals B2 and B7 mesophases while the orientational order parameter for DBPPD is found to be 0.84 with a bent angle of 120.5°.
Collapse
Affiliation(s)
| | - E. Varathan
- Chemical Laboratory and Polymer Laboratory
- CSIR-Central Leather Research Institute
- Chennai 600020
- India
| | - B. Jacintha
- Soft Condensed Matter
- Raman Research Institute
- Bangalore
- India
| | - Nitin P. Lobo
- Department of Physics
- Indian Institute of Science
- Bangalore 560012
- India
| | - Arun Roy
- Soft Condensed Matter
- Raman Research Institute
- Bangalore
- India
| | - T. Narasimhaswamy
- Chemical Laboratory and Polymer Laboratory
- CSIR-Central Leather Research Institute
- Chennai 600020
- India
| | - K. V. Ramanathan
- NMR Research Centre
- Indian Institute of Science
- Bangalore 560012
- India
| |
Collapse
|
17
|
Lobo NP, Phani Kumar BVN, Narasimhaswamy T, Mandal AB. (13)C NMR investigations and the molecular order of 4-(trans-4'-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT). Phys Chem Chem Phys 2014; 16:14713-21. [PMID: 24919592 DOI: 10.1039/c4cp01569j] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The static 1D (13)C and 2D Proton Encoded Local Field (PELF) NMR experiments are carried out in the nematic phase of a less viscous liquid crystal 4-(trans-4'-hexylcyclohexyl)-isothiocyanatobenzene (6CHBT) with a view to find orientational order. The PELF spectra provide better resolution which facilitates the assignment of cyclohexyl and phenyl ring carbons relatively easy. For the cyclohexyl unit, four pairs of dipolar splitting are clearly noticed in contrast to earlier reports on structurally similar mesogens where only two pairs of doublets are seen. The linear relationship between anisotropic chemical shifts and orientational order is established and semi-empirical parameters are obtained to aid the study of the order behaviour of 6CHBT over the entire nematic range. The data further fitted to the Haller equation and a reasonably good agreement is observed. The temperature dependence trends of orientational order parameters extracted for various carbons using (13)C-(1)H dipolar couplings with those of (13)C chemical shifts are compared. A gradual decrease in the order parameter is noticed for different molecular segments while traversing from the core to the aliphatic chain via the cyclohexyl ring. The notable decreasing trends of order parameters along the chain are observed similar to those of the corresponding phenyl cyclohexanes reported earlier.
Collapse
Affiliation(s)
- Nitin P Lobo
- Chemical Physics Laboratory, Council of Scientific and Industrial Research (CSIR)-Central Leather Research Institute (CLRI), Adyar, Chennai 600020, India.
| | | | | | | |
Collapse
|
18
|
Abstract
A facile way of estimating the order parameter and the molecular orientation from 13C–1H dipolar couplings for three ring based nematogens with a terminal C–H vector.
Collapse
Affiliation(s)
- Nitin P. Lobo
- Department of Physics
- Indian Institute of Science
- Bangalore 560012, India
| | - Bibhuti B. Das
- Department of Physics
- Indian Institute of Science
- Bangalore 560012, India
| | - T. Narasimhaswamy
- Polymer Laboratory
- CSIR-Central Leather Research Institute
- Chennai 600 020, India
| | - K. V. Ramanathan
- NMR Research Centre
- Indian Institute of Science
- Bangalore 560012, India
| |
Collapse
|
19
|
Kesava Reddy M, Subramanyam Reddy K, Yoga K, Prakash M, Narasimhaswamy T, Mandal AB, Lobo NP, Ramanathan KV, Rao DSS, Krishna Prasad S. Structural Characterization and Molecular Order of Rodlike Mesogens with Three- and Four-Ring Core by XRD and 13C NMR Spectroscopy. J Phys Chem B 2013; 117:5718-29. [DOI: 10.1021/jp4000126] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- M. Kesava Reddy
- Department of Chemistry, S. V. University, Tirupati 517502, India
| | | | - K. Yoga
- Polymer Laboratory and Chemical
Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - M. Prakash
- Polymer Laboratory and Chemical
Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - T. Narasimhaswamy
- Polymer Laboratory and Chemical
Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - A. B. Mandal
- Polymer Laboratory and Chemical
Laboratory, CSIR-Central Leather Research Institute, Adyar, Chennai 600020, India
| | - Nitin P. Lobo
- Department of Physics, Indian Institute of Science, Bangalore, 560012, India
| | - K. V. Ramanathan
- NMR Research Centre, Indian Institute of Science, Bangalore, 560012, India
| | - D. S. Shankar Rao
- Centre for Soft Matter Research, Jalahalli, Bangalore, 560013, India
| | - S. Krishna Prasad
- Centre for Soft Matter Research, Jalahalli, Bangalore, 560013, India
| |
Collapse
|
20
|
Reddy MK, Reddy KS, Narasimhaswamy T, Das BB, Lobo NP, Ramanathan KV. 13C–1H dipolar couplings for probing rod-like hydrogen bonded mesogens. NEW J CHEM 2013. [DOI: 10.1039/c3nj00271c] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
|
21
|
Lobo NP, Prakash M, Narasimhaswamy T, Ramanathan KV. Determination of 13C Chemical Shift Anisotropy Tensors and Molecular Order of 4-Hexyloxybenzoic Acid. J Phys Chem A 2012; 116:7508-15. [DOI: 10.1021/jp302291u] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Nitin P. Lobo
- Department of Physics, Indian Institute of Science, Bangalore-560012, India
| | - M. Prakash
- Chemical Lab & Polymer Lab, CSIR-Central Leather Research Institute, Adyar, Chennai-600 020, India
| | - T. Narasimhaswamy
- Chemical Lab & Polymer Lab, CSIR-Central Leather Research Institute, Adyar, Chennai-600 020, India
| | - K. V. Ramanathan
- NMR Research Center, Indian Institute of Science, Bangalore-560012, India
| |
Collapse
|
22
|
Kalaivani S, Narasimhaswamy T, Das BB, Lobo NP, Ramanathan K. Phase Characterization and Study of Molecular Order of a Three-Ring Mesogen by 13C NMR in Smectic C and Nematic Phases. J Phys Chem B 2011; 115:11554-65. [DOI: 10.1021/jp203388v] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- S. Kalaivani
- Polymer Laboratory, Central Leather Research Institute (Council of Scientific & Industrial Research, CSIR), Adyar, Chennai 600 020, India
| | - T. Narasimhaswamy
- Polymer Laboratory, Central Leather Research Institute (Council of Scientific & Industrial Research, CSIR), Adyar, Chennai 600 020, India
| | - Bibhuti B. Das
- Department of Physics and ‡NMR Research Center, Indian Institute of Science, Bangalore 560 012, India
| | - Nitin P. Lobo
- Department of Physics and ‡NMR Research Center, Indian Institute of Science, Bangalore 560 012, India
| | - K.V. Ramanathan
- Department of Physics and ‡NMR Research Center, Indian Institute of Science, Bangalore 560 012, India
| |
Collapse
|
23
|
Lobo NP, Ramanathan KV. Sensitivity Enhancement in Solid-State Separated Local Field NMR Experiments by the Use of Adiabatic Cross-Polarization. J Phys Chem Lett 2011; 2:1183-1188. [PMID: 26295323 DOI: 10.1021/jz200345q] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Measurement of dipolar couplings using separated local field (SLF) NMR experiment is a powerful tool for structural and dynamics studies of oriented molecules such as liquid crystals and membrane proteins in aligned lipid bilayers. Enhancing the sensitivity of such SLF techniques is of significant importance in present-day solid-state NMR methodology. The present study considers the use of adiabatic cross-polarization for this purpose, which is applied for the first time to one of the well-known SLF techniques, namely, polarization inversion spin exchange at the magic angle (PISEMA). The experiments have been carried out on a single crystal of a model peptide, and a dramatic enhancement in signal-to-noise up to 90% has been demonstrated.
Collapse
Affiliation(s)
- Nitin P Lobo
- †Department of Physics and ‡NMR Research Centre, Indian Institute of Science, Bangalore 560012, India
| | - Krishna V Ramanathan
- †Department of Physics and ‡NMR Research Centre, Indian Institute of Science, Bangalore 560012, India
| |
Collapse
|